Drought followed by brain: How climate change spurred evolution of human intelligence

Scientists show shifts from dry to wet and back in East Africa's Rift Valley caused the development of the human brain

Humans evolved their very large brains in response to the dramatic shifts in the climate of East Africa, the cradle of humanity where man's ancestors are thought to have originated about two million years ago, a study has suggested.

Scientists have matched exceptionally wet periods and very dry periods in the East African Rift Valley to sudden spurts in the evolution of the hominid ancestors of Homo sapiens, which resulted in the evolution of the modern human brain.

Academics have long argued about what led to the unusually large brain of humans with its capacity for language, abstract thought and consciousness. The latest theory suggests it was triggered by the need to adapt to dramatic changes in the local environment of early man.

“It seems modern humans were born from climate change, as they had to deal with rapid switching from famine to feast - and back again - which drove the appearance of new species with bigger brains and also pushed them out of East Africa into Eurasia and South Africa,” said Professor Mark Maslin of University College London, the co-author of the study published in the on-line journal Plos-One.

The Rift Valley is an extensive geological fault marked by mountains, lakes and fertile valleys. Many of the most important fossil remains of early humans have been unearthed in the region, leading to suggestions that it was the most important place for the early origins of man.

The study looked at climate change over the past 5 million years, where there have been large fluctuations between wet periods where lakes were far higher than they are today and dry periods where sand dunes formed in former lake beds.

The scientists found that there were relatively short periods lasting about 200,000 years when East Africa became very sensitive to the cyclical changes in the Earth's orbit around the Sun - known as Milankovitch cycles - which lead to global-scale changes to the climate, such as ice ages.

In East Africa, these orbital changes to the Earth led to rapid shifts between very dry and very wet periods of about 20,000 years, when typically the lake valleys repeatedly filled up with freshwater and then dried out several times, forcing the human inhabitants to move north or south.

“Due to these changes in orbit, the climate of East Africa seems to go through extreme oscillations from having huge deep freshwater lakes surrounded by rich, lush vegetation to extremely arid conditions, like today, with sand dunes in the floor of the Rift Valley,” Professor Maslin said.

“These changes resulted in the evolution of a new species with bigger brains, and also forced early humans to disperse out of East Africa,” he said.

The study found that there were three time periods in particular when this kind of climate change corresponded to important stages in human evolution.

The first occurred about 2.6 million years ago when the Rift Valley dwellers were pushed into southern Africa and a new species called Homo habilis emerged. The second happened about 1.9 million years ago when an important species called Homo erectus emerged from Africa to colonise much of Asia, while the third occurred about 1 million years ago when Homo heidelbergensis emerged.

Professor Maslin said that the technique is not accurate enough to deal with the past 150,000 years, when Homo sapiens first evolved, but that it nevertheless could explain the earlier evolutionary transition leading to Homo erectus, which is the first large-brained hominid with truly human-like skeleton showing a distinctive adolescent growth-spurt.

Susanne Shultz of Manchester University, the co-author of the study, said that climate change can be linked directly to the evolution of this important human species at a time when there were several species occupying the same geographic region at about the same time.

“We found that around 1.9 million years ago a number of new species appeared, which we believe is directly related to new ecological conditions in the East African Rift Valley, in particular the appearance of deep freshwater lakes,” Professor Shultz said.

“Among these species was early Homo erectus with a brain 80 per cent bigger than its predecessor,” she added.

The present-day lakes of the Rift Valley are much smaller than they would have been at the height of a wet period. Lake Logipi at the northern end of the Kenyan rift valley, for instance, once occupied the entire Suguta Valley, which is presently littered in sand dunes, and was about 300 metres deeper than it is today.

News
Jeremy Paxman has admitted he is a 'one-nation Tory' and complained that Newsnight is made by idealistic '13-year-olds' who foolishly think they can 'change the world'.
peopleThe idea has been greeted enthusiastically by the party's MPs
News
Michael Buerk in the I'm A Celebrity jungle 2014
people
Voices
File: David Cameron offers a toast during a State Dinner in his honour March 14, 2012
voicesAnd nobody from Ukip said babies born to migrants should be classed as migrants, says Nigel Farage
Arts and Entertainment
Avatar grossed $2.8bn at the box office after its release in 2009
filmJames Cameron is excited
PROMOTED VIDEO
Arts and Entertainment
Stik on the crane as he completed the mural
art
News
Happy in his hat: Pharrell Williams
people
Arts and Entertainment
Stella Gibson is getting closer to catching her killer
tvReview: It's gripping edge-of-the-seat drama, so a curveball can be forgiven at such a late stage
News
Brazilian football legend Pele pictured in 2011
peopleFans had feared the worst when it was announced the Brazil legand was in a 'special care' unit
News
i100(More than you think)
Sport
Brendan Rodgers seems more stressed than ever before as Liverpool manager
FOOTBALLI like Rodgers as a manager but Liverpool seem to be going backwards not forwards this season
News
ebooksNow available in paperback
News
The Magna Carta
archaeologyContemporary account of historic signing discovered
News
Phyllis Dorothy James on stage during a reading of her book 'Death Comes to Pemberley' last year
peopleJohn Walsh pays tribute to PD James, who died today
Sport
Benjamin Stambouli celebrates his goal for Tottenham last night
FOOTBALL
Life and Style
Dishing it out: the head chef in ‘Ratatouille’
food + drinkShould UK restaurants follow suit?
News
peopleExclusive: Maryum and Hana Ali share their stories of the family man behind the boxing gloves
Latest stories from i100
Have you tried new the Independent Digital Edition apps?
Independent Dating
and  

