Question

why do fish and frog lay more number of egg where as cow and human biengs give birth to only one at time

Answer 1

fish and frogs lay more number of egg because they leave their eggs vulnerable and some of them might not take birth due to natural reasons

Answer 2

Because the babies of that organism are born with simple body and later on converts to complex body design.

But when we discuss about humans and some another animals they are born with complex body design so they are born in number 1 or sometimes geneticaly 2