Sadly the linked article hardly has anything to say about giraffes, giraffe breeding, giraffe evolution, or giraffe necks. Should have used the original https://www.science.org/doi/10.1126/science.abl8316
One question that comes to mind about this hypothesis, is if there is sexual dimorphism in neck length.
Apart from the sexual prowess demonstrations, many of these ale traits for sexual combat are in fact a disadvantage. For example the brightly colored peacock, or the massive deer antlers, or as the article mentions, the massive sizes of walruses.
In those cases, the female has a more optimal body, optimizing for survival vs sexual combat.
If the neck of giraffes was primarily for sexual combat, you would think there might be some dimorphism.
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.
Based on what I've previously seen (top comment in here seems to be a nice summary), it's more like neither explanation really has a lot going for it, despite how much sense they make if you don't look too closely.
Is there empirical evidence that giraffes with longer necks have a better chance of reproducing? A better chance of obtaining food? And, if so, what is the statistical benefit per extra centimeter of neck length?
That would be science.
But evolutionists rarely test these things.
Do you know what happens when you remove a peacocks feathers? He gets just as much peahen action as any other peacock. The peahens couldn’t care less. This entire idea of tail feathers (or necks) lengthening as it confers a slight reproductive advantage is nonsense.
I have no clue how these are and would be studied and proven, as a dude that just casually reads stuff on the webs and comes to my own hair-brained ideas; it seems completely possible that the necks originally evolved for a condition that could not be observed in the current world. Hypothetically, the high leaves theory could be based on a plant/tree that has since gone extinct. How would we know? We know the earth/climate and terrain where giraffes live now has changed significantly on evolutionary time scales.
The mating example could also evolve. Using the peacock example you mention, the feathers are a result of past mating preferences and behaviors. It's possible that the current state of affairs is a preference for song/dance/etc, so the males will become good at that. If the feathers get the way and are not important for mating, they will likely go away or change in time. My point being, mating behaviors evolve too and they must change first in order for the natural selection to occur over generations and thus change the anatomy. We can't assume every species is at some resting or steady state of evolution just because we humans decided to start studying everything, I'd completely expect that some species anatomically do not represent the current state of their mating preferences and are thus are initiating a fork in their code.
I'm always reluctant to assume a particular selective pressure for every biological trait[1], but for a species that puts up a large feather train and does an elaborate dance with it to attract a mate, my prior would be really really low on that just being a coincidence. In the case of the 2008 study the parent poster linked, they got null results but it appears based on more recent research they just weren't investigating the relevant parameters, which was improved later on the field with a better understanding of peahen vision and the biomechanics of the feather shaking dance.
Agree I'm pretty reluctant too in a case as pronounced as peacocks but wanted to take the research at face value and can still find a way to devil's advocate my away around it a plausible way [to layman me] without doing any research at all
There's no reason to expect that in modern giraffes, increased neck length would lead to increased opportunities to reproduce. Or even a better chance of obtaining food. Nature is full of trade-offs. There's a balance between how much advantage you get from an extra inch of neck length and the extra calories and increased stress on the body from that extra inch.
Giraffes aren't just going to keep getting taller until they have to bend over to eat leaves.
Astute point. Similarly in pools of high level athletes you can't find correlations between sports success and certain traits that are well understood to promote performance.
It would be too expensive to maintain many generations of giraffes with less sexual selection pressure to breed the equivalent of couch potato average Joes to test, but that's what model organisms are for.
In the study reported on in the article you cite, they do no such thing. Rather, they fail to find a statistical correlation between display size and mating success.
The people doing the study, incidentally, are also 'evolutionists'.
When reading about biology, I am always wondering if sometimes evolution happened just because it could?
It is clear that natural selection exists, but it looks like there is no space for chance in evolutionary science (while the entire process of evolution seems based on chance).
Not talking about giraffes particularly, cause it’d be weird that they got their very special anatomy from chance only, but in general I find it strange to always assign some agency to a process that is mostly random and whose success is only to produce species that survive.
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_.
I don't understand. If anything I would guess that our (human) perception of "weirdness" is not a good measure of the (dis)advantages of a particular attribute. Octopuses and angler fish are weird as hell (to me at least) but they fit their biological niche pretty well. (Of course we could say that any attribute has advantages and disadvantages but at that point the claim becomes vacuous.)
That is why they are rare. The trait needs way more luck to survive. That does not imply there must have been advantage. If there was clear advantage, the trait might have been more frequent.
As females have also a long neck, and suffer a lot of physiological troubles for it, most probably not.
Or at least not only for that. There must be other reasons playing a role here. Finding that a long neck is an advantage in sexual combat can be just a bonus of having developed it first for other purposes.
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?
> I could imagine that you can't have 2 genders of the same species that are completely different.
This is called sexual dimorfism and is not a rare event. Really extreme examples appear in some deep sea fishes in the order Lophiiformes
I mammals is not so extreme, but it occurs also. Both genders having a different size is common and is what we would find in giraffes if the neck were developped just for fighting.
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.
