Kevin Arbuckle answered on 18 Mar 2014:
Evolution is actually quite complicated, but the basic idea is (thankfully) fairly simple. To start with, remember that evolution just means change, it is not ‘directed’ in any way and does not have a purpose. Animals evolve simply because some individuals survive and pass on their genes better (have more kids who have more kids; what we call ‘fitness’) than others. The ones that leave the most grandchildren are more common in the population and so the species gradually changes to be made up of the more ‘successful’ ones.
So how does this happen? Will, evolution can happen in different ways, but the most common (and easiest to understand) is by natural selection. The word ‘selection’ is a technical term, but you can think of it simply to mean why some do better than others. For natural selection, we need three things: inheritance (usually genes), variation, and selection. Since we know that most things have at least some inheritance (e.g. you look for like your parents than you do to a stranger), and that there is almost always variation in things (e.g. people are different heights), the only question is selection.
So does selection exist? Well, think about two types of brown lizards of the same species. One is a bit lighter (a beige colour), the other is a bit darker (a darkish brown). This species of lizard lives on the floor in a wet forest, where there are a lots of dead leaves. Because wet, dead leaves are quite dark brown (at least in this imaginary forest), the dark brown lizards are well camouflaged. The beige lizards are also camouflaged, but not as well as the dark brown ones. Because of this, predators eat more of the beige lizards (because they can see them better) which means that more of the dark brown ones survive and reproduce. This leads to more and more of the species being of the dark brown type (in other words, they are evolving), because they are leaving more children and grandchildren.
Now let’s say that the climate changes and over time the habitat dries up and changes to become quite dry. Now the floor is made of dry, light coloured leaves. Even though the beige lizards are now few in number, the changing environment means that they are now better camouflaged than the dark brown ones. Predators love this because the really common dark brown lizards are now easy to see and they therefore ‘select against’ the dark brown lizards by eating lots of them, and ‘select for’ the beige lizards because they can’t see them and so they let more survive. Now it is (gradually) the beige lizards that survive better and leave more children and grandchildren, and so the species evolves again.
Now, this is basically evolution by natural selection, but there are two other things that are really important in evolution: novelties (or new things) and sexual selection.
Novelties happen when a gene mutates (which just means changes) and makes something new in the organism. That new thing might be a slightly longer arm than was possible before, a slightly bigger brain, or a completely new colour pattern, but the point is that it is something new for evolution to act on. This is evolution in itself, because if you remember from above evolution just means change, but it’s only the start as selection can then act on the novelty to make it more common in the population (if it gives the individual an advantage). It is worth noting that mutations are not rare – they happen all the time – and in fact each of us probably has ~10 mutations compared to our parents! But they are not always beneficial (most have no effect at all) and the effect is usually minor. Still, novelties are important for evolution over longer time scales.
To understand sexual selection, you have to remember that an animal’s success in evolutionary terms, its fitness, is measured by the number of children it has. In otherwords, it doesn’t just have to survive, but it has to attract a mate and often fight off other individuals who also want a mate. This leads to sexual selection. There are two types of sexual selection: intrasexual selection (which is competing with rivals for a mate), and intersexual selection (which is making sure that, for example if you are a male, a female chooses you to mate with). This explains things like peacock tails, tall height in men, and (maybe) intelligence in humans – because female peacocks like males with pretty tails and girls tend to like tall, smart men.
As for the details of human evolution, there are obviously quite a lot of differences, but most of them may be related to our big brains. When we evolved big brains and so became smarter, we were able to make clothes, which led to us having less body hair. We also had ‘ideas’ that we wanted to communicate to other people, which led to the evolution of language and the development of tools and others ‘human’ characteristics. This is a big area of research, but one that is interesting to look into.
As for our relationships with other monkeys, remember that evolution isn’t ‘directed’ so it’s wrong to say that we are higher or better or more evolved than monkeys. Other living monkeys have been evolving for exactly the same amount of time as we have, it’s just that they’ve evolved down their own line. We are related to them because we share a common ancestor with them, but since that ancestor we have evolved separately under different forms of selection. This is really why we look different, but also why different species of monkey look different too. We are not really particularly special, but just one ‘twig’ on the end of the tree of life in exactly the same way as every other species is.
I hope this has at least partly answered your question (it was a big one, but a good one!), but if you have more questions just ask. I’ve also given you some links (see below) that might help you find out more if you are interested.
Aled Roberts answered on 21 Mar 2014:
Excellent answer by Kev there!
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