How would I evolve horns on humans?

Question

How would I change the evolution of humans to result in horns on humans as a result of reproductive fitness, instead of social fitness. Meaning, NEITHER "Horns are sexy", or some strange infection.

Note:

https://worldbuilding.stackexchange.com/a/14907/6812

A predatory creature with claws and large teeth is unlikely to evolve horns. Unlike herbivores, carnivores have evolved to kill things, and don't tend to need to evolve extra weapons like horns. Furthermore, effectively using horns would require that the creature put energy into growing them, and into growing and sustaining the supporting structure needed to make them useful. Horned creatures need strong necks to support use of their horns, and the neck musculature wouldn't be critical to anything else for a creature evolved to run down and claw up its prey.

However, Hair is Keratin, Nails are Keratin, could hair evolve into horns?

Answer 1

Yes, horns are made of the same protein as hair and nails, so yes, humans (as mammals) have the potential to develop horns.

The way to select for horns is to make them advantageous to survival. That might occur (over many millions of years) if humans, in order to protect territory (food source), were forced to fight for limited supplies primarily by head blows. If this were consistently the case, any mutation which would offer an advantage in head-butting competitions (thicker scalps, harder/thicker cranial vaults, better supportive structures for the brain protecting against concussion, etc.) would be advantageous and horns could reasonably be selected for.

That's the only way I can imagine, and that's basically how evolution works: any mutation that offers a survival advantage is likely to be selected for eventually given enough numbers carrying the mutation.

That explains why a mutation spreads through a population, be it deleterious (one sickle cell gene protects against malaria, but two copies of the mutation produces a disease that shortens lifespan) or beneficial (the continued production of lactase such that people can continue to digest milk after infancy.)

However, since humans have arms (both in the sense of appendages and weapons), such a scenario would be unlikely, but wildly inventive if convincing.

_{The Evolution of Horn-Like Organs}

Answer 2

As anongoodnurse has already mentioned -- since humans have arms, it is highly unlikely that they will develop a weapon and all the necessary modifications just so that they can do their fighting by butting heads.

So, since weapons are pretty much out -- how about sensory equipment?

Unlike hair or nails, horns are NOT entirely dead material! Google "Broken horn" for goats, cows, or any other horned creature -- they bleed, they hurt, and they contain very well-circulated and sensory-rich tissue at the base inside!

So, if you somehow manage to voodoo some kind of evolutionary necessary sense or skill located in this special horn-tissue, you've got a reason for humans developing horns. The ceratin layer around it (the visible horn) could then be either protection or a resonance space. And if humans need this special sense / instrument for mating, like e.g. sensing when a female is receptive or triggering ovulation, you'd even fulfill the 'reproductive fitness' checkbox. One thing they'd never do is fighting with the horns, though (no stags clashing in autumn...)

Answer 3

It can happen that hair mutates into, basically, nails. It is (thankfully) incredibly rare, and disturbing to look at the victims of this affliction (Google it if you're brave enough).

However, humanity will not suddenly start evolving horns - there is no imperative for this, as well as requiring a tremendous number of changes for them to be "functional" (as you yourself list in your question).

That doesn't leave room for a lot of options:

Change History

Simply make it so that our genetic ancestors developed these, and we kept them. Basically, hand-wave it into your story.

For example:

There once existed 3 species of human: Homo Sapiens, Neanderthals, and -name for horned humans here-. Of the three species only -name for horned humans here- survived into the modern age.

Genetic Alteration

People get bored and start genetically modifying themselves. Something goes wrong (nanovirus, etc.), and everyone is modified to grow horns. People then kept them because women find themselves overwhelmingly attracted to horned men, and men will never willingly lower their chances at being found attractive.

Note: Consider the implications of horns as far as modern military and safety equipment is concerned. If humans grow magnificent horns they will not be able to wear helmets very well. They might also not fit into cars, or fighter jet cockpits, etc.

Answer 4

I know this is an old question but I'm looking for an answer myself... maybe confirmation of my own theory.

