Evolution…

This entry is part 1 of 1 in the series Natural Selection

The theory of evolution is often seen as the basis of modern biology, indeed it has been said that nothing in biology makes sense without evolution. Evidence from fossils, the geographical distribution of organisms and recent discoveries about genes all support the theory that organisms have changed over time. These changes are incredibly slow and result from random changes that occur as the genes rearrange themselves to form gametes (sperm and eggs). Some of these changes (mutations) are so serious that no fertilisation occurs or the organism quickly dies. Some changes don’t appear to make any difference but these can build up over time to have a cumulative effect. Other changes provide an immediate advantage. Any organism gaining a survival advantage is more likely to pass on its genes to the next generation. Alone, this is not enough to cause evolution, but if the environment changes sufficiently then the organisms with the inherited mutations may start to dominate and eventually replace other organisms without the mutation. This is called natural selection or survival of the fittest (fittest here means ‘best suited to survive’).

Simple evolutionary changes are obvious to anyone who owns a dog. All domestic dogs share a common ancestor – the wolf. Over time, man has selectively bred dogs into the many different types we see today. They are all the same species even though they look very different. The same could be said for a host of organisms now very important to man. Our food crops are very different to their wild ancestors; cattle and pigs are only passingly similar to their ancient relatives. Cross-breeding has taken the place of natural selection.

When organisms become sufficiently different, often as a result of geographical isolation, so that they are no longer able to reproduce with other similar organisms, they are a new species. Speciation usually takes a great deal of time, so it is not easy to observe it happening. Life on Earth has had 3.8 billion years to evolve so there has been plenty of time to produce the vast array of different species we see today. Each one is uniquely adapted to its environment which is why changes in the environment (caused by natural events or more recently by the activities of man) can have such a devastating effect upon a population.

There are many sorts of advantages that might be transferred from one organism to its offspring. They might be…

a slightly increased ability to cope with cold weather
an increased resistance to disease
an ability to digest a new type of food
a better ability to evade predators
higher intelligence than others of its kind

The list is enormous. What they all have is an increased probability, under the right conditions, that the organism’s genes will be passed on to the next generation. Don’t forget that humans are organisms too. Whilst the papers often get excited that recently unearthed fossils might be the ‘missing link’ between humans and other apes, it is important to understand that there is no such thing as a missing link. Every organism that has ever existed has been a member of its own species and there has never been a moment when an animal has given birth to a different species.

Evolution describes the change in the genetic code of a population over time.

These two videos discuss firstly, what we know about the origin of life and secondly what evolution is.