Rewriting humanity’s origins: How fossils evolved across Africa

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Rewriting humanity’s origins: How fossils evolved across Africa

For years, scientists believed that humans evolved in a single spot in Africa and this large band of people spread around the world.

It is as though there was a ‘Garden of Eden’, where humanity first began, before going forth and multiplying.

But a new study says the fossil record does not support humans being fully formed when they spread across the world.

Instead early humans had a huge variation in the sizes and shapes of their heads, undergoing a series of genetic and cultural shifts that led to modern humanity.

Primitive skulls and bones of homo sapiens do not show a linear progression from primitive to modern.

Instead the development is much more patchy – showing that it took hundreds of thousands of years before all humans began to look as we do today.

Studies of the DNA of modern day Africans – the most genetically diverse continent on Earth – paints a similar picture.

It shows human populations across the continent are so different they must have been separated for huge chunks of time.

Scientists now suggest there must have been, multiple areas where different groups of humans developed different physical features.

These early bands of early humans then interbred over millennia. Only then did modern humans as we know them develop.

The fossil record suggests early homo sapiens were a patchwork quilt of different groups.

Dr Eleanor Scerri, an archaeologist at Oxford University, who led the international research, told The Guardian: “This single origin, single population view has stuck in people’s mind … but the way we’ve been thinking about it is too simplistic.”

Modern humans have small, slender faces, large round braincases, and chins.

If these features only evolved in one group of humans, we might expect to see a series of skulls going from larger to smaller faces, and gradually bigger, rounder braincases.

The fossil picture is much more complicated.

For example, skulls dating to 300,000 years ago found at Jebel Irhoud in Morocco – have small faces like modern humans.

But instead of a spherical braincase, theirs is long and elongated.

Read: Homo sapiens exhibited unexpected sophistication, Kenya artifacts reveal

Also read: Infant Kenyan ape fossil skull illuminates humankind’s remote past

‘COMPLEX MIX OF ARCHAIC FEATURES’

Meanwhile early human fossils dating more recently to 160,000 years ago – at Herto in Ethiopia – had big ‘robust’ faces – unlike us – but with ‘globular’ braincases like ours.

Professor Chris Stringer of the Natural History Museum and Dr Scerri have put forward the case in the journal Trends in Ecology and Evolution.

The authors said early humans were largely kept apart by a combination of diverse habitats and shifting environmental boundaries, such as forests and deserts.

Many of the most inhospitable regions in Africa today, such as the Sahara, were once wet and green, with interwoven networks of lakes and rivers, and abundant wildlife.

Similarly, some tropical regions that are humid and green today were once arid.

The shifting nature of these habitable zones meant human populations would have gone through many cycles of isolation.

This led to local adaptation and the development of unique primitive technologies – stone tools – and genetic makeup.

Professor Stringer pioneered the idea one big human population developed in Africa and spread worldwide – but now concedes this does not fit the facts.

He said when we look at human bones over the last 300,000 years “we see a complex mix of archaic and modern features in different places and at different times. We do see a continental-wide trend towards the modern human form, but some archaic features are present until remarkably recently.”

When it comes to the development of stone tools, the pattern is also mixed.

Sometimes sophisticated tools appear further back in the fossil record, while cruder ones appear more recently – suggesting innovations occurred at different spots on the map at different times.

Prof Chris Stringer added: “Although I am one of the researchers who originally helped to develop the view that our species, Homo sapiens, had originated in Africa, I have increasingly come to the realisation that our African origin was a complex process.

“The great diversity of African fossils between 200,000 and 400,000 years ago suggests that multiple lineages existed on the African continent at that time.”

Dr Scerri, said the stone tools discovered across Africa also don’t show a clear progression from crude to sophisticated.

She added that while there “is a continental-wide trend” to greater sophistication over time.

She said “this ‘modernization’ clearly doesn’t originate in one region or occur at one time period.”

Professor Mark Thomas said the genetic patterns found in modern day Africans also support the idea.

He said: “It is difficult to reconcile the genetic patterns we see in living Africans, and in the DNA extracted from the bones of Africans who lived over the last 10,000 years, with there being one ancestral human population.”

Dr Scerri said: “The evolution of human populations in Africa was multi-regional. Our ancestry was multi-ethnic. And the evolution of our material culture was, well, multi-cultural.”

More on this: Human origin a stew that is still cooking

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