Humans began eating plants 180,000 years ago - allowing us to leave the fish-filled lakes and migrate across Africa

• Adapting to a part-vegetarian diet helped early humans lose their dependence on fish
• Genetic study suggests plant fats accelerated development of the brain, and allowed mass-emigration from Africa
  
• Findings 'may explain why diverse racial and ethnic populations respond differently to the modern Western diet'

By Eddie Wrenn for MailOnline

Published: 04:36 EDT, 21 September 2012 | Updated: 04:36 EDT, 21 September 2012

Early man: Without an adaptation which allowed us to process vegetables, modern man's brain may have remained under-developed

Modern humans were able to emerge from Africa after a genetic mutation allowed them to become vegetarian, a new study claims.

The change meant humans were able to move away from water sources and spread across the continent.

Geneticists have compared DNA sequences from numerous people around the world to determine how different populations relate to one another and when they might have gone their separate ways.

Now three teams of American scientists have found that a key genetic variant was the ability to convert fats from plants into necessary nutrients for the brain.

The development would have allowed early humans to leave the waters of central Africa, where they ate fish, according to the study published online on the Public Library of Science (PLOS).

Researchers from the Wake Forest Baptist Medical Centre in North Carolina, the Johns Hopkins University School of Medicine in Baltimore and the University of Washington School of Medicine, Seattle, analysed the genes of 1,092 individuals from 15 different human populations.

They claim homo sapiens first appeared 180,000 years ago, but stayed in one location around bodies of water in central Africa for almost 100,000 years.

Senior author Doctor Floyd Chilton, professor of physiology and pharmacology and director of the Centre for Botanical Lipids and Inflammatory Disease Prevention at Wake Forest Baptist, said the location was critical as the ready supply of fish and shellfish provided the fatty acid Docosahexaenoic acid (DHA), which was necessary for brain development.

'This may have kept early humans tethered to the water in central Africa where there was a constant food source of DHA,' he said.

'There has been considerable debate on how early humans were able to obtain sufficient DHA necessary to maintain brain size and complexity.

'It's amazing to think we may have uncovered the region of genetic variation that arose about the time that early humans moved out of this central region in what has been called the 'great expansion.'

Varied diet: Two members of the Mardi tribe use bows in East Sudan to fish, following the tradition of their ancestors

This conversion meant that early humans didn't have to rely on just one food source, fish, for brain growth and development.

According to Joshua Akey, lead scientist at the University of Washington, the development was particularly important because the genetic variant arose before organised hunting and fishing could have provided more reliable sources of the necessary fats.

'The power of genetics continually impresses me, and I find it remarkable that we can make inferences about things that happened tens of thousands of years ago by studying patterns of genetic variation that exist in contemporary populations,' he added.

The researchers said the findings added to a study in 2011 which found people of African descent have a much higher frequency of the gene that converts plant-based fatty acids to polyunsaturated fats that cause inflammation.

Compared to Caucasians, African Americans in the United States have much higher rates of hypertension, type 2 diabetes, stroke, coronary heart disease and certain types of cancer.

'The current observation provides another important clue as to why diverse racial and ethnic populations likely respond differently to the modern western diet,' Dr Chilton said.