Margot Taylor, of Port Chalmers School, asks :-

Why did people evolve with four fingers and one thumb? Why not some other combination?

Nancy Tayles, a biological anthropology with Otago University's School of Medical Sciences, responded.

Human hands are unique in the animal world because of the way we can use them to improve our lives by significantly altering our environment.

Since more than five digits on our hands would have made them even more useful, there are really two sub-questions to be addressed here. Why do we have only five digits? Why is only one of these a thumb? Looking at the first question, research suggests that the explanation is genetic. It seems that the genes that would provide us with more than five digits also have other, disadvantageous, functions - such as causing malformed limbs. Why the genes act this way is not clear but it does explain why we have evolved no more than five digits on our hands (and our feet).

Many other vertebrates also have five digits and although some have less, very few normal, healthy, animals have more. This characteristic therefore appeared a very long time ago in the evolution of animals. Why do we have only one thumb? The ability to use your thumb to oppose the fingers has obvious advantages. Try picking up a glass of water, doing up a button, or text-messaging without using your thumb! Considering the value of our thumbs, why haven't we evolved more than one on each hand? This question doesn't seem to have been researched but perhaps the explanation also lies in our genes. Very few other animals have thumbs, and the thumbs of those that do (apes and some monkeys) are much less useful than ours, so this feature of our hands evolved relatively recently.