Question: how does evolution work?

Heather Eyre answered on 26 Jun 2013:

Evolution can only work when there is variety within the individuals in a group, and when there is some environmental pressure to drive the change.

A good example is giraffes – their neck looks a bit silly and has to have risks, so there need to be a good reason for it to be there!

So a group of giraffes have necks from 30cm to 1.2m in length, and the savannah summers are getting longer, and food hard to reach.

The giraffes with longer necks can reach leaves much higher on the trees – so they are much healthier. When mating season comes round the long neck giraffes will be stronger and healthier that the short neck giraffes and can out compete for the females. Also as the long neck females can reach more food they have more chance of having enough energy to survive pregnancy.

In the next generation of giraffes there will be more of those with longer necks and fewer of those with shorter necks. This process repeats within each generation, you might only see an increase of 2cm per generation but this adds up over hundreds of years to create the change. Mutations that change neck length can occur randomly too and if they are an advantage then it is likely that it will be passed on in lots of offspring!