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Fire would have provided our early humans, like the Neanderthals shown in the artists rendition above, warmth but also allowed them to cook their food.
Early humans may have first started cooking their food to make carrion safer for them to eat, new research has suggested.

Anthropologists at Harvard University in Cambridge, Massachusetts, have found humans scavenging for meat from carrion would risked exposure to dangerously high levels of bacteria.

They claim that simply roasting meat on hot coals can kill most of the bacteria that grows on carrion, making it safer for human consumption.

This they say could have helped to transform the diet of early humans, allowing them to access a rich supply of meat long before the development of weapons made hunting more efficient.

The findings provide strong support for theories that early humans obtained much of their meat by scavenging the kills of other predators.

The research was led by Professor Richard Wrangham, from the department of human evolutionary biology at Harvard University.

Writing in the Journal of Human Evolution, Professor Wrangham and his colleagues said: 'Meat scavenged by early Homo could have contributed importantly to a higher quality diet.

'Scavenging has received increased attention over the years partly because it has been observed among African foragers, especially in open habitats.

'The time when cooking was first practiced is not known.

'One possibility is that it was initiated by early Homo, as predicted from biological evidence.

'Cooking increases the effective energetic value of meat and cooked meat is spontaneously preferred to raw meat by living hominoids.

'Therefore, hominins who cooked scavenged meat could have increased their overall energy gain by increasing their access to another high-quality source of food.

'Our results support the proposal that consumption of scavenged meat would have led early Homo to ingest significant populations of bacteria, and that the advent of cooking would have greatly reduced the exposure to meat-borne bacteria.

'Since bacteria growing on meat commonly include pathogenic types, our data indicates that the risks of costly disease or toxicity from eating meat would have been markedly reduced by eating it freshly cooked.'

The researchers used the carcass of a wild boar - left in the open but protected from scavengers - to study how bacterial growth on carrion can change over time.

They found the levels of common food poisoning bacteria such as E. coli, Staphylococcus and enterobacteria on the meat increased dramatically after 12 hours.

The researchers say the levels of the bacteria reached potentially dangerous levels 24 hours after the animal had been killed.

However, when they cooked the meat by placing it on hot coals - the way many anthropologists believe early humans would have first cooked meat - the bacteria levels fell by 88 per cent.

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The researchers studied how bacteria grows on carrion using a boar carcass left outside and found that after 24 hours bacteria levels reached potentially dangerous levels, as shown in the graphs above. Cooking the meat by roasting on hot coals, however, caused bacteria levels to fall by around 88 per cent, as seen above
The researchers also found that bacteria levels in bone marrow tended to be far lower than in the raw meat.

This they say could suggest early humans may have also preferentially scavenged bone marrow from carrion without ill effect.

However, early humans did not have strong jaws necessary for crushing bones to access the marrow within so they would have had to rely upon other large predators to have done this when eating their kills first.

They also say it is possible early humans may have been able to cope with greater levels of bacteria in their food than modern humans, but chimpanzees, our closest living relatives, tend to avoid carrion in favour of fresh meat.

Recent research has also shown that chimpanzees also prefer cooked food to raw food.

It is thought humans such as Homo erectus first began controlling fire around 400,000 years ago, although some anthropologists believe early humans may have begun using fire up to 1.9 million years ago.

There is a growing debate among anthropologists about whether early humans obtained meat primarily through hunting or through scavenging.

Professor Wrangham and his colleagues say there is growing evidence early humans tended to exploit whatever meat was available but cooking may have emerged as a result of this.

They said: 'Though the earliest dates of controlled fire - use may extend into the Lower Paleolithic, the role of cooking has been largely ignored by those who have investigated meat - eating by hominins.

'The hunting versus scavenging debate is premised on the concept of a sharp distinction between two behaviors that in reality combine to form a relatively fluid and adaptable meat - eating dietary strategy.

'Our results indicate that, along with modern hunter - gatherers and chimpanzees, the first members of the human genus would have had a problem in coping with pathogens from scavenged raw meat.

'How they solved this problem is an important question.'