Human Evolution: Winners and Losers Selected.

by Kenneth W. Krause.

Kenneth W. Krause is a contributing editor and “Science Watch” columnist for the Skeptical Inquirer.  Formerly a contributing editor and books columnist for the Humanist, Kenneth contributes regularly to Skeptic as well.  He may be contacted at krausekc@msn.com.

“It has often and confidently been asserted that man’s origin can never be known,” observed Charles Darwin in The Descent of Man.  But “it is those who know little, and not those who know much,” he continued, “who so positively assert that this or that problem will never be solved by science.”  Indeed, in the October 2, 2009 issue of Science, anthropologists again demonstrated the overwhelming might of Darwin’s dangerous idea.  Reporting a 4.4 million-year-old hominin species first discovered in the Ethiopian Afar rift in 1992, Tim White’s international team announced that Ardipithecus ramidus “resolves many of the uncertainties about early human evolution, including the nature of the last common ancestor we shared with the line leading to living chimpanzees and bonobos.”

But 2009 was an exciting year for popular books on human evolution as well.  Some deserved a great deal of attention; some not so much.  Let’s start with Darwinius masillae—remember “Ida”?  On May 19 the world was introduced to the alleged “missing link” between primitive primates and humans—an exceptionally well-preserved, 47-million-year-old cat-sized fossil belonging to an extinct branch of early primates called adapiforms.  As a team led by Jørn Hurum of the University of Oslo, Norway, released the PLoS One paper, Ida was ceremoniously unveiled at the American Museum of Natural History to an enthusiastic New York City audience including Mayor Michael Bloomberg.  Science writer Colin Tudge’s book, dubbed The Link:Uncovering Our Earliest Ancestors (Little, Brown and Co., 2009), quickly followed.

Hurum’s claim was that, although Ida plainly resembled some prosimians (lemurs, tarsiers, and their extinct ancestors), her fossil also revealed anthropoid-like—and thus human-like—features including a partially fused lower mandible and a talus foot bone.  She also lacked a “toothcomb” and “grooming claw,” more typical of lemurs.  Hurum’s team argued that because Ida was recovered from an oil shale pit in Messel, Germany, she also challenged conventional wisdom that anthropoids had originated in Africa.

But criticism rained fast and furiously on Ida’s well-publicized parade.  In the May 30 issue of New Scientist, Chris Beard, curator of vertebrate paleontology at the Carnegie Museum of Natural History in Pittsburgh, Pennsylvania, responded, “Ida’s a fine fossil, but she’s not the missing link.”   Ida “fails miserably” to display any anthropoid features that evolved after that group’s split from other primates, Beard said, bluntly dismissing the New York unveiling as “unbridled hoopla.”

On July 1 Beard published an article in the Proceedings of the Royal Society B, introducing a 38-million-year-old fossil primate from Myanmar (formerly Burma) called Ganlea megacaninaGanlea possessed a distinctive feeding adaptation displayed among modern saki monkeys from the Amazon Basin of South America—an extremely large canine tooth used to pry open tough tropical fruits.  Compared to adapiforms like Ida, Beard concluded, Asian amphipithecids like Ganlea were infinitely stronger candidates for the much-coveted title of ancestors to the anthropoids.

Then, in “Weak Link,” Kate Wong’s short piece in the August issue of Scientific American, Robert Martin from the Field Museum in Chicago and Richard Kay from the paleontology department at Duke University piled onto the now-crowded anti-Ida bandwagon.  Martin pointed out that fused lower jaws had evolved independently in other mammals, including lemurs, but were absent in the earliest anthropoids.  Like Beard, Kay judged that fossil evidence of primitive Asian primates proved that the lady from Messel was not a direct ancestor of monkeys, apes, and humans.