I see no chance of humans developing horns as is. We've evolutionarily invested so much energy into making our brain our primary tool without investing into proper protection - the one we have is enough for the use of our head as main energy and sensory input device. Any advantage horns could theoretically give us would require significant changes to all the surrounding anatomy only to not endanger our brains. And even if you solved this question and equipped our muscles, skeleton, and brain cushioning adequately for functional horns, there's still the open question of their advantage to us. Arms have more reach, more mobility, hands can craft and grab dangerous objects to give even more reach, they're just so far superior, except maybe for stabbing other people, but brains and hands can craft stabby tools. So, if not as a weapon, and ruling out sexual selection, what else could their purpose be?

Looking for a use

If you look at horned creatures, they use all of their limbs for locomotion and they're herbivorous and basically have no other form of protection. Their horns are mostly a tool to discourage predators or used as weapon of self-defense should the attacker try anyways, or fight rivals for reproductive rights. Maybe to dig out roots or other food, but then again, we have hands... and the brains to craft the Bagger 293, try to outdig that one with your puny horns.

Weapon?

Now, considering our own evolutionary ancestry, we once were mostly herbivorous (or fructivorous to be more precise) and led an arboreal lifestyle. Go far enough into the past and our arms become increasingly used as a tool of locomotion and less for manipulation. Our brains were smaller and less important than they are today. So, maybe the ancestors of those horned humans led an exclusively arboreal lifestyle and had an advantage if they were able to use all of their limbs for locomotion, but still had to fight rivals to secure the right to mate. In come horns, not having to use hands as weapon could give them the ability to out-manoeuvre their rivals, but still attack, although probably only under specific circumstances; certainly a stronger neck, maybe also a longer one to increase reach and flexibility. I guess you'd have to go far back in time to make that a somewhat viable explanation. Later on the horns could merely be a remnant without any disadvantage and thus remain in one form or another, maybe over time the useful horns developed into a symbol of sexual selection, then they could remain viable to our horny Homos even when they develop into a detriment - male peafowl feathers have grown so large due to sexual selection, they've actually become a disadvantage when trying to escape a predator.

Social RAMifications

Our ancestors also grouped up to increase survivability, because they had no anatomic feature to defend themselves against predators - although some can be deterred by a good smack on the snout (sharks can and I think crocodiles, too) but I'd still not recommend trying to punch a lion's nose unless it's your absolute last option and you'd die anyway. A group of weak individuals can more easily overwhelm a stronger attacker than any single one could. It also helped develop our social behaviour; and our brain, finding out on how to work together requires brainpower after all. Maybe only the male (or female for that matter) individuals of the Homo Horniensis ancestors developed horns and roamed the forests solitarily while the other sex grouped up to raise the young and nurture their brains. I'd certainly be glad about a couple of dangerous spikes on my head alone in the woods with predators.

Conclusion?

In the end, if you go that far back to make horns a viable option and change all the variables required to do so, what environmental changes would then have to happen to force the hornys into the same evolutionary path we humans took? Take away the trees, okay sure. maybe make their main food source die out and their alternatives harder to reach to force their arms into a path of manipulation > locomotion. In the end though, I guess by that point you'd basically have to make the horns a non-functioning remnant, otherwise evolution would probably solve the obstacles we humans faced in a different fashion and you end up with a baboonicorn or somesuch.

What about spikes instead?

A different idea would be to give them spikes, like hedgehogs or porcupines have. After the forests dwindled and savannahs emerged around Cape Horn (yes, I know there's no savannahs there but there's also no spiky humans), our humans had already evolved bipedal locomotion, maybe even basic tool usage, but due to resource limitations shrunk in size (keyword island dwarfism). Now, large aerial predators hunted the pygmys, swooping down and snatching them up basically grabbing whole heads with their claws. With their heads most exposed and in danger not only helped their hair growing together into thin spikes blend in with the tall and dense grasses from bird perspective, they would also severly hurt the predators should those try to catch one, who didn't see the danger early enough to hide. I've heard porcupine stings hurt like hell, and they can detach and get stuck in your flesh... ouch. A bird certainly needs their feet to land, they can't limp like a quadruped can to releive pain in the affected limb or just lie down on the side. They'd certainly think twice about trying to catch another one of those little spiky human buggers should they get through the injury. Why the body size changes? Well, basically limitiations on the size of aerial predators. Even the largest birds to date couldn't snatch up a human. The largest extinct bird capable of flight? Argentavis Magnificens with a wingspan of up to 6.5m standing at human height size and weighing about 70kg is thought to have been mostly a scavenger. Pelagornis Sandersi with a wingspan of up to 7.4m but only up to about 40kg is thought to have been mostly a glider flying long distances over oceans and catch fish mid-flight with their "toothed" beaks. The largest bird of prey, the Haast's Eagle grew only up to 15kg with a wingspan of up to only 2.6m; it is presumed to have hunted the giant moa, much larger than a human, though didn't snatch them up. Then again, I guess that is already enough. You could also go wild and say the gravity of their planet is lower or its atmosphere denser and create monstrous flying birds.

