How did eukaryotic cells evolve prokaryotic cells?

The hypothesis that eukaryotic cells evolved from a symbiotic association of prokaryotes (endosymbiosis) is particularly well supported by studies of mitochondria and chloroplasts, which are thought to have evolved from bacteria living in large cells.

Explanation:

Both mitochondria and chloroplasts are similar to bacteria in size, and like bacteria, they reproduce by dividing in two.

Google defines it as:

"a region of the forebrain below the thalamus which coordinates both the autonomic nervous system and the activity of the pituitary, controlling body temperature, thirst, hunger, and other homeostatic systems, and involved in sleep and emotional activity."

basically, its a part of the brain below the thalamus and it controls your homeostatic systems. it also helps decide if you're gonna get good sleep and how you feel