This is an area that Darwin knew anything about. When he proposed the theory, any serious study of this was impossible. When this did become possible, it showed the same relationships between animals that had already been calculated. I will concentrate on the animal kingdom, but it should be noted,as can be seen in the diagram below that plants, fungi and bacteria can also be examined in this way.

Phosphanogens

It is known that the animal kingdom can be split into two main arms, chordates and echinoderms on one side and annelids, molluscs and arthropods on the other. This is confirmed with embryology and morphology. The interesting thing is that the use of phosphagens follows the same pattern. Phosphagens are the molecules that living things use to quickly store and release energy for chemical reactions.Chordates/ Echinoderms use phosphocreatine almost exclusively and the other branch uses Phosphoarginine. There are exceptions though, which merit a further look, such as some of the annelids that use Phosphocreatine. This evidence can, though, be used to generally support the main split in the animal kingdom. Now, we need to split it down even more.

Blood pigments

There are four blood pigments, which carry the oxygen around the blood stream of animals, three of which (haemoglobin, haemoerythrin and chlorocruorin) use iron and one (haemocyanin, which is the second most abundant blood pigment) uses copper. The distribution of these in the animal kingdom shows a family relationship.

The point is that the different pigments are not distributed at random around the animal kingdom, but are present in animals which can be grouped together as a family.

By examining the way that the Phosphanogens and the blood pigments show the same relationship, we can see that the evidence shows that what the Theory of Evolution says is correct. The fact that Darwin knew nothing about these chemicals shows that his theory has been substantiated with new evidence.

Seretological tests

Another way of testing closeness of relationship is to use Seretological tests. This is done by taking serum from one animal, say a human and injecting it into another, for example a rabbit. The rabbit will produce antibodies to the serum. Take the antibodies and mix them with some more human serum and a precipitate forms. The more precipitate, the closer the relationship.

This is only a rough guide to closeness, and should not be used on its own as evidence, but combined with the other tests then this confirms exactly the same picture.

These each only give a general picture, though. What is needed is a way of getting more detailed information

Protein comparison

This can be done by testing the closeness of the biochemistry is to look at the mutations which are found in proteins. The more mutations the further apart the creatures being compared are. What can also be investigated is what the particular mutations are. If we see a protein with a particular mutation and then we see proteins from a different that has that and another mutation, we can say that they are closely related. It is of course possible for the same mutation to occur twice, which would cast doubt on the findings. This means to be sure, we should use other proteins and other evidence. On its own, this information cannot be used to form strong conclusions.

Here is a diagram showing the relationship between many different types of the protein cytochrome C, which is found in all eukaryotes*. The numbers represent the number of mutational differences between the red circles.

From 'Biochemistry' 2nd Edition by Lehninger. 1975 from Worth Publishers

Below is a diagram based on a similar study with a totally different protein, called fibrinogen, but this is only showing mammals. It shows the same relationship as the cytochrome C diagram above. What this does demostrate is that the cytochrome C and fibrinogen mutations highlight the family tree of mammals in exactly the way we would expect the family tree to be constructed using knowledge from other disciplines.

The same system has been used with other protreisn and they give the same results, with a few minor exceptions (which is understandable considering we are measuring mistakes!) caused by the same mutation happening in different creatures. These exceptions can be seen to be exceptions by looking at many proteins . The results from these biochemical tests agree with morphological and embryological evidence.

The conclusion is that the living world can be shown to have a family tree based on their cellular molecules. The same conclusion is shown by examining many different proteins and using different methods. This evidence agrees with morphological evidence and embryological evidence.

*annelid - segmented worm
*Eukaryotes - living things, including bacteria that have a nucleus in their cells.
*polychaetes - a form of marine annelid*
* sipunculids - a type of marine worm