Question: why does evolution change the body parts of animals?

Luke Williams answered on 16 Mar 2018:

There are two parts to evolution, the first is random mutation and the second is natural selection.

All the time random mutations happen in our DNA, the instructions that are in every cell. This often happens when the cells divide (needing to copy the DNA), or can be caused by chemicals, or the sun, for example. Our bodies have very effective ways of repairing the damage, but occasionally some gets through. The majority of all these changes are invisible, called silent mutations, because they have no effect. Every so often though, something DOES happen, and then we have something different.

At this stage, everything is randomly happening – there is no purpose, there is no goal or issue to solve. However, if this change helps the person who has it, then they are more likely to live longer and have children. They pass on this change to them, and they have an advantage, and pass it on to their children.

Natural selection is where there are a number of changes in a group of animals, plants, humans, whatever. The environment where they are found means that one part of the group with a specific change is better than the others. This group then grows in number, and the others eventually die off.

This whole process is evolution. Over time the animal will change to become better adapted to its environment. There could be another group of them in another place that evolve differently because the environment over there is different. Eventually you may go from one species to two species! This is how evolution works. So, there won’t be a difference in a specific animal, but changes over time in an animal’s children, grandchildren and so on.