“Common knowledge” has said for some time that the human brain has about 100 billion neurons to say nothing of at least as many glial cells and who know how many of other cells that may not yet have been identified. [Remember that it was only 2015 when researchers discovered that the brain does have an immune system, with immune vessels having been found in all three protective layers (meninges) that surround and protect brain tissue.] There is some emerging evidence that the brain may not contain nearly this many neurons. And the male brain, being larger, may have a couple billion more neurons than the female brain—the consensus previously being that the numbers of neurons were equal in male and female brains with those in the female brain just more tightly packed. If this holds up there will be yet more textbooks that need revision . . .