Is the pious loved by the gods because it is pious, or is it pious because it is loved by the gods?
Socrates, Euthyphro

I recently skimmed Barbara Oakley’s Evil Genes, which explores the relationship between genes and behaviour. Oakley aggregates some interesting research from genetics, molecular biology, and psychology to try and answer whether people are born bad or made bad.

The nature vs. nurture debate is the psychology equivalent of the chicken-or-egg question. Most researchers agree that adulthood personality largely boils down to two factors:

1. Genetic predispositions (the hardware).
2. Early childhood experiences (the software updates).

But genes don’t act in a vacuum, nor do they dictate outcomes. Certain genes can turn on or off, or express differently in response to environmental stimuli. This is epigenetics.

Simply put, DNA behaves more like an adaptive program that responds to input (external conditions) than a deterministic script.

Oakley points to research on boys with a predisposition for lower levels of MAOA (monoamine oxidase A), an enzyme that regulates neurotransmitters. These low-MAOA variants are linked to impulsivity and aggression. But genes alone don’t predict behavior here:

• Boys with low-MAOA raised in abusive homes are vastly more likely to engage in violent or criminal behaviour.
• Boys with low-MAOA raised in stable homes display no significant difference from the general population.

The genetic potential for aggression exists in both cases. But the expression depends entirely on context.

This is why studies on identical twins raised apart are so fascinating. If behavioural traits were purely genetic, twins raised separately would be identical in personality. If traits were purely environmental, they’d be as different as any two random people.

What we actually see is a spectrum. Certain traits (like IQ and temperament) remain highly heritable, while others (like moral values and personal ambitions) diverge more depending on upbringing.

HPA Axis

The HPA axis (hypothalamic-pituitary-adrenal axis) is one of the most important and criminally underrated biological systems in our body. It regulates many neurological and physical processes, including body’s response to stress.

There’s ample evidence that dysregulation of HPA axis is responsible for a vast majority of functional disorders and has downstream effects on personality, impulse control, and emotional stability.

• Prenatal stress exposure (e.g., maternal depression) leads to a hyper-reactive HPA axis and higher baseline cortisol and corticosterone (both stress markers) levels in infants.
• Early-life neglect results in smaller hippocampal volume and reduced emotional regulation.
• Rats subjected to extreme stress as pups (e.g., being separated from their mothers) grew up with permanently overactive stress responses.

This means there’s a critical early-life window when HPA axis gets calibrated by the external environment. Get this wrong, and you end up with an adult who is permanently biased toward either overreacting or shutting down in response to stress.

The results of this dysregulation extend far beyond psychological. The immune system, metabolism, even gut microbiota get wired based on early experiences. Stress-prone children grow up to have higher inflammation levels, greater risk of autoimmune disease, and worse long-term health outcomes.

Free Will

If genes shape temperament and environment shapes gene expression, then how much of “you” is actually you? If we are just the sum of our genes and learned behaviour, is there such a thing as human agency?

Most of us like to believe in free will because the alternative is terrifying. If everything about us is dictated by biology and experience, then responsibility, morality, and justice are all mere social fictions.

Schopenhauer, in his 1838 essay On the Freedom of the Will, famously wrote:

Man can do what he wills, but he cannot will what he wills.

Much of what we call “free will” is post-hoc rationalization. The brain makes a decision before we’re even conscious of it and our sense of agency is mostly just the brain explaining its own behavior after the fact.

For example, studies on split-brain patients show that the left hemisphere (which constructs our internal narrative) makes up explanations to rationalize the behaviours it didn’t even initiate.

This doesn’t mean we’re robots. Just that the forces driving our choices (genes, hormones, past experiences) operate largely outside conscious awareness.

Human nature isn’t a thing. It’s a process. And that process is recursive, self-reinforcing, and deeply dependent on context. Change the environment, and you change the expression of human nature itself.

It’s about time we ditched nature vs. nurture for nature + nurture.