The Molecule of More

THE MOLECULE OF MORE

unknown, genes that give a person a more active dopamine system pro-

vide an advantage and become more common over time.

WHICH IS RIGHT?

That leaves us with two competing theories:

1. Dopaminergic genes propelled people to seek new
   opportunities. As a result these genes are found more
   frequently among populations who migrated from their
   evolutionary origins.


2. Something else made them seek new opportunities, and the
   dopaminergic genes allowed some of them to survive and
   reproduce more successfully than others.

How do we decide which one is correct?
This is where it gets a little complicated. If dopaminergic genes got
people started (i.e.,  set  them off  to  seek a  better life), then we  should 
see lots of 7R alleles in every group that left Africa. That would be the
case whether they migrated for a few generations and ended up close to
their origin, or migrated for many generations and ended up far away.
That’s because if it takes lots of dopamine to get started, where the
tribe ended up shouldn’t matter. Those who left would have a lot, and
those who stayed would have less.
On the other hand, if people got started without the need for the
7R allele, then we’d see a more gradual change in the number of peo-
ple who carry it. Here’s why. If a tribe migrated only a short distance,
only a few generations would experience unfamiliar environments.
Once they stopped moving, the unknown became the familiar, and
the 7R allele no longer conferred an advantage. Once the playing
field was  level, the 7R  allele  carriers lost  the ability to  have more
children than their less dopaminergic neighbors. At this point, all the
different alleles were  passed along equally to  subsequent generations
of offspring.