Few DNA differences can be
seen between our two species. Researchers are looking hard at those differences
in hopes of identifying uniquely human stretches of the genome that help science
narrow down what makes humans truly human. Two different stretches of DNA were
found to be uniquely human that include the genome for larger brains.
One gene was found to not only cause bigger
brains but also causes more surface folds as well. It seems to be a
characteristic of primarily primates and the human brain. These folds increase
the brains surface area which in turn gives more room for neurons to be able to
process and store information.
The Max Planck Institute of
Molecular Cell Biology and Genetics in Dresden, Germany, looked for a gene the
was only active during the development period of the cortex very early in the embryo
development. The cortex that is the thin outer layer of the brain is used to
memory, attention, awareness, thought, language, and consciousness.
Researchers found this gene by observing gene
activity in an aborted human fetus while comparing it to tissue from a mouse
embryo. They identified 56 human genes the mouse tissue lacked. The most active was a gene called ARHGAP11B, a partial duplication of an existing gene.
The duplication arose sometime after human evolution split off from the line
that led to chimps some 5 or 6 million years ago. It is uniquely human, being
present in Neanderthals and Denisovans, our long-gone kin, as well as
anatomically modern humans, the last Homo standing.
(That’s us.)
The researchers found out what ARHGAP11B did by putting it into transgenic mice.
It doubled the mice’s cortical stem cells and increased their brain size.
