The Molecule of More

In which dopamine ensures the survival of early humans 
and the extinction of the human race.
OUT OF AFRICA
Modern humans evolved in Africa about 200,000 years ago and began 
spreading to other parts of the world approximately 100,000 years 
later. This migration was essential for the survival of the human race, 
and there’s genetic evidence that we almost didn’t make it. One of the 
unusual characteristics of the human genome is that there is far less 
variation from person to person compared to other primate species 
such as chimpanzees or gorillas. This high level of genetic similarity 
suggests that we are all descendants of a relatively small number of
ancestors. In fact, early in our evolutionary history, unknown events 
. . . the beginning is where the end gets born.
—Catherynne M. Valente, writer

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THE MOLECULE OF MORE
killed off a large portion of humans, and the population dwindled to 
less than 20,000, representing a serious risk of extinction.
That near-extinction event illustrates why migration is so impor tant. 
When a species is concentrated in a small area, there are many ways in 
which the entire population can be wiped out. Drought, disease, and 
other disasters can easily cause extinction. Dispersing throughout many 
regions, on the other hand, is like an insurance policy. The destruction 
of one population doesn’t result in total extinction.
Based on the appearance and frequency of genetic markers in 
modern peoples, scientists estimate that early humans spread out across 
Asia about 75,000 years ago. They reached Australia 46,000 years ago 
and made it to Europe 43,000 years ago. Migration to North America 
occurred later, sometime between 30,000 and 14,000 years ago. Today, 
humans occupy nearly every corner of the globe—but not because 
humans recognized the threat and dispersed.
THE ADVENTURE GENE
Research on mice has shown that drugs that boost dopamine also 
increase exploratory behavior. Mice given these drugs move around their 
cages more and are less timid about entering unfamiliar environments. 
So could dopamine have helped propel early humans out of Africa and 
across the globe? To answer this question, scientists from the University 
of California compiled data from twelve studies that measured the fre-
quency of dopaminergic genes in different parts of the world.
They focused on the gene that tells the body how to make the D4 
dopamine receptor (DRD4). You may recall that dopamine receptors 
are proteins that are attached to the outside of brain cells. A dopamine 
receptor’s job is to wait for a dopamine molecule to come along and 
bind to it. Binding sets off a cascade of chemical reactions inside the 
cell that changes the way the cell behaves.
We encountered this gene before when we described the connection 
between novelty-seeking and political ideology. Recall that genes come 
in different varieties called alleles. Alleles represent slight variations in 

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the coding of genes that give people different characteristics. People 
who have a long form of the DRD4 gene, such as the 7R allele, are 
more likely to take risks. They pursue new experiences because they 
have a low tolerance for boredom. They like to explore new places, 
ideas, foods, drugs, and sexual opportunities. They are adventurers. 
Worldwide about one in five people have the 7R allele, but there’s sub-
stantial variation from place to place.
MORE DOPAMINE, MORE DISTANCE
The researchers obtained genetic data from the most well-known 
migration routes in North America, South America, East Asia, South-
east Asia, Africa, and Europe. When they analyzed the data, a clear 
pattern emerged. Among populations that remained near their origins, 
fewer people had a long DRD4 allele compared to those who migrated 
farther away.
One of the migration routes they evaluated began in Africa, 
went through East Asia, across the Bering Strait to North America, 
then down to South America. That’s a long way—and the research-
ers found that the group that made it all the way, indigenous South 
Americans, had the highest proportion of long dopamine alleles, 69 
percent. Among those who migrated a shorter distance and settled in 
North America, only 32 percent had the long allele. Indigenous pop-
ulations in Central America were right in between at 42 percent. On 
average, it was estimated that the proportion of long alleles increased 
by 4.3 percentage points for every 1,000 miles of migration.
Once it was established that the 7R allele of the DRD4 gene was 
related to how far a population migrated, the next question was why? 
How did the 7R allele become more common in far-flung populations? 
The obvious answer is that dopamine makes people seek out more. 
It makes them restless and dissatisfied. It makes them long for some-
thing better. These are exactly the kinds of people who would leave an 
established community to go out and explore the unknown. But there’s 
another explanation as well.

