Not So Dumb As Was Thought

Our earliest ancestors had a developed 
incipient social structure, reports Biplab Das 

A recent finding overhauls the impression that our earliest ancestors were just another modified type of dim-witted hairy ape that roamed the African plains three to four million years ago. According to researchers at Kent State University, they behaved in a much more "human" way than was previously thought. Drawing clues from a fresh look at fossils discovered in 1975 at site 333 in Ethiopia's Afar Triangle, the Kent team has proved they had a developed incipient social structure. 

What rivetted the team's attention was the extent of sexual dimorphism - differences in size between the males and females of these earliest ancestors. These differences were minimal, according to a report in the 5 August issue of Proceedings of the National Academy of Sciences. Which means that our earliest ancestors - Australopithecus afarensis which gave birth to Homo habilis - lived in a more cooperative and less competitive society. 

The Kent team worked with the fossils 13 afarensis individuals and compared these with those of 'Lucy', a widely known afarensis female. They narrowed their comparison to the "head" size of the femur, a bone that lies in the upper half of the lower limb. This bone was thought to be a key to extrapolate the size of the individuals from site 333. 

The comparison showed that the sex-based size differences among the fossils were no greater than those for modern humans. This suggests that a human-like social structure with cooperating males prevailed during the period of Australopithecus afarensis. "I think what we are seeing here are the very first glimpses of humanness in these early hominids," said Clark Spencer Larsen, an anthropologist at Ohio State University. 

According to the Kent researchers, the social structure of our earliest ancestors comes close to humans and chimpanzees than it does to gorillas and orangutans, as had been previously thought. Gorillas, orangutans and baboons live in a society where there is fierce competition among males. Despite being competitive, chimps and humans are far more cooperative. 

The Kent study, Larsen believes, shows convincingly that there was very little sexual dimorphism in these early hominids. From this study, he said, we could extrapolate some behaviours - specifically that males were cooperating more than they were competing among themselves, a distinctly 'human' trait. 

Donald C. Johanson, an anthropologist with the Institute for Human Origins, Berkeley, California, has also studied afarensis fossils extensively. He discovered fossil bones of a male which supports the view of the Kent team. The crowns of this individual's canine teeth - the parts that protrude from the gums - were significantly smaller, closer in size to female afarensis canines. This implied, Johanson said, that this male did not need those teeth as much as his great ape cousins did. "It is well known that male gorillas keep harems and use their canines in combat with other males to establish dominance or to compete for females." 

Perhaps afarensis had evolved a different strategy which made the males more compromising. Owen Lovejoy, a palaeoanthropologist at Kent State University, suggests that smaller canines mean that there was much less competitions for females among afarensis males - an indication that monogamy may have evolving more than three million years ago. 

According to Johanson, afarensis lived in social groups maybe 25- to 30-strong. This provided them an edge over other animals. "Without having the protection of fire, howling afarensis could have hurled rocks at a threatening saber-toothed cat," he said. 

Other fossils found at Laetoli in Tanzania, about 50 km south of Olduvai Gorge, also in Tanzania, have also shown human-like traits and behaviour. Mary Leakey, a palaeoanthropologist and wife of legendary palaeoanthropologist Louis Leakey, discovered two mandibles at Laetoli which showed incompletely erupted dentition patterns. According to her, these remains show an eruption pattern that more resembles humans than apes. 

According to Larsen, this male cooperation is the product of evolution. "The success of this cooperation proved valuable to these early ancestors and has become a trait among humans," he said. 

Palaeoanthropologists have long suspected that pre-humans might have had minimal size differences like humans. But the recent study has ended that suspicion. The Kent study, Larsen said, was the best to date at linking sexual dimorphism in early hominids to their probable social structure.