Evolution is the change of heritable traits in a population over time- the process giving rise to new species. In the mid-19th century, Charles Darwin and Alfred Russell Wallace proposed the theory of evolution by natural selection (in the book On the Origin of Species). The theory was that certain traits give individuals in a population a selective advantage, meaning they are more likely to survive, reproduce and give rise to a progeny better adapted to that environment (as they are more likely to possessive the adaptive trait). A good example of evolution by natural selection is the evolution of resistance to pesticides:
A recent example of evolution by natural selection is that of different morphs of the peppered moth (Biston betularia) during the industrial evolution. The light morphs of the peppered moth dominated the environment as they could rest on trees covered with white-coloured lichens and be camouflaged enough to avoid being predated. When more sulfur dioxide polluted the environment, these lichens died, giving the darker morphs a selective advantage as they could now blend in with the dark colored bark. Once the lichens recovered the darker forms died off, and the lighter morphs once again proliferated. This is an example of population genetics, and can be used to monitor genes in different populations.
Convergent Evolution: The same or similar traits arise in groups from independent lineages (which are unrelated). For example, the wing: