Re: How do we really know where babies come from?

I'm not exactly sure what you're referring to in your question. You list your grade level as 10-12, so I'm assuming that you've had the sex education class. If your question of "where babies really come from" refers to the act of procreation or conception and birth, then I suggest you consult your parents or a biology textbook. However, if you are asking about how do we "prove" the genetic parentage of babies or how do we "prove" that a fertilized egg really develop into a baby, then I will answer your question.

It is pretty amazing to think that a tiny egg cell and a tinier sperm cell unite and then "grow" to become a baby. But this is exactly what happens. Each human egg and each human sperm cell carries half of the genetic material needed to make a human being. When united by the act of fertilization, there is a full complement of genetic material and the fertilized egg starts to divide and divide and divide. The dividing cells follow a "program" of development where some cells end up becoming muscle cells; some become nerve cells etc. This has to do with turning on or off specific genes during development. This process of fertilization and division can be seen; in vitro fertilization takes an egg and sperm and the fertilzation and early stages of development happens outside the body and can be observed under a microscope.

The stages of early human development can be seen at The Visible Embryo.

As to the genetic inheritance, each parent contributes an equal share of genetic material, DNA, to the child. The mother's share is in the egg; the father's share is in the sperm. There are DNA tests that can verify parentage proving that each parents' DNA is present in the child. The DNA tests looks at the differences we all have at certain place in our DNA. By matching the differences you can tell whether or not the child is a product of the parents.

I hope this answers your question.