Human evolution
This week we’re reading Chapter 7 (pages 250-293) of Fitch (2010) (available online via DiscoverEd).
As usual, read this blog, do the Fitch reading, and then take the quiz on Top Hat to test your understanding.
Chapter 7 tells the (as of 2010) story of human evolution, focusing on our trajectory since our last common ancestor with chimpanzees. And, as with most evolutionary stories, the tale from early australopithecines to modern Homo sapiens is a messy one: far from being a steady, obvious, unbroken chain, human evolution is littered with false starts and dead ends, with most of our species’ history having been spent alongside a variety of closely-related hominids. If you want to see some pictures or a slightly more user-friendly graphical depiction of the human family tree, check out The Smithsonian’s interactive family tree.
In this chapter, Fitch draws upon three main sources of evidence: fossil, archaeological, and genetic.
The first major conclusion from the fossil record is that bipedalism arose relatively early on: from what we can ascertain, thanks to hints from recovered skeletons and the famous Laetoli footprints, it appears australopithecines were standing (somewhat) upright round 3.6 million years ago. However, australopithecines and other early hominids were relatively small-brained, which leads us to the second main conclusion: that substantial changes to cranial capacity did not occur until Homoerectus came onto the scene approximately 1.9 million years ago. But,as Fitch notes, cranial capacity is not always indicative of more sophisticated behaviour – and we should be cautious when making such interpretations.
The arrival of Homo erectus also coincides with substantial changes in the archaeological record: it is during the time of Homo erectus that we observe the transition from the Oldowan to the Acheulean mode of production. The Acheulean tool industry would last for a million years and it is not until the arrival of Neanderthals around 300,000 years ago that we see any substantial changes in this technology. The next major industry that Fitch discusses is the Aurignacian. Also known as the Upper Paleolithic Revolution, the Aurignacian is closely linked with the spread of modern humans around 40,000 years ago, and is marked by the appearance of sophisticated artwork and diversification in tool industries.
Paleogenetic data is one of the major success stories in this chapter. Fitch discusses how genetic data is useful in providing clarity on several issues, including: dating our last common ancestor with chimpanzees, the possibility of interbreeding between Neanderthals and anatomically modern humans, and the hunt for genetic variants underpinning our cognitive and neurological anatomy. And as we shall see below, genetic evidence is playing an increasingly important role, especially as technology improves in extracting and sequencing genomes from extinct species.
Taken together, these three lines of evidence offer a compelling story about human evolution, providing insights into when hominids first began to walk upright and lose their thick hair to the shift toward a meat-based diet and the increased reliance on a material culture. Yet, despite considerable advances in what we know about human evolution, the long-standing debates surrounding when and how language emerged remain largely unsolved. As it currently stands, the available evidence has been argued to be consistent with the relatively early emergence of language in Homo erectus, or extremely late in modern Homo sapiens, with there being many proponents on both sides of the debate. In short, there is still a lot we don’t know.
One of the big mysteries Fitch presents is the gap between the emergence of morphologically modern humans and the approximately 100,000 year gap until the Upper Paleolithic Revolution. One hypothesis is that the gap represents a genuine change in the fundamental makeup of human cognition. That is to say: while early Homo sapiens had bodies which looked remarkably human, their brains were fundamentally different. After all, there is no biological reason to suspect that changes in cognition are concomitant with changes in skeletal morphology. Fitch raises an interesting parallel with that of modern songbirds: despite having very similar skeletal forms, songbirds vary considerably both genetically and behaviourally (a nice example is the differences between white-rumped munias and a domesticated variety known as the Bengalese Finch).
There are other hypotheses that Fitch does not mention. For instance, one interesting possibility is that changes in demography allowed humans to sustain more advanced levels of technology (see Richerson, Boyd & Bettinger, 2009; Lycett & Norton, 2010). Under this hypothesis, demography influences cultural evolution through its effects on the rate of innovation. Assuming that useful innovations are rare, then small isolated populations will have low rates of invention, whereas larger and denser populations will have higher rates of invention. As such, increases in population size might allow for greater levels of cumulative cultural learning, with large and dense populations being better equipped to mitigate against the loss of innovations in skills and abilities. Conversely, smaller populations are more susceptible to losing new innovations as they pop up, decreasing the probability of them being successfully transmitted from one generation to the next.
Since Fitch first published his book in 2010 there have been some major breakthroughs in study of human evolution. Many of you might be aware of the two new additions to the Homo lineage: Denisovans and Homo naledi. The picture has also changed somewhat in terms of genetic evidence. Another exciting discovery is that it seems Neanderthals and Denisovans interbreed with modern humans: an estimated 1.5-2.1% of the Eurasian genome is believed to be derived from Neanderthals, and the remains of a (probably sterile) individual with a Neanderthal mother and a Denisovan father were discovered in Russia. And the arrival of modern humans has been implicated in the extinction of Homo floresiensis, also known as “Flores Man” or “hobbits”.
For information on Neanderthals and Denisovans, you could watch these videos by John Hawks (a paleoanthropologist who was involved in the discovery of Homo naledi and has written a considerable amount on Neanderthal-human admixture):
Fitch, W. T. (2010). The Evolution of Language. Cambridge: Cambridge University Press.
Lycett, S., & Norton, C. (2010). A demographic model for Palaeolithic technological evolution: The case of East Asia and the Movius Line. Quaternary International, 211 (1-2), 55-65 DOI:10.1016/j.quaint.2008.12.001.
Richerson, P.J., Boyd, R., & Bettinger, R.L. (2009). Cultural innovations and demographic change. Human biology; an international record of research, 81 (2-3), 211-35 PMID: 19943744.
This blog post was originally written by James Winters.
All aspects of this work are licensed under a Creative Commons Attribution 4.0 International License.