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THE MOLECULE OF MORE
SURVIVAL OF THE FITTEST
Maybe the migratory tribes left for some other reason that had noth-
ing to do with novelty-seeking. Maybe they left because of conflict, or 
perhaps they were hunting migratory animals. There could have been 
many reasons unrelated to dopamine, but the question remains: Under 
these circumstances, why would the migratory population end up with 
lots of 7R alleles among its members? The answer is that maybe the 7R 
allele didn’t set off the migration, but once it began, the allele gave its 
carriers a survival advantage.
One advantage provided by the 7R allele is that it drove its carri-
ers to explore the new environment in which they found themselves in 
order to seek out opportunities to maximize resources. In other words, 
it promoted novelty-seeking. For example, a tribe might have started 
out in a geographical area where there was a consistent climate, and 
the same type of food was available all year round. However, after mov-
ing to a new location, the members of the migratory tribe may have 
experienced rainy and dry seasons, and they needed to learn how to 
switch food sources as the seasons changed. Figuring out how to do that 
involved risk-taking and experimentation.
There’s also evidence that people who carry the 7R allele are 
faster learners, especially when getting the answer right triggers a 
reward. In general, 7R carriers are more sensitive to rewards; they 
have stronger reactions to both wins and losses. Consequently, when 
they found themselves in an unfamiliar environment and needed to 
adapt to new routines to stay alive, the 7R carriers worked harder to 
figure things out because their experiences of success and failure were 
more intense.
Another advantage is that the 7R allele is associated with some-
thing called low reactivity to novel stressors. Change is stressful—both good 
change and bad change. For example, there are few things more stress-
ful than divorce, but getting married is hard, too. Going bankrupt is 
stressful but so is winning the lottery. Bad changes may cause more 
stress than good changes, but the most important factor is the size of
the change. Bigger change means more stress.

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Stress isn’t good for human health. In fact, stress kills. Stress 
increases the likelihood of developing heart disease, poor sleep, diges-
tive problems, and immune system impairment. It can also trigger 
depression, which leads to low energy, poor motivation, hopelessness, 
thoughts of death, and simply giving up, all of which militate against 
survival. Among our evolutionary ancestors, people who were sensitive 
to stress had a harder time extracting resources from environments that 
represented a large change from what they were used to. They were 
less successful hunters and less productive gatherers. That made it hard 
for them to compete for reproductive mates, and sometimes they didn’t 
even live long enough to have children who would carry their genes 
forward to the next generation.
Not everyone gets stressed by change, though. A new job, a new 
city, even a whole new career can be exciting and energizing for people 
with dopaminergic personalities. They thrive in unfamiliar environ-
ments. In prehistoric times, they were more likely to cope well despite 
radical changes in their way of life. They competed more successfully 
for mates, and as a result they passed along their dopaminergic genes. 
Over time, alleles that helped people adjust to unfamiliar environments 
with ease became more common in the population, while other alleles 
became rarer.
Of course, carriers of the 7R allele weren’t well suited to every 
environment. People with dopaminergic personalities may do well 
when coping with novel situations, but they often have difficulty with 
relationships. That’s important because skillful social functioning also 
provides an evolutionary advantage. No matter how big, how strong, or 
how smart a person is, he’s not going to be able to compete with people 
who work together as a group. Individuals shouldn’t fight gangs. In this 
situation, when the need for cooperation is paramount, a dopaminergic 
personality is a liability.
So it all depends on the environment. Under familiar conditions, in 
which social cooperation counts the most, highly dopaminergic genes 
become less common because their survival and mate-seeking advan-
tages diminish relative to the benefits of more balanced dopamine lev-
els. On the other hand, when a tribe picks up and heads off into the 

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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.

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Tribes that kept going, however, would experience unfamiliar envi-
ronments generation after generation after generation. The repro-
ductive advantages of 7R would continue, and 7R carriers would live 
longer and have more children. Over time the 7R allele would become 
more and more common among these long-distance travelers. And 
that’s what we do see. The farther a population migrated, the greater 
the frequency of the 7R allele. It didn’t start them moving, but it did 
help them survive as they went along.
IMMIGRATION
Movement across the globe today is different from what our prehistoric 
ancestors experienced. Emigration away from one’s native country is a 
personal decision rather than a tribal decision. And although the rea-
son may be similar—seeking better opportunities—the 7R allele of the 
D4 dopamine receptor doesn’t seem to play a role. Immigrant popu-
lations have about the same percentage of the 7R allele as the people 
who remained in their home country. Nevertheless, dopamine seems to 
be involved, but in a different way.
In chapter four, when we discussed the role of dopamine in cre-
ativity, we compared creativity to schizophrenia, a mental illness char-
acterized by excessive dopamine in the desire circuit. We discussed 
ways in which psychotic delusions have things in common with highly 
creative ideas and even ordinary dreams. But schizophrenia is not the 
only illness characterized by excessive dopamine activity. Bipolar disor-
der, sometimes called manic-depressive illness, also has a dopaminergic 
component, and the condition seems to be linked to immigration.
BIPOLAR MANIA: ANOTHER CONDITION 
OF TOO MUCH DOPAMINE