Human earth shapers/ETHS101/Ecology and Evolution/Concepts of Evolution

=Concepts of Biological Evolution=

This section is about biological evolution. In fact there are other important types of evolution. Cultural evolution is very important - how did all our attitudes, cultures and technologies come into existence? The answer is that they evolved, though they used a different mechanism from biological evolution. Instead of being carried by genes, culture is transferred from generation to generation by speech, writing and images. Also it is very directly under the control of logical thought (though sometimes that is hard to believe). Geologists talk about geological evolution - how did continental drift, and the burying, folding, faulting and weathering of rocks create the Tasmania we know now? However, this section only explains what we often think of as evolution - biological evolution.

How does the DNA code work?
In summary: DNA is molecule made up of two long, parallel chains of four kinds of components called bases or nucleotides (guanine, adenine, thymine and cytosine – called G, A, T and C for short). The code is defined by the order in which the bases occur. This is called the “sequence”: for example “...AGTCTT...” could be part of a sequence. The codes for species are extremely complex: humans have a code over 3 billion nucleotides long.

In effect, the code is a set of rules that, along with the influence of many features of the environment (such as how much food is available and how good it is), determine what the organism is like. Genes are sections of the code that control certain characteristics of the organism. Typically, genes do this by determining what kind of protein is produced. This matters because the proteins control the structure and function of all organisms. So, one major reason that you look (and function) a bit differently from your sister, quite a lot differently from a chimpanzee and very differently from a cane toad is that your proteins are slightly different from those of your sister, quite different from those of a chimpanzee and very different from those of a cane toad.

The code is carried from generation to generation (it is inherited) by complex processes that allow different organisms to have different codes. For this argument, the first important process is that the DNA is copied each time a new cell is formed, and this process is imperfect – the new copy can a different code. When the new copy is different, it is said to have mutated1. This is critically important to evolution because mutations are the building blocks for change. Sex is an important part of how this inheritance works – the process of sexual reproduction involves random mixing of genes from each parent. This means that the offspring can have different combinations of genes from either of their parents. This in turn means that evolution can operate not only on the individual genes but also on combinations of genes.

We’re all mutants, yes indeed – each of us has very large numbers of mutations. A few are beneficial, a larger number are harmful, but most seem to have no effect.