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Evolution: Nature's Problem Solving Method

The survival of life on earth depends upon its ability to adapt to changes in its environment. Essentially a species must be capable of solving the problems that are presented to it, such as changing food sources, threats from predators or climatic variations.

The way that species adapt to address these obstacles is linked closely to the theory of survival of the fittest. The world is, on the whole, a cruel environment and does not reward failure, those who are not strong or fit enough to survive die. Even in species in which the weak are supported by the strong the same applies, as the success of the species as a whole depends on the presence of the strong individuals. If a species does not have the problem solving skills it needs to survive then it becomes extinct.

It is possible for individuals to become better at solving particular problems during their lives, by developing stronger muscles or learning useful techniques and tricks. Unfortunately (perhaps?) the traits we develop during our lives can not be passed directly to our offspring.

To recap on some pretty simple theory, which most of us probably learned in school: The traits of individuals are governed by the structure of their DNA, a molecular "specification" which controls the behaviour and growth of cells and thus the characteristics of the individual. The structure of the DNA molecule is shown in figure 1.

Simplified structure of DNA
Figure 1: Simplified structure of DNA

DNA is coiled up in chromosomes which can be found within the nucleus of every cell in every living thing. The DNA molecules act as templates for manufacturing proteins which govern the behaviour and development of the cell. DNA is essentially a string of very simple building blocks - the bases. Each base can bond to one other (A with T and C with G) to form a base pair. Base pairs bond together to form a ladder-like structure which is then twisted into a double helix, each rung of the ladder being one of four possible combinations (CG, GC, AT or TA), each of which can be though of as a single cipher in a very long coded message. Generally speaking, when creatures reproduce two gamites (sex cells), one from each parent, combine to form a single cell which will become the new creature. Each gamite carries some of the DNA of the parent from which it came. When the gamites join, a new, complete, DNA strand is formed by combination of the DNA fragments from the parents. Thus, the traits of the parent are passed to it's offspring.

Genes: It might be worth briefly mentioning what genes are at this point. Genes are essentially strings of base pairs in the DNA strand which form defined groups of varying length. There is some argument about how to actually define genes, some state that genes are defined strings, delimited by 'terminator' base combinations. Others define genes as strings of bases which can be associated with given behaviours - for example the production of a specific protein. From our point of view it's enough to think of genes as parts of the genetic code that can be associated with specific traits of the organism. From this point on we shall be dealing in terms of genes rather than base pairs. Figure 2 shows the way in which genes are combined from parents, note that this is a totally random process...

Combination of Genes
Figure 2: Combination of Genes

The copying process for DNA is not, however, entirely accurate. Figure 3 shows some common errors that occur. These are known as mutations. Mutations can cause changes in the features of the offspring for better or worse.

Some types of mutation
Figure 3: Some types of mutation

The principle of survival of the fittest dictates that weaker individuals are more likely to die, so those born with detrimental mutations will be less likely to reach adulthood, and thus less likely to breed and pass on their traits to the next generation. Individuals who are lucky enough to undergo mutations which give them a better chance of survival (longer necks in giraffes, opposable thumbs and a large brain in a certain breed of ape...) will, by the same principle be more likely to pass these beneficial features on to their progeny.

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