NOTES

This book has two sets of endnotes. The notes below contain basic references to some of the scientific and philosophical work that informed this book, along with comments and reflections. The other set of notes is online, here: https://petergodfreysmith.com/living-on-earth-online-notes. Those notes have additional references and go further on some philosophical and scientific paths. The online notes include all the material in the briefer notes and give full citation information for journal articles and books, including internet links. Below, journal articles are referenced with just the journal and the year.

1. SHARK BAY

Sometime around 3 billion years ago: My early chapters have been informed often by Tim Lenton and Andrew Watson’s book Revolutions That Made the Earth (2011). For cyanobacteria, see Patricia Sánchez-Baracaldo and Tanai Cardona, “On the Origin of Oxygenic Photosynthesis and Cyanobacteria,” New Phytologist, 2020.

Below that level, you will be poisoned by oxygen itself: As you descend, the oxygen is not chemically concentrated, but each breath taken at depth brings in more of everything, including more oxygen, cramming it into your body. Some of what comes in under pressure in this way does not do too much in larger doses, but oxygen does, because of those “oxygen radicals.”

2. EARTH ENLIVENED

The age of the universe: Unsurprisingly, there’s some controversy. NASA’s number is about 13.8 billion. https://lambda.gsfc.nasa.gov/education/graphic_history/age.html.

Animals might be 650 million years old or so: Here, as in other cases discussed in this book, there’s a gap between estimates based on fossils and those based on molecular genetic data. In the case of animals, the first fossils are around 575 million years old, while estimates of their origin based on molecular genetics stretch back to 800 million years ago, or older. Some of my correspondents are becoming more skeptical about molecular genetic estimates. The dates I use in this book tend to be compromises. For the animal case, see Ross Anderson et al., “Fossilisation Processes and Our Reading of Animal Antiquity,” Trends in Ecology and Evolution, 2023.

One setting in which this might get started: See Eugene Koonin and William Martin, “On the Origin of Genomes and Cells Within Inorganic Compartments,” Trends in Genetics, 2005.

Darwin imagined a warm pond as the site: See Cairns-Smith, Seven Clues to the Origin of Life: A Scientific Detective Story (1985). The Darwin speculation is in a letter to Joseph Hooker, 1871.

The choice between the origin stories I compared just now: For a discussion of “metabolism first” and “replicator first” scenarios, see Freeman Dyson, Origins of Life (2nd ed., 2010).

the “century of the gene,” as the historian of science Evelyn Fox Keller: See her book The Century of the Gene (2002).

One place to see this is a coral reef: Here I draw on J. Scott Turner’s book The Extended Organism (2000).

For Bohr, complementary properties of an object: See, for example, his “Natural Philosophy and Human Cultures,” Nature, 1939, which is discussed in Henry Folse’s “Niels Bohr, Complementarity, and Realism,” PSA: Proceedings of the Biennial Meeting of the Philosophy of Science Association, 1986.

I am sitting out in the garden: This is another area where I was helped by Lenton and Watson’s Revolutions book, and by discussion with Jochen Brocks.

Andrew Knoll, a Harvard biologist: See Knoll’s “The Geological Consequences of Evolution,” Geobiology, 2003.

James Barber, who admittedly worked for much: See Barber, “A Mechanism for Water Splitting and Oxygen Production in Photosynthesis,” Nature Plants, 2017.

The light-harvesting molecules in bacteria and plants: See Minik Rosen et al., “The Rise of Continents—An Essay on the Geologic Consequences of Photosynthesis,” Palaeogeography, Palaeoclimatology, Palaeoecology, 2006.

this change was still important enough to be called “The Great Oxygenation”: See Lenton and Watson, Revolutions (though they call it, as some do, the Great Oxidation). The early stages may have seen an “oxygen overshoot” that briefly took the level much higher. This is still controversial. Here, and in other places in this chapter, I have been helped by Andrew Knoll and Jochen Brocks.

New kinds of minerals: See Robert Hazen et al., “Mineral Evolution,” American Mineralogist, 2008.

The rainforests are the lungs of the Earth: For clarification of all this, see Scott Denning, “Amazon Fires Are Destructive, but They Aren’t Depleting Earth’s Oxygen Supply,” The Conversation, August 26, 2019. Another article along similar lines is Jean-Pierre Gattuso et al., “Humans Will Always Have Oxygen to Breathe, but We Can’t Say the Same for Ocean Life,” The Conversation, August 12, 2021. They give different numbers for thought experiments where photosynthesis instantly ends and we have to keep breathing. The Gattuso article says we’d be okay for millennia, the Denning article for millions of years. They have different scenarios in mind. I continue along this path in the online notes.

This slower “inorganic” carbon cycle: See James Kasting, “The Goldilocks Planet? How Silicate Weathering Maintains Earth ‘Just Right,’” Elements, 2019.

Some corals have also been found with cyanobacteria: See Michael Lesser et al., “Discovery of Nitrogen-Fixing Cyanobacteria in Corals,” Science, 2004.

As oxygen levels increased: See Douglas Fox, “What Sparked the Cambrian Explosion?,” Nature, 2016.

We are also a material continuation: In philosophy, Jim Griesemer is the person responsible for pressing the importance of this point. See especially his “The Informational Gene and the Substantial Body: On the Generalization of Evolutionary Theory by Abstraction,” Poznan Studies in the Philosophy of the Sciences and the Humanities, 2005.

Back in the 1970s, James Lovelock and Lynn Margulis: See Lovelock and Margulis, “Atmospheric Homeostasis by and for the Biosphere: The Gaia Hypothesis,” Tellus, 1974, and Lovelock’s Gaia: A New Look at Life on Earth (1979).

it was Margulis who rescued this idea: Her original paper, published under the name Lynn Sagan, is “On the Origin of Mitosing Cells,” Journal of Theoretical Biology, 1967.

Ford Doolittle, one of the early critics of Gaia: See Doolittle’s “Is Nature Really Motherly?,” The CoEvolution Quarterly, 1981.

Although salt water is in many ways friendly: For the saltiness of Martian water, see Nicholas Tosca et al., “Water Activity and the Challenge for Life on Early Mars,” Science, 2008.

Lovelock wondered whether the Great Barrier Reef: See Gaia, chapter 6. Lovelock said in this book that 6 percent is an upper limit for almost all organisms, but this was perhaps an exaggeration. The water around the stromatolites at Shark Bay is apparently around 6 percent salinity, and there’s quite a lot of life there (including the fish I watched). Ordinary seawater is around 3.5 percent. See the online notes for more detail.

The biologists David Queller and Joan Strassmann: Queller and Strassmann, “Beyond Society: The Evolution of Organismality,” Philosophical Transactions of the Royal Society B, 2009.

These acacias build living quarters: I discuss these cases in “Agents and Acacias: Replies to Dennett, Sterelny, and Queller,” Biology and Philosophy, 2011.

That led to objections from evolutionary biologists: See Doolittle’s “Is Nature Really Motherly?” and Richard Dawkins, The Extended Phenotype (1982).

Talk of Gaia invites us to think the Earth will take care of itself: Here’s another point along the same lines. The Earth does seem to have a good amount of life-friendly feedback in its processes. If the Earth is not like an organism, then the existence of one feedback process of this kind gives us no reason to expect another. There’s no reason why there should be a general pattern. If the Earth is organism-like, then it has been shaped to have a general capacity for self-maintenance, to some extent. Then we should expect a pattern—not an exceptionless one, probably one with many gaps, but this is the sort of thing we’d expect to see.

Sometimes people just want to use talk of Gaia: For a simple discussion of “weak” versus “strong,” see Ian Enting’s “Gaia Theory: Is It Science Yet?,” The Conversation, February 12, 2012. For versions of Gaia, see also Tim Lenton and David Wilkinson, “Developing the Gaia Theory: A Response to the Criticisms of Kirchner and Volk,” Climatic Change, 2003. I mentioned Ford Doolittle earlier, as a Gaia critic. Doolittle has been rethinking the question and defends the possibility of Darwinizing Gaia, partly through selection processes based on survival or persistence. Doolittle has a somewhat organism-like way of thinking about Gaia. See his “Making Evolutionary Sense of Gaia,” Trends in Ecology and Evolution, 2019.

On the other side, I’ve seen scientists keep the “Gaia” term around as a nod to Lovelock and the broadening of perspective that he introduced, even if they reject anything like an Earth-as-organism view.

In this case, when conditions are warmer: For these feedback processes, see Lenton’s book Earth System Science: A Very Short Introduction (2016). For the effects of life on weathering, see David Schwartzman and Tyler Volk, “Biotic Enhancement of Weathering and the Habitability of Earth,” Nature, 1989.

How about the salt in the oceans?: Here I draw on Eelco Rohling, The Oceans: A Deep History (2017). On the question of whether feedback is present, and the uncertainties, this passage is notable, from Stephanie Olson et al., “The Effect of Ocean Salinity on Climate and Its Implications for Earth’s Habitability,” Geophysical Research Letters, 2022: “The salinity evolution of Earth’s ocean is not yet well constrained, but constant salinity through time would be a notable coincidence or imply some currently unknown feedback.” I don’t think people believe salinity was constant, but it might have been kept in a fairly narrow range.

