3 ms·

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 t

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.

conductr 4y ago
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.
- kadoban 4y ago
  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.
- lurquer 4y ago
  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. https://www.abc.net.au/science/articles/2008/03/27/2200822.htm https://www.abc.net.au/science/articles/2008/03/27/2200822.h...
  - escape_goat 4y ago
    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'.
  - msrenee 4y ago
    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.
    - kuhewa 4y ago
      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.
  - conductr 4y ago
    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.
xenadu02 4y ago
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.

conductr 4y ago

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.

kadoban 4y ago
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.
lurquer 4y ago
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. https://www.abc.net.au/science/articles/2008/03/27/2200822.htm https://www.abc.net.au/science/articles/2008/03/27/2200822.h...
- escape_goat 4y ago
  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'.
- msrenee 4y ago
  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.
  - kuhewa 4y ago
    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.
- conductr 4y ago
  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.

xenadu02 4y ago

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.