Quote Originally Posted by Moira
What I meant was the idea that everything has simply happened by chance, which a lot of people believe is the case.
But then you're not talking about evolution.

Evolution is not "directed", and nor is it "random". A snowflake does not form "at random". It has aspects of randomness, but very simple underlying principles ("ice crystals make this lattice pattern") cause a complex result. The snowflake was not "designed", nobody said "I want it to look this way, with little flakes here and here". But it also isn't entirely by chance, because it has a symmetrical structure. The basic idea is that simple rules and a source of random change can combine into a wide range of complex results, with nobody directing the situation or making nudges here or there, and that therefore complex results in general do not require a director or designer. Emergent behavior.

You can consider biological species as really just sets of compatible patterns which repeat and change (and merge and split) over time, just as your own physical body is a pattern that largely persists even as every molecule is replaced every X years, or how an ocean wave keeps moving even though it doesn't carry the water with it.

Just like with waves, some changes to a pattern can make the thing collapse, and the pattern falls apart. Other changes can make the pattern stronger, or faster moving, or better at starting smaller repeating patterns. Bad changes mean patterns that stop repeating and touching off little ripply copies. Good ones mean more (different) copies. Ones which aren't clearly good or bad just mean different patterns.

Just because we only see the really cool patterns doesn't mean that they arose "totally by chance". And we wouldn't call the system anywhere near perfect if we could see how many bazillions of bad patterns once existed but never persisted.