Question about evolution

Ok so I wanted someone who is more educated on the subject to clarify some confusion Ive had about evolution.
So if evolution has no goals then why didn't it stop at bacteria. Bacteria is probably the most successful species on earth and in alot of ways is more efficient at survival than we humans are. Why the need to keep evolving into more and more complex organisms? Im just entertaining a thought here but is it possible that evolution does have a goal, to produce the rational animal, us, perhaps the universes way of knowing itself? I know Im skeptical of such an anthropocentric view too, and Im not necessarily saying humans are the pinnacle of creation as some theists claim, but perhaps we are not done evolving? Thoughts?

It's a good question. The basic answer is that if evolution can be described as having any kind of 'driving force', it would be to fill empty ecological niches. An ecological niche means a unique way of surviving. For example, the ecological niche of a squirrel and a deer are different, because squirrels eat nuts and deer eat grass. This means that they are not competing with each other. However, it is not thought that two organisms can fill an identical ecological niche; one will be slightly better than the other and in the end will out compete the other, so it's an unstable equilibrium. Now, if the only ecological niche on Earth was doing what bacteria do, then you would be right. However, there are other niches to be filled, for example the niche of eating bacteria. If there were only bacteria in the world, I'd imagine one day, due to variation, one of those bacteria would have a mutation which allowed it to penetrate other bacteria and steal their energy. Then by the basic process of natural selection this bacteria would split off into a whole new class of organism which would become better and better adapted to eating other bacteria. As a matter of fact, it is thought that the evolution of eating others for energy (heterotrophy as opposed to autotrophy) was a major factor in the evolution of more and more complex life (something which actually only occurred recently in the history of life), as it started a kind of 'biological arms race'.

A lot of the complexity is as Xei points out, due to a biological arms race. The actual complexity can be rather ridiculous and costly, but it still confers an advantage and so it evolves. For example, let's say Cheetahs are 5% faster than Gazelles, their main source of prey. Now let's say that some Gazelles have stronger legs, which narrows the speed difference to 4%, and so they're more likely to survive, so Gazelles get faster. A Cheetah that can run 5% faster than the new and improved Gazelles and so will be less likely to starve, and so Cheetahs get faster still.

At the end of this hypothetical situation, the situation is back where it started, but both the Cheetah and the Gazelle now pay increased costs. The Gazelle has to build, maintain, and carry a greater amount of muscle (and likely other factors such as requiring increased bone density, etc. etc.) Similarly the Cheetah has the costs of whatever adaptation that allowed it to run faster. From the starting point they're actually worse off, yet these situations still occur because the changes are advantageous.

There are so many ways that these kind of situations could occur. For example a Cheetah might evolve better camouflage so it can sneak closer up, or it might evolve more efficient lungs to increase endurance. Whatever. I've stuck to a single factor here (speed), for the sake of simplicity, but you can see how complexity can increase, even if the net gain in the overall scheme of things is nothing, or even negative.

Xei's example of a species evolving to prey on bacteria is a good example of how something more complicated could evolve. If there are a lot of bacteria, then anything that could use them as a food source would have a big advantage. The process continues from there, and the situation leads to more opportunities for success, and so complexity increases to take advantage of that.

Bacteria are very successful as a group, but there are things where other organisms have significant advantages over them, and at the species level they don't tend to be so successful. By that I mean that they tend to have specific niches, though they are successful within those.

It's a good question, and it's hard to do the subject justice in so few words, so I can only advise on reading a book on the subject for more details. Hopefully I've written enough that you can understand my point though.

The biological arms race also works within a species. With sexual reproduction (as opposed to asexual), females will be more likely to reproduce with bigger, stronger males or males with large colourful feathers or other attributes. This way, the fanciest, most complex males of a species tend to pass down their genes more often (besides fertility, the attributes of the female aren't nearly as important).

This is funny because it can sometimes clash with the arms race against other species. For instance a peacock is evolved to be very visually impressive in order to attract a mate, but is also highly visible to predators. It just so happens that the fancy plumage gets a peacock laid more often than eaten.

Thanks for the explanations everyone they helped me out tremendously considering Im writing a research paper on evolution right now. I dont know why I have trouble wrapping my head around evolution sometimes. Can anyone recommend any books on the subject or is Origin of the Species my best bet?

Anything written by Richard Dawkins.

Dawkins' books on the subject (save The Extended Phenotype which is more technical) are excellent for the layman. In particular I recommend The Blind Watchmaker, The Selfish Gene, and Climbing Mount Improbable.

Bigger animals means they are harder to kill. Survival of the fittest. It's also due to randomness, something mutated to have multiple cells that worked together. Actually, this is sort of a grey area. How multicells creatures came about is actually one of the biggest mysteries of evolution. But that doesn't make it wrong.

I second "The Selfish Gene." Brilliant book. Jerry Coyne's "Why Evolution Is True" is also very good but obviously the purpose of that book is a little different.

Evolution is a very dumb mechanism. It doesn't absolutely pay heed to what helps the organism survive or breed more. Even if some of a creature's mutations don't affect or slightly lower its possibility of survival and breeding, it can still potentially continue its genetic line. Even if there is no 'need' to change, mutations will still continue to happen and therefore evolution will continue to happen so long as the products of those mutations can survive and breed to some degree, even if it is to a lesser degree than the creature's predecessors.

I'm not saying this is why we're here, but just that it's something to consider.

Also, food for thought:

http://www.youtube.com/watch?v=TUlx0...eature=related

It's been a while since I read either but from my recollection, The Extended Phenotype pwned The Selfish Gene. It's true that it's more technical but he did write it to be understandable by laymen. He includes an excellent glossary and with wikipedia, it should be accessible to anybody willing to make the effort. The idea of the extended phenotype (which was not discussed in The Selfish Gene IIRC) is pretty profound.