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Most animals look almost identical to their peers. To distinguish lions we record the spots on their face; with whales we look at the blemishes on their tail or flukes. In other words, we have to try hard to distinguish one lion from another.

In the case of dogs, we have created many different looking breeds - but within each breed they look the same: one poodle looks very much like the next one.

On the other hand, with humans we have not only the different races (cf. dog breeds), but even within one race no two people are alike. And, not only are the faces different, the body shapes vary equally much. We use face and body shape (and voice) to recognise each other. Most other animals use smell or sound.

I thought the reason for our uniqueness might be that, with civilisation, we are not constrained us to look the same. However, even in hunter-gatherer tribes each person looks different from every other one.

So what is it in human evolution that made us unique in this regard? And, are we unique? I cannot think of any other species with as much variation as ours, but are there others?

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    $\begingroup$ This really isn't the case. Humans do look pretty much alike. Take for instance blonde Hollywood actresses: most are perfectly interchangable, and their male counterparts only marginally less so. You only think humans look different because you have long practice (mostly unconscious) in recognizing the small differences between them. Apply the same effort to studying e.g. dogs, and you will likewise begin to recognize the differences. $\endgroup$ – jamesqf Sep 22 '17 at 5:40
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    $\begingroup$ "Most animals look almost identical to their peers." That's our perception, not theirs. $\endgroup$ – user24284 Sep 22 '17 at 6:27
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Because we as humans are really really good at picking up small differences in humans and really really bad at detecting them in anything else.

Animals are often quite good at telling each other apart, far better than humans are, birds in particular are known for this. Just because you as a human are bad at it does not mean they are.

There is a pretty strong evolutionary pressure for humans to be able to tell other humans apart and not much of an advantage for being able to tell two lions apart. We need to be able to tell mates, rivals, relatives, and strangers apart easily. We don't need to differentiating one black bird from another.

We also spend a lot of time around other humans, so we are more familiar with their differences, but the same thing happens to animal researchers whale researchers who spend a lot of time around whales can easily tell two whales apart at a glance. this is also part of the reason some people have trouble telling individuals from a different "race" apart, they are to unfamiliar and uninterested to spot differences. Or the way a car guy can spot the difference between two models at a diffrence but someone else might not.

You see the same effect chimps can tell each other apart but can't tell humans apart, unless they spend a lot of time around humans then they can. They can also match voice to face meaning the can recognize both.

Then of course you have the fact you are focusing on vision, try to tell two people apart by smell and you will likely fail but a dog will have no problem with it. likewise many monogamous song birds can identify their mates from song along, just as we recognize others by voice, penguins are another example. Humans are very visual creatures so much of our identification ability relies on vision we see the same thing in other visual species, animals tend to use whichever sense are their dominant ones. Saying organisms are more visually similar because organisms with far worse vision than humans can't tell them apart by vision alone is simply an unreasonable conclusion.

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    $\begingroup$ I wouldn't say that humans are inherently bad at recognizing those small differences in other species, it's just that most don't invest the amount of effort needed to learn to recognize them - a learning we do unconsciously by growing up among humans. But if you grow up on a dairy farm, for instance, you learn to recognize cows as individuals. $\endgroup$ – jamesqf Sep 22 '17 at 18:48
  • $\begingroup$ We are generally worse at recognizing difference in other species mostly by comparison because of how good we are at each other, there is an entire aspect of our neural processing keyed to notice things about faces. $\endgroup$ – John Sep 22 '17 at 20:34
  • $\begingroup$ I didn't say animals can't recognise each other; I said they use smell and sound, whereas we use vision. Is that the main reason for our variability? I take your point about chimps. But, do they use vision or smell? Ignoring faces, what about body shape - is there an animal species with long/short, thin/fat, muscular/flabby individuals? But I suppose evolution will rule that out in other animals $\endgroup$ – hdhondt Sep 23 '17 at 0:41
  • $\begingroup$ @hdhondt if you had read the linked paper you wild see they are suing vision,, in fact the same portion of the visual cortex we use, size and robustness variation is quite common in animals it is by no means unique to humans. You are assuming a lack of variation that just isn't there. $\endgroup$ – John Sep 23 '17 at 1:29
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    $\begingroup$ @jamesqf If you want to ask this as a separate question I would be more than happy to go into it, there are well documented brain injuries that impair the ability to recognize faces without impairing the ability to recognize objects and vice versa, the fact one can be damaged without affecting the other means they are separate. The condition is called Prosopagnosia. $\endgroup$ – John Sep 23 '17 at 13:11
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There IS in fact less difference in other species's faces than there is in humans. And you can in fact recognize subtle difference in animals as well, when they are there. The idea that we're somehow blind to very similar shape variants to human faces in other animals is absurd. You can see subtle difference in everything, you are human, you can pay attention to detail. You can do it with an object it's not very hard, how do you figure humans manage to master drawing and painting? The reason why most animals have less diverse faces than ours is because we evolved to be easily recognizable. Since other animals can identify eachother by such things as smell or sound, they don't need distinctive facial features, factors that we're less sensitive to.

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    $\begingroup$ Please provide references for your claims. $\endgroup$ – iayork Oct 25 '18 at 19:46

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