system
Given the following post, respond as if you're commenting on Reddit:
human
I guess I don't understand evolution. It is 100% purely random mutation?

So, I feel like a fucking idiot, here, because this has always confused me.  I thought I understood the theory of evolution, but years ago I had my understanding of the concept turned upside down when someone explained to me that evolution does *not* mean that a species evolved in order to adapt.  Rather, species evolve constantly due to mutation for no specific reason, and the ones that *just so happen to have evolutionary traits that help them adapt* are the ones that survive.

Maybe it's because I grew up thinking that evolution had a reactionary part to it, but it's just hard for me to grasp the idea that we seem to only have evidence of species with evolutionary traits that seemed to serve a purpose in the environment.  I mean, if evolution is truly random, is there a reason we don't have evidence of species with seemingly random traits, such as a mouth on ones hands?

Maybe people just find a way to explain how the mutations of different species are beneficial, which gives the illusion that there is causation there, but I just feel like there's this veil over my ability to understand this that I'd love some clarity for.
gpt
Evolution is not goal-oriented in the sense you originally thought. It has no agency. Mutations are definitely random. But the process of evolution that acts on those mutations is not really. 

Natural selection (the mechanism of evolution) is often described as survival of the fittest. Another way to think of it (that is perhaps a little more accurate) is elimination of the unfit. (Fitness in this sense just means the capacity of an organism to reproduce and pass on its genes to subsequent generations.)

Random mutation generates genetic diversity. Some traits that result from these mutations are adaptive ("useful"). This will allow individuals with those traits to survive to reproduce at higher rates than organisms without those traits. Some random mutations generate maladaptive ("bad") traits that do actually are detrimental to an individual's survival. Organisms with maladaptive traits therefore don't survive long enough to reproduce. Or if they do, it isnt at the same rate as organisms with more adaptive traits. 

So what traits appear is random. But what traits persist in a population (what is or is not adaptive) is not really random. It is entirely dependent on the environment. For your example, a mouth on the hands of a colobus monkey would likely be maladaptive. Yeah, it seems super cool, but the colobus monkey uses its hands to manipulate the environment around it and to locomote. A mouth-hand would get in the way, be prone to infection or irritation, etc. So any colobus that randomly developed that trait due to mutation wouldn't survive very long and therefore wouldn't reproduce, deleting the maladaptive trait from the gene pool. This is natural selection at work. 

Tl;dr: mutations are random, but natural selection (the mechanism of evolution) is not.