Gendering singlur pronouns is one way to avoid ambiguity.

Take these sentences:

I met a boy and a girl. They gave me a toy.

If it said "he" or "she" gave me the toy, you would know who specifically gave me the toy. The fact it says "they" likely means they acted together to give me th toy (otherwise I'd have said "he" or "she").

You could dump gendered pronouns and make everyone "they". But then you lose information. Who gave me the toy?.

You could dump pronouns all together, but then you would have to specifically name all the people/groups and use their full names all the time. That's long and complex.

Both pronouns, and semi-specific pronouns (gendered or plural/singular or cased ones or any combo of those) let you push more information in less time. They're a hack, but a very useful one.

In the same way many (perhaps reading Douglas Adams' puddle analogy) sided with evolution over creationist fervor, I think eventually many will begin to sympathize with the minority of thinkers who have "made sense" of why it was so important for pre-21st-century speakers to know the sex of everyone in a discussion, over an explanation that might be more incentivized...

To stretch your biology analogy even further: sort of like how humans have an appendix.

I wouldn’t try to read anything into culture based on the specific set of pronouns any language has. Turkish and (spoken) Chinese have never distinguished between “she” and “he” and it’s not because knowing someone’s sex is less important in their cultures than it is in Indo-European ones; it’s just random chance.

And even if they arose purely for convenience, why did they stick around? If today's populations really developed the self-reflection to operate critical of importance of sex, why are "he/his" not as weird to say as "whitey/whitey's" would be as pronouns?

Is not "it" the third person singular? Although that does carry its own overtones.