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Thread: What leads certain species to get horns (and the like)?

  1. #1 What leads certain species to get horns (and the like)? 
    Forum Freshman GreatBigBore's Avatar
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    I posted on another forum and got scolded for asking questions. So I'll try it here. Why is it that horns, antlers, tusks, and the like are limited to such a narrow range of species? Is there some general evolutionary rule that guides a species to get horn-like things on its body? I wonder why no really small mammals have them, like rabbits and mice. I wonder why, given that fish have been around for so long, there aren't a lot of fish species with horn-like things. I wonder why in the animal kingdom it's mostly limited to grazing herbivores.

    Anyone have any thoughts on these ruminations?


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    Hi,
    I do not know the answer to your question, and zoology is not my forte. However, after a few minutes mulling over organisms which have horns and horn-like things, the most 'obvious' ones seem to be - typically - fairly big, slow-moving herbivores that are susceptible to predation. Perhaps the driving force for the evolution of horn-like appendages in these organisms, was to 'allow' them to grow to a large (but necessarily slow-moving) size; whilst still being able to defend themselves against sleeker, fast-moving predators - by virtue of having horns. This might also shed light on why small mammals (e.g. rabbits and mice) lack horns - their mode of defence against predation is speed, instead. Having horns would only slow such mammals down.

    I'm not sure how true this is, but would refer you to somebody who can treat the material in more depth.

    E.g. 'The Evolution of horn-like organs' by Valerius Geist (1966) Behaviour.

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    Forum Sophomore schiz0yd's Avatar
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    It is likely that many, many creatures over our planet's history have evolved horns, but only the animals which it was useful for their survival passed the genetics on. Many animals carried meaningless mutations of horns that either eventually died out due to impracticality or continued to evolve until they became useful and helped maintain survival in whatever way the animal in question was capable of. even horns with no physical purpose can become an important factor in survival of the individual in the case that it becomes an aesthetic sexual preference. this not only goes for horns, but for all mutations/evolutions.
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    Moderator Moderator AlexP's Avatar
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    Horns simply will arise where they make sense and will confer an evolutionary advantage. If a mutation leads to a horn-like structure in fish, and the horn increases the chance that it will survive and reproduce, then it will be passed on, confer the advantage to the next generation, the horned offspring will be more likely to survive and reproduce, they will pass it on, and so on. However, a horn-like structure requires energy to produce, so if the fish is already able to effectively swim away from predators, the horn may simply not be necessary, and thus be nothing but an extra burden. So in this case, non-horned individuals are already very able to avoid predation, and do so without horns and thus the extra energy spent, so they will be favored and a horn will not evolve. It really depends all on the context and what is best for a given species in a given environment.
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    Forum Freshman GreatBigBore's Avatar
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    Quote Originally Posted by schiz0yd
    ...only the animals which it was useful for their survival passed the genetics on...
    Quote Originally Posted by AlexP
    Horns simply will arise where they make sense and will confer an evolutionary advantage.
    Well, yeah, but that's the answer to every "why" about animals: survival value, evolutionary advantage. What I'm trying to start a conversation about is why horns and similar adaptations appear in the specific way that they do, in such specialized niches. From what I can tell, among the mammals, it seems that horns are almost exclusive to ungulates, and then there are a few species of insects and fish with something similar.

    I'm just wondering what it is about ungulates that makes them more likely to get horns than other mammals, or what it is about horn-like adaptations that makes them so unlikely in the animal kingdom in general.
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    Forum Sophomore schiz0yd's Avatar
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    I would guess that it is something to do with a unique part of their genetics that is uncommon in other creatures, which can mutate into horns in the long run.
    Things are not always as simple as they seem in evolution. A rhino's horn is made not of bone, but of keratin; the same substance that hair and fingernails are made of. It is that the keratin took the shape of a horn that made it useful. So the initial mutation that would eventually become the horn was not the same as most animals, but proved just as effective.
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    evoluttion
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    Forum Sophomore schiz0yd's Avatar
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    evolution
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  10. #9  
    Forum Freshman GreatBigBore's Avatar
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    Quote Originally Posted by schiz0yd
    a unique part of their genetics that is uncommon in other creatures, which can mutate into horns in the long run...
    Well, yeah, but...that's what has already been said. Not that I object to your answers, but I'm really wondering why, not wanting just to put some words on it. I want to understand which "unique part of their genetics" or which unique aspects of the environment, causes horns to appear where they do, and nowhere else.

    Sort of like asking why mammals have fur. Sure, you can say that it's because it confers an evolutionary advantage, or you can say that it's due to a unique part of their genetics, but the real why has to do with maintaining body temperature, which allows them to exploit their environment more effectively by allowing them to get food without having to rely on the sun to warm their muscles first. That's the kind of why that I'm really trying to discuss.

    Edit: actually, not even that particular kind of why, but a much deeper kind of why. Anyone can say that horns are for sexual display and competition. What I'm really after is why just the ungulates, why not other animals, why are horns relatively rare, what environmental mechanism causes them to happen only where they do and nowhere else. That sort of thing.
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    Veracity Vigilante inow's Avatar
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    In addition to evolutionary advantage and survival assistance, it's really about the sexual selection. Maybe doe just dig bucks with big pokey things on their heads... Also, when it comes to fighting for territory, the male with the bigger spears on its skull tended to do better than the one with a flat skull when fighting... Not all animals compete for territory the same way, and not all animals find the same things attractive. That's why some have horns and others don't. There's no deeper mechanism at play, no matter how much you crave one.

