Figure 3.1 Summary of Human Migrations
Has the scientific method produced a timeline for the appearance of Homo sapiens? Has science identified our relation to other species? Has it produced an accurate picture of our early history?
If so, how complete is that information?
Evolution is the scientific theory to explain the appearance of life on earth, including Homo sapiens. The fossil record documents the history of Homo sapiens from their first appearance until thousands of years ago. Fossils present a clear outline for the appearance of life over the past 3.5 billion years. This record is independent of any theory, such as evolution, because it simply documents the timing of fossils as they are discovered, categorized, and dated. In addition, we are able to study and date other remains, such as tools and ancient soils, to extract further clues about earlier beings, e.g., the food they ate. Finally, recent development of the science of genetics allows us to extract genetic evidence from skeletons or remains (less than 100,000 years old) and compare it to current species. More importantly, the mapping of the human genome (the entirety of an organism’s hereditary information) and other genomes, such as that of the chimpanzee, gives us a window onto the biology and the behavior of past beings far beyond that provided by a basic skeleton.1
The purpose of this chapter is to examine what both the fossil record along with other buried remains and genetic evidence tell us about the appearance and history of Homo sapiens. The information in this chapter summarizes the current state of scientific knowledge (as of 2012), relying upon peer reviewed articles and books written by well-respected scientists.
The scientific method provides a robust way to measure things, such as the age of bones. Over time, the scientific method has proved conducive to correct results—as long as these results can be tested. The scientific method has consistently yielded outstandingly accurate and useful findings on which we rely, and in fact trust, in our lives every day. There is no reason to doubt the fundamental accuracy of the body of knowledge comprising the age and nature of the fossil record and DNA analysis, although refinements continue to emerge on a routine basis.
A comparison of the Genesis creation narrative to scientific findings cannot be made without first understanding that testable knowledge, developed using the scientific method, is, by and large, accurate.
Fossils (from Latin fossus, literally “having been dug up”) are the preserved remains or traces of animals, plants, and other organisms from the remote past. The accumulation of fossils, both discovered and undiscovered, and their placement in fossil-containing rock formations and sedimentary layers (strata) is known as the fossil record. The study of fossils across geological time, their formation, and the evolutionary relationships among them are key functions of paleontology.
The fossil record depicts life’s history as it unfolded over the span of 3.5 billion years.
Fossils can be microscopic, such as single bacterial cells only one micrometer in diameter, or gigantic, like dinosaurs and trees many meters long and weighing several tons. A fossil normally contains only a portion of the deceased organism, usually the part that was partially mineralized during life, such as the bones and teeth of vertebrates or the protective external skeletons of invertebrates. Fossils also may consist of marks left behind by the organism while it was alive, such as a footprint or feces. These are called trace fossils.
Since the early 1900s, absolute dating methods, such as radiometric dating (including potassium/argon, argon/argon, uranium series, and, for very recent fossils, carbon14 dating), have been used to verify the relative ages of fossils and to provide absolute ages for many fossils. Radiometric dating has shown that the earliest known fossils are more than 3.4 billion years old. Various dating methods continue in use today. Despite some variance in these methods, they offer evidence for a very old earth, a planet of approximately 4.6 billion years.
Radioactive dating compares the amount of a naturally occurring radioactive isotope and its decay products, making use of known decay rates. All ordinary matter combines chemical elements, each with its own atomic number, indicating the number of protons in the atomic nucleus. Additionally, elements may exist in different isotopes, with each differing in the number of neutrons in the nucleus. A particular isotope of an element is called a nuclide. Some nuclides are inherently unstable. Eventually, an atom of such a nuclide will spontaneously decay (i.e., radioactively decay) into a different nuclide.