By clicking 'Search' you
are agreeing to our
Terms of Use.

iJobs Job Widget
iJobs General

Ashdown Group: Senior PHP Developer - OOP, Javascript, HTML, CSS, SQL

£39000 per annum: Ashdown Group: Senior PHP Developer - OOP, Javascript, HTML,...

Austen Lloyd: Commercial / Residential Property - Surrey

Excellent Salary: Austen Lloyd: SURREY MARKET TOWN - SENIOR PROPERTY SOLICITOR...

Recruitment Genius: Graduate Programme - Online Location Services Business

Negotiable: Recruitment Genius: What do you want to do with your career? Do yo...

Recruitment Genius: Senior QC Scientist

Negotiable: Recruitment Genius: This company is a leading expert in immunoassa...

Day In a Page

Homeless Veterans Christmas Appeal: ‘We give them hope. They come to us when no one else can help’

Christmas Appeal

Meet the charity giving homeless veterans hope – and who they turn to when no one else can help
Should doctors and patients learn to plan humane, happier endings rather than trying to prolong life?

Is it always right to try to prolong life?

Most of us would prefer to die in our own beds, with our families beside us. But, as a GP, Margaret McCartney sees too many end their days in a medicalised battle
Thomas Cook's outgoing boss Harriet Green got by on four hours sleep a night - is that what it takes for women to get to the top?

What does it take for women to get to the top?

Thomas Cook's outgoing boss Harriet Green got by on four hours sleep a night and told women they had to do more if they wanted to get on
Christmas jumper craze: Inside the UK factory behind this year's multicultural must-have

Knitting pretty: British Christmas Jumpers

Simmy Richman visits Jack Masters, the company behind this year's multicultural must-have
French chefs have launched a campaign to end violence in kitchens - should British restaurants follow suit?

French chefs campaign against bullying

A group of top chefs signed a manifesto against violence in kitchens following the sacking of a chef at a Paris restaurant for scalding his kitchen assistant with a white-hot spoon
Radio 4 to broadcast 10-hour War and Peace on New Year's Day as Controller warns of cuts

Just what you need on a New Year hangover...

Radio 4 to broadcast 10-hour adaptation of War and Peace on first day of 2015
Cuba set to stage its first US musical in 50 years

Cuba to stage first US musical in 50 years

Claire Allfree finds out if the new production of Rent will hit the right note in Havana
Christmas 2014: 10 best educational toys

Learn and play: 10 best educational toys

Of course you want them to have fun, but even better if they can learn at the same time
Paul Scholes column: I like Brendan Rodgers as a manager but Liverpool seem to be going backwards not forwards this season

Paul Scholes column

I like Brendan Rodgers as a manager but Liverpool seem to be going backwards not forwards this season
Lewis Moody column: Stuart Lancaster has made all the right calls – now England must deliver

Lewis Moody: Lancaster has made all the right calls – now England must deliver

So what must the red-rose do differently? They have to take the points on offer 
Cameron, Miliband and Clegg join forces for Homeless Veterans campaign

Cameron, Miliband and Clegg join forces for Homeless Veterans campaign

It's in all our interests to look after servicemen and women who fall on hard times, say party leaders
Millionaire Sol Campbell wades into wealthy backlash against Labour's mansion tax

Sol Campbell cries foul at Labour's mansion tax

The former England defender joins Myleene Klass, Griff Rhys Jones and Melvyn Bragg in criticising proposals
Nicolas Sarkozy returns: The ex-President is preparing to fight for the leadership of France's main opposition party – but will he win big enough?

Sarkozy returns

The ex-President is preparing to fight for the leadership of France's main opposition party – but will he win big enough?
Is the criticism of Ed Miliband a coded form of anti-Semitism?

Is the criticism of Miliband anti-Semitic?

Attacks on the Labour leader have coalesced around a sense that he is different, weird, a man apart. But is the criticism more sinister?
Ouija boards are the must-have gift this Christmas, fuelled by a schlock horror film

Ouija boards are the must-have festive gift

Simon Usborne explores the appeal - and mysteries - of a century-old parlour game