In The Descent of Man, Darwin considers the difference between the minds of humans and other creatures. He speculates on the cognitive abilities of a hypothetical ape, and notes that while it could crack a nut with a stone, it would not be able to fashion a tool from that stone. Nor could that ape “follow out a train of metaphysical reasoning, or solve a mathematical problem, or reflect on
God, or admire a grand natural scene.”
But Darwin goes on to suggest that “emotions and faculties, such as love, memory, attention, curiosity, imitation, reason” may be found in some incipient form in other animals. He writes that the difference between the mind of humans and other animals is one of “degree and not kind.”
This section is a beautiful piece of prose, and that is a memorable phrase, which has been appropriated by fields well outside of biological evolution to describe things which differ not fundamentally, but merely by position on a spectrum.
As for its original meaning in the evolution of us, I no longer know if it is true. As we have seen, in technology, in sex, in fashion, we are different from other animals. But the implication that the differences between us and them are determined by our relative position on a line is questionable. Our use of tools is so very much more sophisticated than that of a crow or dolphin, or even a chimpanzee, that it doesn’t seem fair to simply attribute this to our more advanced position on a spectrum. Our sexual desires and proclivities may resemble behaviors in some animals, but the motivation for the rampant sexual behavior of the bonobos serves a very different social function, even if the various physical mechanics are familiar to us. On the other hand, maybe our enjoyment of oral sex is not really different from those two unusual bears in Zagreb. Is Julie’s ear-twig merely a simpler, incipient version of any extravagant fashion that we adorn ourselves with today?
We have a culture that doesn’t only surpass all others in sophistication, it simply doesn’t exist in any other species, and the way in which our knowledge is passed around, among contemporaries and down the generations, is barely glimpsed outside of the genus Homo.
Perhaps the phrase “different in degree and not kind” is too simple, too binary to be of use in understanding the story of the human animal. Perhaps it is better to revel in the complexities of our evolution, and just acknowledge, without superiority or judgment, that we are different.
How did this arise? Why are we different? We strive so desperately to find it: the switch that turned us from one being into another, the thing that made us human. In our stories, and in science to a certain extent, we crave triggers. We search for clarity and hope for narrative satisfaction, and that in our searching we will reveal the story of how we became us.
Here’s the rub: evolution doesn’t work like that. Even as a metaphor for some real transition in our origins, drama imposes a flip which never happened. Certainly, there are nodes in the story of life on Earth. These pivotal events are few and far between, but there are singular moments when the trajectory of evolution is forever altered. For example, the birth of complex life some two billion years ago—when one cell climbed inside another, and in so doing spawned everything else on the tree of life. That appears to have happened just once. There was only one meteorite that triggered the end of the dinosaurs’ 150-million-year reign, and in doing so, freed up environmental niches in which small mammals and small birds could thrive. These are undeniable events—things were different the day after—but mostly life evolves messily and slowly, much like our own lives. It may be punctuated by moments, but you are mostly a connivance of four billion years of biology, and a few years of living in and among other organisms and your environment.
It is not easy to consider our own story. Evidence from prehistory is scarce, and we put together a narrative using fragments from our past. Two factors significantly hamper our ability to get our heads around our own evolution and existence. Time is a concept that plays against us. The timescales we think about in evolution are inconceivable and bear almost no relationship to a lived life. We can think sensibly about two, maybe three generations in either direction from us—our great-grandparents, or great-grandchildren. But when thinking about the foundations of our species, we are talking about thousands or more. Homo habilis, for instance, emerged more than two million years ago, a period filled with hundreds of thousands of generations.
And there’s another rub. Singular moments or single causes are easier for us to process than an inscrutable system millions of years in the making. Science is inadvertently responsible for fomenting both granularity and linearity in understanding complexity, because that is how we have to pick apart intensely integrated systems such as our bodies, our minds, or our evolutionary story. We find one tooth or a hyoid bone in the dirt from an age ago and try to extract every ounce of data out of it, and then fit it back into the bigger picture of the lives of ancient people. Or we take one gene, and look at how it changed in people, and where they took that gene all over the world. Each of these elements is but one part in a giant four-dimensional puzzle; four because living organisms pass through time as well as physical space. As a species, all the things we do are unique, and are also seen all over the natural world.
And so we chip away at ourselves, perpetually introducing new ideas and new data and striving to ignore or file away the preconceptions or baggage that might hamstring our understanding of our own story.
But why are we different? Separating biological from cultural evolution creates a false divide between them, when in fact they are intrinsically interdependent—biology drives culture and vice versa—but it is necessary to look at the individual pieces of the puzzle before we can fit them back together. Let’s deal first with the biological, which in evolutionary terms means DNA.