Evolution

[dave_c]

Basicially how doe's evolution occur? OK a organism might evolve to adapt to a certain environment to survive, so does that mean the environment inadvertently effect's the creature down to it's genetic make up? In a word changes the sperm and eggs for the evolve offspring?

[Loosehead]

The theory of evolution is based on Natural selection, or "the survival of the fittest". Essentially over millions of years the strongest and most sucessful species survive at the expense of the weakest . So you have many species dying out as, what you might call, natural dead ends are reached. At the same time species who find a way of reliable reproduction and are resilient to available living conditions prosper. There are many ways in which species survive and prosper, the simplest just sheer weight of numbers, ie a reproductive system so effective that extinction is an impossibility. The more advanced animals prosper by being at the top of a food chain.

Even within individual species natural selection is at work, ie the strongest lions get to breed, ensuring the best combination of dna is passed on so yes at a fundemental level the genetic code is continually being revised to take account of living conditions.


There's much more detail but you get the idea.

[smadge]

Dave, you're thinking of Lamarkism, which has been refuted, but which is making something of a comeback (but I think it's wrong). It's based on the idea that evolution occurs because an individual passes on adjustments or qualities it has developed in its lifetime, through genetic change, to its offspring.
This is not what occurs at all. I can do nothing to my DNA to make it change for the better of my offspring.
It all comes down to differential survival of certain genes. Basically, the only warrior is not the species, not the individual, not the group, but each individual gene. Each gene which confers on the individual a better chance of REPRODUCTIVE success (ie being able to give rise to young, and then ensure that they are able to give rise to young) will be more likely to survive. That's it. That's evolution. There is some genetic mutation at the moment of reproduction (which Darwin was NOT aware of), which provides opportunity for nonrandom environmental effects to have an impact on a genes survival.
Evolution is commonly misunderstood, mostly by those who profess to understand it.

[bernardo]

For example:

There is a type of insect which looks 5% like a leaf.  There are various insect-eaters which eat most of the insects.  However, there are hundreds of insects in each new generation, so there are enough to survive.

When Mummy and Daddy insect have lots of baby insects, most of them will look 5% like a leaf.  But they are all slightly different (they are not clones) so some of them will be 6% like a leaf, and some of them will be 4% like a leaf.

The predators will miss slightly more of the 6% ones, and catch slightly more of the 4% ones, due to their different levels of visibility.  So when all the babies grow up, the ones which have survived will be (on average) slightl more than 5% like a leaf.

After thousands of generations, the same effect will mean that the insects will look very much like a leaf.

The two essential processes which cause this to happen are random variation (the offspring are all slightly different) and natural selection (the bad ones are more likely to be killed by the predators).  Thus the process of evolution happens without any conscious or deliberate action by the parents in any one generation.

[Calvesy]

It's happening right now to you. There are inherited predispositions in your personality and physical make up that make it more or less likely than your siblings and peers that you will have offspring that survive to parenthood. It's mundane, gradual and impersonal but 100 million generations ago you were a fish. The environment cannot reprogram genes, merely filter out the non-starters.