While the exact time at which a particular nucleus decays is unpredictable, a collection of radioactive nuclide atoms decays at a rate described by a parameter known as the half-life, usually given in units of years. After one half-life has elapsed, half of the nuclide’s atoms will have decayed into a daughter nuclide, or decay product. Often, the daughter nuclide is radioactive, leading to the formation of another daughter nuclide, and eventually to a stable (non-radioactive) daughter nuclide; each step in this chain-like process is characterized by a distinct half-life. Usually the half-life of interest in radiometric dating is the longest in the chain, which is the rate-limiting factor in the ultimate transformation of the radioactive nuclide into its stable daughter. Isotopic systems that have been used for radiometric dating have half-lives ranging from only about ten years (tritium) to many thousands of years (carbon 14), to a billion years (potassium-argon), and to even longer periods of time.
A nuclide’s half-life depends on its nuclear properties; it is not affected by external factors such as temperature, pressure, chemicals, or magnetic or electric fields. Nuclear properties and, therefore, the half-life of nuclides have remained stable2 as the earth has evolved and undergone volcanism and weathering (including the Flood described in Genesis). Given this stability in materials containing a radioactive nuclide, the proportion of original nuclide to its decay product(s) has changed in a predictable way owing to the effects of decay over time. In this manner the abundance of related nuclides can be used as a clock to measure time between the incorporation of the original nuclide(s) into a material and the present.
Thus, every bone that is buried and contains radioactive material contains its own nuclear clock. When we uncover a bone today, we can read its age. Similar methods help us keep time, in a basic sense with nuclear clocks, and as a component of advanced systems requiring precise time measurement, from GPS satellite technologies to military weaponry.
By synthesizing the fossil record, classifying fossils, determining their age, and placing them in the context of the geologic scale, scientists have revealed the sequence of life on earth:
1. The fossil record begins with 3.5 to 3.0 billion-year-old rocks from Australia and South Africa, in which are preserved the remains of blue-green algae. In rocks more than a billion years old, only fossils of single-celled organisms are found. In rocks that are about 550 million years old, fossils of simple, multi-cellular animals can be identified. Approximately 530 million years ago (Ma) there was an explosion of life, followed by the gradual appearance of new animals—yet, each within relatively short and even abrupt time frames: fish with jaws 400 million years ago, amphibians 350 million years ago, reptiles 300 million years ago, mammals 230 million years ago, and birds 150 million years ago.3
2. Fossilization is rare. Scientists have unearthed only 250,000 fossil species. Given the vast number of species throughout history, this is a remarkably small fraction. Indeed, the millions of species alive today constitute approximately one percent of all species that have existed.
3. In some cases, the fossil record can be interpreted to show that certain organisms progressed systematically over time, each version displaying what appears to be a modification over the earlier. In other cases, there are large gaps in the fossil record, and the developmental process for some organisms is not as clear. Often, organisms lead to a dead end.
4. Throughout geologic time, life was punctuated by distinct events. Large numbers of organisms appeared in a short time span, and periodic mass extinctions occurred, such as at the end of the Cretaceous Period, when a majority of species disappeared over a relatively short time period.4
Table 3.1 summarizes the timeline for the appearance of life on earth up to the emergence of hominins.
