Eli5: How come all animals look like each other (ex. You won’t tell the difference between 2 squirrels) but humans differ so heavily? Why do humans have so many unique facial an body features?

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Eli5: How come all animals look like each other (ex. You won’t tell the difference between 2 squirrels) but humans differ so heavily? Why do humans have so many unique facial an body features?

In: Biology

People that spend a lot of time with animals can usually tell them apart by look. Animals differ greatly if you know where to look, you just don’t have the massive number of points of reference that you do for human faces. You see hundreds and hundreds of faces every day.

I’m sure this isn’t the *only* answer, but:

Many animals rely on other cues for communication, mate selection, etc. A squirrel may attract a mate using pheromones or its own special scent, while humans attract mates by looking pretty (among other things). Primates can convey a lot of body language through facial expression, so it’s no surprise that the face is very important in our body language, which broadly includes attraction. A lot of development goes into facial features, which in turn leads to a diversity of face types.

Many other animals already have ways of communicating: scents, noises, etc, so from an evolutionary perspective having body/face diversity wasn’t necessary.

The human brain is exceptionally good at recognizing human faces. An entire section of it is dedicated to that purpose. [There is a neurological disorder that screws up that part of the brain and breaks its ability to recognize faces](https://en.wikipedia.org/wiki/Prosopagnosia). People can still tell who other people are, but using other ‘methods’ that aren’t as powerful as straight up facial recognition.

Humans also spend a lot of time and energy distinguishing themselves in terms of clothes, hair, cosmetics, and other style choices.

* You have *years* of practice in telling *humans who live around you* apart. You learned what’s the same in everyone and what features change, and you use those features to tell people apart.
* We don’t all give the same weight to the same features. Hence some people will claim that a brother-sister duo look incredibly similar (“I immediately knew you must be siblings”) while to you they might seem completely different.
* You don’t even need to go to squirrels. We are not trained on people we don’t see often, hence the stereotype that to most westerners all people from east Asia look the same. They really can *look* alike, because you need to look at a different set of features than the ones you are trained to use.
* If you spend enough time with animals, you will absolutely learn to tell them apart, too. They also have all those unique features, you just didn’t spend any time yet learning them.

You aren’t trained enough to notice the differences/don’t spend enough time looking at squirrels to notice the differences among them. They probably think all humans look alike.

Incorrect. There is just as much difference between different squirrels as there is between different people. It’s just we are trained and primed to distinguish between people. We have to in order to function in a society and we are tribal creatures by nature, so that’s actually a survival feature.

We, on the other hand, do not need to identify individual animals as much. That does not benefit out survival. Animals are for food or avoiding danger. Recognizing individuals is not something our ancestors needed to survive.

That being said, we can learn to do so. Are brains are flexible enough.

What other answers have said about familiarity is true but humans and domesticated animals like dogs and cats do have more obvious physical differences between individuals than wild animals.
The reason for that is neoteny, the evolutionary process by which a species leaves certain chromosome ‘switches’ which activate adult physical and behavioural characteristics inactive.
In a fairly well known Russian experiment on wild arctic foxes cubs of weaning age were selected from dens in the wild, based on a very quick determination of their apparent relative lack of aggression, and taken to a reserve where they lived with no other human contact. Subsequent offspring of these foxes were selected and separated in the same way. After only 8 generations the arctic foxes in the reserve looked very little like wild foxes. They had a variety of fur colours and patterns, ear shapes, tail shapes, etc, and they were extremely friendly and non aggressive, despite having no human contact after their initial selection. They had been selected for non aggression, and their normal adult physical characteristics were tied to the same chromosomes, the inactivity of which made their whole genetic expression more ‘plastic’ or flexible.