The handicap principle was invented by Prof. Amotz Zahavi from Tel Aviv University. It claims to explain the fact that some animals have characteristics that do not necessarily help them survive. Lets take the peacock for example. The peacock's tail is long and heavy and actually diminishes its chances to survive. So why did it evolutionary survive?According to the principle, one day, a mutant female peacock that likes peacocks with longer tail, looked for a male with this characteristic. The mature male she found was strong enough to survive even though it had a long tail and therefore it is probably stronger than the average peacock. therefore, its predecessor males are going to be stronger and also to have a long tail while the newborn females are going to like long tails, passing the ideals of the principle to the next generations.
This principle comes in addition to the well known evolution theory claiming that only the one who fits best to its environment survives.