| Time | Fossil record event |
| 3.5 BY ago | The oldest fossils of single-celled organisms date from this time. |
| 2.4 BY ago | The great oxidation event occurs, when oxygen begin? to build in the atmosphere. |
| 2.2 BY ago | Fossil evidence emerges of complex celled organisms. |
| 535 Ma | The Cambrian explosion begins, with many new body forms appearing. |
| 500 Ma | Animals were exploring land at this time. |
| 425 Ma | First primitive macroscopic plants appear on land. |
| 400 Ma | Oldest known insect lives about this time- |
| 39” Ma | First four-limbed animals emerge. |
| 310Ma | Fossil forebears of all modern reptiles, dinosaurs, and birds have appeared. |
| 215 Ma | Firs: mammal; appear. |
| 150 Ma | First bird lives in Europe. |
| 130 Ma | First flowering plants emerge. |
| 65 Ma | The Cretaceous-Tertiary (k/T) extinction wipes out several species, including dinosaurs. |
| 63 Ma | Primates split into two groups: dry-nosed primates and wet-nosed primates. |
| 40 Ma | New World monkeys diverge from higher primates. |
| 25 Ma | Apes split from Old World monkeys. |
| 6-8 Ma | Hominins appear. |
BY = billion years / Ma = million years ago
Table 3.1 Timeline for Appearance of Life on Earth5
Humans leave behind much more than traditional fossils, for example, the cave paintings of Lascaux and other sites. Thus, a richer study of human origin and history can be made by considering not just the fossil record, but also other buried remains. Initially, paleoanthropologists studied how the human skeleton compared to other primates and ancient fossil remains. Then archaeologists studied how the stones and animal bones left by ancient people might relate to their behavioral patterns. Today, we also look at microscopic features of bone, teeth, and ancient soils that preserve evidence of ancient foods, growth rates, and cultural practices.6
Despite the rich knowledge obtained thus far, it must be understood that the fossil record of man and apes is very sparse. Approximately 95 percent of all known fossils are marine invertebrates, about 4.7 percent are algae and plants, about 0.2 percent are insects and other invertebrates, and only about 0.1 percent is vertebrates (animals with bones). Finally, only the smallest imaginable fraction of vertebrate fossils consists of primates (humans, apes, monkeys, and lemurs).7
Recently, genetics has made a major contribution to understanding our origins and expansion across the globe.8
The human body is made of 50 to 100 trillion cells, which comprise the basic units of life and combine to form more complex tissues and organs. Inside each cell, genes form a blueprint for protein production that determines how the cell will function. Genes also determine physical characteristics, or traits. The complete set of some 20,000 to 25,000 genes is called the genome. Only a tiny fraction of the total genome sets the human body apart from that of animals.
Most cells have a similar structure. An outer layer, called the cell membrane, contains a gel-like substance called cytoplasm. Within the cytoplasm are many different specialized “little organs,” called organelles. The most important of these is the nucleus, which controls the cell and houses the genetic material in structures called chromosomes. Another type is the mitochondria, which have their own genome and do not recombine during reproduction.
Chromosomes carry hereditary, genetic information in long strings of DNA (deoxyribonucleic acid) called genes. Humans have 22 numbered pairs of chromosomes and a single pair of sex chromosomes (XX in females and XY in males). Each chromosomal pair includes one inherited from the father and one from the mother.
DNA is the set of genetic instructions for creating an organism. Genes determine which proteins individual cells manufacture, and thus, which function particular cells will perform.
Mutations are random changes in an individual’s DNA sequence that occur rarely in each new generation. They manifest during reproduction when particular DNA strands replicate themselves for the next generation, but not always perfectly. In this manner, genetic markers (a variation that leads to an observed trait) are inherited and passed down through the generations.
Y chromosome DNA, passed from father to son, and mitochondrial DNA, passed from mother to daughter, both occasionally experience mutations leading to markers. These mutations occurring in otherwise continuous genetic replication serve as signposts as part of the historical record of humans on earth. By following a marker back through time, geneticists identify the most recent common ancestor of all who have a particular marker. This way a full family tree of humans can be built and traced back to a common ancestor.
Thus, the study of genetics whereby genes of current human populations are compared to each other, to previous remains or fossil samples9 and to the rest of the primates, further informs what we learn from the fossil record and other buried remains. This process of combining DNA and physical evidence to reveal the history of ancient humanity constitutes the emerging field of genetic anthropology. Genetics provides key information on how genetically similar or dissimilar we are to different primates, to prior hominids, and to each other.
In particular, genetics has helped to establish our single common ancestry in Africa and allowed us to trace our travels throughout the planet.
Much of this advance has been made possible by the scientific endeavors that aim to determine the complete genome sequence of humans and chimpanzees; the endeavors are known as genome projects.
Completed in 2003, the Human Genome Project10 (HGP) was a 13-year project coordinated by the U.S. Department of Energy and the National Institutes of Health. The UK, Japan, France, Germany, China, and other nations contributed to the project. Goals included identification of all the approximately 20,000 to 25,000 genes in human DNA, determination of the sequences of the 3 billion chemical base pairs that make up human DNA, and storage of the information in databases accessible to research and industry.
