Microchimeric sharing means that, even if the mother loses a child, she'll have a small memento of him or her secreted away inside her. Similarly, a bit of our mothers live on in all of us no matter how long ago Mom died.

To be sure, ASPM isn't the gene responsible for building big brains - there's no such single gene. But it's critical to the process, and the primate line has almost certainly benefited from distinct changes in ASPM.

If stem cells divide equally, so both daughter cells look more or less the same, each one becomes another stem cell. If the split is unequal, neurons form prematurely.

Sam Kean Quotes