It is true that we are observing the fastest rate of extinction of many species on the planet. Currently humans are the main cause of this widespread extinction of many species (refer http://alienworld.wordpress.com/2007/04/03/man-%e2%80%93-a-reason-for-extinction-of-many-species/). But before humans, the nature was the key player in deciding what species to evolve or extinct.
In Darwin’s words it is also known as Nature’s selection. If you see how the animals mate for reproduction only the best or most powerful male gets a chance to mate. This is only because the best genes should be passed to next generations, also known as survival of the fittest. Let me give you an example- fully grown male elephant seals can weight up to 2 tons and can be as long as 18 ft. One of the surprising facts is that 97% of the male elephant seals do not get a chance to mate in their entire life. The 3% who does get the chance are the most powerful in the clan. Their power can be estimated from the fact that in a week they can mate with 300 female seals. Now this is what we call the survival of the fittest – only best genes get a chance to pass on to next generation.