What is that, pterosaurs you say? Sure, some of them got much larger but like Pelagornis Sandersi they were gliders and either caught fish during their flight out in the oceans or the largest ones actually hunted on land, stalking the beaches where flocks of smaller pterosaurs nested and just prance about gobbling up any youngling out in the open in front of their terrified parents. Maybe that works, too ...

Answer 5

How it Happens

Hair is Keratin, Nails are Keratin, could hair evolve into horns?

Yes, this is exactly how horns evolved. Mammals first evolved nails and hair, and then a long time latter, some mammals mutated and evolved horns. Because the mutation was useful, it stuck around and became a defining characteristic for a whole branch of the mammalian evolutionary tree. The key here is usefulness. When ungulates developed horns, they were really useful because they did not have other natural weapons or hands already. But if a tree swinging monkey mutates some horns, that linage will tend to die off pretty fast because they risk getting tangled in the branches while not offering any distinct advantages, so for humans to even have a chance to evolve horns, it has to happen after we come down from the trees so it does not work against us AND it has to confer a significant survival advantage against other humans over a significant number of generations.

Why it Happens: Built in Helmet

While the big causes of injury related death for most animals is starving to death from broken legs, infected wounds, or neck injuries caused by predation, humans have gotten really good at dealing with these killers while inventing all sorts of new ways to die that seem to mostly focus on head injuries. We crack our skulls open in acts of war, from construction site accidents, playgrounds, bicycles, skate boards, cars, etc. According to the AAST, Traumatic Brain Injuries (TBI) are the single largest cause of death from injury in the United States leading to 50,000 deaths and 80-90,000 major disabilities each year. In other words, the human head is poorly designed to survive human ingenuity.

So, if a population of humans were to develop with a mutation that gave use ram like horns, we would have a permanent extra layer of defense to protect us from ourselves. If you take the general concept of ram horns, but reshape them to start low and on our forehead, and then wrap over the top and around the sides of the skull, they will form a sort of helmet providing protection against impacts to the front, top, and sides of our heads.

When analyzing ancient battlefields where one side had helmets and the other did not, the side with helmets typically performed 50-100% better than the opposing army given otherwise equivalent armaments and training; however, if you take this mutation back to the stone age when no one knew how to make an effective helmet, and the most common weapons were clubs and thrown rocks, it becomes an especially beneficial adaptation.

If these Homo Cornigers were to evolve alongside other proto-humans like Homo Heidelbergensis and Homo Neanderthalensis, then they would have been able to significantly out fight other proto-humans in stone-age style warfare giving them not just an advantage on the battlefield itself, but in the bigger sense, the advantage in driving out other proto-humans populations and establishing territories.

The oldest evidence of people bashing each other's brains in goes back to about 430,000 years ago, but the first helmet was not invented until about 3300 years ago. So, in an evolutionary since, this is plenty of time for the Homo Corniger mutation to exploit its natural advantage and evolve into a species of its own.

Answer 6

This could also occur due to benign tumors, as in the case of the Jackalope. No, I'm not joking, I'm actually being serious here. There are cases of rabbits that grow 'horns' due to a disease. The disease isn't harmful to the rabbits, who are able to live quite normally, however the disease is contagious which would explain why a whole civilization would have them.

http://www.isciencetimes.com/articles/5556/20130703/worlds-scariest-rabbit-horns-shope-papilloma-jackalope.htm

Answer 7

Horns as combat on a humanoid is out of the question. It's simply not something that would evolve without sexual selection and is useless for combat. For a sensory organs it could work rather well. Think radar. Perhaps it's hollow with magnetite and some organic piezoelectric. Then it can act as a resonance chamber for radar, both sending and receiving simple signal. Partially to be hyper aware of ones surroundings and partially to give off a warning call to ones fellows without other animals being able to hear it.

Best I've got.