Ask Mr Brain...all will be explained

PUBLISHED : Tuesday, 06 April, 1999, 12:00am
UPDATED : Tuesday, 06 April, 1999, 12:00am

How many strands of hair do we have? VICTORIA The average human has between 100,000 and 150,000 hairs on his head. People with red hair have the fewest hairs, while those with fair hair have the most.

On average, we lose 50-100 hairs a day, but we don't go bald because we also - usually - grow between 50 and 100 new hairs every day.

Hair is made from keratin, which is an adaptation of skin cells, as are toe- and fingernails, fur, feathers, hooves and horns.

Hair on your head is different from body hair. Head hair can grow for years and years, which is why it can grow very long if you don't cut it.

Just how long your hair can grow before falling out is genetically determined, which is why some people can't grow very long hair, while others can grow hair down to their ankles if they wish.

In contrast, the hairs on your arms and legs and the very fine hairs on your body only grow for a few weeks and then fall out, which is why people don't need to be sheared, unlike sheep.

Why is the structure of the human body different from that of other living things? NIC CHAN Jockey Club Government Evening Secondary School While the human body looks totally different to that of other animals, there are in fact many surprising similarities. Apart from being hairier and uglier than us (well, most of us), chimpanzees, gorillas and orangutans - our nearest evolutionary relatives - look very similar to humans.

While mammals come in a huge variety of shapes and sizes, from mice to humans to blue whales, their skeletons are basically the same. In sea-dwelling mammals such as whales, dolphins and seals, the bones that are fingers in humans and chimps are flippers, but they have the same pattern of bones. These similarities show that these very different animals evolved from one common ancestor in the very distant past.

Over time, animals adapted their skeletons to suit their particular way of life, but the underlying pattern of bones remained the same. As the first whales gradually adapted to life in the ocean, the need for hind legs diminished and the bones became smaller and smaller.

Now, all that remains of their hind limbs in whale skeletons are tiny unused bones. Similarly, human ancestors lost the need for a tail, but the remains of the tail are seen in the modern day coccyx - the bony part at the base of the spines of humans and apes.

Did you know that you have seven bones in your neck? How many bones do you think a giraffe has in its incredibly long neck? The same number - seven - like all mammals. But they have become greatly elongated as early giraffe-like creatures evolved to have ever longer necks.

On a genetic level, there are similarities between humans and every living thing. We share some genes in common with everything from trees and flies to elephants and chimps.

The more closely related two species are, the more genes they share. Humans and chimps share about 97 per cent of the same genes, and the figure is even higher for pygmy chimps. So you could say chimps are 97 per cent human, or humans are 97 per cent chimp (though some individuals seem to be about 99 per cent gorilla). Some researchers say that according to biological classifications, we are in fact simply the third chimpanzee.

Jared Diamond's book The Rise and Fall of the Third Chimpanzee offers a thought-provoking examination of the evolution of human behaviour and that of our primate counterparts.