Giant Leaps For Man

Biplab Das describes the 
genetic transition of an African ape

What makes humans unique? Language? Art? Upright gait? Yes, all these attributes are the signs of humans' uniqueness. But the most important aspect lies somewhere else. We are the only ones who ask, "Where do we come from?" 

The first answer to this question came from Darwin, who theorised that humans have descended from apes. Darwin also said that humans originated in Africa. But he did not have the slightest idea about how the process took place. Dr. Didier Marchand from the Centre for Earth Studies, Dijon, France, recently discussed this process in his lecture on, 'The Wonder of Human Evolution.' The lecture was organised by M. P. Birla Institute of Fundamental Research (MPBIFR) and Alliance Francaise De Calcutta at the MPBIFR seminar hall. 

The story of transition  from apekind to mankind is a fascinating one. It began in the thick tropical forests of Africa where apes emerged. "The first prominent ape called Aegyptopithecus, better known as Egyptian ape, appeared on the scene around 28 million years ago. It lived in a forest which is now Sahara desert," said Marchand. 

Before the advent of the next major ape, eight million years elapsed. The stage then shifted to Rusinga Island in Lake Victoria where the next ape Dryopithecus emerged around 20 million years ago. From Africa, this venturesome ape extended its base to Asia and Europe. While Dryopithecus flourished, many insignificant apes emerged and became extinct. A few of them, like the baboon and gibbon, survive to this day. 

About 10 million years ago, the common ancestors of great apes and humans arrived on the scene, dislodging Dryopithecus from centrestage, said Marchand. "As the drama of evolution unfolded, great apes came into prominence one after another," he continued. 

Among the great apes, orangutan emerged first, followed by the gorilla and chimpanzee. The earliest ape-like ancestors of humans evolved around five million years ago. 

Studies of fossilised remains have revealed that chimpanzees and humans are descended from a common ancestor. "This notion has been bolstered by genetic study," revealed Marchand. Comparison of our genes with those of chimpanzees shows that they share almost 99 per cent of our genes. 

But despite this kinship, chimpanzees and humans are not alike. They are poles apart in looks and behavior. "The upper portion of a chimpanzee's face is small, but the lower is large and juts out," said Marchand. The reverse is true in the human face. 

Marchand pointed out further differences. Chimpanzees are qudruped (four-legged) and walk on their knuckles. Humans are biped (two-legged) and walk erect. Chimpanzees are more hairy than humans. They do not have any language like humans. What is more, humans have a large, rounded brain compared to the chimpanzees' smaller one. 

These and other differences between chimps and humans have been caused by a handful of genetic mutations that we humans have accumulated over a period of five million years. "In prehistoric times, a single mutation might have happened over a span of one million years," said Marchand, explaining that "such a mutation, especially in architect genes that shape the developmental stages of life, might have triggered the first step of the transition from apes to humans." 

The spread of the mutation through the general population might take a million years, but the initial step would not have taken that long. "Instead, it could have happened within a couple of generations among a small isolated group of apes comprising 15-20 individuals, making them evolve into our earliest biped ancestors," explained Marchand. 

Owing to a few more mutations in genes, the brain size of our ancestors increased. "Those brainier ancestors made inventions like stone tools and discovered fire." Gradually, they evolved into a species that could talk and carve out wonderful artifacts and sophisticated tools. "In fact, they began to look and behave like us only about twenty thousand years ago," concluded Marchand.