Much of it was probably brought in on asteroids: See Lenton and Watson, Revolutions. Rohling, in The Oceans, views this as less clear, as a fair bit of water might have been in place when the planet formed.

an event like a flow of adrenaline has a purpose: This example is used often by Ruth Millikan, in her classic book Language, Thought, and Other Biological Categories (1984).

the American philosopher Larry Wright: See his Teleological Explanations (1976). Wright is the main source for me here; Millikan’s Language, Thought, and Other Biological Categories is also important. The broad way I am applying these concepts is reminiscent of Daniel Dennett’s concept of a “design stance,” but I see his treatment of these ideas as more instrumentalist. For Dennett, the language of goals and functions provides an interpretive stance, a way of seeing complex phenomena that is justified if it helps us discern patterns. The framework doesn’t have to be understood in terms of a definite set of mechanisms. See his Darwin’s Dangerous Idea (1995).

This rehabilitation does not carry over: In a traditional way of using teleological concepts, the function of something is what it is supposed to do, and if it does not have that effect, something has gone wrong. This link might be seen as a bridge to a moral theory. I am not endorsing inferences of that kind at all.

we can find borderline cases: Some of these borderline cases were discussed as problems for Wright’s analysis of biological functions—see Chris Boorse, “Wright on Functions,” Philosophical Review, 1976. They were seen as problems because Wright seemed to be committed to saying that biological functions were present in cases where they appear to be absent. I discussed this as a problem in one of my first papers, “A Modern History Theory of Functions,” Noûs, 1994. I wish I’d not approached these interesting cases in this way. It was an opportunity to explore the borderline and marginal cases in themselves, rather than worrying about how they are categorized.

conversations with the evolutionary theorist William Hamilton: See Lenton et al., “Selection for Gaia Across Multiple Scales,” Trends in Ecology and Evolution, 2018.

The possible snowball Earth events were rare: In the more powerful kinds of learning by trial and error, a learner adds improvements in stages while keeping the good elements of what they had. The snowball Earth events seem more like a crash plus a new roll of the dice—not with respect to features that make for individual advantage, but those that are helpful to life as a whole. I explore this further in the online notes.

3. THE FOREST

The young Charles Darwin: The account is in his Journal of Researches, known also as The Voyage of the Beagle. This wording is from the 1845 second edition. The 1839 first edition (Journal and Remarks) is very similar in the quoted “bold sea-coast” passage, but does not have the geological speculations.

central to the work of Charles Lyell: The crucial work was his Principles of Geology: Being an Attempt to Explain the Former Changes of the Earth’s Surface, by Reference to Causes Now in Operation, 3 volumes (1830–33). Darwin dedicated the second edition of his Beagle book to Lyell.

the geologist Charles Wilkinson hypothesized: See J. L. Pickett and J. D. Alder, Layers of Time: The Blue Mountains and Their Geology (1997), and J. Milne Curran, The Geology of Sydney and the Blue Mountains: A Popular Introduction to the Study of Geology (1899). Darwin: “To attribute these hollows to the present alluvial action would be preposterous,” Voyage of the Beagle, second edition, chapter 19.

Ted Hughes, in his poem “Sugar Loaf”: Published as “Sugar-loaf” in The Atlantic, 1962, and as “Sugar Loaf” in Wodwo, 1967.

The Bark-Palaces We Call Plants: “Mayer of Bonn, basing his theory upon molecular motions, considers the smallest granules of the cell-contents as individuals possessing animal life (biospheres) which build up plants for their dwellings. ‘Like hamadryads these sensitive monads inhabit the secret halls of the bark-palaces we call plants, and here silently hold their dances and celebrate their orgies.’” Alexander Braun, The Vegetable Individual, in Its Relation to Species (translated by C. F. Stone, 1855).

A forest of this kind: See Graeme Lloyd et al., “Dinosaurs and the Cretaceous Terrestrial Revolution,” Proceedings of the Royal Society B, 2008; Jose Barba-Montoya et al., “Constraining Uncertainty in the Timescale of Angiosperm Evolution and the Veracity of a Cretaceous Terrestrial Revolution,” New Phytologist, 2018.

Land plants arose from colonies: See Karl Niklas, The Evolutionary Biology of Plants (1997), and Tais Dahl and Susanne Arens, “The Impacts of Land Plant Evolution on Earth’s Climate and Oxygenation State—An Interdisciplinary Review,” Chemical Geology, 2020.

A new group, flowering plants: The evolutionary line that led to flowering plants probably branched off from others well before this, though the date is controversial. For one discussion, see Daniele Silvestro et al., “Fossil Data Support a Pre-Cretaceous Origin of Flowering Plants,” Nature Ecology and Evolution, 2021.

Insects are sprinkled through the fossil record: Dates using molecular genetics push the origin of insects back to around 479 million years ago, but the fossil record starts much later. See Bernhard Misof et al., “Phylogenomics Resolves the Timing and Pattern of Insect Evolution,” Science, 2014.

something like 85 percent of species: See Geerat Vermeij and Richard Grosberg, “The Great Divergence: When Did Diversity on Land Exceed That in the Sea?,” Integrative and Comparative Biology, 2010. Eighty-five percent is their lower estimate; it could be as high as 95 percent. This number does not include microbes.

Rivers, however, are not just inevitable consequences: Apparently the fossil record shows quite a dramatic effect on river shape of the evolution of plants—see Neil Davies and Martin Gibling, “Paleozoic Vegetation and the SiluroDevonian Rise of Fluvial Lateral Accretion Sets,” Geology, 2010, and the more recent Alessandro Ielpi et al., “The Impact of Vegetation on Meandering Rivers,” Nature Reviews Earth and Environment, 2022. Thanks to Mark Westoby for comments on this. Soil, too, was largely a product of plants themselves, along with fungi.

This list is not supposed to cover everything: What about drinking at a water hole? I include that as feeding. I leave out “elimination” behaviors, such as defecation, and also some self-directed behaviors such as grooming and cleaning oneself. Wound tending is important in other contexts; it is evidence for felt pain. I am trying to keep the list as simple as I can, in order to focus on some categories that matter most to the themes of this book. As will be evident, I don’t think “four Fs” summaries suffice.

All of these forms of action are probably very old: For building by unicellular organisms, see Mike Hansell’s Built by Animals (2009) on Difflugia coronata. The case I am not sure about, in unicellular organisms, is action with the goal of information gathering. There are cases where protists hunt in a way that is informationally efficient, sampling the environment (see Scott Coyle et al., “Coupled Active Systems Encode an Emergent Hunting Behavior in the Unicellular Predator Lacrymaria olor,” Current Biology, 2019). This is not the same as acting with the sole or main purpose of information gathering. But perhaps there is a case of this kind.

Now a cell can crawl, swim quickly: Although a cytoskeleton with this sort of power is usually seen as a eukaryotic innovation, it, too, has precursors. The Archaea are a bacteria-like group of organisms, and a rare variety called the Asgard archaea have an internal skeleton that is similar to the ones within cells like ours. These archaea are seen with long, tentacle-like projections coming out from their bodies. See Thiago Rodrigues-Oliveira et al., “Actin Cytoskeleton and Complex Cell Architecture in an Asgard Archaeon,” Nature, 2023. Bacteria do have a form of cytoskeleton. In addition, engulfing is not wholly absent in bacteria: see Takashi Shiratori et al., “Phagocytosis-Like Cell Engulfment by a Planctomycete Bacterium,” Nature Communications, 2019.

The term “niche construction”: See John Odling-Smee, Kevin Lala, and Marcus Feldman, Niche Construction: The Neglected Process in Evolution (2003).

A few small worms may have hunted: I discuss this in more detail in Metazoa, chapter 3. See James Gehling and Mary Droser, “Ediacaran Scavenging as a Prelude to Predation,” Emerging Topics in Life Sciences, 2018.

the British biologist Nicholas Butterfield: See his “Animals and the Invention of the Phanerozoic Earth System,” Trends in Ecology and Evolution, 2011.

The phrase “ecosystem engineer”: See Clive Jones, John Lawton, and Moshe Shachak, “Organisms as Ecosystem Engineers,” Oikos, 1994.

Earthworms, present-day descendants: See Renée-Claire Le Bayon et al., “Earthworms as Ecosystem Engineers: A Review,” in Earthworms: Types, Roles and Research (edited by Clayton Horton, 2017).

Action is different on land and in the sea: See Geerat Vermeij, “How the Land Became the Locus of Major Evolutionary Innovations,” Current Biology, 2017. I discussed these ideas in Metazoa, chapter 9.

The novelist Arthur C. Clarke, of 2001: A Space Odyssey, said this: This is in his 1956 book The Coast of Coral and various biographies (e.g., https://www.imdb.com/). The screenplay of 2001: A Space Odyssey was written by director Stanley Kubrick and Clarke, based on some Clarke stories, especially “The Sentinel” (1951).

Early animals in the sea, and their: There’s more on this in Metazoa, chapter 3. When I say there are no radially symmetrical animals on land, I exclude anemones who live in the intertidal zone.

Termites don’t usually live inside the towers: See Turner’s The Extended Organism and Lisa Margonelli’s Underbug: An Obsessive Tale of Termites and Technology (2018).

