Jun. 12, 2015

What Lemurs Can Teach Us About Human Evolution

by Ian Tattersall

Click to enlarge images
The following is an excerpt from Ian Tattersall's The Strange Case of the Rickety Cossack. Listen to SciFri on June 12, 2015, to hear the full interview with Tattersall.
Anyone who knows the lovely Comoro Islands and their good-natured people—a blend of African, Arab, and Malagasy influences with a dash of errant European added—must wish them a more settled and more prosperous future. But meanwhile, the outlook for the archipelago’s unusual flora and fauna remains dire. When I first went to the Comoros in 1974, the total human population of all four islands in the archipelago was reckoned to be about 250,000; today just the three islands of the Union of the Comoros are home to three times that many people, maybe more. Even in Mayotte, where the environment is threatened by development rather than by poverty, there has been a marked drop in lemur numbers over the past decade. This matters, because most lemur populations are under huge and increasing pressure in Madagascar. Mayotte is their only homeland controlled by a developed nation that—if it wished—could easily afford to protect them.
Yet for all the neglect that has been lavished on them, the lemurs must occupy a very special place in the heart and mind of anyone interested in the long evolutionary history of humankind. This is because, as I’ve hinted, in certain respects they resemble our own remote ancestors of the Eocene epoch, around 50 million years ago. Ranging today from animals the size of a mouse to that of a large house cat (and, until not very long ago, up to the size of a gorilla), lemurs have smaller brains relative to their body sizes than we “higher” primates do, and they depend much more on the sense of smell. Still, they are clearly not as dumb as these attributes have led many to suppose. Primate psychologists have tended to evaluate lemur intelligence using tests developed for monkeys and even people: forms with much greater manual skills, and a strong tendency to evaluate objects entirely visually rather than also by smell. This has been a huge drawback to understanding how exactly lemurs apprehend the world; and as researchers devise ways of testing the lemurs’ cognitive skills in ways more appropriate to their own ways of relating to the environment around them, we can hope to gain valuable insight into the kind of cognition that preceded our own unusual way of dealing with information. In this context alone, the lemurs have an enormous amount to teach us, as they do about our ancient ancestors’ social and ecological strategies. But in my own particular case, they had an even more significant lesson to impart.
Most of my research nowadays is in paleoanthropology, as I try to understand the fossil and archaeological evidence for human evolution. Like all of my contemporaries in the English-speaking world, I was initially trained to look upon the biological history of the human family as a single-minded (and implicitly heroic) struggle from primitiveness to perfection. The going assumption, when I was a graduate student, was that evolution is a process of fine-tuning that, over the eons, gradually makes its subjects ever more perfectly adapted to the environments in which they live. That perspective was hardly surprising, since it intuitively appeals to members of a species that is the only representative of its group in the world today. This lonely state of ours makes it appear logical to reconstruct the story of our evolution by projecting the single species Homo sapiens back in time, in a single, gradually modifying lineage. And of course, in one very limited sense this view is accurate; for we are certainly the product of a unique series of ancestors, each of which existed over a definable period of past time. But that is purely in hindsight; in prospect, which is how evolution works, things would have looked very different. The upshot is that what I’d been taught about human evolution was very far indeed from the whole story, and it was my involvement with lemurs, beginning in the late 1960s, that gave me my very first inkling of this.
What any observer of the lemurs of Madagascar immediately notices, before anything else, is that they are amazingly diverse. There are way north of 50 species of these lovely primates, arrayed into five different families. These range from the tiny scurrying mouse lemurs, to the cat-sized quadrupedal “true” lemurs, to the long-legged leaping sifakas and lepilemurs that typically hold their bodies vertical, to the bizarre, bat-eared, bushy-tailed aye-aye. What’s more, if you’d been fortunate enough to visit Madagascar a mere 2,000 years ago, you would additionally have seen the hanging “sloth lemurs,” the giant koala-like megaladapids, and the vaguely monkey-like archaeolemurids, all of them weird and wonderful, and much bigger than their surviving relatives.
In other words, the whole lemur fauna loudly blares diversity at you. Not just diversity in body forms and lifestyles, but evolutionary diversity too, with several distinctive families, lots of genera, and huge numbers of species. What’s more, it turns out that diversity, even on this eye-catching scale, is hardly unusual among successful groups of mammals. In fact, it is rather routine. Successful mammal families have a strong tendency to spread geographically and to diversify phylogenetically. Applying this lesson from my studies of the lemurs to the very varied human fossil record, I soon realized that our own hominid family is actually no exception. Far from having been the linear, perfecting process that most of us were taught about—if we were taught anything about it at all—human evolution actually witnessed high drama, as one new species after another was pitchforked out into the ecological arena to do battle for survival and success—and, as likely as not, to become extinct in the process.
Acknowledging this pattern of events entirely changes our perspective on how we became the highly unusual creatures we are. For it rapidly becomes apparent that we hvuman beings are not the burnished product of incremental improvement over the eons. Instead, we are one particular outcome of an active process of experimentation with the evidently many ways there are to be a hominid. This, in turn, casts considerable doubt on the received assumption that we were fine-tuned by evolution to be a creature of a particular kind.
Yet because there is undeniably something very unusual about us today—so unusual, indeed, that our species really has radically changed its relationship to nature—it has proven very difficult for paleoanthropologists to perceive our hominid precursors as just another bunch of primates, and to see the process that produced us as merely another example of something that occurs widely among mammals. Right from the point at which it was realized—over a century and a half ago—that we have a fossil record, there has been a distinct leaning toward what one might call hominid exceptionalism: the instinctive assumption that, because we are so different today, our own ancestors did not necessarily play the evolutionary game by the same rules that apply to everything else out there. It is this vague exceptionalist feeling that accounts for the notable conservatism in paleoanthropology that I began by complaining about. In one form or another, it has existed from paleoanthropology’s very earliest beginnings—where any account of our understanding of ourselves has to start.

Excerpted from The Strange Case of the Rickety Cossack. Copyright © Ian Tattersall, 2015. All rights reserved.

Author photo by Denis Finnin
About Ian Tattersall

Ian Tattersall is Curator Emeritus in the Division of Anthropology of the American Museum of Natural History in New York City.

The views expressed are those of the author and are not necessarily those of Science Friday.
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