In early 2002, the National Human Genome Research Institute (NHGRI) agreed to support an initial chimpanzee genome sequencing project, which was expanded to include a higher quality gene sequencing objective in late 2003.
Significant information has been obtained from these projects and other studies. This information is usually quoted in a percentage of difference or similarity in genes. However, percentages can be calculated in varying ways and thus differ. Nonetheless, for any particular method of calculation, relative similarities and differences can be ascertained. For example,11 the genetic difference between individual humans today is estimated at about 0.1% on average; study of the same aspects of the chimpanzee genome indicates a difference of about 1.2% (or 2% measured in a different manner).12 The bonobo, which is a close cousin of chimpanzees, differs from humans to the same degree. The DNA difference with gorillas, another of the African apes, is about 1.6%. Most importantly, chimpanzees, bonobos, and humans all show this same amount of difference from gorillas. A difference of 3.1% distinguishes us and the African apes from the Asian great ape, the orangutan. The great apes and humans differ from rhesus monkeys, for example, by about 7% in their DNA.
Scientists synthesize observable characteristics or traits of humans and their precursors, these including morphology, genetics, development, biochemical or physiological properties, behavior, and products of behavior (cave paintings and the like), to arrive at the timeline for the appearance of humans. The timeline encompasses the development of the genus Homo, including the emergence of Homo sapiens as a distinct species and a unique category of hominids and mammals.
The term “human” in the context of human evolution refers to the genus Homo, but studies of human evolution usually include other earlier hominins, such as the Australopithecines (a species that was bipedal and dentally similar to humans but with a brain size not much larger than that of modern apes), from which the genus Homo is thought to have diverged about 2.3 to 2.4 million years ago in Africa.13
The billions of human beings living today all belong to one species: Homo sapiens. As in all species, there is variation among individual human beings, from size and shape to skin tone and eye color. But we are much more alike than we are different. We are, in fact, remarkably similar. The DNA of all human beings living today is 99.9% alike.14
Humans are primates. Physical and genetic similarities show that the modern human species, Homo sapiens, has a very close relationship to another group of primate species, the apes. Hominins and the great apes (large apes) of Africa, chimpanzees and gorillas, are believed to share a common ancestor that lived between 8 and 6 million years ago.15 Hominins first appeared in Africa. The fossils of early hominins who lived between 6 and 2 million years ago come entirely from Africa.
Most scientists currently recognize some 15 to 20 different species of hominins. Scientists do not all agree, however, about how these species are related, or which ones simply died out. In particular, several species and subspecies of Homo existed and are now extinct; examples include Homo erectus (which inhabited Asia, Africa, and Europe), and Neanderthals (which inhabited Europe and Asia). Archaic Homo sapiens appeared between 400,000 and 250,000 years ago.
The dominant view among scientists concerning the origin of anatomically modern humans, Homo sapiens, is the hypothesis known as Out of Africa, or recent African origin hypothesis,16 which argues that Homo sapiens arose in Africa about 200,000 years ago17 and had developed modern behaviors and migrated out of the continent by around 60,000 years ago. They then went on to replace populations of Homo erectus in Asia and Neanderthals in Europe, with the last of the other homo species (Neanderthals) becoming extinct about 30,000 years ago.
Behavioral modernity18 is a term used to refer to a set of traits that distinguish present-day humans and their recent ancestors from both living primates and other extinct hominid lineages. It is the point at which Homo sapiens began to demonstrate a reliance on symbolic thought and to express cultural creativity. Modern human behavior19 is characterized by:
1. Abstract thinking: the ability to act with reference to abstract concepts not limited in time or space
2. Planning depth: the ability to formulate strategies based on past experience and to act upon them in a group context
3. Symbolic behavior: the ability to represent objects, people, and abstract concepts with arbitrary symbols, vocal or visual, and to reify such symbols in cultural practice
4. Behavioral, economic and technological innovativeness
Furthermore these developments are thought to be associated with the origin of language.20
The onset of modernity is not easy to define. Is it when humans first made sophisticated tools? When they first made elaborate cave paintings? When they first made jewelry for decoration or self-ornamentation? The debate continues.
