If humans had developed from the type of mammals that laid eggs, or from marsupials similar to kangaroos. how would we be different? The way we are is affected greatly by the live-birth process and subsequent child-rearing of a dependent infant. .Taking many factors into account, too many to write here, I think we would be very different if by some evolutionary chance we were marsupials. We would actually not be We, if you know what I mean. .I always thought that Star Trek missed a cool opportunity to portray aliens with exterior pouches and squirming young developing inside. .Consider it junk food for thought.