There are tube-building worms, and shrimp-like animals: For the amphipods, see Nikolai Neretin, Anna Zhadan, and Alexander Tzetlin, “Aspects of Mast Building and the Fine Structure of ‘Amphipod Silk’ Glands in Dyopedos bispinis (Amphipoda, Dulichiidae),” Contributions to Zoology, 2017. For the pistol shrimp, see Hansell’s Built by Animals and references he gives (also my online notes). The pufferfish are the white-spotted pufferfish (Torquigener albomaculosus); see Hisoshi Kawase et al., “Spawning Behavior and Paternal Egg Care in a Circular Structure Constructed by Pufferfish, Torquigener albomaculosus (Pisces: Tetraodontidae),” Bulletin of Marine Science, 2015.

At “Octopolis” and “Octlantis”: These sites are described in detail in my books Other Minds and Metazoa. Storms and floods have affected the bay where the sites are located in recent years. When I last visited Octopolis, in early 2023, it was very quiet, with only a couple of octopuses present. Octlantis was livelier on that trip, with five octopuses, though well below the maximum we’ve seen there, which is around fifteen.

A tunicate or sea squirt called Oikopleura: See Hansell, Built by Animals.

Why do I think there were tunnels?: See Takeshi Takegaki and Akinobu Nakazono, “The Role of Mounds in Promoting Water-Exchange in the Egg-Tending Burrows of Monogamous Goby, Valenciennea longipinnis (Lay et Bennett),” Journal of Experimental Marine Biology and Ecology, 2000.

The feature that is basic to tool use: In my earlier discussion of categories of action, I said that often the goals of an action form chains—you might move in order to interact with another person, and might do all that in order to make some change to the environment, and so on. I said that my categorization looks to the first goal, when there are chains like this. Why isn’t the first goal, in some cases, the use of a tool? Then tool use could become a sixth element added to the earlier list. You might set things up like this, but I think the other way is also okay. I am treating tool use as how you might pursue another goal, rather than ever being a goal of its own.

I learned of a wonderful case from David Scheel: He sent this in an email.

Chimps, bonobos, and crows are the most adept: For the compound tool and “metatool” use of New Caledonian Crows, see Auguste von Bayern et al., “Compound Tool Construction by New Caledonian Crows,” Scientific Reports, 2018, and Alex Taylor et al., “Spontaneous Metatool Use by New Caledonian Crows,” Current Biology, 2007.

The list of seagoing tool users is short: For a review, see Janet Mann and Eric Patterson, “Tool Use by Aquatic Animals,” Philosophical Transactions of the Royal Society B, 2013.

Octopuses are on the list. Our study of projectile use by octopuses, first mentioned in Other Minds, is now published: Godfrey-Smith et al., “In the Line of Fire: Debris Throwing by Wild Octopuses,” PLOS ONE, 2022. Another notable case is their carrying and assembling of half coconut shells for protection: see Julian Finn, Tom Tregenza, and Mark Norman, “Defensive Tool Use in a Coconut-Carrying Octopus,” Current Biology, 2009.

the neuroscientist and engineer Malcolm MacIver: See Malcolm MacIver and Barbara Finlay, “The Neuroecology of the Water-to-Land Transition and the Evolution of the Vertebrate Brain,” Philosophical Transactions of the Royal Society B, 2022, and other papers.

Still, I think MacIver might be onto something: With respect to differences between land-based and seagoing brains, another factor to consider is warm-bloodedness. Warm-bloodedness, which is seen in all the plan-using animals that MacIver discusses, makes for a higher-powered brain. You might say that animals have more need for a higher-powered brain on land, and this may well be true, but warm-bloodedness is also easier to achieve on land than it is in the sea. I looked at this in Metazoa, chapter 9.

This picture has impressed a number of thinkers: The framework was influenced by cybernetics, the mid-twentieth-century theory of control systems and feedback that fed into computer science and robotics. The theory was developed by William Powers. For a recent exposition and defense, see Timothy Carey, “Consciousness as Control and Controlled Perception—A Perspective,” Annals of Behavioral Science, 2018.

the “predictive processing” framework: See Karl Friston, “The Free-Energy Principle: A Unified Brain Theory?,” Nature Reviews Neuroscience, 2010; Andy Clark, Surfing Uncertainty (2015); and Anil Seth, Being You (2021).

The main problem has been expressed: This is discussed in lots of places; see Andy Clark’s Surfing Uncertainty.

Uexküll was a German-Estonian biologist: A new book looks more closely at his political side: Gottfried Schnödl and Florian Sprenger, Uexküll’s Surroundings: Umwelt Theory and Right-Wing Thought (translated by Michael Taylor and Wayne Yung, 2021).

His work had a wide influence: Heidegger praises him in The Fundamental Concepts of Metaphysics: World, Finitude, Solitude (lectures from 1929–30). There’s also a mention of the Umwelt in Being and Time. He is discussed in Merleau-Ponty’s second lecture course on nature at the Collège de France.

The insect situation is sometimes referred to as the “insect apocalypse”: For butterflies, see Martin Warren et al., “The Decline of Butterflies in Europe: Problems, Significance, and Possible Solutions,” PNAS, 2021; for the windshield effect, see Anders Møller, “Parallel Declines in Abundance of Insects and Insectivorous Birds in Denmark Over 22 Years,” Ecology and Evolution, 2019, and Damian Carrington, “Car ‘Splatometer’ Tests Reveal Huge Decline in Number of Insects,” The Guardian, February 12, 2020. For the forests, see https://ourworldindata.org/deforestation.

4. ORPHEUS

From the Rose-breasted Cockatoos (or Galahs): Ornithology seems to have a special tendency toward controversy (perhaps following the lead of the birds of the chapter opening), and this extends to naming and capitalization. Some say that because birds, unlike other animals, have official common names, it’s apt to capitalize the first letters (https://ornithology.com/upper-case-bird-names/). Others reject this. I am following my publisher’s preference.

Their evolution began in the Jurassic: Through here, I use Stephen Brusatte, Jingmai O’Connor, and Erich Jarvis, “The Origin and Diversification of Birds,” Current Biology, 2015.

Communication has borders: A lot of this is discussed in Ronald Planer and Peter Godfrey-Smith, “Communication and Representation Understood as Sender–Receiver Coordination,” Mind and Language, 2020. It gives citations to a large recent literature, which stems in part from Brian Skyrms’s revival of David Lewis’s model of conventional signaling (see Skyrms’s Signals, 2010), and also from Ruth Millikan’s Language, Thought, and Other Biological Categories (1984).

Vervet monkeys, for example, give alarm calls to one another: Robert Seyfarth, Dorothy Cheney, and Peter Marler, “Monkey Responses to Three Different Alarm Calls: Evidence of Predator Classification and Semantic Communication,” Science, 1980.

The idea that nearly anything could be used: The classic discussion of arbitrariness is Ferdinand de Saussure’s Course in General Linguistics (1916).

bacteria use chemical communication: See Steven Rutherford and Bonnie Bassler, “Bacterial Quorum Sensing: Its Role in Virulence and Possibilities for Its Control,” Cold Spring Harbor Perspectives in Medicine, 2012. There are many papers on this topic.

In the unusual circumstances of Octopolis and Octlantis: See David Scheel, Peter Godfrey-Smith, and Matthew Lawrence, “Signal Use by Octopuses in Agonistic Interactions,” Current Biology, 2021. This paper discusses the Nosferatu behavior, though not under that name.

The earliest two operas that have survived: These are Euridice by Jacopo Peri and Ottavio Rinuccini (1600), and Orfeo by Claudio Monteverdi and Alessandro Striggio (1607). Peri’s 1597 Dafne, which is mostly lost, is sometimes regarded as the very first opera.

The ornithologist Richard Prum uses the phrase: I draw especially on his paper “Coevolutionary Aesthetics in Human and Biotic Artworlds,” Biology and Philosophy, 2013, as well as his book The Evolution of Beauty (2017).

Once we put insects, and their all-important relation: Insect consciousness is no longer a fringe idea. See Andrew Barron and Colin Klein, “What Insects Can Tell Us About the Origins of Consciousness,” PNAS, 2016, and Matilda Gibbons et al., “Motivational Trade-Offs and Modulation of Nociception in Bumblebees,” PNAS, 2022.

But now it is thought likely that the initial role of feathers: This is in Brusatte, O’Connor, and Jarvis, “The Origin and Diversification of Birds,” and many other papers.

The colors in a coral reef: See Jörg Wiedenmann and Cecilia D’Angelo, “Revealed: Why Some Corals Are More Colourful Than Others,” The Conversation, January 30, 2015, and (a more technical version of the same work), John Gittins et al., “Fluorescent Protein-Mediated Colour Polymorphism in Reef Corals: Multicopy Genes Extend the Adaptation/Acclimatization Potential to Variable Light Environments,” Molecular Ecology, 2015. Also Alya Salih et al., “Fluorescent Pigments in Corals Are Photoprotective,” Nature, 2000.

Thanks to Meryl Larkin for help here. This site has more information: https://www.gbrbiology.com/knowledge-and-news/how-corals-get-their-colour/. It raises the possibility that some coral colors may be matched to fish vision, and that would qualify the claim that coral colors are not produced to be seen. See also Mikhail Matz, Justin Marshall, and Misha Vorobyev, “Are Corals Colorful?,” Photochemistry and Photobiology, 2006.

They form long-lasting bonds: See Amanda Vincent and Laila Sadler, “Faithful Pair Bonds in Wild Seahorses, Hippocampus whitei,” Animal Behaviour, 1995.

the whole enormous branch of passerines: This section draws often on Tim Low’s excellent book Where Song Began (2014).

