system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: why is it that our bodies are symmetrical on the outside, but not on the inside?

I have always wondered but, well, today i was prompted to ask. We are from head, to genitalia to feet symmetrical and then our heart, stomach etc is all wack, please explain.
gpt
Overall symmetry makes movement and maintaining balance easier since it keeps your center of mass centered inside your body, so there's some selection pressure on evolution to keep such a shape. Sometimes asymmetry still sneaks into living beings where it either provides enough advantage to outweigh the disadvantage (look up the pistol shrimp for an example of this), or else is too minor to get in the way.

The exact placement of the different organs inside your body matters less to evolution, as their density doesn't differ that much. Because of this it can sometimes get away with just placing them where it is convenient and inexpensive in terms energy spent on growth and upkeep.

As far as center of mass is concerned, your insides can be abstracted as a nearly-uniform distribution of generic biomass contained inside a humanoid-shaped container made of skin suspended on bone.