The hunt for the missing link goes on

The hunt for the missing link goes on
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First Published: Thu, Oct 01 2009. 09 30 PM IST
Updated: Thu, Oct 01 2009. 09 30 PM IST
New Delhi: Palaeontologists, with their chisels and crowbars, have over the last century steadily wedged modern man’s ancestry away from a simian family called the Great Apes, comprising chimpanzees, gorillas and orangutans. Now, they have distanced humans farther away from the apes.
With a paucity of bones, most evolutionary theorists concerned themselves with fossils that were no more than a million years old, most being the Homo erectus or later species, that immediately preceded Homo sapiens (modern species of humans).
These finds moulded the popular image of a tool-making, hairy hunter with high cheek bones and a protruding jaw.
In all of this, the other apes were slotted as distant ancestors, who chucked the forest for the trees. Rather than walk, they chose to maintain long, powerful arms to navigate branches. They also chose the more energy-efficient strategy of distributing body weight on all four limbs and scamper on their knuckles, instead of standing upright.
By the 1940s, there was a broad consensus that the “smarter” ancestors of Homo erectus, gradually developed bigger brains and stepped off the trees to use and invent more tools. This was a consequence of their expanding mental faculties. That’s when Lucy came, and upset the neat, evolutionary flow chart. Palaeontologist Maurice Taieb and his team unearthed several fossils between 1972 and 1978 from the Hadar desert in Ethiopia; most prominently a skeleton nicknamed Lucy that was about 40% complete, which emphatically proved that hominids—or Homo erectus’ ancestors—walked, before they thought.
Lucy, named after a hit Beatles song, was dated as 3.2 million years old. She had a small chimpanzee-sized brain but walked upright. This landmark finding triggered fossil hunters’ quest for the “missing link”, a six-seven-million-year-old ancestor believed to be man’s vestigial connect to the apes, especially chimpanzees.
Chimpanzees were a special lot, different from the other apes. It helped that the 1960s and 1970s were the time when scientists were beginning to supplement fossil hunting with molecular diagnostic techniques to link man and ape. DNA samples by researcher Mary White showed that chimpanzees shared 99% of their genes with humans. This and a branch of chimpanzee research buttressed ideas that chimpanzees were the template to understand the evolutionary history of human nature and man.
The fossil hunters think otherwise. If chimpanzees were really that close to humans, then the common human-chimp ancestor ought to be more chimpanzee than human, given that chimpanzees were the older stage in evolution. Increasing evidence over the last two decades—some molecular and a few fossil finds—are reinforcing their doubts.
Scientists at Buffalo University reported in June in the Journal of Biogeography that a comparison of the physical characteristics of humans and the other great apes put man closer to orangutans than chimps. Mathew Hahn of the Indiana University in Bloomington reported in 2006 that chimp and human genomes were only 94% similar. A 5% difference in genomes can make or break a species.
Since then, several fossil finds such as Lucy’s baby, Abel and now Ardi—all from East Africa—suggest that chimpanzees’ diet, their dental structure and toes (used to grip a branch) suggest a markedly different evolutionary strategy from humans. Lucy and Ardi, it now seems, point to a different kind of missing link. Neither chimp nor man.
jacob.k@livemint.com
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First Published: Thu, Oct 01 2009. 09 30 PM IST