One study found that even other birds can’t always tell lyrebird counterfeits: Anastasia Dalziell and Robert Magrath, “Fooling the Experts: Accurate Vocal Mimicry in the Song of the Superb Lyrebird, Menura novaehollandiae,” Animal Behaviour, 2012. Females also call, and mimic; the function of their calls is less clear, but they may play a role in nest defense and competition between females for breeding territories. See Anastasia Dalziell and Justin Welbergen, “Elaborate Mimetic Vocal Displays by Female Superb Lyrebirds,” Frontiers in Ecology and Evolution, 2016. The females I’ve heard also seem to sing more softly than males.

The smaller cluster includes another group of birds: This cluster also includes the treecreepers (not included in my tree diagram). These early branchings seem to attract some controversy. I use Carl Oliveros et al., “Earth History and the Passerine Superradiation,” PNAS, 2019.

Male bowerbirds build a nest-like structure: In this section I draw on some books by Clifford Frith and Dawn Frith: Bowerbirds: Nature, Art and History (2008) and (more academic) The Bowerbirds (2004).

Charles Darwin, during the visit to the Blue Mountains I described in chapter 3, observed Satin Bowerbirds, and they informed his realization of the importance of female choice in his theory of sexual selection.

In the case of preferences for blue: See Gerald Borgia, Ingrid Kaatz, and Richard Condit, “Flower Choice and Bower Decoration in the Satin Bowerbird Ptilonorhynchus violaceus: A Test of Hypotheses for the Evolution of Male Display,” Animal Behaviour, 1987. Prum does not endorse this view.

I emailed some experts to ask about all this, and they were cautious—no clear pattern has emerged. Thanks to Gerald Borgia for the “far from civilization” comment about blue objects; I have only seen these bowers closer in. The Great Bowerbird I saw had some dark green ornaments.

Jared Diamond, in the course of some intrepid work: See his “Animal Art: Variation in Bower Decorating Style Among Male Bowerbirds Amblyornis inornatus,” PNAS, 1986. See also Joah Madden, “Do Bowerbirds Exhibit Cultures?,” Animal Cognition, 2008.

Their courting behaviors seem to employ: As birds can see into the ultraviolet part of the spectrum, and different parts of the male’s body reflect differently, what looks to us like a pretty uniformly blue-black bird dancing in unusual ways might look more psychedelic to a female.

Gerald Borgia, after studying the birds extensively: “Why Do Bowerbirds Build Bowers?,” American Scientist, 1995.

Biology has seen a long-running and sometimes tense: This debate is central to Prum’s The Evolution of Beauty.

In 1964, the lyrebirds down there: See F. Norman Robinson and Sydney Curtis, “The Vocal Displays of the Lyrebirds (Menuridae),” Emu—Austral Ornithology, 1996. While on the topic of whipbirds: their whiplike sound has a standard reply call from a partner, a bit like a cheery wave. Sometimes a lyrebird will include the reply as well.

5. HUMAN BEING

The group we visited on this first encounter: These gorillas are in Volcanoes National Park, Rwanda. The online notes contain links to resources about the park, the Kwitonda and Igisha groups, and other material. These are the gorillas studied by Dian Fossey, as described in her Gorillas in the Mist (1983) and the movie of that name. The tour operation is impressive. Each gorilla group can be visited by one small human group once a day for one hour, maximum.

Mammals arose back in dinosaur-dominated times: See Steve Brusatte, The Rise and Reign of the Mammals (2023).

One branch within primates is the great apes, or hominids: See Sergio Almécija et al., “Fossil Apes and Human Evolution,” Science, 2021.

But sometime over 5 million years ago, a primate line made its way: From here I start to make use of Joseph Henrich’s book, The Secret of Our Success (2015).

The primatologist Sarah Hrdy offers: See her Mothers and Others (2009).

Culture in this sense refers to the establishment and development: As well as Henrich’s book, see Robert Boyd and Peter Richerson’s pioneering Culture and the Evolutionary Process (1985).

For Sterelny, human societies continually rebuild: As well as The Evolved Apprentice (2012), see Sterelny’s The Pleistocene Social Contract (2021), which bears on later topics in this chapter.

Until recently, researchers tended to think: See Andrew Whiten, “Blind Alleys and Fruitful Pathways in the Comparative Study of Cultural Cognition,” and the accompanying commentaries, Physics of Life Reviews, 2022. The Whiten paper is rather combative in tone, but the whole collection is valuable. For the bees, see especially Sylvain Alem et al., “Associative Mechanisms Allow for Social Learning and Cultural Transmission of String Pulling in an Insect,” PLOS Biology, 2016.

Is it due to brainpower, or perhaps a more cooperative: The suggestion about cooperation is made by Sterelny in his commentary on the Whiten paper just above.

Children often seem to have an eye out for transgressions: For one of the original studies, see Marco Schmidt et al., “Eighteen-Month-Old Infants Correct Non-Conforming Actions by Others,” Infancy, 2019. More research is described in the online notes. Cecilia Heyes is a critic of some of this work; see her “Rethinking Norm Psychology,” Perspectives on Psychological Science, 2023.

practices involving the detection and punishment of sorcery: See Ron Planer and Kim Sterelny, “The Challenge of Sorcery,” forthcoming.

This view was championed by the American linguist Noam Chomsky: See, for example, his Rules and Representations (1980).

This has come to seem unlikely: See especially Michael Tomasello, Origins of Human Communication (2008). See also Ron Planer and Kim Sterelny, From Signal to Symbol (2021).

John Locke, in the late 1600s, saw language: See Locke’s Essay Concerning Human Understanding (1689).

a phrase from the philosopher Josh Armstrong: See his “Communication Before Communicative Intentions,” Noûs, 2021.

The first evidence of stone tools dates: Through here I follow Henrich’s The Secret of Our Success.

The scale of Göbekli Tepe is substantial: David Graeber and David Wengrow’s fascinating book The Dawn of Everything (2021) has much to say about many of the topics of this chapter from this point onward.

Discussion in Australia, where stereotypes: Bruce Pascoe’s Dark Emu (2014) has been an influential contribution to this discussion. Pascoe argues that some Aboriginal Australian groups farmed and lived in settled societies. In Farmers or Hunter-Gatherers? The Dark Emu Debate (2021), Peter Sutton and Keryn Walshe criticize the book, not to reassert an old view of Aboriginal Australian life as simple and “primitive,” but to argue that “the old people” of Australia were mostly complex hunter-gatherers (“hunter-gatherers-plus”).

The political scientist James Scott’s book: This is his Against the Grain: A Deep History of the Earliest States (2017). Graeber and Wengrow’s The Dawn of Everything is an absorbing counterpoint to Scott’s book, and Graeber and Wengrow discuss Scott near the end. They are skeptical about the causal story and the account of typical transitions that Scott offers, arguing, for example, that many early states were not notable for a rise in inequality. See the online notes for more detail. The view I outline here is somewhat Scott-ish, informed also by correspondence.

when I first learned that, in old hunter-gatherer skeletons: This was in Jared Diamond, The Third Chimpanzee (1991): “Corn, first domesticated in Central America thousands of years ago, became the basis of intensive farming in those valleys around AD 1000. Until then, Indian hunter-gatherers had skeletons ‘so healthy it is somewhat discouraging to work with them,’ as one paleopathologist complained. With the arrival of corn … [t]he number of cavities in an average adult’s mouth jumped from fewer than one to nearly seven, and tooth loss and abscesses became rampant.”

Play that involves explicit pretense: See Alison Gopnik, “What Good Comes from Pretending?,” The Wall Street Journal, January 19, 2023. For primates, see Juan-Carlos Gómez, “The Evolution of Pretence: From Intentional Availability to Intentional Non-Existence,” Mind and Language, 2008, and Tetsuro Matsuzawa, “Pretense in Chimpanzees,” Primates, 2020.

The outlines of Lévi-Strauss’s sketch: Here I draw on Olivier Morin’s work, especially “The Piecemeal Evolution of Writing,” Lingue e Linguaggio, 2022, and Olivier Morin, Piers Kelly, and James Winters, “Writing, Graphic Codes, and Asynchronous Communication,” Topics in Cognitive Science, 2020. The suggestion about proper names and sound-based codes is from Morin.

The “memory palace” or “method of loci”: See Frances Yates, The Art of Memory (1966).

An older tradition of memorization: See David Reser et al., “Australian Aboriginal Techniques for Memorization: Translation into a Medical and Allied Health Education Setting,” PLOS ONE, 2021. For memory skills in Aboriginal Australian societies and others, see Lynn Kelly, Knowledge and Power in Prehistoric Societies (2015). The message-stick technology is discussed in Piers Kelly, “Australian Message Sticks: Old Questions, New Directions,” Journal of Material Culture, 2020.

Written language is not just a combination of sender-receiver interaction and engineering: This passage is from “Writing, Graphic Codes, and Asynchronous Communication,” by Olivier Morin, Piers Kelly, and James Winters (Topics in Cognitive Science, 2020): “Writing systems are the only graphic codes that can rival the richness and versatility of spoken languages, while remaining sufficiently productive [that is, organized with smaller elements that can be recombined in many ways] to be learnable. The only way that writing achieves this is by encoding a natural language, working as a meta-code (so to speak).”

