Neanderthals' Brains Evolved Differently Than Those of Modern Humans

Modern humans' brain stem cells are more accurate in how their chromosomes are distributed to the daughter cells

About one hundred amino acids, the building blocks of proteins in cells and tissues, changed in modern humans when their ancestors diverged from those of Neanderthals and Denisovans, their Asian relatives. This shift extended to practically all modern people. These alterations' biological relevance is mainly unknown.

However, three proteins that are essential in the distribution of chromosomes, the genetic information carriers, to the two daughter cells during cell division, underwent six of those amino acid alterations. In a new paper in Science Advances¹, researchers first introduced the modern human variations in mice in order to examine the importance of these six modifications for neocortex development. Mice were used as a model for the contemporary human brain's development because they differed at only six amino acid sites from Neanderthals.

Fewer chromosome segregation errors in modern human than Neanderthal neural stem cells. Left side: microscopy image of the chromosomes (in cyan) of a modern human neural stem cell of the neocortex during cell division. Right side: same type of image, but of a cell where three amino acids in the two proteins KIF18a and KNL1, involved in chromosome separation, have been changed from the modern human to the Neanderthal variants. These “neanderthalized” cells show twice as many chromosome separation errors (red arrow). © Felipe Mora-Bermúdez / MPI-CBG