MUSCULAR PHYSIQUE? Check. Hairy chest? Check. Full set of teeth? Check. A love of the outdoors? Check. Communication skills? Mainly guffaws and grunts but, hey, that’s males for you. Check.

I’m afraid my imagination has run riot, inspired by a story in Nature suggesting that our human ancestors interbred with chimpanzee ancestors. It’s not quite as explosive as suggesting that human beings slept with chimps, but it isn’t far off. It would mean a two-legged human ancestor possibly having carnal relations with an ancient chimp that was still on all fours, and such fumblings resulting in fertile, human-chimp hybrids.

Some palaeontologists are wide-eyed in disbelief — who can blame them? — but to others such interbreeding resolves a conundrum in the fossil record of human evolution.

It has long been known that chimps are genetically man’s closest relative. Many DNA segments in the two species look almost identical, meaning that they were bequeathed by a common ancestor. Note the “almost”: by looking at the minuscule differences, geneticists can pinpoint when human DNA began diverging from chimp DNA (when species break off and evolve separately, random mutations accumulate in the genome at a steady rate, and counting up these mutations gives a rough idea of when divergence occurred). So, geneticists at the Broad Institute, a collaboration between Harvard University and Massachusetts of Technology, put the human genome next to the chimp genome and totted up the numbers.

If chimps and humans made a clean break, say, six million years ago, then segments of chimp and human DNA should differ consistently by six million years’ worth of mutations. But the Broad team, led by David Reich, found that instead some segments of human DNA were acquired four million years later than others.

This suggests there was no clean break — we seem to have acquired some ancestral DNA from an early split, and other DNA from a final break that could have been as recent as 5.4 million years ago.

This makes sense, Dr Reich says, only if there was continuous genetic exchange between the two evolving species over a long timespan — in other words, interbreeding — and the resulting hybrids evolved into us.

This would explain an important puzzle: Chad Man. Also known as Toumai, Chad Man was the skull of a hominid (early human ancestor) found by fossil hunters in the Sahara in 2001. He was dated as living around seven million years ago, before the supposed split between chimps and us. “It is possible that the Toumai fossil is more recent than previously thought,” said Nick Patterson, a co-author. “But if the dating is correct, the Toumai fossil would precede the human-chimp split. The fact that it has human-like features suggests that human-chimp speciation may have occurred over a long period with episodes of hybridisation between the emerging species.” The researchers caution, however, that there is no proof that such hybrids existed.

• IF THERE really was a School of Hard Knocks, it would be languishing at the bottom of the Ofsted rankings. Researchers at Leeds University have found that, instead of toughening people up and making them more streetwise, adversity in early life makes them more gullible.

  Kim Drake, of the university’s School of Psychology, interviewed 60 people and found that those who had suffered more setbacks during childhood — such as serious illness, bereavement, parental divorce or bullying — were more likely to make a false confession under police interrogation. Drake speculates that they may feel, wrongly, that their own judgment contributed to their early misfortune. In turn, they lose faith in themselves and are more easily led.

• I CAN’T resist resuscitating a story from last year that unites two current cultural obsessions: Leonardo Da Vinci and the secret of happiness.

  A researcher at the University of Amsterdam used emotion recognition software to analyse the Mona Lisa’s wan smile. The enigmatic sitter, thought to have been the wife of Florentine gentleman Francesco del Gioconda, was calculated to be 83 per cent happy, 9 per cent disgusted, 6 per cent fearful and 2 per cent angry. And, no doubt, 100 per cent bemused by all the fuss.

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