system
Given the following post, respond as if you're commenting on Reddit:
human
I just read that we share 90% of our genes with the fruit fly. How is this possible considering the vast difference?
gpt
I guess the question should be "what did you expect?"  We and fruit flies share a common ancestor, so it would actually be shocking if our genes were totally different.  We don't actually share *any* genes in common with them.  Rather, 90% of the genes in a fruit fly are *related* to the genes in a human.  This makes sense, as a fruit fly does a lot of the same things a human does.  Biologically speaking, we're actually quite similar.  You see light, they see light.  You move your muscles, they move their muscles.  They have nerves, so do you.  They metabolize glucose, their cells grow, their cells divide.  They make proteins and replicate their DNA the same way we do.  Most of those genes are the same, or at least very similar.  Things like body shape and size are mere window dressing compared to most of the fundamental biological processes that animals use.  This is sort of like being shocked that both an iPhone and a desktop computer both have silicon microprocessors that use binary.

One mistake people always make with evolutionary bio is to think that because we are bigger and smarter, that it somehow makes us more evolved than fruit flies.  They think that our DNA should be more complex, more nuanced, more unique than a tiny fly.

The fact is that fruit flies are probably more evolved than us.  Their generation times are much shorter, so they have gone through many more rounds of natural selection than humans have.  They have just gone in a different way for their evolution since our lineages diverged.  They have maximized efficiency, small size, and short generation times, which enable them to thrive on food sources and amounts that humans wouldn't be capable of living on.  That said, they do a ton of the same things, and so you'd expect a lot of commonalities between us.