The archaeological evidence available leaves little indication that Homo sapiens behaved any differently from earlier Homo until at least 120,000 years ago (or 120 KYA where KYA means one thousand years ago). They retained the same stone tools and hunted less efficiently than did modern humans. It is hard to date when modernity began, although most agree that the full set of modern behaviors had appeared by 60,000 years ago.
There are two main theories regarding the emergence of modern human behavior.21 One theory holds that behavioral modernity occurred as a sudden event about 60,000 years ago. The second theory suggests that there was never any single technological or cognitive revolution. Proponents of this view argue that modern human behavior developed gradually. They point to arguably modern behaviors, such as use of pigment, decorations,22 and burial of the dead, as far back as about 100,000 years ago. However, these early examples are only a few of the full set of key modern behaviors that had appeared by 60,000 years ago.
The migration of humans out of Africa to the entire world is a remarkable account reconstructed from buried remains and genetic analysis. It is not known why humans left Africa after being there for over 100,000 years, and why they felt compelled to inhabit every part of the world. However, various studies and simulations have revealed that climate change was a significant factor.23 Climate affects food supply and human migration patterns match reasonably well with the availability of food. Furthermore, major climate change events facilitated the worldwide expansion. For example, the migration to Australia was facilitated by an ice age that lowered the sea level—making the island hopping journey from Asia to Australia possible.
Despite the role that climate change may have played in aiding the migration, what it took to accomplish the task was remarkable.24 Migration required the rapid development of a vast range of new knowledge, tools and social arrangements. In Africa, people were tropical foragers. When humans moved toward northern Eurasia, they experienced a hostile climate where temperatures fell to −20°C for months at a time and there were often high winds. Surviving in such environments required tailored clothing, well-engineered shelters, and techniques for creating light and heat. Other travels and environments presented different problems. For example, much of the Americas were conquered by humans traveling in small water crafts, segment by segment, along the west coast. No small task—and still difficult today even with modern kayaks, VHF radios (to obtain regular weather and marine forecasts), and GPS!
Figure 3.1 shows a summary of the migrations.25 Not shown are many smaller migrations, for example those to the interior of continents culminating with migrations into northern Canada and Europe, as well as the Sahara, by about 8,000 years ago.
Figure 3.1 Summary of Human Migrations
Table 3.2 shows a very brief summary of the timeline for the appearance of humans and their early history.
| Time | Appearance |
| 6-8 Ma | Hominins. |
| 4.4 Ma | Ardipithecus, a very early hominin, had a small brain measuring about 350 cm3. It lived largely in the forest and was likely bipedal, although its feet were adapted for grasping rather than walking long distances. |
| 3.6 Ma | Australopithecus afarensis, compared to modern and extinct great apes, had canines and molars that were reduced although still relatively larger than those of modern humans. A. afarensis also had a relatively small brain size (~380—430 cm3). |
| 2.5 Ma | First Homo: Homo habilis, compared to modern humans, was short with disproportionately long arms and a brain slightly less than half the size of our brain. First to use stone tools. Became extinct by 1.4 Ma. |
| 1.8 Ma | Homo erectus bore a striking resemblance to modern humans, but with a brain about 74% of modern size. Its forehead was less sloping and teeth were smaller. Lived side by side with Homo habilis until 1.4 Ma and became extinct by 400 KYA. |
| 1.3 Ma | Homo in Europe. |
| 200 KYA | Neanderthals, compared to humans, had more robust build and distinctive morphological features; were likely much stronger. Made advanced tools. Extinct by 30 KYA. |
| 200 KYA | Homo sapiens, anatomically modern humans. |
| By 60 KYA | Behaviorally modern humans had appeared and left Africa. |
| 60 KYA | Migration to South Asia. |
| 50 KYA | Migration to Australia and Europe. |
| 14 KYA | Migration to Americas, reaching southern Chile. |
| 10 KYA | Evidence of farming and domestication of animals. |
Table 3.2 Human Timeline26
Language is an important and unique aspect of human behavior. It is still unknown how and when language emerged.
