1. If evolution results in increasing fitness within each species, will we eventually reach a point of perfect fitness and end the possibility of further change?
2. How can natural selection, a single mechanism for change, produce such diversity in living forms?
3. Can order be imposed upon the diversity of life

1. No -- first of all, there is no one "perfect form", only forms that are well adapted to a particular environment.  And there are many thousands of different environments on Earth (deep sea, small ponds, tundra, Starbucks, etc.)  And second, environments don't stay the same, so what's perfect now won't be in ten or a hundred or a thousand or a million years.

2. Diversity comes from branching on the tree of life.  A single lineage, if split by (for example) a geographical barrier will become two, and all things being equal they will tend to diverge.  Repeat until you have as much diversity as you want :-)

3. The diversity of life already has order: the tree of common descent.  Modern taxonomy is basically an attempt to discover that tree (or at least approximate it as best we can) and to put names on the nodes and branches that we consider "important" or "interesting".

Hope this helps.

To add to Mike's thoughts..

1) Because the environment is always changing, the "perfect form" that would maximise fitness is going to be a moving target for selection to chase. Also, while many people don't think about this, a large part of the environment is actually the biota that any organism interacts with (food, predators, pathogens, competitors etc). Since they are all evolving, at one level we can also think of the environment as evolving too. A good example is in the evolutionary arms races that occur between parasites and hosts. It's very hard to become a perfect parasite when host defences are evolving too.

2) As a geneticist I'd say that natural selection is not the only mechanism of importance in evolution. Mutation is ultimately where the variation comes from, and that genetic varition is "sorted" by selection. However the diversity of life that we see is also shaped by gene flow (migration) and genetic drift (basically chance). This means that even without selection, two populations that are isolated from each other will tend to become different over (evolutionary) time.

3) I agree with Mike. Taxonomy is our (i.e. as biologists) attempt to impose order on the diversity of life. There are probably other ways that this might be attempted - depending largely on what you mean by "order".

Last edited by Alistair Wilson (3rd Dec 2007 12:25:23)

Total agreement with Mike and Alistair, but with some other points:

1) Fitness can be a misleading name, since it can be used to mean a variety of things. In this context fitness means the suitability of traits for a particular environment or set of selection pressures. 'Survival of the fittest' means 'survival and reproduction of the organisms within a population that are best adapted to the conditions experienced by that population' - obviously the full version isn't as snappy! As Mike and Al said, conditions change, so what makes something fit also changes.

2) Natural selection works on vast numbers of organisms over huge lengths of time. Variation is essential, as Al says, and other selection mechanisms also play an important role in diversity. Sexual selection, for instance, can lead to a huge amount of increased diversity by segregating sections of populations that go on to form new species. Beetles (the most diverse group of animals on the planet) are a good example of this, since their genitals are like a lock and key, meaning that small changes in shape provide a barrier within a population. Speciation carries on as Mike has described.

3) Again, Mike and Al have covered this one - life is already in a kind of order determined by a chain of relationships between species sharing common ancestry. Understanding the pattern of relationships is the hard part. To do it we rely on shared characteristics between organisms. The more similar organisms are to each other, the more closely related they are. Probably.

Last edited by Paolo Viscardi (3rd Dec 2007 11:55:11)