Finally, in the October 22 issue of Nature, a team led by Erik Seiffert at Stony Brook University in New York compared the fossil traits of two adapiforms, Ida and the 37-million-year-old Afradapis longicristatus, to those of more than a hundred other living and extinct primates.  After evaluating 360 morphological features, Seiffert decided that, although the adapiforms shared certain traits with anthropoids—the loss of a third upper and lower premolar, for example—those characteristics had arisen more than once among primates and were “most parsimoniously interpreted as evolutionary convergences.”  Ida was not a haplorhine anthropoid, in other words, but rather a strepsirrhine (a group including lemurs and lorises) that “left no known descendants.”

Hurum’s team continues to defend Ida as the so-called “missing link,” but her claim to fame appears to be falling on increasingly deaf ears.  Tudge’s hastily assembled book, sans reference notes of any kind, offers some stunning photographs and valuable background information on early primate evolution.  But The Link never lived up to its colossal promise—and not merely because Ar. ramidus stole Ida’s show.  Despite its tendency toward spectacle and its cache of exceptionally contentious personalities, paleoanthropology is still a vibrant and exacting science.

And no recent book proves that point better than evolutionary ecologist Clive Finlayson’s The Humans Who Went Extinct: Why Neanderthals Died Out and We Survived (Oxford, 2009).  Perhaps the world’s foremost expert on Neanderthal extinction, Finlayson is renowned for his work in Gorham’s Cave, Gibraltar—recently confirmed as the Neanderthals’ last stronghold.  Even so, along with its well-reasoned argument and thoroughly absorbing storyline, this book’s most impressive feature is its pre-historical range.  From the early Eocene primates and Miocene apes to the later pioneers of Gravettian and, finally, farming cultures that ultimately took Europe and Asia by storm, Finlayson explores the related fates of several hominid forms.

Contrary to popular opinion, the Neanderthals—who, by the way, thrived in Eurasia for nearly half-a-million years—were no less clever than the ancestors who eventually replaced them.  Though other prominent scientists disagree, Finlayson argues that our predecessors had little or nothing to do with the Neanderthals’ demise.  Rather than lack of intelligence, the Neanderthals and all but one extremely fortunate group of H. sapiens fell victim to fluctuating climates that in some way drastically altered their ecological circumstances beyond their adaptive capabilities.

Burly Neanderthals performed quite well in forests where they perfected the art of ambush hunting from cover.  Then, by about 100 thousand years ago, quick climatic pulses of cold, dry air began to push the trees slowly southward, creating and expanding a new Eurasian environment called the steppe-tundra.  Red deer became scarce, and the herds of grazing reindeer that replaced them could spot their hungry attackers from a safe distance away.  Because Neanderthals had no reason to modify their tactics during periodic warm-ups, their numbers gradually but steadily decreased.  By about 30 thousand years ago, only the mild southern extreme of Iberia could provide sustenance to the doomed few who remained.

Meanwhile, lady-luck had smiled more brightly upon a different, but by no means inherently superior group of hominins who, according to Finlayson, just happened to be in “right place at the right time.”  Between 50 and 30 thousand years ago, peripheral populations of Eurasian H. sapiens were faced with two options: adapt or perish.  Most of the ancestors fared no better than Neanderthals.  But by 30 thousand years ago, at least one group had fully committed to the technological means of exploiting the steppe-tundra’s resources.  Thus, the European floodgates had opened.  “The jump onto the steppe-tundra was indeed a small step,” Finlayson writes, “but its impact was to be greater than Man’s first landing on the Moon.”

Wielding light tools and weapons—probably crafted from reindeer antlers and mammoth bones—and hunting collectively from seasonally mobile base camps, the Gravettians had “entered the information age.”  The frigid climate allowed them to preserve food underground, so their numbers quickly multiplied.  Surplus and population growth resulted in division of labor, more complex language, and even art.  This “edge” population of scrappers and innovators, the author posits, succeeded in Europe where Neanderthals had failed—not because of a revolution in brain physiology and intelligence, but rather because their bodies were more gracile from the beginning.  The ancestors, in other words, came prepackaged for climatic caprice.

