The human body is incredibly complex. It consists of about 30 trillion cells organized into around different cell types. It contains miles of nerves and blood vessels and about 20 square feet of skin. There are about 100 trillion connections between the different cells in the human brain. Yet despite all this complexity, we all started life as a single cell. To get from one fertilized egg to an adult organism, cells have to differentiate—that is, they have to change their contents, shapes, behaviors, etc. All of this differentiation is coordinated by the release and reception of signaling molecules, like hormones and neurotransmitters.
The following images are inspired by (but do not accurately depict) some of the hormones and neurotransmitters that are known to play a role in human development and behavior.
These illustrations were drawn using Stable Diffusion 2.1.