    There is no why here. It's ALL about how.
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    Forum Sophomore schiz0yd's Avatar
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    I'm admittedly just winging this but perhaps it has something to do with the ungulates tendency to use their heads as a form of attack. Even giraffes do this. This would mean that any horns evolving there would instantly become an advantage in attack. Though I have no idea what came first: their tendency to use their heads to attack or their evolution of horns.

    Also, perhaps I am wrong, but you seem to be convinced that something about ungulates is directly related to the evolution of horns, while it may be that horns are carried into ungulates from an earlier ancestor and ungulates are of the only surviving descendants. Studying evolution is difficult as you can only refer to what you have found, and information on many pre-existing creatures is completely inaccessible to us. Sometimes the best we can do is make an educated guess.
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    Like inow said, it's a lot down to sexual selection. Sure some animals actually use their horns in attack/defense, but I'm not sure if it's the same case with antlers, for instance. Maybe antlers started out as a variation of horns, but then they were driven by intra-species competition, changing it's shape and function. Most deer and elks use their antlers to "battle" (or show off to females if you prefer) other individuals of the same species. This guarantees more mates and alpha-male status in the group.

    The tusks on an elephant might have some real use as a tool and defense/attack weapon, so it probably evolved by means of natural selection. But antlers appear in males only (in all but one species actually) and if it was used to combat and hunting, females would have them as well.
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    Forum Freshman GreatBigBore's Avatar
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    Quote Originally Posted by inow
    In addition to evolutionary advantage and survival assistance, it's really about the sexual selection. Maybe doe just dig bucks with big pokey things on their heads...
    Ahh, yes, this is the sort of conversation I was hoping to start. But it can't be just because girls like big headgear. If sexual selection is driving the headgear, then the headgear must imply a survival advantage. Dawkins talks about this a lot in The Selfish Gene. The peacock's tail isn't just sexy; it implies that he can survive even with this cumbersome thing weighing him down. If it didn't imply a survival advantage, the females would evolve a means of detecting a cheat.

    So I could buy sexual selection as an explanation in any species where their flamboyant headgear is also a liability, like those mountain goats with oversized horns. I could buy it for antelope with long horns that could get caught in the brush. I can't see it as an explanation for wildebeest or giraffes.

    Quote Originally Posted by inow
    There's no deeper mechanism at play, no matter how much you crave one.

    There is no why here. It's ALL about how.
    It's a good thing Charles Darwin never caught your pessimism. Cheer up! There are deeper mechanisms and why's all over the place. I find them all the time. That's why I remain unafraid to ask "dumb" questions.
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    A tree of placental mammals:





    That's one reason why horns don't pop up all over the animal kingdom.
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  16. #15  
    Forum Freshman GreatBigBore's Avatar
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    Quote Originally Posted by Zwirko
    That's one reason why horns don't pop up all over the animal kingdom.
    That's a reason I can sink my teeth into. Weird, they're useful but really rare, like complex societies. Could you post a link to that tree? Seems like it could be a wealth of info.
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  17. #16  
    Forum Professor Zwirko's Avatar
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    I got that from the Tree of Life Web Project. It's quite useful at times for a quick overview of things.


    I drilled down the tree to this page
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  18. #17  
    Veracity Vigilante inow's Avatar
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    Quote Originally Posted by GreatBigBore
    If sexual selection is driving the headgear, then the headgear must imply a survival advantage.
    No, sir. This is a false assertion. There are countless examples in nature where sexual selection favors characteristics which are themselves quite disadvantageous in terms of survival.


    Quote Originally Posted by GreatBigBore
    I could buy sexual selection as an explanation in any species where their flamboyant headgear is also a liability, like those mountain goats with oversized horns. I could buy it for antelope with long horns that could get caught in the brush. I can't see it as an explanation for wildebeest or giraffes.
    Nature has no need to comply with what you personally find incredulous or not.


    Quote Originally Posted by GreatBigBore
    Quote Originally Posted by inow
    There's no deeper mechanism at play, no matter how much you crave one.

    There is no why here. It's ALL about how.
    It's a good thing Charles Darwin never caught your pessimism. Cheer up! There are deeper mechanisms and why's all over the place. I find them all the time.
    Err? From everything I've seen, you are misusing the term "why" in this instance since it's so clear you are asking questions related to "how."
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  19. #18  
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    Quote Originally Posted by inow
    Quote Originally Posted by GreatBigBore
    If sexual selection is driving the headgear, then the headgear must imply a survival advantage.
    No, sir. This is a false assertion. There are countless examples in nature where sexual selection favors characteristics which are themselves quite disadvantageous in terms of survival.
    Yeah. Evolution doesn't always select for survival. Sometimes it selects for further self-reproduction in a way that makes survival harder. The male peacock, with all his feathers, is easier for females to find and mate with, but also easier for predators to find and kill.

    The ones who actually need to do the surviving are the females, and they don't have all those crazy feathers.



    [quote]
    Quote Originally Posted by GreatBigBore
    I could buy sexual selection as an explanation in any species where their flamboyant headgear is also a liability, like those mountain goats with oversized horns. I could buy it for antelope with long horns that could get caught in the brush. I can't see it as an explanation for wildebeest or giraffes.
    Maybe the horns have other uses beyond fending off predators. Maybe they help prevent the giraffe from banging his head on the branches while he's eating leaves off of a tree.

    Human fingernails are hardly valuable as weapons, and yet we grow them.
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