Book Review: The Humans Who Went Extinct

Occasional contributor Nasa, of Old English translation fame, returns to us with a book review. Like all of Nasa’s work, it is scholarly in both topic and length, and comes with a list of citations for your perusal. Given the size of it, and my desire to keep to a proper odd-Tuesday even-Friday schedule as far as Nathaniel Cannon numbering goes, I think I’ll let it stand for this week’s content. Enjoy! -Fishbreath

Imagine a campfire under a starry sky, and across the little, flickering fire from you, a storyteller. The light of the fire extends only a few feet, and only the closest patch of ground is really distinct; beyond, shadows that flicker with the shifting light of the fire quickly dim off into the vast, unbroken blackness of night in the great outdoors—the great unknown. Whatever may be out there in the vastness, submerged in the impenetrable dark, you can’t see it for yourself, but the storyteller weaves imagination and inference, dotted here and there with references to the few landmarks that you can recognize, perhaps, in the faint starlight, into a compelling narrative about the shape of the land around you, and the reasons why it has come to be so.

Appropriately enough, this analogy of a tiny campfire in the vast darkness of the landscape, and the contents of that darkness filled in by a canny storyteller, is a good fit to the narrative journey which we take under the guidance of Clive Finlayson as he traces the emergence from early hominins of modern humans and modern human society in his recent The Humans Who Went Extinct. The narrative is interesting, compelling, and plausible, carried by the author’s considerable knowledge, inference, and above all, his powerful imagination, but if we ask whether the story Finlayson tells is an accurate description of what lies covered by the vast, thick darkness of deep time, we are forced to admit firstly that it is probably inaccurate in many details and even some of its core points, but moreover and with much greater certainty, that we still do not know. The darkness of time still blinds us almost completely to the enormous majority of our past.

The scale of Finlayson’s book is nothing if not ambitious. He seeks, in a handy and trim 220 pages of prose (in the mass-market paperback, ISBN 978-0-19-923919-1) to trace an arc of cause and effect all the way from the climate-driven expansion of the earliest primates at the dawn of the Eocene, 55 million years ago, to the rise of agriculture within the last ten to twelve thousand. If, as the saying goes, “history doesn’t repeat itself, but it often rhymes” then Finlayson takes a step further, rendering a portrait of history as no mere casual rhymester, but as an intensely persistent poet, as a few key notions are brought to bear on situations again and again, all the way from the squirrely eocene ancestors we share with lemurs and capuchin monkeys up to the development of anthropogenic global warming: climate and geography determine history; stressed, marginal populations are better positioned to adapt and expand under changing conditions than their conservative and less stressed counterparts; luck often conquers all. Though I fully believe that Finlayson’s own conception of human history across this enormous swath of time is much subtler and more acute than this, pop-sci books that fly off the shelves because they’re tractable and interesting don’t lend themselves to nuance, and what we find ourselves being told in Finlayson’s volume is not that history has a certain rhyme to it, but that, essentially, the cause for the success of miocene apes is the same as the cause for the success of hominins, or anatomically modern humans, or Siberian big game hunters, and you don’t need to be a career paleoanthropologist to raise your eyebrow at that.

There are two unfortunate results of this: the smaller and lesser of the two is that occasionally Finlayson must allow facts a little more slack than some will be comfortable with (or, more precisely, a little more slack with the question of what is settled fact and what is still debated or speculative), but by far the larger and—to my mind—by far the more unfortunate is that he profoundly neglects honest reflection of the scale of what we don’t know. A single example of the latter may suffice to clarify what I mean.

A large part of the book (though not nearly as large as the subtitle might lead one to believe) is devoted to explaining why Neanderthals went extinct without a trace, while modern humans survived. First of all, though the evidence at the time Finlayson was writing seemed to be leaning in the opposite direction, we now have a much greater certainty that in fact, Neanderthal people didn’t go extinct without a trace at all— they are the ancestors (albeit the minority ancestors) of most human beings on the globe today, contributing a few percent of the heritage of probably all modern people whose background is not exclusively rooted in sub-Saharan Africa (see Racimo et al., 2015; et alibi). In light of this increasing certainty, Finlayson’s explanations for why Neanderthals and modern humans did not interbreed are obviously somewhat embarrassed.

A greater embarrassment for Finlayson’s narrative, however, is the mounting evidence that what has yet to be explained or understood is not the interaction between Neanderthal people on the one hand and our majority ancestors on the other, but rather a history of interaction between an as-yet unknown but certainly larger variety of human and hominin populations: we can now say with some certainty that an otherwise extinct population known as the Denisovans, only slightly more closely related to the Neanderthals than they were to our majority ancestors, recently inhabited central and South or Southeast Asia, and contributed a few percent to the genomes of populations who nowadays live in Australia, Papua, and Melanesia (Reich at al., 2011; Mendez et al., 2012). Beyond the contributions of Neanderthal and Denisovan people to modern gene pools, there is also emerging but less certain evidence for possible contributions from a fourth archaic population in sub-Saharan Africa (Hammer et al., 2011) and a fifth perhaps also in South Asia (Mondal et al., 2016a), although debate continues regarding the latter especially (Skoglund et al., 2016; Mondal et al. 2016b). There is also better certainty now than there was when the book was published that Homo floresiensis is a real taxon, deeply separated from our own ancestry (Argue et al., 2017; Van Den Bergh et al., 2016), although conversely we are now less certain whether they actually ever encountered our recent ancestors face-to-face, although they certainly overlapped chronologically, at least briefly, in island Southeast Asia (Sutikna et al. 2016).