The twentieth-century biologist Richard Lewontin: The essay can be found in Richard Levins and Richard Lewontin, The Dialectical Biologist (1985). While on the topic of loops, Fred Keijzer, Gáspár Jékely, and I wrote about how general the phenomenon might be in “Reafference and the Origin of the Self in Early Nervous System Evolution,” Philosophical Transactions of the Royal Society B, 2021. Another person who has written richly about them is the computer scientist Douglas Hofstadter. A “strange loop,” for Hofstadter, is one in which the viewer views themself, or a sentence is about itself, or there is some other self-directedness that has this mind-bending, head-over-heels character. (Hofstadter says that when he was young, he went to a store selling the first video cameras that sent an image to a screen in real time and was going to aim the camera at the screen itself, and was told: “No!” See his I Am a Strange Loop [2007].)

The Greek philosopher Socrates: Socrates’s comments about writing appear in Plato’s Phaedrus. Socrates and his ideas were also described in writing by the historian Xenophon and the playwright Aristophanes.

Literacy, in particular, has significant effects: See Stanislas Dehaene et al., “Illiterate to Literate: Behavioural and Cerebral Changes Induced by Reading Acquisition,” Nature Reviews Neuroscience, 2015. See also Cecilia Heyes’s book Cognitive Gadgets (2018), which emphasizes the many effects of culture on our brains.

The French composer Olivier Messiaen wrote “Quartet for the End of Time”: This was the first of Messiaen’s works to engage with birdsong. Aspects of his dramatic recollection of the first performance in the prison camp have been questioned by others who were there (in relation to the condition of the instruments and size of the audience, for example). See Rebecca Rischin, For the End of Time: The Story of the Messiaen Quartet (2003).

I’m reminded of a quote from an interview: This is from Malcolm Knox, “After the Booker: Why Richard Flanagan Isn’t Playing Safe,” Sydney Morning Herald, September 22, 2017.

Stephen Jay Gould imagined a “replaying of the tape”: This is in Gould’s Wonderful Life (1989). See also Simon Conway Morris, The Crucible of Creation (1998).

In a variant of this story, Sterelny sees the formation: See his The Evolved Apprentice.

Another biologist, Antone Martinho-Truswell: In his book, The Parrot in the Mirror (2022).

Dolphins are large-brained animals: See Ann Weaver and Stan Kuczaj, “Neither Toy nor Tool: Grass-Wearing Behavior Among Free-Ranging Bottlenose Dolphins in Western Florida,” International Journal of Comparative Psychology, 2016.

Octopuses have trouble with these sorts of things: For an imaginative exploration of a change in course, see Ray Naylor’s The Mountain in the Sea (2022).

In his book Built by Animals, which was helpful to me: This is in his first chapter.

Contrast all this with our primate-style life: Here I echo and modify a phrase from the philosopher Donald Williams, in “The Argument for Realism,” The Monist, 1934, within a passage that was somewhat celebrated when I was a student. “Philosophy is not ‘higher’ and suprascientific. It is the lowest and grubbiest inquiry round the roots of things, and when it answers real questions about the world, it is and can only be an inductive science.”

In Greek myths and later reflection on them, especially in writers like Nietzsche: See his The Birth of Tragedy (1872).

6. CONSCIOUSNESS

There’s something it feels like to be us: This well-known formulation of the problem comes from Thomas Nagel, “What Is It Like to Be a Bat?,” Philosophical Review, 1974.

I won’t give arguments: For more detailed discussions, and some defenses, see Metazoa; “Gradualism and the Evolution of Experience,” Philosophical Topics, 2020; and “Evolving Across the Explanatory Gap,” Philosophy, Theory, and Practice in Biology, 2019.

Nervous systems may have first arisen: Fred Keijzer’s work has influenced me here, and Fred Keijzer, Marc van Duijn, and Pamela Lyon, “What Nervous Systems Do: Early Evolution, Input–Output, and the Skin Brain Thesis,” Adaptive Behavior, 2013. See also Gáspár Jékely, Fred Keijzer, and Peter Godfrey-Smith, “An Option Space for Early Neural Evolution,” Philosophical Transactions of the Royal Society B, 2015.

More of what goes on in our brains matters than that, most likely: Here I have been influenced by Rosa Cao. See her “Multiple Realizability and the Spirit of Functionalism,” Synthese, 2022. The views of Anil Seth and Ned Block are also related; see Seth’s Being You (2021), and Block, “Comparing the Major Theories of Consciousness,” in Michael Gazzaniga (ed.), The Cognitive Neurosciences (2009).

An example is the oscillation in electrical activity: There’s more about this in Metazoa. Also see Wolf Singer, “Neuronal Oscillations: Unavoidable and Useful?,” European Journal of Neuroscience, 2018.

Some decades ago, Francis Crick (of DNA fame), Christof Koch, and others: See Francis Crick and Christof Koch, “Towards a Neurobiological Theory of Consciousness,” Seminars in the Neurosciences, 1990; and Lucia Melloni et al., “Synchronization of Neural Activity across Cortical Areas Correlates with Conscious Perception,” The Journal of Neuroscience, 2007.

The large-scale rhythmic patterns that Crick and Koch wrote about: See, for example, Bruno van Swinderen, “The Remote Roots of Consciousness in Fruit-Fly Selective Attention?,” BioEssays, 2005.

Back in the 1960s, the neurobiologist L. M. “Mac” Passano: See his “Primitive Nervous Systems,” PNAS, 1963.

This oscillatory activity in the brain: See Singer’s “Neuronal Oscillations: Unavoidable and Useful?”

The situation is different with another technology that is developing very quickly: One example of this work: Ranmal Samarasinghe et al., “Identification of Neural Oscillations and Epileptiform Changes in Human Brain Organoids,” Nature Neuroscience, 2021.

Rats make use of map-like representations: See John O’Keefe and Lynn Nadel, The Hippocampus as a Cognitive Map (1978), and (among much recent work) H. Freyja Ólafsdóttir et al., “Hippocampal Place Cells Construct Reward Related Sequences Through Unexplored Space,” eLife, 2015. For a philosophical discussion, see Nicholas Shea, Representation in Cognitive Science (2018).

A 2022 paper found that crows could learn to generate “recursive” patterns: See Diana Liao et al., “Recursive Sequence Generation in Crows,” Science Advances, 2022.

Stanislas Dehaene, a French neuroscientist: The paper is Dehaene et al., “Symbols and Mental Programs: A Hypothesis About Human Singularity,” Trends in Cognitive Sciences, 2022. The paper is about “human singularity”—“We suggest that humans owe their singularity to [internal] symbols.” The crow paper in the note above may push back a little on this.

Language, especially speech, is lateralized in our brains: Through here I make use of work by Michael Gazzaniga, Lesley Rogers, and Giorgio Vallortigara. Here are a couple of papers (the online notes have more): Michael Gazzaniga, “Shifting Gears: Seeking New Approaches for Mind/Brain Mechanisms,” Annual Review of Psychology, 2013; Lesley Rogers, “A Matter of Degree: Strength of Brain Asymmetry and Behaviour,” Symmetry, 2017; Giorgio Vallortigara, Lesley Rogers, and Angelo Bisazza, “Possible Evolutionary Origins of Cognitive Brain Lateralization,” Brain Research Reviews, 1999.

I have used these remarkable cases to work through some puzzles: In both Other Minds, chapter 5, and Metazoa, chapter 6.

Some simple but striking work has been done: See Victoria Bourne, “How Are Emotions Lateralised in the Brain? Contrasting Existing Hypotheses Using the Chimeric Faces Test,” Cognition and Emotion, 2010. This paper has a good series of photos showing the effect, as well as a review of hypotheses.

The presence of this highway seems to allow specialization: See Michael Gazzaniga, “Cerebral Specialization and Interhemispheric Communication: Does the Corpus Callosum Enable the Human Condition?,” Brain, 2000.

In one experiment, a patient had the word “bell” shown: This case is in Gazzaniga’s “Cerebral Specialization and Interhemispheric Communication.”

In some further experiments, split-brain patients were shown: See Elizabeth Phelps and Michael Gazzaniga, “Hemispheric Differences in Mnemonic Processing: The Effects of Left Hemisphere Interpretation,” Neuropsychologia, 1992.

People have come up with a number of evolutionary sequences: As well as the Gazzaniga, Rogers, and Vallortigara work, see Iain McGilchrist, The Master and His Emissary (2009).

An intriguing difference that bears on conscious experience: See Rogers, “A Matter of Degree: Strength of Brain Asymmetry and Behaviour,” Symmetry, 2017.

In the memory experiments I mentioned a moment ago: See Michael Miller and Michael Gazzaniga, “Creating False Memories for Visual Scenes,” Neuropsychologia, 1998.

What I have in mind is conscious thought: Here we reach the territory of “dual system” views of cognition. See Daniel Kahneman, Thinking, Fast and Slow (2011).

the French cognitive scientists Hugo Mercier and Dan Sperber: See Mercier and Sperber, The Enigma of Reason (2017). I commented on an earlier version of their view in a note with Kritika Yegnashankaran. See our “Reasoning as Deliberative in Function but Dialogic in Structure and Origin,” Behavioral and Brain Sciences, 2011.

An example of an error we all tend to make is confirmation bias: Mercier and Sperber argue that the phenomenon is a bit misdescribed with this term—it would be better called “myside bias” (“myside” as in my side).

