Oh, wow, oh, oh, whoa, oh, wow.

Oh, wow.

Oh, James. You're listening to The Science of Everything podcast, episode 155, Embryology and Development.

I'm your host, James Fodor.

Today we're going to be talking about the process of development from starting with fertilization

right through to the later stages of the development of the fetus.

The focus is going to be on a mammalian and

specifically human embryonic development, although I will mention a few differences between

different types of animals as we go. Recommended pre-listening is episode 25, tissues, organs,

and systems, just for a bit of general background. And one of the reasons I'm doing this

episode is to provide some useful context for the next few episodes where we're going to be

talking about the evolution of life and the development of different types of animals,

and comparative development is very important for that. So I thought this episode

would be useful as well as a good standalone topic. One thing that I'll mention is that I'm not

really going to focus so much on the reproductive organs and things like the role of different

hormones and reproductive cycle and so forth. I'll do a separate episode on that. Here we're just

going to be focusing on,

particularly the development of the embryo. Until relatively recently, maybe the late 18th century,

it was thought that semen contained a premature miniature person, a miniature infant,

that then just becomes larger and larger during development.

And that was known as pre-formation.

A competing theory is known as epigenesis, which is the idea that an animal gradually develops

...