Language is a very distinct and complex form of communication. Unlike visual communication, where one grasps a full picture at once, language is a form of communication that is serial. Language has to follow a specific order and requires great coordination. People make sounds using the vocal tract, throat, and mouth. Those sounds are transmitted to a listener, who hears them with his ears and then processes them with his brain. Not only is special equipment required to produce sound and to hear it, but also great intelligence is required to structure the communication resulting from sounds while maintaining full coordination with the breathing process. This is akin to playing music on an instrument. Not only is a musical instrument required, but one must also possess the intelligence and skill to work the instrument to produce the music.
For example, chimpanzees and bonobos don’t have the vocal channel that humans do and therefore can’t produce human speech sounds. However, they can learn how to make signs, and for this reason could be expected to communicate via sign language. Nonetheless, they simply do not possess the intelligence required to do so. Scientists27 have taught a chimp, Kanzi, hundreds of signs. However, Kanzi has never mastered the combination of signs into longer utterances, something humans can manage by age two or three. Compared to humans, there seems to be a difference in chimpanzees’ ability to generate this higher level of structure known as grammar.
The fossil record contains scant evidence of language development because it preserves very little about the structure of the brain and, in particular, the structure of the brain areas that may be related to language. Nonetheless, through genetic analysis and fossil remains, one can attempt to determine when the equipment to make and receive human language sounds emerged.
It is mostly undisputed that Australopithecines did not have communication systems significantly different from those found in great apes in general. Anatomical features such as the L-shaped vocal tract have appeared gradually in an evolving fashion, as opposed to appearing suddenly.28 Hence it is most likely that Homo habilis and Homo erectus had some form of communication intermediate between that of modern humans and that of other primates.29 Hominins who lived earlier than 300,000 years ago had a cranial nerve leading to the tongue (which is believed to reflect speech abilities) more akin to those of chimpanzees than modern humans.30
In 2007, the discovery of a Neanderthal with a modern-looking hyoid bone (or lingual bone, a horseshoe-shaped bone situated in the neck that serves as an anchoring structure for the larynx and is critical for speech production) suggests to some that Neanderthals may have been anatomically capable of producing sounds similar to modern humans.31 However, many researchers conclude that the presence of this modern lingual bone is not sufficient to establish that the species was anatomically capable of making modern language sounds.32
In addition, even if Neanderthals may have been anatomically able to speak, scholars doubt that they possessed a fully modern language.33 Neanderthals behaved the same as earlier hominin populations that did not have language apparatus; had Neanderthals possessed a fully modern language capability we would expect them to have behaved more like modern humans. As we have seen with Kanzi, the key to our complex form of communication is not equipment, but rather the ability to structure communication via grammar.
Grammar has always been the central focus of linguistics. One of the most famous figures in the study of grammar is the linguist Noam Chomsky. He argues34 there are patterns that occur in human languages that cannot be learned by simply listening to what other people say. Humans seem to be born with an innate ability to sift out patterns that aren’t obvious from the speech around them so they can create those patterns. Chomsky calls this argument the poverty of the stimulus—the stimuli that are present in an environment aren’t enough to master a natural language.
Today’s linguists disagree with Chomsky about the extent to which language is innate.35 Many believe that language is largely learned uniquely and differently by different kinds of people. However, a recent finding obtained by research with infants suggests that the neural foundations of language acquisition are present at birth.36 In summary, there is scientific consensus that language is unique to our species, and there is evidence that suggests that language could be innate. Finally, as is the case with the emergence of modern human behaviors, there is no agreement on the exact time when language emerged, although most believe it evolved concurrently with modern human behavior.
* * * * * * * * * * * * * * *
1 John Hawks, The Rise Of Humans: Great Scientific Debates, (U.S.A. The Teaching Company, 2011), Introduction.
2 G.T. Emery, “Perturbation of Nuclear Decay Rates,” Annual Review of Nuclear Science (ACS Publications) v. 22, 1972, pp. 165–202. Note that the most reliable dating involves the use and overlap of several radioactive isotope series.