A related way in which language and culture: See Daniel Dennett, “The Self as a Center of Narrative Gravity,” in Self and Consciousness (edited by Frank Kessel et al., 1992), and Anil Seth, Being You (2021).

Over thirty years ago, Jyotsna Vaid and Maharaj Singh wondered: See their “Asymmetries in the Perception of Facial Affect: Is There an Influence of Reading Habits?,” Neuropsychologia, 1989.

On the other hand, a leftward bias in looking at faces: See Kun Guo et al., “Left Gaze Bias in Humans, Rhesus Monkeys and Domestic Dogs,” Animal Cognition, 2009. See also Lesley Rogers, Giorgio Vallortigara, and Richard Andrew, Divided Brains: The Biology and Behaviour of Brain Asymmetries (2012).

Giorgio Vallortigara, writing about animals: “Comparative Neuropsychology of the Dual Brain.”

This has gone from being semi-implicit lore: See Matthew Egizii et al., “Which Way Did He Go? Film Lateral Movement and Spectator Interpretation,” Visual Communication, 2018; Roger Ebert, “How to Read a Movie,” RogerEbert.com, 2008.

In a study of how soccer goals were interpreted: See Anne Maass, Damiano Pagani, and Emanuela Berta, “How Beautiful Is the Goal and How Violent Is the Fistfight? Spatial Bias in the Interpretation of Human Behavior,” Social Cognition, 2007. As the authors say, this tells against the idea that a general, species-wide hemisphere asymmetry is behind the left/right distinctions people make in the interpretation of action. But, they add, it does not mean that there can’t be a role for a different style of processing across the two hemispheres. Perhaps the way our brain hemispheres develop during socialization is affected by the way language is handled in one’s culture? Other left-right differences, affecting how we perceive things other than language, might stem from that.

Here is another study that complicates things: Anne Maass, Caterina Suitner, and Faris Nadhmi, “What Drives the Spatial Agency Bias? An Italian– Malagasy–Arabic Comparison Study,” Journal of Experimental Psychology: General, 2014: “A comparison of 3 language communities (Italian, Malagasy, Arabic) differing in script direction (left–right for Italian and Malagasy and right–left for Arabic) and in subject–object order (subject–verb–object in Italian and Arabic and verb–object–subject in Malagasy) provides evidence for the assumption that both mechanisms contribute” to differences in how actions are perceived.

You can, as the philosopher John Dewey said a century ago: This is in his Experience and Nature (1925).

A 2002 paper set a lot of work in motion: P. Read Montague et al., “Hyperscanning: Simultaneous fMRI During Linked Social Interactions,” NeuroImage, 2002.

In fact, there was an earlier experiment, published in 1965: T. D. Duane and Thomas Behrendt, “Extrasensory Electroencephalographic Induction Between Identical Twins,” Science, 1965.

The EEG method itself was introduced: I discuss this episode in Metazoa, chapter 7.

This study was done very informally, with no statistics: Duane and Behrendt looked at fifteen pairs of twins. In the test, one twin would close their eyes in a lit room. Closing the eyes tends to initiate alpha rhythms in the brain. Would the other twin, in a separate room, enter the same brain wave pattern also? The other twin was about six meters away. The researchers said that two pairs of twins out of their fifteen could do it, and the others could not. One brain would start alpha rhythms, and the other would also. The pairs who could do this did so repeatedly. Unrelated pairs of individuals never did. The paper has no statistics or even detailed numbers. The authors just looked at the readouts to see if alpha patterns were visible and when they started. This experiment would have to be done carefully. The fact that most pairs of twins do not show the effect does not kill the result; if a few special pairs could do it over and over, that would be a big deal. In a response to critics, the authors gave a bit more detail: the channel between twins worked in both directions, and “in the successful twins transmission seemed to occur always.” See Charles Tart, George Robertson, Thomas Duane, and Thomas Behrendt, “More on Extrasensory Induction of Brain Waves,” Science, 1966.

This 1992 experiment, using EEG scans: See Jacobo Grinberg-Zylberbaum et al., “Human Communication and the Electrophysiological Activity of the Brain,” Subtle Energies and Energy Medicine, 1992. The most detailed account of Grinberg-Zylberbaum’s work and his disappearance I have found is a recent one: Ilan Stavans, “The Grinberg Affair: One of Mexico’s Most Curious MissingPersons Cases Involves a Scientist Who Dabbled in the Mystical Arts,” The American Scholar, 2023.

Several different kinds of scanning are used: As well as EEG and fMRI, which are described in the text, there is MEG (magnetoencephalography) and fNIRS (functional near-infrared spectroscopy). MEG, like EEG, picks up electrical patterns but does so using magnetic influences. fNIRS, like fMRI, looks at changes in oxygen use, but does so with light. Though the original “hyperscan” experiment used fMRI, this method can’t pick up fine-grained synchronization in temporal patterns.

The picture emerging is a surprising one: The online notes will have a lot of references; here are a few. Yan Mu, Cindy Cerritos, and Fatima Khan, “Neural Mechanisms Underlying Interpersonal Coordination: A Review of Hyperscanning Research,” Social and Personal Psychology Compass, 2018; Edda Bilek et al., “Information Flow Between Interacting Human Brains: Identification, Validation, and Relationship to Social Expertise,” PNAS, 2015; Adrian Burgess, “On the Interpretation of Synchronization in EEG Hyperscanning Studies: A Cautionary Note,” Frontiers in Human Neuroscience, 2013.

Two people playing a guitar duet do synchronize: For teamwork, see Caroline Szymanski et al., “Teams on the Same Wavelength Perform Better: Inter-Brain Phase Synchronization Constitutes a Neural Substrate for Social Facilitation,” NeuroImage, 2017. For the cocktail party effect, see Bohan Dai et al., “Neural Mechanisms for Selectively Tuning In to the Target Speaker in a Naturalistic Noisy Situation,” Nature Communications, 2018.

The most radical option: See Ana Lucía Valencia and Tom Froese, “What Binds Us? Inter-Brain Neural Synchronization and Its Implications for Theories of Human Consciousness,” Neuroscience of Consciousness, 2020.

Valencia and Froese also discuss an argument that was given: See Andy Clark, “Spreading the Joy? Why the Machinery of Consciousness Is (Probably) Still in the Head,” Mind, 2009.

In an old experiment done first by chance in the seventeenth century: See Burgess, “On the Interpretation of Synchronization in EEG Hyperscanning Studies.”

All this is very much on the edge: See Antonia Hamilton, “Hyperscanning: Beyond the Hype,” Neuron, 2021, and Clay Holroyd, “Interbrain Synchrony: On Wavy Ground,” Trends in Neurosciences, 2022.

a distinctive part of human life is the formation of shared intentions: See Michael Tomasello, Becoming Human (2021).

That evolutionary thicket has proved hard to fully resolve: See James Tarver et al., “The Interrelationships of Placental Mammals and the Limits of Phylogenetic Inference,” Genome Biology and Evolution, 2016.

we see giraffes walking, as Karen Blixen said: This is in her Out of Africa (1937). She wrote this book as “Isak Dinesen.”

7. OTHER LIVES

I’m going to begin by thinking about this in terms of the biomass: Here, and often below, I use this fascinating paper: Yinon Bar-On, Rob Phillips, and Ron Milo, “The Biomass Distribution on Earth,” PNAS, 2018.

I am going to use “ethical” and “moral” nearly interchangeably: Some people use “ethical” about issues that involve harm to others, equality, and so on, and “moral” for more personal questions (sexual morality). But I’ve seen people distinguish them with those two meanings switched. The terminology is all over the place.

Behind many of these debates lies a deeper division: In this area I have been influenced by Simon Blackburn’s Ruling Passions (1998), though Blackburn’s view is closer to traditional “expressivism” than mine. That is the view that ethical claims express an emotional response, or something like a preference, in the speaker, rather than making a claim that might be true or false. Christine Korsgaard’s work has also influenced me, though more as a foil, as here the disagreements are larger. See her The Sources of Normativity (1996) and Fellow Creatures (2018). The literature here is enormous.

A picture like this is seen in historical sketches: See Philip Kitcher’s The Ethical Project (2011); Kim Sterelny and Ben Fraser, “Evolution and Moral Realism,” British Journal for the Philosophy of Science, 2017; Kyle Stanford, “The Difference Between Ice Cream and Nazis: Moral Externalization and the Evolution of Human Cooperation,” Behavioral and Brain Sciences, 2018.

The social psychologist Jonathan Haidt: See Jonathan Haidt and Jesse Graham, “When Morality Opposes Justice: Conservatives Have Moral Intuitions That Liberals May Not Recognize,” Social Justice Research, 2007. This is one of many discussions of these ideas, recommended by Haidt as an accessible introduction. Here they use these five categories: harm/care, fairness/reciprocity, ingroup/loyalty, authority/respect, purity/sanctity. In recent work Haidt and his colleagues have sometimes recognized six “moral foundations”: care, equality, proportionality, loyalty, authority, and purity. (See https://moralfoundations.org.)

Ethical claims are a kind of valuation: Back in chapter 4, I talked about “evaluation” when we looked at communication and sender-receiver systems. Evaluation there was a category of behavior seen in receivers of signals and displays. Here we’re looking not at communication, but at a more general phenomenon.

