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Darwin's theory of evolution

Charles Darwin (1809 - 1882) was an English naturalist who made a study of variation in plants and animals during a five-year voyage around the world in the mid 19th century. Although he was not the only scientist working on evolutionary theory - Alfred Wallace was coming to the same conclusion around the same time - it was Darwin who published his ideas first. On the Origin of Species, which came out in 1859, is possibly the most influential scientific book ever written.

Whilst studying wildlife on the Galapagos Islands he noticed that the Galapagos finches showed wide variations - eg in beak shape and size - from island to island. Darwin deduced that these differences made the finches better adapted to take advantage of the food in their particular local environment - thin, sharp beaks prevailing where the birds' main food was insects and grubs, and large claw-shaped beaks where their diet was buds, fruit and nuts. In each locality the finch population had somehow developed beaks, which were suitable for that particular environment.

Darwin concluded that in each locality one or more individual finch happened to acquire, by random mutation, a beak shape more suitable for the food sources in that locality. These individuals then had a competitive advantage over their fellow finches, enabling them to grow and reproduce more successfully, and pass on their more specialized beaks to successive generations - until eventually the characteristic had spread throughout the finch population in that locality.

He studied hundreds more animal and plant species, and made the following key observations:

· That living things tend to produce far more offspring than will survive to maturity

· That within a species population numbers tend to stay more or less constant over time

· That each species displays a wide variation in features

· That some of these variations are passed on to the next generation

Darwin's theory explained these key facts. He inferred that living things are in continuous competition with each other - for access to space, food, and mates, for example - and that only the best suited, or 'fittest' survive to reproduce and pass on their genes. Any characteristic acquired by chance mutation that gives an individual an advantage in the struggle will be naturally selected for.

Natural selection means the survival of organisms that are best suited to surviving and reproducing in their environment. Over millions of years, this process produces not just variations within species, but entirely new species as well. It is the engine of evolution.

Picture: http://www.swarthmore.edu/NatSci/cpurrin1/evolk12/posse/chazhasaposse.htm

Theory: http://www.bbc.co.uk/schools/gcsebitesize/biology/variationandinheritance/3evolutionrev1.shtml