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Would humans have to become "wild" for this to happen?

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  • $\begingroup$ Usually, if a change occurs in the form of any animal, it comes from the need to change. IOW, to have longer canines, a human would have to have the need to use them. It's natural selection (in this case, the stronger trait of longer canines) which would drive this. $\endgroup$ Commented Nov 14, 2015 at 21:20
  • $\begingroup$ Does he or she need to drain blood from the victim and turns hairy during full moon? $\endgroup$
    – user6760
    Commented Nov 15, 2015 at 3:20
  • $\begingroup$ Note that humans have a very shallow gene pool, with exceptionally low variation. So such evolution is unlikely as there is not enough to select for. $\endgroup$
    – JDługosz
    Commented Nov 16, 2015 at 17:11

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From a practical standpoint, humans would have to be deprived of all current civilization and technology in order to naturally evolve anything. Since it is easier to modify the environment than to adapt to it, humans preferentially do things like invent steak knives and night vision goggles rather than evolve canines and cat eyes.

To actually need to evolve canines, savage humans would need a reason to kill and tear into their prey with their teeth over any other method of killing and eating. Humans are omnivores, so would have to change to a largely carnivorous diet to require long canines. They would probably need to re evolve a muzzle as well to allow teeth to be used more effectively than is currently the case.

Evolving efficient night vision in the manner of cats would also require humans to preferentially move and hunt at night. Over thousands of years night humans with better night vision would pass their genes on the their children, who would be more likely to survive and pass on enhanced night vision to their children, and so on.

For both of these to be true would involve some sort of natural or artificial catastrophe which forced surviving humans to hunt for meat at night, since foraging for food during the daytime would be far too dangerous. Humans after tens or even hundreds of thousands of years living in these conditions would exhibit a host of other changes, ranging from a redesigned gut and digestive system to efficiently process raw meat, redesigned limbs to allow for more efficient hunting (depending on what is being hunted. Humans who stalked and pounced would be designed differently from those that ran down their prey), grasping claws to catch fleeing prey and hold it, a redesigned face to employ teeth more efficiently and possibly fur or other body coverings which allowed for camouflage, protection from the elements and so on. As carnivorous hunting creatures, it is questionable if they would retain intelligence and civilization. They might devolve into something resembling baboons:

While they might be descended from humans, they would be in no way Homo Sapiens

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Aesthetics is the key. If one A List supermodel takes the bold step of using cutting edge genetic engineering to gene-jump into a human-feline hybrid, then there would be no stopping it.

If she makes it look good, millions will follow her.

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    $\begingroup$ I can't believe I'd forgotten about genetic engineering. That's stretching the definition of "evolve", but depending on the world, that might not matter. $\endgroup$ Commented Nov 16, 2015 at 14:28
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"Going wild" is definitely the most likely way for that to happen.

If you're looking for another option, you could always go for aesthetics. If women consistently choose men for the length of their teeth, and women consistently choose men for the narrowness of their pupils, that's what you'll get.

Additionally, the timeframe is dependent on how strong the selection is. 5000 years is an eyeblink in terms of evolution, so to get that type of change in that amount of time (or less), you'd have to have an extremely strong source of selection. Think of the various dog breeds we have. We've developed very strong traits over a very short amount of time (hundreds of years), but that has required human intervention and very careful breeding. And it can rebound even today. If you let a few dog breeds interbreed, within a few generations you have a mutt that just looks generally doglike, and much closer to its ancestors.

If you want a similar timeframe, the tribe would have to be isolated with very strict breeding conditions (whether those conditions are environmental, aesthetic, religious, or whatever). Basically, only a small number from each generation would be allowed to breed, and would be bred prolifically to maintain numbers.

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The main block for human evolution is that we have learned to modify our environment to suit and protect ourselves. For mankind to develop long canines then there has to be a condition in our world that makes not having them more-or-less fatal before you reach sexual maturity.

Then just sit back and hope that some convenient mutation arrives before we all die out. Getting people to fancy people with long teeth would work but if you take a look around then its clear that variety is very much in vogue. The downside to that kind of selection of course is that people with the long teeth might not have such good resistance to (say) certain infections.

People who are naturally resistant to malaria usually (also) have sickle-cell anemia for example.

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