HomeFAQsWhy are humans born with eyes open and puppies are born with eyes closed?

Why are humans born with eyes open and puppies are born with eyes closed?

The reason why dogs’ eyes are closed at birth and humans’ eyes are open at birth is a puzzle with a lot of parts. So, I’ll lay out the pieces first and put them together at the end.

First, the brains of most mammals grow at a very constant rate. Eye opening is linked to brain growth, and the eyes open when the brain is at a certain maturational point, whether or not there is anything to look at!

Second, body growth, particularly important things like being able to breathe and nurse, can be separated from brain growth. Different mammals are born and can live outside the mother at many stages of brain maturity, from just starting (like hamster pups) to nearly complete (like fawns).

Third, how long a mammalian mother keeps her babies inside to grow compared to giving birth and nursing them depends on what kind of animal she is, big or small, carnivore or grazer. It saves energy to keep a growing baby in the uterus for as long as possible, but it’s hard on the mother. If she can give birth to an immature baby, protect it, and still get food for herself and the baby, it’s easier on her.

Finally, different mammals have different strategies to be sure they have at least some babies who survive to adulthood. Mammals like humans and deer have just one baby at a time (usually) and spend lots of time, energy and attention on that baby. Others, like hamsters, have a lot of babies, sometimes as many as 15-16 at once, but aren’t careful parents, hoping that with luck one or two might survive. So (though it’s hard for us to imagine) a hamster mother will abandon her pups if the least thing goes wrong. Then she can be ready to have more right away if conditions improve.

So, now we can go back and see the different strategies dogs and humans have by comparing them to other animals. Dogs are carnivores, and before they lived with humans, depended on speed and agility to hunt their food. Pregnancy is a big disadvantage in hunting! Also, dogs are big and fierce compared to most animals. Since the mothers can defend the pups, they don’t have to defend themselves right away. When the mothers go to hunt, they can leave the pups because few animals will go into a large carnivore’s burrow. So dog mothers do best to give birth to very immature pups, in both brain and body. Deer have a different set of problems. A deer mother can’t defend her fawn very well once it’s born, so she does best to keep the fawn inside until it is mature enough to run on its own. Fawns are born with eyes open and can walk, even run, within hours of birth, so both theirs brain and bodies are relatively mature at birth.

Finally, the open eyes of human babies at birth tell us that our brains are quite mature compared to hamsters and puppies, ready to learn right away, but in an immature body. Defended often by two parents and a whole community, a human baby has the luxury of a long childhood to learn all we need for successful adulthood.


Barbara Finlay

  • W.R. Kenan Professor of Psychology
  • Psychology; also Neurobiology & Behavior, Cornell University

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