BBC Starch 'fuel of human evolution'

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Starch 'fuel of human evolution'

Man's ability to digest starchy foods like the

potato may explain our success on the planet,

genetic work suggests.

Compared with primates, humans have many more

copies of a gene essential for breaking down

calorie-rich starches, Nature Genetics reports.

 

And these extra calories may have been crucial

for feeding the larger brains of humans,

speculate the University of California Santa Cruz

authors.

 

Previously, experts had wondered if meat in the diet was the answer.

 

Brain food

However, Dr Nathaniel Dominy and colleagues argue this is improbable.

 

" Even when you look at modern human

hunter-gatherers, meat is a relatively small

fraction of their diet.

 

" To think that, two to four million years ago, a

small-brained, awkwardly bipedal animal could

efficiently acquire meat, even by scavenging,

just doesn't make a whole lot of sense. "

 

They discovered humans carry extra copies of a

gene, called AMY1, which is essential for making

the salivary enzyme amylase that digests starch.

 

Survival benefit

Next the team studied groups of humans with

differing diets and found those with high-starch

diets tended to have more copies of AMY1 than

individuals from populations with low-starch

diets.

 

For example, the Yakut of the Arctic, whose

traditional diet centres around fish, had fewer

copies than the related Japanese, whose diet

includes starchy foods like rice.

 

The researchers believe our earliest human

ancestors began searching for new food sources

other than the ripe fruits that primates eat.

 

These were starches, stored by plants in the form

of underground tubers and bulbs - wild versions

of modern-day foods like carrots, potatoes, and

onions.

 

In work earlier this year, the team found that

animals eating tubers and bulbs produce body

tissues with a chemical signature that matches

what has been measured in early fossilised humans.

 

Dr Dominy said that when early humans mastered

fire, cooking starchy vegetables would have made

them even easier to eat.

 

At the same time it would have made extra amylase

gene copies an even more valuable trait.

" We roast tubers, and we eat French fries and

baked potatoes. When you cook, you can afford to

eat less overall, because the food is easier to

digest. "

 

And marginal food resources can become part of the staple diet.

 

" Now you can have population growth and expand into new territories. "

 

Speculation

Professor John Dupré, a professor of philosophy

of science at Exeter University in the UK, urged

caution when interpreting the findings.

 

He said it was impossible to conclude that the

introduction of starchy foods into the diet lay

behind the emergence of larger brains in humans.

 

" Lots of things differ between ourselves and our

closest relatives and apart from the difficulty

of establishing the relative places in the

evolutionary sequence of any of these, the

assumption that there is any one fundamental to

such change is dubious.

 

" The results on amylase genes are quite

interesting, and a good indication of something

we are beginning to appreciate more widely - the

functional plasticity of the genome. "

 

Story from BBC NEWS:

http://news.bbc.co.uk/go/pr/fr/-/2/hi/health/6983330.stm

 

Published: 2007/09/09 23:26:55 GMT

 

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