One reason fingers and toes may be so strongly correlated, scientists feel, is that they share a similar genetic and developmental ‘blueprint’. "So, if you have a long big toe, you tend to have a long thumb," they say

The evolution of the human hand was a side-effect of changes in the shape of our feet, Canadian scientists have claimed. With this, scientists at the University of Calgary may have solved the mystery of how human hands became nimble enough to make and manipulate stone tools.

The study, published in the journal Evolution, found that changes in our hands and fingers were a side-effect of changes in the shape of our feet. “This shows that the capacity to stand and walk on two feet is intrinsically linked to the emergence of stone tool technology,” they said.

Lead author Campbell Rolian added: “This goes back to Darwin’s The Descent of Man. Darwin was among the first to consider the relationship between stone tool technology and bipedalism. His idea was that they were separate events and they happened sequentially — that bipedalism freed the hand to evolve for other purposes.” He added, “What we showed was that the changes in the hand and foot are similar developments... and changes in one would have side-effects manifesting in the other.”

The scientists used a mathematical model to simulate the changes, the BBC reported. Mr. Rolian and his colleagues took measurements from the hands and feet of humans and chimpanzees to find out how they would have evolved.

The researchers’ measurements showed a strong correlation between similar parts of the hand and foot. “So, if you have a long big toe, you tend to have a long thumb,” Mr. Rolian explained. “One reason fingers and toes may be so strongly correlated is that they share a similar genetic and developmental ‘blueprint’, and small changes to this blueprint can affect the hand and foot in parallel,” he said.

With this anatomical data, the researchers were able to create their mathematical simulation of evolutionary change. “We used mathematical model to simulate the evolutionary pressures on the hands and feet,” Mr. Rolian said that essentially adjusted the shape of hands or feet, recreating single, small evolutionary changes to see what effect they had.

They found that changes in the feet caused parallel changes in the hands, especially in the relative proportions of the fingers and toes. These parallel changes or side-effects, said Mr. Rolian, may have been an important evolutionary stem that allowed human ancestors, including Neanderthals, to develop the dexterity for stone tool technology.

“I am not personally convinced that the foot and hand of chimpanzees are a good model [of human ancestors’ hands and feet] — the foot of the lowland gorilla may be more interesting in this respect,” Robin Crompton, professor of anatomy at U.K.’s Liverpool University said.

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