Evidence for Evolution

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Evidence for Evolution

There is much evidence for the process of evolution and that natural selection is the mechanism by which it occurs.

The study of fossils.

Palaeontology

In the oldest rocks there are very few types of organism that have been found. Those that have been discovered have a relatively simple structure.

In younger rocks there is a greater variety of organisms and they are much more complex. Species do appear and disappear from the fossil record. This disappearance is probably due to climate or other environmental changes.

The record is not continuous though, which can lead to questions about how much store we should put by evidence from fossils.

It is not surprising though that there are gaps since many organisms would decompose quickly, well before they would have had a chance to fossilize.Other organisms would have been eaten, many would have been soft bodied and of course, many have not even been found.

It has also been suggested that evolution is not a gradual process, occurring all the time. Instead, it may not occur at all for a long period of time and then, as conditions change, occur very rapidly. If this is the case, so-called "missing links" may never be found, as change occurred so rapidly.

Many island populations will evolve rapidly, due to high levels of competition and several niches may be filled by different species originating from a single ancestor.

Divergent evolution

Also called adaptive radiation.

When a group of organisms all possess a structure that appears to have come from a common ancestor and which has the same microscopic structure and body position, as well as other features, they are said to have homologous structures.

These may have been specialised in each group for a particular function (e.g, the pentadactyl limb. All mammals share this, but in some it is used as a hand, in others as a flipper, in others as a wing and so on.

They look different in different species and are used for different things because of the particular selection pressures on those species.

Convergent evolution

This is the opposite of adaptive radiation; it is where structures that on first appearance are similar but are actually found to be unrelated.

Examples include:
  • Insect wing and bird wing.
  • The eye of a mollusc (e.g, squid) and the eye of a vertebrate.

These structures are said to be analogous. In these cases, selection pressures from the environment in which each species lives have caused particular structures to be advantageous.

Various chemicals have been studied in order to find evidence of evolution, DNA and proteins such as cytochrome c in the electron transport chain of respiration are often used.

Looking at the order of bases in the lengths of DNA and the order of amino acids in a protein, it is possible to determine how similar they are in different species.

Species that are closely related have the most similar DNA and proteins, those that are distantly related share far fewer similarities. A comparison of DNA sequences show that it is 99.9% certain that chimpanzees are humans' closest relatives.

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