Who am I?

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How are you different?

Our history is written in our genes. Your genes tell your body how to make all the different proteins it needs to survive, develop and grow. A change (DNA mutation) in a gene can alter what it does, so the body makes a slightly different protein. Different versions of genes are called alleles. The types and numbers of alleles in a population can provide clues about the lives of our ancestors: their diet and the diseases they encountered.

Different versions of several genes influence eye colour.

Can we evolve disease resistance?

As the population grew, diseases like typhoid, cholera and malaria thrived. This may explain why so many people carry the sickle-cell and cystic fibrosis (CF) alleles. Both cause serious genetic conditions in people who inherit two copies. But people with just one copy of the sickle-cell allele are unaffected and are resistant to malaria. Some scientists believe that similarly, carriers of CF alleles resist cholera and typhoid.

Electron micrograph of sickled and normal red blood cells

Can you drink milk?

In some parts of the world, certain adults cannot drink large amounts of milk because they are unable to digest lactose, the sugar found in milk. Drinking fresh milk causes discomfort and diarrhoea, but they can eat dairy products treated to break down lactose – like yoghurt. In other parts of the world most people have a version of a gene (allele) that allows them to digest lactose in adulthood. This characteristic probably spread through some populations thousands of years ago, as their ancestors began farming cattle.

Ancient carving of domestic cattle from Mamallapuram, India.

Why do populations differ?

Some alleles spread through a population because the people that have them are more likely to survive, and to pass those alleles on to future generations. For example, peoples living in hot countries have alleles that give them darker skin. Their skin contains more of the pigment melanin, which absorbs the sun's harmful rays and prevents damage to the surrounding cells.

This microscope image of human skin shows black melanin under the skin.