How Much Do Genes Affect Human Behavior? [Quick Guide]


This article explains to what extent genes affect human behaviors.

So, if you want to know:

How genes and behavior are linked…

…and how genes affect human behaviors…

…you will find interesting answers to those questions by reading the following chapters.

Read on!

Genes In Everyday Language

Intro header for genes and behavior chapter of this article.

In everyday conversations, genes directly affect human behaviors. Obesity has something to do with one’s genes.

There are genetic underpinnings to aggressive behaviors.

And if someone ends up a criminal, it was a predetermined story written in their genome.

If people accept that mental disorders are biological diseases, sufferers are deemed less responsible for their actions.

Yet, this kind of thinking invents new cognitive biases:

The sufferers are now thought of as more unalterably dangerous, who, then, feel less in control of their illness…

…and are more likely to fall into depression.

One survey showed that 76 percent of American adults believe “single genes directly control specific human behaviors.”

In a British survey, people support that the police should take DNA samples for individuals charged with a crime.

What affects the amount of support this action got?

The seriousness of the crime:

If the person charged with a crime was caught shoplifting, 36 percent of the surveyed participants showed support for DNA testing.

Drunk driving? 56 percent.

Murder? A staggering 98 percent!

Moreover, if the participants had low levels of knowledge…

…and/or said that their religious beliefs had something to do with the outcome of their judgment…

…they were more likely to consider this procedure appropriate.

DNA and Politics

In a 2013 study, Elizabeth Suhay and Toby Epstein Jayaratne demonstrated that people’s political views affect the perceived link between genes and behavior.

Conservatives are more likely to endorse genetic explanations for differences in race and socioeconomic status; liberals attribute these differences to discrimination and inequalities.

But when it comes to questions about sexual orientation, liberals more readily point to genes for an explanation…

…and conservatives show a tendency toward viewing environmental factors and personal choices as the underlying causes.

Interestingly enough:

The ideological positions show no predispositions toward attributing genes as being the underlying cause of a given behavior.

Instead, it seems to be more a question of what ideological position people want to defend, pointing to motivated reasoning; post-hoc rationalizations for an automatic emotional response.

In other words:

Genetics is merely the card being played to win the rhetorical game.

Generational Realm

In 2012, Eric Luis Uhlmann and colleagues showed that the belief in genetic determinism—the notion that there exists a direct and immutable relationship between genes and behaviors—works like a slow poison, running through multiple generations.

If an adoptee who has never met the biological parents finds out that their father is a criminal, the adopted child is now viewed as capable of committing the same kind of crime.

The child is tainted by “the sins of the father.”

That same study showed that if an adoptee’s grandfather hurt an innocent family, a “moral spillover effect” emerges, making people judge it likely that the adopted grandchild has an inborn tendency to do the same and should therefore help the victim’s grandchildren.

Genetic kinship > determines > behavioral tendency.

The blood of your parents is not lost in you” as Menelaus stated in The Odyssey.

Or is it?

Let’s find out!

The Blood of Your Parents

How much of our genes code for a behavior that comes from our parents?

In fact, half of a person’s genetic makeup comes from the mother’s eggs; the other half is from the father’s sperm.

Well, kinda.

Moving on:

This information is tightly packed into 46 chromosomes.

It is where the genetic material of mitochondria…

…the “powerhouse” in eukaryotic cells that produces adenosine triphosphate (ATP)…

…called mitochondrial DNA (mtDNA)…

…is found, which is exclusively extracted from the mother’s genetic contributions.

However:

One study by Shiyu Luo and colleagues shows that fathers occasionally contribute to this process.

Although not everyone agrees.

Following this line of reasoning, it is not unlikely, but instead plausible, that genes have something to do with our behaviors.

Perhaps even a direct causal relationship.

Why?

Because why would we look like our parents, but not inherit any behavioral traits and thus provide living evidence for the fact that genes have something to do with behaviors?

Enter the worm Caenorhabditis elegans—or C. elegans for short.

C. Elegans: Genes That Influence Behavior

With its mere 1 mm in body length, 13,000 genes, and 1,000 cells (of which roughly 300 are neurons), C. elegans, a terrestrial organism living in soil (particularly in rotten vegetation for some reason), is a perfect candidate for scientific undertakings.

How come?

It is due to its genome having functional counterparts in humans.

At one level of analysis, humans are about 1,3-fold as complex as the nematode worm.

A study from 2000 shows that 83 percent of the protein sequences in C. elegans has homologous human genes.

So the worm is a great model for many neurological disorders and various human diseases.

But, what does this have do to with the link between genes and behavior?

Look:

In the nematode worm, different genes code for clusters of neurons.

These neurons are then needed to mediate a particular behavior…

…with frequently overlapping neural circuits…

…pointing to greater complexity than initially expected.

In other words:

One gene develops many neurons that work together like an orchestra to mediate different behaviors.

That is:

No single gene mediates one single behavior in C. elegans.

The biological building process from start to finish, from gene to behavior, is stochastic rather than deterministic.

Randomness in the form of environmental factors plays a significant role in the development and shaping of the neural networks that ultimately produce behaviors.

As Robert Sapolsky, neuroscience professor at Stanford, wrote in Behave:

“Genes are not autonomous agents commanding biological events.”

Genetics and Human Behavior

If there is no single gene that codes for a single behavior in such a simple organism as a 1 mm long nematode worm such as C. elegans…

…it is unlikely that one gene has direct control over human behaviors.

To put it more bluntly:

There is little to be gained from explaining complex human behaviors using one categorical “bucket.”

If one looks at hormones to try and explain a particular behavior, that same person is implicitly pointing to the gene that codes for that hormone.

It is not simply a matter of endocrinology.

It is also a question of genetics, which has been subject to selection. Thus evolution has something to do with that behavior, and so on.

Also:

Reaching the conclusion that genes have a direct causal effect on behaviors is also ignoring the fact that genes can be turned on and off by environmental factors…

…such as temperature…

…the concentration of ions…

…as well as “the random nature of chemical reactions within a cell” called noise, whose stochastic effects cause various cellular messengers to bump into each other…

…so that particular proteins are never built, which means that…

Let’s save that discussion for another article, shall we. 😉

Conclusion: Genes & Behaviors

In the same way a book cannot use telepathy to upload its content into a reader’s mind without someone actually reading the book, genes do not directly cause human behaviors.

People do not randomly pick what book to read but are influenced by environmental factors.

Such as what book the student is required to read for a university class.

In the same fashion, not all genes are expressed simultaneously to mediate a particular behavior.

Thus:

Genes make no sense outside of their environment because the environment regulates genes.

The notion that genetic determinism holds water is merely an idea from folk biology.

No one gene codes for criminal behaviors, aggression, or obesity.

But it is instead a question of tendencies and experiences.

In other words, the gene-environment interaction.

What are examples of environmental factors that affect gene expression and ultimately behaviors?

We will examine this question in-depth in future articles.

Stay tuned!

P.S. To make sure you do not miss it when a new article is published, sign up for the newsletter because leaders are readers.

Christoffer <strong>Hagenmalm</strong>
Christoffer Hagenmalm

Psychology student at Gothenburg University, publicly learning how the brain mediates complex human behaviors.

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