Biology - Natural Selection

The usual story behind Darwin's theory of evolution gives the impression that he came up with it when he visited the Galapagos Islands during the voyage of the Beagle. But that is not the case. It was more than 50 years later when it was published. It is true that it was down to the birds that he observed on his trip but it was only many years later that he started to develop his ideas.

Whilst looking through his notes, he came to believe that the Galapagos Islands birds were all types of finch that had somehow 'transmuted' (that's just a long way of saying 'changed') from one form into another. The main difference between the birds was their beaks. He kept his ideas to himself for a long time because he had no idea how or why that could have happened.

Darwin read a lot and at some point had read about biological competition. To you, that is simple but in the 19th Century it was a radical idea. But it still wasn't enough. It was only when he read an essay about population that he began to understand. This essay prompted Darwin to suggest that plants and animals produce more offspring than are needed for survival. There will be variation amongst the offspring and only the ones that are well suited to the environment will survive and breed, passing on the favorable characteristics. This is the process by which natural selection, one of the key mechanisms at work in evolution, occurs.

Darwin proposed that natural selection had worked on the Galapagos Islands finches. He realized that if all of the finches had the same beaks, they would be eating the same food. Islands the size of the Galapagos would not have enough food for the large number of birds he had seen. He suggested that variation in the original finch population included some that had different beaks. This meant that they could eat food that was different to the other finches and so they were successful, bred and passed on their characteristics. Any variations that could not compete became extinct.