Paleolithic humans ate animals' brains and interior organs, so it's healthy for us modern day humans to eat them too, right?

No: Not at all. First, early humans life expectancy was about 30-40. Part of that was infectious disease such as parasites from eating such organs. Second, they were far more physically active on a daily basis than anyone today - out of necessity and survival. There is no need to eat high fat, high cholesterol things like that. And it's unhealthy overall to the renal, hepatic, and cardiac systems.

Yes: It is okay to eat internal organs of animals including their brain . In some countries the brain of a lamb is highly valued delicacy. However recognize that you can expose your self to various diseases if the animal is unhealthy. Also limit the amount of animal fat consumed.

Approach w common: Sense . A diet rich in fats in cholesterol takes it's toll. The basic tenant of the paleolithic diet is that it reflects the life of paleolithic (stone age) forager- hunters. The assertion is that man's body has not acclimatized to diets that are heavily impacted by industrialization ; crop cultivation. Diet incorporates meats, fish, fruits, nuts ; vegetables w attempts to avoid processed ; junk.