The giraffe neck evolved for sexual combat?

long standing... I see what you did there.

As long as it isn't too disadvantageous for female giraffes it highly likely that it is easier for evolution to end up with both sexes having long necks, for the same reason male mammals have nipples.

Sometimes the genes involved are so disconnected from sex-specific genes or the body plan/development process such that it would require very high selective pressure to make it a dimorphic trait. Or those tissues just don't have sex hormone receptors so they don't respond to them. Or it just so happens that certain structures are built in an earlier phase of development before sex hormones can be produced. Evolution is not directed; it is far easier to tinker with what already exists than make wholesale changes. Selective pressure for nipples exists but for whatever reason it was easier for evolution to just give all bodies nipples even though they don't do anything in males. The metabolic cost is a rounding error so there's little pressure to get rid of them.

If I had to guess the hox genes or whichever genes that encode the repeat division sequences to make the neck bones be any size at all have no pathway to differentiate by hormones because it happens far too early... so it is simpler to have all giraffe body plans build the same basic neck structure in the fetal stage. If you compare to humans boys and girls are born with the same hip structure and probably for the same reason - it is only during puberty that they diverge. And even then they don't undergo a complete remodeling.

Just a casual passer by that found your question valid and interesting. I wonder if in this case, it just happened to be an advantage? It would start as a sexual combat thing, that result in access to food and increased visibility of predators, so there was no need for dimorphism. Perhaps even helps or explains why/how the trait became so pronounced. When compared to the other species you mentioned, giraffes are the broke clock being right twice a day.

> It is clear that natural selection exists, but it looks like there is no space for chance

Sure there is, it is called 'neutral evolution'. You can get wandering genetic drift when there is zero selection pressure on a particular trait.

The teleology is just shorthand, scientists aren't actually assigning agency. It's still possible to discuss drivers of selection pressure though, sometimes just easier (especially in sci comm) to explain some things quasi-teleologically. There's a number of ways to test how much 'chance' is involved. For example take independent emergence of a novel trait across many different taxa. Or take difference that emerge after a genetic bottleneck, like when a very small founder population establishes in a new isolated habitat. In the case of a giraffe neck, probably not that parsimonious that such a distinct feature would just arise due to drift.

Its useful to think about natural selection like the R value for a virus. A gene + environment has an R value (like a virus + its environment. e.g. masks, geography, etc), if this value is higher than 1 it will, over time spread into the gene pool, and under 1 it will die out of the gene pool.

If you think a gene proliferated into the gene pool just because, your still saying its R is 1+, only that the environment played a larger part than the gene.. which is probably always the case anyway.

>It is clear that natural selection exists, but it looks like there is no space for chance in evolutionary science

I've always assumed it's because evolution requires something happening thousands of times. The more events that are included in something, the less impact chance can have.

There's no _agency_ involved, but in general if an organism has some really weird attribute, it probably gives, or at least gave, it an advantage, because really weird attributes usually come with _disadvantages_.

Isn't that exactly what genetic drift is?

Is there a limit to how much male and females can practically diverge in mammals?

I'm not at all schooled in genetics, so genuinely curious. But I could imagine that you can't have 2 genders of the same species that are completely different. Perhaps the neck length is such an attribute?

There has to have been some child giraffe that went out into deep water where it didn't reach the bottom? You could maybe extrapolate from that.

Dog swimming surely ought to be unstable with that long of a neck and legs.

How does this save me a google search? Either it can swim (someone's seen it swimming) or it can't (nobody has seen it swim). If it maybe can swim, I have to google it.

Male giraffes evolved to impress females by fighting each other with their necks.

Male humans evolved to impress females by sending them a text message about how male giraffes impress female giraffes.