Evolution Logic

Let's see if I can't help answer your questions. The answer is 'need' but not necessarily in a way you might think (or maybe I'm wrong). It is 'need' in a similar way that 1 + 0.5 + 0.25 + 0.125 + ... will tend towards '2'. It's a mathematical thing (only its based around probabilities).A simple model:
If we have an environment that can sustain 100 adults and each adult can give birth to 3 infants before it dies (perhaps they are asexual). Every generation then there are 300 adolescents who are vying to be one of the 100 reproductive adults.If anyone of these adolescents has an advantage that means it is either more likely to survive to reproduce (ie be in the top 100), or has an advantage that means it (on average) gives birth to 3.1 infants, will by definition be a set of genes that is likely to reproduce, perhaps more than its competitors. Conversely 'bad' genes are likely to fall into the bottom 200 'losers'.If this kind of set up existed, then it is pretty much inevitable that the organisms will find an 'equilibrium' point to hover around where any change is going to be harmful. They will stay around this equilibrium point (in a 'stasis' of sorts) until something happens to shift what makes the genes bad or good (for example an ice age coming to a tropical zone means that thick fur becomes much more 'good' than it used to be). At this point the equilibrium point shifts and the population starts to undergo relatively rapid change until finds the new equilibrium point.And so on and so forth. Naturally this model is a simplification and I'm assuming certain things about your knowledge of evolution. If you aren't happy with some elements, let me know.Naturally the other options 'curiosity and want' are falsified for reasons you outlined.

I'm afraid it needs a little more thinking about than that. Would that it was so straightforward. Any property change that happens to a single characteristic could be described as microevolution. Macroevolution is simply the result of property changes to multiple characteristics (the exact number is arbitrary and basically subjective). It makes simple dialogue cluttered to talk in such terms, so we concentrate on a single characteristic.That is why I stressed in my post that the model I was using for illustrative purposes was simple.The central theme of my post was aimed towards the concept of equilibrium points and stasis. When the environment changes from tropical conditions to ice age conditions, you can bet that more than a single characteristic's equilibrium point will shift. Indeed, if you want to talk in more depth we can start talking about balanced scales in many many dimensional space, but that is getting ahead of ourselves.We can see that it isn't just the equilibrium point for fur length that might change - but also for colouring, metabolism, body weight, eye sight, hearing, digestive system, circulatory system, surface area, reproductive behaviour, hunting/foraging behaviour and so on and so forth. There is another subtle thing to consider here, when all the organisms in the area start to change because of the climate, their environment changes too (because the 'landscape' of their competitors changes). This means that when equilibrium points shift it tends to be dramatic, a form of feedback can begin akin to an arms race.It gets doubly subtle when we start considering genes as the unit of selection, since now we see that their environment changes massively during these times. As far as we know it happens for no more reason that things fall when we drop them. Some people believe there is a reason for evolution, but that is belief. Edited by Modulous, : Ridding the world of redundancies one step at a time. Also, deleted a repeated point because it was redundant.