This view is closer to the made side: I say a little more about this view in “Philosophers and Other Animals,” Aeon, 2021. It’s around here that I depart from Blackburn, whom I acknowledged above, as I see his view as too close to “expressivism” or “sentimentalism.” My unpublished Whitehead Lectures (Harvard, 2022, available on my website) also discuss the topic.

About 73 million pigs are alive at any time in the United States alone: The numbers are always changing, and some are contested. The USDA’s figure for 2022 was 73 million pigs. I make use of reports from the Humane Society, available here: https://www.humanesociety.org/resources/pigs and https://www.humanesociety.org/resources/poultry/, along with some others: https://sentientmedia.org/u-s-farmed-animals-live-on-factory-farms/.

On questions about intensive farming of these: A classic defense of utilitarianism is John Stuart Mill’s Utilitarianism (1861). Peter Singer’s Animal Liberation (1975; recently updated as Animal Liberation Now, 2023) is written from a utilitarian perspective. For the updated Kantian view, see Christine Korsgaard’s Fellow Creatures (2018). For an introduction to all these issues, see Lori Gruen, Ethics and Animals (2011).

Imagine that after you die: This reincarnation test is also discussed in my article “If Not Vegan, Then What?,” Aeon, 2023.

A welfarist can approve of humane farming: Welfarism, in this sense, has features in common with both utilitarianism and Kantianism, but it departs from both. Welfarism is akin to utilitarianism in its focus on experienced well-being, but it does not follow utilitarianism in its willingness to justify harm to one through benefits to another. In its focus on the individual rather than the total sum of an action’s effects, welfarism sounds a bit like the Kantian view. But the Kantian and the welfarist may diverge about humane farming. Welfarism allows a kind of paternalism toward animals: controlling them can be acceptable when their lives are peaceful and good. That kind of paternalism is at odds with the Kantian respect for autonomy. As emphasized in the main text, welfarism in this sense is not an ethical theory that stands alongside utilitarianism and Kantianism, as it does not (yet) have anything to say about clashes of welfare, and trade-offs.

That is the concept of betrayal: On this topic, see Steve Cooke, “Betraying Animals,” The Journal of Ethics, 2019.

Quite a few philosophers find themselves: For a discussion of abolitionist and various welfarist views, see Gruen, Ethics and Animals. Gary Francione is a prominent abolitionist. See, for example, “Are You a Vegan or Are You an Extremist?,” Think, 2023.

Animal advocates often contrast life: I discuss an example in “If Not Vegan, Then What?”

The idea of inner maps had been conjectured in the 1940s: The early work was by E. C. Tolman, “Cognitive Maps in Rats and Men,” Psychological Review, 1948. Central to the next round was John O’Keefe and Lynn Nadel, The Hippocampus as a Cognitive Map (1978). Recent work includes H. Freyja Ólafsdóttir et al., “Hippocampal Place Cells Construct Reward Related Sequences Through Unexplored Space,” eLife, 2015.

how bad this experience would be for the rats: At a recent conference in New York City (ASSC 2023), May-Britt Moser, who won a Nobel Prize for her contribution to the “inner map” work, gave a talk in which, at several stages, she emphasized her lab’s concern with their animals’ welfare, and suggested, from their behavior in videos, that they were not in a traumatic situation.

I won’t go through horror stories here in this chapter’s main text: Here are a few examples. Tens of thousands of dogs are used in the United States each year in the testing of potentially harmful substances such as industrial chemicals, which they are forced to ingest in various ways, and also in the investigation of diseases, which are induced. In 2019, the USDA’s number was about 58,000 dogs, most of which are beagles. Some of these studies involve many months of daily forced administration of harmful substances. The dogs are kept in small cages. A dog thirty inches long, for example, can be legally kept in a cage whose floor space is three feet by three feet. If the cage is a bit larger (4.25' × 4.25', doubling the floor area), the dog need never be let out of the cage for exercise.

For more detail, see Glenn Greenwald and Leighton Woodhouse, “Bred to Suffer: Inside the Barbaric U.S. Industry of Dog Experimentation,” The Intercept, May 17, 2018. Regarding the theme of betrayal, see the Intercept article and also this news story: Maya Trabulsi, “Used, Reused or Euthanized: A Dog’s Life in Animal Research,” KPBS, August 12, 2022. “‘The docile nature of beagles is what makes them the victim here,’ said Kathleen Conlee, a former animal researcher.”

In mice and rats, the “forced swim” is widely used to test antidepressants. The animal is put into a water-filled cylinder with no escape and watched as it tries to keep itself afloat and able to breathe. Eventually, it reaches what is sometimes called “behavioral despair” and gives up. Antidepressants tend to make the animal swim for longer.

A pair of studies looked at the creation of “nightmares” in rats, caused by either experiencing an electric shock to the feet or perceiving other rats experience the shock (a shock strong enough to make the rats scream). Well after this experience, rats froze when they were returned to the site of the trauma, and some exhibited sleep patterns suggesting nightmares. See Bin Yu et al., “Different Neural Circuitry Is Involved in Physiological and Psychological Stress-Induced PTSD-Like ‘Nightmares’ in Rats,” Scientific Reports, 2015; and see David Peña-Guzmán, When Animals Dream (2022), for more detail on this work.

Margaret Livingstone’s laboratory at Harvard studied the development of visual parts of the brain by suturing shut the eyelids of two baby macaques for their first year, and raising four more apart from their mothers in a way that gave them almost no experience of faces—their human keepers all wore welding masks. See Michael Arcaro et al., “Anatomical Correlates of Face Patches in Macaque Inferotemporal Cortex,” PNAS, 2020. Controversy arose around this project in 2022, when Livingstone published some observations on maternal bonding, also in PNAS, and several hundred scientists called for the work to end; see David Grimm “Harvard Studies on Infant Monkeys Draw Fire,” Science, October 2022.

Let’s focus on animals that are pretty clearly sentient: Which animals can feel pain and can suffer? These are distinct—stress is suffering that need not involve physical pain, and, more tendentiously, some physical pain might not be minded much. In the food discussion in this chapter, all the animals discussed probably feel physical pain (and at least in many cases, other forms of suffering). There we were looking at mammals, a few birds, and fish. A longer discussion would include crustaceans. In the case of experiments, a lot of work takes place in the uncertain area populated by flies, worms, and others. People tend to look for a cutoff, a border. Who is sentient and who is not? Which side of the line are flies on? That question is understandable as a first move, but the more likely situation is one with no sharp border. The presence of sentience will be not a simple yes-or-no matter, but one with graded and indefinite cases. Papers about animal pain often use fairly similar charts and tables with lists of features that are taken to be relevant to the question—not decisive, but relevant. A list from Lynne Sneddon (“Comparative Physiology of Nociception and Pain,” Physiology, 2017) includes features like avoidance learning, making trade-offs between different kinds of benefits and harms, wound tending, responsiveness to analgesic chemicals, and some others. In many cases, though, these capacities are found both in clear forms and also in borderline, just-barely-visible, or semi-visible versions. The traits involving learning are very much like this. Flatworms, with small and simple nervous systems, can show “conditioned place preference,” avoiding locations where they’ve encountered adverse conditions, and so on. I doubt that a sharp line between yes and no cases will appear as we learn more.

early-twentieth-century work on the role of insulin in diabetes: Examples include Philip Kitcher, “Experimental Animals,” Philosophy and Public Affairs, 2015, and Korsgaard in Fellow Creatures.

The philosopher Philip Kitcher wrote an article: This is also in his “Experimental Animals.”

Macaques, which are small monkeys: In 2018, more than 70,000 nonhuman primates were used in research in the United States, according to the USDA. Most of these would be macaques.

A few initiatives have built and supported retirement facilities: In the United States, these include Chimp Haven, Chimpanzee Sanctuary Northwest, and Primates Incorporated.

8. WILD NATURE

The point made by Pollock and Krasner: This is from the transcript of “Oral History Interview with Lee Krasner, 1964 Nov. 2–1968 Apr. 11,” at the Archives of American Art, Smithsonian Institution. The italics on “am” do not appear in the transcript, but the emphasis is clear if you listen to the recording.

That story can make the whole sequence seem “natural”: James Lovelock, in A Rough Ride to the Future (2014), sometimes seems to be heading toward saying something like this, but I don’t think he does.

Martha Nussbaum has argued that wild nature no longer exists: See her Justice for Animals: Our Collective Responsibility (2023), and especially “A Peopled Wilderness,” The New York Review of Books, December 8, 2022.

a new geological epoch, the “Anthropocene”: The term’s introduction is usually credited to Paul Crutzen and Eugene Stoermer, “The ‘Anthropocene,’” Global Change Newsletter, 2000, though there were some earlier uses, often with slightly different meanings.

I quite like James Lovelock’s way: This is also in A Rough Ride to the Future.

The Cretaceous, the time of the formation of chapter 3’s forests: See Jessica Tierney et al., “Past Climates Inform Our Future,” Science, 2020.

This is a problem for many shell-building invertebrates: I said earlier that the slow, “geological” carbon cycle works in part through sea creatures locking carbon away in their shells, which eventually become limestone. If the ocean becomes so acidic that many of these organisms can’t function, then the laying down of carbon in limestone may slow. It won’t stop, apparently; see James Kasting, “The Goldilocks Planet? How Silicate Weathering Maintains Earth ‘Just Right,’” Elements, 2019.

In the case of birds, a recent report: See Kenneth Rosenberg et al., “Decline of the North American Avifauna,” Science, 2019.