3 Michael Marshall, “Timeline: The Evolution of Life,” New Scientist, 14 July 2009.
4 Stephen Jay Gould, “The Evolution of Life on Earth,” Scientific American, October 1994, pp. 85–91.
5 (i) Michael Marshall, “Timeline: The Evolution of Life,” New Scientist, 14 July 2009.
(ii) Stephen Jay Gould, The Book of Life: An Illustrated History of the Evolution of Life on Earth, Second Edition (New York: W. W. Norton Inc., 2001).
(iii) David M. Raup and J. John Sepkoski Jr., “Mass Extinctions in the Marine Fossil Record,” Science v. 215 No. 4539, 19 March 1982, pp. 1501–1503.
(iv) John Alroy, “Dynamics of Origination and Extinction in the Marine Fossil Record,” The National Academy of Sciences of the USA, 105 Supplement 1 (2008 August 12), pp. 11536–11542.
6 John Hawks, The Rise Of Humans: Great Scientific Debates, (U.S.A. The Teaching Company, 2011), Introduction.
7 “Facts on fossil record,” Wisconsin Regional Primate Research Center, April 26 2001, Primate Info Net. www.primate.wisc.edu/pin/askfaq.html.
8 (i)Chris Johns (Editor) “The Greatest Journey Ever Told: The Trail of Our DNA,” National Geographic, Vol. 209, No. 3, March 2006.
(ii) Noah A. Rosenberg, et al, “Genetic Structure of Human Populations,” Science, v. 298 no. 5602, (20 December 2002), pp. 2381–2385.
(iii) Mark Stoneking and Johannes Krause, “Learning about human population history from ancient and modern genomes,” Nature Reviews Genetics, 12, September 2011, pp. 603–614.
9 DNA fragments can survive for 50,000 to 100,000 years.
10 U.S. Department of Energy Genome Programs, genomics.energy.gov.
11 Mark Stoneking and Johannes Krause, “Learning about human population history from ancient and modern genomes,” Nature Reviews Genetics, 12, September 2011, pp. 603–614.
12 The Chimpanzee Sequencing and Analysis Consortium, “Initial sequence of the chimpanzee genome and comparison with the human genome,” Nature, 437, 1 September 2005, pp. 69–87.
13 John Hawks, The Rise Of Humans: Great Scientific Debates, (U.S.A. The Teaching Company, 2011), p. 3.
14 Noah A. Rosenberg, et al, “Genetic Structure of Human Populations,” Science, v. 298 no. 5602, (20 December 2002), pp. 2381–2385.
15 (i) John Hawks, The Rise Of Humans: Great Scientific Debates, (U.S.A. The Teaching Company, 2011). The time of the first common ancestor maybe revised to as much as a few million years earlier, although current consensus is still 6-8 million years ago. See Catherine Brahic, “Our true dawn,” New Scientist, v. 16, No 2892, (November 24, 2012) pp. 34–37.
(ii) Katherine Harmon, “Shattered Ancestry” Scientific American 308(2), February 2013, pp. 42–49.
16 Paul Mellars, “Why Did Modern Human Populations Disperse from Africa ca. 60,000 Years Ago?” Proceedings of the National Academy of Sciences, v.103/25 (2006), pp. 9381–9386.
17 The earliest fossil evidence comes from skulls dated at 195,000 years ago. See Michael Hopkin, “Ethiopia is top choice for cradle of Homo sapiens,” Nature News (2005-02-16), doi:10.1038/ news050214-10.
18 Kate Wong, “The Morning of the Modern Mind,” Scientific American, July 2005, No. 23, pp. 12-19.
19 Sally McBrearty, Alison S Brooks, “The Revolution That Wasn’t: A New Interpretation of the Origin of Modern Human Behavior” Journal of Human Evolution, 39, 2000. pp.453–563.
