This is an article about evolution in the Earth Science category. Therefore I will make no mention in the main body of the following text to religion or religious beliefs. To do so would be to conflate the issue of understanding evolution and the issue of whether evolution is the best theory available to us. What follows is a brief outline of the theory of evolution as I understand it.
I am not a biologist, or even a scientist. I am a mathematician and philosopher (or at least, that's what my degree certificate will say). I have read a lot about evolution and I feel reasonably qualified to outline the process that is claimed takes place.
The first thing to understand is that this process takes place over unimaginably large timescales. No experience in our lives can help us come to terms with the vastness of the stretches of time we are talking about here.
Evolution then, at its most basic is this; those organisms that are most suited to their environment are more successful than their less suited counterparts. This is almost a tautology, for what do we mean by "most suited" if not those that turn out to be the most successful? Given the tautological nature of this assertion how can it fail to be true?
The next supposition needed is that successful organisms pass on their "more suited" traits to their offspring. This is of course not always true, procreation is essentially a lottery, but taken over the entire population, the more successful traits will be more prevalent in the next generation.
So given that there is a population with some genetic variation and some competition for resources it follows inevitably that some organisms do better and these in general will be the ones best suited to the environment. They have more or better cared-for offspring and the process will continue. The population as a whole progresses ever upwards.
Only one more supposition to make evolution. This is that random genetic variations take place within the population. Some of these variations will be harmful to the organism and will be "selected against". "Selected against" is a shorthand for the idea that the organism will be less suited so they will not do as well as their superior competitors and they will lose out so they will have fewer, weaker offspring. Sometimes a random genetic mutation will have a positive effect on some aspect of the animal or plant in question. This advantage will be selected for, meaning that this mutation will allow the organism to be more successful thus reproduce more and pass it on to the next generation.
I would like to reiterate the lengths of time we are dealing with are vast, truly unimaginably massive. Huge enough that tiny accumulations of beneficial genetic variations have brought us from LUCA (last universal common ancestor) to a bewilderingly rich world of diversity and complexity. Given that these mutations accumulate rather than being random and arbitrary as is sometimes suggested, the plausibility of our current situation given the age of our planet becomes reasonable.
The beauty of this process is that it is inevitable. Given a few empirically verifiable (and indeed verified) propositions, evolutionary theory cannot fail to be true. For evolution not to take place, given the above mentioned conditions would mean that some aberrant force were interfering with the natural flow of things. There is something of a mathematical beauty in evolution in that given some very simple assumptions or axioms, sophisticated and moreover useful theories are the result.
Incidentally, there is no suggestion, anywhere in any of the literature on evolution that we are "descended from monkeys." There is certainly suggestions that we ARE monkeys. Taxonomically we probably should be. There is also the suggestion that monkeys and humans share a relatively recent common monkey-like ancestor.
That's it. My a-religious (or nearly) look at evolution as a beautiful inevitability.