In the case of the cheetahs of chapter 6, only about 7,000 remain: The cheetah number is from the IUCN Red List of Threatened Species, 2021. The Gouldian Finch number is from the World Wildlife Fund. Also according to the World Wildlife Fund, a little over 1,000 mountain gorillas survive. See the online notes for more detail.

That is an exaggeration; the mass extinctions of the past: Peter Brannen, “Earth Is Not in the Midst of a Sixth Mass Extinction,” The Atlantic, June 13, 2017.

The Earth, surprisingly, is a now a bit greener: See Abby Tabor, “Human Activity in China and India Dominates the Greening of Earth, NASA Study Shows,” NASA, Feb 11, 2019.

A “CO₂ fertilization effect”: See Zaichun Zhu et al., “Greening of the Earth and Its Drivers,” Nature Climate Change, 2016.

I understand the alarm that many feel about climate change: When I talk about mobility as part of a solution, I do not intend to minimize the stresses and costs of moving. A sense of place, of home, is a central source of purpose and well-being in the lives of many people. Losses of community patterns, of ways of living in a physical environment, are real and significant.

The Clean Water Act (as it is commonly known) became law in 1972: John Waldman, “Once an Open Sewer, New York Harbor Now Teems with Life. Thank the Clean Water Act,” The New York Times, December 30, 2022.

The reef was saved by a small but energetic conservation movement: See Ann Jones and Gregg Borschmann, “Harold Holt, the Poet and ‘the Bastard from Bingil Bay’: How Reef Conservation Began,” ABC Science, August 11, 2018.

Insects also seem much more likely to have experiences of this kind: If a form of subjective experience exists in some kind of animal, it should generally have some point. It should be part of what helps those animals steer their way through the world. If there was a species in which pain had no useful role at all—if it could never guide an animal toward something better for it—then we might expect this kind of experience to fade as evolution went on. That fact probably does constrain the extent of negative experience in the natural world. But not much; even if pain does have to be selective in order to be useful, it could be extremely common in animal life.

Might experience in some animals not have this other, positive side?: Heather Browning and Walter Veit have written several articles on this topic; see especially “Positive Wild Animal Welfare,” Biology and Philosophy, 2023.

The next step seems to be to think about an overall accounting: On this topic, see the Browning and Veit article cited in the preceding note.

Whether a human life is a good one depends on more: On this topic, see also J. David Velleman, “Well-Being and Time,” Pacific Philosophical Quarterly, 1991.

They prepared a nest in a tree hollow: These two (probably—the identification is not certain) also engaged in physical battles with other birds while establishing the nest. I described these episodes on my MetaZoan blog (metazoan.net).

a number of nonhuman animals have recently been shown: See Alex Schnell et al., “Cuttlefish Exert Self-Control in a Delay of Gratification Task,” Proceedings of the Royal Society B, 2021, both for a very interesting case and for a quick survey of what has been shown in this area.

The philosopher Jeff McMahan has argued: See “The Moral Problem of Predation,” in Philosophy Comes to Dinner (edited by Andrew Chignell et al., 2015).

Lori Gruen has emphasized this problem, in response: This is in her Ethics and Animals, and McMahan responds in the paper cited in the preceding note.

Nussbaum’s view of how animals should be treated: See her Justice for Animals. Here is a point of agreement with Nussbaum. In these recent writings, she is very critical of “safari” tourist experiences that feature the observation of animals being killed by predators. She finds this indicative of something wrong in many human attitudes to wild nature. I think that if one encounters a situation of this kind in an eco-tourism context, it is good to look away.

McMahan draws on a view offered by the philosopher Thomas Nagel: McMahan quotes these passages from Nagel and Regan. See Thomas Nagel, The View from Nowhere (1986), and Tom Regan, The Case for Animal Rights (1983, updated edition 2004). McMahan compares the two editions of Regan.

The total number of poultry, pigs, and cattle: Here I draw on the dissertation work of Rachael Banks (“Experimental and Theoretical Studies of Non-Equilibrium Systems: Motor-Microtubule Assemblies and the Human-Earth System,” Caltech, 2023) and other sources (including https://ourworldindata.org).

Themajority of these animals probably live within: The 74 percent figure is from the Sentience Institute, https://www.sentienceinstitute.org/global-animal-farming-estimates. Their estimate is based in part on the numbers of animals within farming operations of various sizes. As they note, animals can be confined in cruel ways within facilities that do not meet a “CAFO” criterion. In the main text, I emphasize modern chicken and pig farming as the paradigm cases of “factory farming.” See the online notes for more detail.

I don’t discuss fish farming and other forms of aquaculture much here. For some figures and arguments (the numbers are huge), see Becca Franks, Christopher Ewell, and Jennifer Jacquet, “Animal Welfare Risks of Global Aquaculture,” Science Advances, 2021. From 2018: “The farmed aquatic animal tonnage represents 250 to 408 billion individuals, of which 59 to 129 billion are vertebrates (e.g., carps, salmonids).”

Wild mammals, mostly very small, outnumber livestock by something like eighteen to one: See Lior Greenspoon et al., “The Global Biomass of Wild Mammals,” PNAS, 2023. The situation with birds is similar, but not quite as extreme in how the relationships change. Most wild birds are smaller than farmed birds, but the difference is not as big as with mammals. Two recent estimates of the wild bird population are 50 billion (Corey Callaghan, Shinichi Nakagawa, and William Cornwell, “Global Abundance Estimates for 9,700 Bird Species,” PNAS, 2021) and 100 billion (the 2018 biomass distribution paper). Farmed birds are 25 billion or so. I don’t discuss marine mammals here, but their biomass is large. See “The Global Biomass of Wild Mammals.”

If we just think about mammals with bodies larger than one kilogram: See “The Global Biomass of Wild Mammals.”

With these questions on the table, this is also the right point: My third friend was fairly close to the second, but also said that humans have had a natural span that is coming to an end, a fact that is reflected in our present destructiveness.

As we peer forward from our current vantage point: I’ll put more in the online notes. See Jack O’Malley-James et al., “Swansong Biospheres: Refuges for Life and Novel Microbial Biospheres on Terrestrial Planets Near the End of Their Habitable Lifetimes,” International Journal of Astrobiology, 2013. To add insult to injury, we’ll apparently lose our oxygen as well. See Kazumi Ozaki and Christopher Reinhard, “The Future Lifespan of Earth’s Oxygenated Atmosphere,” Nature Geoscience, 2021.

9. SEAMOUNT

In rare and fascinating cases, physically conjoined twins: I have in mind especially Tatiana and Krista Hogan. They are described in Tom Cochrane, “A Case of Shared Consciousness,” Synthese, 2020.

Could the mind, as a feature of life on Earth: Stanislaw Lem’s Solaris (1961) explores this theme.

Here is a broad distinction between kinds of living things: I discuss this distinction in my Darwinian Populations and Natural Selection (2009), and apply it to the evolution of the mind in “Individuality, Subjectivity, and Minimal Cognition,” Biology and Philosophy, 2016. For discussion of the spatial and temporal dimensions of this topic, I am indebted to Rebecca Mann and her forthcoming PhD dissertation, “Complex Individuality: The Spatial, Temporal, and Agential Dimensions of the Problem of Biological Individuality.”

The “immortal jellyfish,” Turritopsis: See Stefano Piraino et al., “Reversing the Life Cycle: Medusae Transforming into Polyps and Cell Transdifferentiation in Turritopsis nutricula (Cnidaria, Hydrozoa),” Biological Bulletin, 1996.

Thinking all this through, Parfit came to see: See his Reasons and Persons (1984). The glass tunnel passage is from chapter 13.

Nagel opposes Parfit’s view of survival and death: This material is from his book The View from Nowhere (1986).

One reply to this argument applies an idea from another philosopher, Bernard Williams: “The Makropulos Case: Reflections on the Tedium of Immortality,” in his Problems of the Self (1973). Thanks to Christine Korsgaard for alerting me to this discussion.

Some parts of the poem: This is the original 1865 version. Later versions have small changes, including deleting the word “beautiful” in the line that begins “My dead absorb.”

PENSIVE, on her dead gazing, I heard the Mother of All,

Desperate, on the torn bodies, on the forms covering the battlefields gazing;

As she call’d to her earth with mournful voice while she stalk’d:

Absorb them well, O my earth, she cried—I charge you, lose not my sons! lose not an atom;

And you streams, absorb them well, taking their dear blood;

And you local spots, and you airs that swim above lightly,

And all you essences of soil and growth—and you, O my rivers’ depths;

And you mountain sides—and the woods where my dear children’s blood, trickling, redden’d;

And you trees, down in your roots, to bequeath to all future trees,

My dead absorb—my young men’s beautiful bodies absorb—and their precious, precious, precious blood;

Which holding in trust for me, faithfully back again give me, many a year hence,

In unseen essence and odor of surface and grass, centuries hence;

In blowing airs from the fields, back again give me my darlings—give my immortal heroes;

Exhale me them centuries hence—breathe me their breath—let not an atom be lost;

O years and graves! O air and soil! O my dead, an aroma sweet!

Exhale them perennial, sweet death, years, centuries hence.

Whitman also tried to have some things both ways: This discussion of Whitman’s attitudes to death draws on David Reynolds, “Fine Specimens,” The New York Review of Books, March 11, 2018.