20 Paul Mellars, “Why Did Modern Human Populations Disperse from Africa ca. 60,000 Years Ago?” Proceedings of the National Academy of Sciences, v.103/25 (2006), pp. 9381–9386.
21 Hillary Mayell, “When Did ‘Modern’ Behavior Emerge in Humans?” National Geographic News, February 20, 2003. news.nationalgeographic.com/news/2003/02/0220_030220_human origins2.html.
22 Abdeljalil Bouzouggar, et al, “82,000-year-old shell beads from North Africa and implications for the origins of modern human behavior,” Proceedings of the National Academey of Sciences USA, 104(24), 2007 June 12, pp. 9964–9.
23 (i) Mati Milstein, “Climate Change Allowed Humans to Migrate Out of Africa”, National Geographic Adventure, August 29 2007, http://news.nationalgeographic.com/news/2007/08/070829-africa-rains_2.html.
(ii) Robert Marshall, “Climate change key to world domination”, New Scientist, Vol. 215, No. 2883, September 22 2012, p. 12.
24 Robert Boyd, et al, “The cultural niche: Why social learning is essential for human adaptation,” PNAS, v. 108 no. Supplement 2 June 28, 2011, pp. 10918–10925.
25 (i) Chris Johns (Editor) “The Greatest Journey Ever Told: The Trail of Our DNA,” National Geographic, Vol. 209, No. 3, March 2006.
(ii) Heather Pringle, “The 1st Americans,” Scientific American, November 2011, pp. 36–45.
26 John Hawks, The Rise Of Humans: Great Scientific Debates, (U.S.A. The Teaching Company, 2011).
27 John Hawks, The Rise Of Humans: Great Scientific Debates, (U.S.A. The Teaching Company, 2011), p. 93.
28 Steve Olson, Mapping Human History (Boston: Houghton Mifflin Books, 2002). “Any adaptations produced by evolution are useful only in the present, not in some vaguely defined future. So the vocal anatomy and neural circuits needed for language could not have arisen for something that did not yet exist.”
29 Merritt Ruhlen, Origin of Language (NY: Wiley, 1994). p. 3 “Earlier human ancestors, such as Homo habilis and Homo erectus, would likely have possessed less developed forms of language, forms intermediate between the rudimentary communicative systems of, say, chimpanzees and modern human languages.”
30 B. Arensburg, A. M. B. Vandermeersch, H. Duday, L. A. Schepartz and Y. Rak, “A Middle Palaeolithic human hyoid bone,” Nature 338, 1989, pp. 758–760.
31 B. Arsenburg, et al., “A reappraisal of the anatomical basis for speech in middle Palaeolithic hominids,” American Journal of Physiological Anthropology 83, 1990, pp. 137–146.
32 Tecumseh W. Fitch, “The evolution of speech: a comparative review,” Trends in Cognitive Science, Vol. 4, No. 7, July 2000, pp. 258–266.
33 (i) Erica Klarreich, “Biography of Richard G. Klein.” Proceedings of the National Academy of Sciences of the United States of America 101 (16), April 20, 2004, pp. 5705-5707.
(ii) Richard G. Klein, “Three Distinct Human Populations,” Biological and Behavioral Origins of Modern Humans. Access Excellence @ The National Health Museum. Retrieved 2011-12-28, www.accessexcellence.org/BF/bf02/klein/bf02e3.php.
(iii) David Robson, “Puzzles of evolution: When did language evolve?,” New Scientist 2857, March 24, 2012, p. 38.
34 John Hawks, The Rise Of Humans: Great Scientific Debates, (U.S.A. The Teaching Company, 2011), p. 93.
35 John Hawks, The Rise Of Humans: Great Scientific Debates, (U.S.A. The Teaching Company, 2011), pp. 94-95.
36 Judit Gervain, Iris Berent, and Janet F. Werker, “Binding at Birth: The Newborn Brain Detects Identity Relations and Sequential Position in Speech,” Journal of Cognitive Neuroscience, Vol. 24, No. 3, March 2012, pp. 564–574.