The best books of the year offered credible answers to big questions, and Richard Wrangham, Harvard professor of biological anthropology, did just that in Catching Fire: How Cooking Made Us Human (Basic, 2009).  Our ancestors certainly consumed meat long before they became recognizably human.  But according to Wrangham, “the transformative moment that gave rise to the genus Homo … stemmed from the control of fire and the advent of cooked meals.”  Cooked animal flesh in particular overhauled not just human physiology, but our social and sexual habits as well.

Though we have yet to discover supporting archeological evidence, Wrangham believes that H. erectus began cooking meat by 1.8 million years ago.  Earlier hominins were more ape-like in overall proportion, burdened with large, distended guts.  Erectus, by contrast, sported long legs and a lean body.  “In fact,” Wrangham quipped in a recent New York Times interview, “he could walk into a Fifth Avenue shop today and buy a suit right off a peg.”  Relative to earlier habilines, his teeth were greatly reduced and his cranium was about 42 percent larger.  Many theories have attempted to account for this transition, but few scientists—not even Darwin himself—have ever assigned much evolutionary significance to man’s consumption of prepared flesh.

But Wrangham argues that only cooked meat can explain our epic transition to slighter bodies and bigger brains.  Cooking not only softens food, making it generally easier to chew and process; it also breaks down starches and “denatures” protein molecules, rendering their amino-acid chains more vulnerable to digestive enzymes in the stomach and small intestine.  More efficient fuel allowed bodies and digestive parts to streamline, and it boosted the energy supply for huge human brains that presently consume 20 to 25 percent of our total calories.  And cooking brought us together around the fire, Wrangham extrapolates, cementing social bonds.  It created a division of labor between man the hunter and woman the chef, thus engendering the fortuitous pair-bonding and, eventually, marriage paradigms.

Like many successful science writers, Wrangham explores his theory’s contemporary implications as well.  The obesity epidemic, he suggests, was not so much caused by overeating, but rather by a sedentary lifestyle for which we did not evolve and a craving of soft, rich, easily digestible food for which we did.  But forget raw food fads, he scolds—these diets can easily result in reduced bone mass and dangerous vitamin and energy deficiencies.  And although we should scrutinize labels at the grocery store, we can’t rely on their calorie counts.  Some foods require bodies to expend more energy in digestion than do others, and finely ground products are more readily absorbed than coarser ones.  Labels describe products only as they sit on the shelf or in the refrigerator.  But cooking, as Wrangham argues, can change everything.

But no discussion of recent books on human evolution would be complete without mention of Lucy’s Legacy: The Quest for Human Origins (Harmony, 2009) by storied paleoanthropologist Donald Johanson and veteran science writer Kate Wong.  Discovered in 1974, Johanson’s 3.2-million-year-old Lucy (Australopithecus afarensis), quickly became the most famous and, until Ar. ramidus, the most informative fossil hominin on earth.  No wonder Johanson refers to her as “the spokeswoman for human evolution.”

Published during the fossil’s first US tour, Lucy’s Legacy relives Johanson’s thorny Ethiopian expeditions and, with a general audience in mind, explains how paleoanthropology is actually done.  Unearthed in the Afar Triangle, Lucy and her kind still reign as the most promising ancestors of the genus Homo.  She was small-brained, yes.  But she likely walked upright, and both she and her male companions had already evolved teeth consistently smaller than those of her predecessors.  To Johanson and many others, low canine dimorphism tends to indicate less male competition for mates, and perhaps even the inauguration of monogamy.

Among the most esteemed professionals in their respective fields, Johanson and Wong also provide expert, yet highly accessible descriptions of subsequent hominin finds including White’s ramidus and H. neanderthalensis.  Though stingy with references, these authors’ credentials are as solid as they come.  Lucy’s Legacy is first-rate introduction to paleoanthropology and evolutionary science more generally.  If only Darwin could witness the most recent chapters in his legacy—I think he would be very proud indeed.

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