Mechanisms

Evolution requires three things; replication (heredity), variation and selection.

We know that organisms replicate and that the carrier of information, the
recipe for creating a new organism is DNA. We can take the DNA from one of an organism's cells
and grow a completely new organism. This proves that, not only is DNA the carrier of the recipe,
it is complete and contains every single instruction required to shape the new creature.

It comes as no surprise then, that we can also prove that variation in the genome causes
variation in organisms. This has also been proved in the laboratory and has been used to good
effect in gene therapy.

Organisms die childless all the time and if the reasons for an organism's demise are congenital,
that is due in some way to some physical or innate behavioural inadequacy, we can see selection
at work.*

Evidence

Over a period of 20 years, beginning in 1970, a research programme headed by Rosemary and Peter Grant
studied the Finches of the Galapagos islands first made famous by Charles Darwin. All but one or two
birds were trapped, measured and photographed and detailed family trees were contructed covering
all 20 generations.

The researchers watched how populations dwindled in times of drought stricken hardship
the smallest variation in beak length made all the difference between surviving and leaving offspring
or dying childless.

Peter Boad has since applied modern DNA testing procedures to blood tests taken at the time
and we can see clearly how variation in the birds' genome, causing variation in the birds' physique
had a direct effect on survival.

Gradual variation in the genome is known to be able to create a new specie. A clear example of this
can be seen when we look at ring species such as the gulls of the northern hemisphere.
The herring gull and the lesser black backed gull, both found in Europe, are quite
clearly diffrent species in that, quite apart from simply looking different, they do not interbreed.
However, if we track the gulls westward, we find that the gulls become less an less like herring
gulls. Each type of gull can interbreed with it's immediate neighbours until we complete our
circumnavigation and reach the start of the chain again in Europe.