Eli5 Why is the gestation period of each mammal different? Opposum only need 12-13 days but why do we get 9months?

Question

Eli5 Why is the gestation period of each mammal different? Opposum only need 12-13 days but why do we get 9months?

In: 1

Answer 1

I want to preface this with the words „I am no expert“. But given that the Opossum is so much smaller than humans and that elephants -who have a gestation period of up to 22 month (almost two years!)- are so much larger than humans, it seems to me like the size of the organism plays a big role.