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
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.
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