What's the driving force behind evolution?

[10ClarionSt]

Why does evolution happen? What makes it move forward? We always hear how things have evolved and adapted, but what is it that makes it happen? Plants, insects, mammals. Is it a survival instinct? If so, where did that come from? Outer space?

[gen2]

Evolution happens as a result of small differences in offspring giving them an advantage over others. That means they are more likely to survive, breed and pass on their genes. This is usually described as 'Survival of the fittest'

All sorts of things may drive evolution in a certain direction. Here are some examples.
Disease
Predators
Competition for food, water, shelter, other resources
Sex - success (or not) in passing on genes.
Climate change
Pollution

I'm sure there are lots more.

[wildwood]

Evolution doesn't move 'forwards', it happens haphazardly and only those which have adaptations to suit the ever changing environment will thrive.

Even with humans there have been a few sub species which have not been successful so have become extinct. Neandethal Man is one of the better known.

[jake-the-peg]

I guess the net effect has been to produce more complex life forms - in that sense it is moving forwards.

That is because each set of variations and extincions produce closer and closer adaptations to the particular environment, building on what had gone before and was sucessfull.

Of course it depends on the environment not changing too rapidly had our ancestors been exterminated in one of the mass extinctions another life form that survived would have evolved to fill the gap in a slightly different way.

You see that around the world where slightly differenct creatures live in similar ways. Lemurs in Madagascar for example live in the same way as monkeys

So there is more than one "forward"

[Cheeris]

I think you have to be very careful about talking about Evolution in terms of 'moving forward' or 'progress'. Most evolutionary biologists or geneticists would attempt to smash any kind of that talk very quickly. Partly because it is very easily for humans to slip into lazy arguments that have an underlying assumption that they are the 'pinnacle of evolution' or something similar, but also because if you reduce it right down they is no real 'progress' in evolution.

Organisms adapt to their environment, that is all.

For example, you could say that humans are highly developed because of our ubiquity and ability to adapt to different climates and landmasses etc. But we are pretty useless on the deepsea bed compared to 'primitive' forms of arthropods and fish. So, which species has 'moved forward' the most'? Neither, its a meaningless statement.

You could say that sharks are highly developed because they are so perfectly adapted to their environment, but some studies think that they would rapidly become extinct if there is quite minor changes in sea temperature and chemistry. Again, have sharks 'progressed' more than other species in their ecosystem'? No again, its a meaningless statement.