Genetics, Race, Gender and Jelly Jars

When we think about genetics, why is it almost automatic to focus on differences? On how our genes make us different from other people—or even from other organisms? As a geneticist, I’ve always found it curious that we instinctively look for differences rather than similarities. Why don’t we ask how much we’re alike?

That was the theme of my talk at the Fronteiras do Pensamento Festival in Porto Alegre, in May 2025. I used the opportunity to talk about differences, similarities, race, gender—and jelly jars (yes, that part will make sense at the end). How Similar Are We?

Here’s a fact to reflect on: humans are about 99.9% genetically identical. Within the remaining 0.1% variation, we find countless SNPs (single nucleotide polymorphisms)—tiny points in the genome that differ but often don’t even code for known genes with a function. These bits of DNA might show up more frequently in one population or geographic region than another. And yet, that doesn’t mean much on its own.

For example, a given SNP may appear in 60% of people sequenced in one part of Africa. Maybe in that same region, heart disease is also more or less common. But we can’t conclude that the SNP causes heart disease. It may be coincidence. That SNP might also appear elsewhere in the world at different frequencies.

The same SNP could show up in 20% of Europeans. From this, we can only calculate probabilities of ancestry—never certainties.

Some quirky facts about these frequencies: high blood pressure is more common in African-American men than in white American men. Yet it’s less common in men from Sub-Saharan Africa than in either group. Similarly, single American men are more likely to develop heart disease than married men. Surely that’s not genetic destiny.

What’s striking is that most variation—about 96% of that 0.1%—occurs within populations rather than between them. In fact, two random people from the same African region are likely to be more genetically different from each other than from someone elsewhere in the world. Which means the differences historically used to define “race”—white, Black, Asian, and so on—account for just 4% of 0.1% of our DNA.

In other words: biologically speaking, humans are overwhelmingly similar. That’s why leading genetics and anthropology societies consider “race” to be a social construct, not a biological one. Race matters for public policy and social justice—because it has been a basis for discrimination—but it isn’t a scientifically valid category. Humans vs. Dogs

To make this clearer, let’s compare humans to dogs. Does it make sense to talk about dog “breeds” biologically? Yes. The genetic differences are stark. In humans, “racial” genetic variation sits in that 4% of 0.1%. In dogs, about 27% of total variation separates breeds.

Within a breed, dogs are extremely genetically similar. That’s the result of artificial selection. Breeders deliberately picked traits—like small, fluffy, docile lapdogs—and inbred animals to reinforce them. Each generation narrowed diversity further, creating “pure” breeds but also health problems: deafness, skin disease, hip dysplasia.

By contrast, mixed-breed dogs are genetically diverse—much like humans. We are all, in effect, mutts. And that’s a good thing.

Could humans be bred into “races” like dogs? In theory, yes. History even tried—think of the Nazi fantasy of the “Aryan race.” But such domestication would reduce diversity, raise disease risks, and undermine resilience. Exactly the problems we see in many purebred dogs. Skin Color and Beyond

So where do visible human differences come from—like skin color, long used as the primary marker of “race”?

Evolutionarily, skin tone correlates with geography and sunlight. Near the equator, darker skin protects against UV radiation. Farther north or south, lighter skin helps absorb scarce UV to produce vitamin D.

Dozens of genes influence pigmentation, producing the vast spectrum of tones we see today. Just look at makeup foundation charts—over 60 shades exist. Even children of the same parents can inherit different tones depending on gene combinations. People from opposite ends of the globe can have nearly identical skin color—yet arrive there through completely different genetic pathways.

Appearance does not define ancestry. Enter the Jelly Jar: Gender Differences

Now let’s shift to gender. Are men and women more alike or more different? To answer, grab a jar of jelly. At some point in life, you’ve either asked someone to open one, or been asked. Odds are, the asker was a woman, the opener a man.

Why? A 2005 meta-analysis by psychologist Janet Hyde pulled together decades of research on gender differences. She quantified each difference on a scale from 0 (none) to 2 (large).

Some differences were obvious: men are, on average, taller, with strong coefficients. Grip strength, throwing strength, and throwing speed also scored high—hence the jelly jar problem.

Sexual behavior differences (like rates of casual sex or masturbation) also ranked higher, though cultural factors may play a role—are women less likely to engage in them, or simply less willing to admit it?

But here’s the striking part: 78% of studied traits showed little to no difference. Nearly half had coefficients below 0.35.

Contrary to stereotypes, men aren’t “naturally” better at math, and women aren’t innately better at language. Differences in competitiveness, problem-solving, and spatial reasoning all scored near zero.

The real story? Just like with “race,” there’s more variation within each gender than between genders. The Plastic Brain

Biology plays a role, of course—hormones, evolution, anatomy. But brains are not hardwired. They’re plastic, constantly reshaped by learning and experience.

A classic example: London taxi drivers, once required to memorize the city’s labyrinth of streets, showed enlarged hippocampi (the brain’s navigation hub) compared to non-taxi drivers. And the longer they worked, the larger the hippocampus grew.

So when studies report brain differences between men and women, are they seeing innate biology—or the cumulative impact of cultural training from childhood toys to social expectations? Why It Matters

Understanding these nuances matters deeply for society. Recognizing race as a social, not biological, category helps fight injustice. Acknowledging the cultural drivers of gender differences can combat stereotypes that limit women’s opportunities.

Bias has real-world consequences. In a Yale study, volunteers rated identical job-interview videos more harshly when the candidate was female. Women’s anger was attributed to personality flaws; men’s anger to external provocation.

Solutions exist: some orchestras adopted blind auditions, with musicians performing behind a screen. Female hires rose from 5% in the 1970s to over 30% today.

Change won’t come overnight. But it begins with awareness. And maybe—with something as simple as a jelly jar. The next time you watch someone struggle to open one, remember: grip strength is one of the few real gender differences. Almost everything else is cultural baggage. Natalia Pasternak is a professor of science and public policy at Columbia University (USA) and president of the Instituto Questão de Ciência (IQC).