We can take from this that the specific narrative which Finlayson offers of the interaction between early modern humans and Neanderthal people isn’t fully accurate, but that misses the much bigger point: in the less than a decade since this book went to press, our understanding of where our ancestry lies, and how different groups of people or less fully human hominins eventually became our ancestors or became extinct, has been completely up-ended. We can now say that the story is much more complex than we appreciated nine years ago, but does that mean that we understand that complexity well now? Of course we don’t. If we ask how many different types of human existed within the last 50,000 years, or which or how many became the ancestors of at least some people alive today, the only honest answer that can be given is that we don’t know. Where did they live, what happened to them, how did we interact, and why? We have only the vaguest shadow of an idea for some, like Neanderthals, and not even that for others.

50,000 years ago, it seems quite probable or certain that our majority ancestors were wearing clothes, building their homes, and speaking languages that would not be notably unlike those spoken across the globe today; they were biologically indistinguishable from us in all but the finest nuances and details, like lactose tolerance and innate immunity; they made and understood art, they were curious and brave explorers and settlers, given the opportunity, and they were creative and flexible innovators who readily invented or adopted new technologies when faced with new problems, not on the scale of geologic time, but in the scale of lifetimes or generations. That is to say, they were us, in every way that matters and in every way that can be said universally of people alive today. So, can the same be said about the other types of human they encountered? We don’t yet know. We know that they encountered others, and that some of those encounters ended with descendants shared between some of those groups, but we don’t yet know how, or why, or where, or even what people we’re talking about— we now know, for instance, that the people we call Denisovans are among our ancestors, but all the Denisovan bones we have would literally fit not just in the palm of your hand, but in a thimble— two molars, part of a toe bone, and a little dust of what was once a finger bone. We know that all our ancestors, along with those who did not survive, saw their world devastated and changed almost beyond recognition in that time by brutal and repeated climate change, by the fickle tyranny of the seas which have abandoned and reclaimed continents’ worth of land, over and over again, on short notice, and by the end-Pleistocene extinctions, which some of them may themselves have caused, but beyond that we know terribly little. The huge majority of history—of the history of people who were indistinguishable from us except in those ways in which we are equally distinct from one another, and whose actions and choices have lead to the world we live in today —the history of people whose lives were shaped not by the “nasty brutish shortness” of animal existence, but by the forces of language and culture, spirituality and technology— our history— is unknown to us. Finlayson’s book is an informative and an interesting read, but that is the critical realization that you simply will not come away from it with.

Argue, D., Groves, C. P., Lee, M. S., & Jungers, W. L. (2017). The affinities of Homo floresiensis based on phylogenetic analyses of cranial, dental, and postcranial characters. Journal of Human Evolution (30), 107-133.

Hammer, M. F., Woerner, A. E., Mendez, F. L., Watkins, J. C., & Wall, J. D. (2011). Genetic evidence for archaic admixture in Africa. Proceedings of the National Academy of Sciences, 108(37), 15123-15128.

Mendez, F. L., Watkins, J. C., & Hammer, M. F. (2012). Global genetic variation at OAS1 provides evidence of archaic admixture in Melanesian populations. Molecular Biology and Evolution, 29(6), 1513-1520.

Mondal, M., Casals, F., Xu, T., Dall’Olio, G. M., Pybus, M., Netea, M. G., … & Bertranpetit, J. (2016a). Genomic analysis of Andamanese provides insights into ancient human migration into Asia and adaptation. Nature genetics, 48(9), 1066-1070.

Mondal, M., Casals, F., Majumder, P. P., & Bertranpetit, J. (2016b). Further confirmation for unknown archaic ancestry in Andaman and South Asia. bioRxiv, 071175.

Racimo, F., Sankararaman, S., Nielsen, R., & Huerta-Sánchez, E. (2015). Evidence for archaic adaptive introgression in humans. Nature Reviews Genetics, 16(6), 359-371.

Reich, D., Patterson, N., Kircher, M., Delfin, F., Nandineni, M. R., Pugach, I., … & Saitou, N. (2011). Denisova admixture and the first modern human dispersals into Southeast Asia and Oceania. The American Journal of Human Genetics, 89(4), 516-528.

Skoglund, P., Mallick, S., Patterson, N., & Reich, D. (2016). No evidence for unknown archaic ancestry in South Asia. bioRxiv, 068155.

Sutikna, T., Tocheri, M. W., Morwood, M. J., Saptomo, E. W., Awe, R. D., Wasisto, S., … & Storey, M. (2016). Revised stratigraphy and chronology for Homo floresiensis at Liang Bua in Indonesia. Nature, 532, 366-369.

Van Den Bergh, G. D., Kaifu, Y., Kurniawan, I., Kono, R. T., Brumm, A., Setiyabudi, E., … & Morwood, M. J. (2016). Homo floresiensis-like fossils from the early Middle Pleistocene of Flores. Nature, 534(7606), 245-248.

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