As a Capricorn, Of Course I’m Skeptical

Inspired by a discussion on “Live From the Table” / “Comedy Cellar Podcast” with Noam Dworman, Dan Naturman and Periel Aschenbrand.

Astrology vs All the Small Things That Actually Shape Us

When I was 17, four friends and another handful of acquaintances shared my birthday. Aside from breathing air, we had nothing in common. If one of us aced a test, it didn’t mean another would. If one of us had a miserable week, another might have the best week of their life, while the rest had nothing particularly notable happen.

Even if I could suspend logic and lean into the spirituality, trust-based aspects of astrology, assigning personality or fate to your birthday never made sense to me. The date ranges for signs have shifted during my lifetime. Some believers insist the real insights come from lunar charts, others swear by tabloid horoscopes. Chinese astrology has its own rotating animal cycles. Variations of astrology appear everywhere, but they never agree with each other.

I’m not someone who rejects unusual ideas. I believe in the collective unconscious. I believe markets move based on mass psychological trust and distrust. I even think a very small number of people—let’s call them witches—are unusually good at reading others and sensing patterns in their lives, perhaps even predicting outcomes by intense observation and intuition that drains their energy. Astrology just doesn’t do it for me.

I’ve always humored astrology fans. I smile as they confidently guess personality traits and miss more often than they hit. I also think, “A trained psychotherapist using logic, context, and probability could do a far better job of reading my past.” and “A mentalist could do a better job of reading my immediate future.”

All that said, I’m a Capricorn, a sign associated with pragmatic and logical decision making. I also happen to have a lot of Capricorn friends who seem fairly pragmatic themselves. You might argue that contradicts almost everything I just said or that it’s coincidence. You have the right to believe or not believe.

As a science-minded Guy / Capricorn, I did what any curious skeptic does: I looked into what science confirms.

Note: As I’ve written before, science isn’t a game of Simon Says where you simply obey conclusions. It’s research you’re welcome to read yourself. The tl;dr: there is no credible evidence that astrology or specific birth dates shape personality or destiny. There is a tiny amount of evidence that season of birth can influence early development through biology, not mysticism. There is strong evidence that institutions, such as school-year cutoffs, can shape life outcomes.

Sorry astrology, but no

The most direct tests of astrology are the simplest: check whether people born at certain times actually share personality traits.

When researchers tested the Big Five personality traits against season of birth, they found no meaningful associations. One study of young adults found no consistent links between season of birth and personality traits like openness, conscientiousness, or extraversion (https://pubmed.ncbi.nlm.nih.gov/19383436/).

Other studies occasionally report weak correlations with temperament scales, but they are inconsistent and small. If astrology were correct, we would expect massive, obvious personality clusters tied to birth timing. We can’t find it.

Even the classic zodiac categories fail basic statistical tests. People who know their horoscope tend to rate its accuracy highly, but blinded experiments show that people who love horoscopes cannot match personality profiles to their zodiac sign better than random guessing.

Astrology survives largely because of something psychologists call the Barnum effect: people recognize themselves in vague, flattering descriptions that could apply to almost anyone.

“You’re independent but appreciate close relationships.”
“You sometimes doubt yourself but are capable of great success.”

These descriptions mean nothing. They can describe anyone.

Which brings us back to my birthday experiment. If astrology worked, sharing a birthday should produce eerily similar personalities. Instead, it produced a group of completely unrelated people who happened to arrive on Earth on the same day. Today, one shared-birthday-friend is an exec, another a jobless bum, me somewhere between.

Real-world mechanisms

While astrology fails, timing of birth is not entirely meaningless.

The difference is mechanism, i.e., biology not astrology.

Researchers have found small statistical associations between season of birth and certain health outcomes. For example, a large meta-analysis confirmed a slightly higher rate of schizophrenia among people born in late winter or early spring (https://pubmed.ncbi.nlm.nih.gov/9428062/).

But the explanation is not celestial influence. It is environmental exposure during pregnancy. Scientists have proposed mechanisms such as seasonal infections, maternal nutrition, or differences in sunlight affecting vitamin D levels.

For instance, maternal influenza during pregnancy has been linked to increased schizophrenia risk in offspring (https://pubmed.ncbi.nlm.nih.gov/15289276/).

These effects are real but extremely small. Most winter babies do not develop schizophrenia, just as summer babies are not protected from it. We are talking very small influence your skeptic friends can get behind.

Even more convincing evidence comes from natural experiments such as famines. Children conceived during the Dutch Hunger Winter of 1944–45 showed increased risks of various psychiatric disorders later in life (https://pubmed.ncbi.nlm.nih.gov/32219197/). That finding has nothing to do with birth month symbolism. It reflects the impact of prenatal nutrition during critical stages of development.

In other words, timing matters when it changes biology. Seaon and year may matter, lunar alignment does not.

The same applies to environmental exposures such as daylight cycles, maternal stress, or disease prevalence during pregnancy. Seasonal effects are simply proxies for those factors.

I did not find any evidence that Mercury in Gatorade (retrograde) matters. #gogators

Institution!

Children born just before school enrollment cutoffs often become the youngest students in their class. Those born just after become the oldest. That small difference can influence academic performance and confidence during childhood. It’s the reason many parents choose to hold their students back from starting school by one year, giving them a major advantage over their peers.

A large cohort study found that apparent season-of-birth differences in intelligence were mostly explained by relative age within the school year rather than seasonal biology (https://pubmed.ncbi.nlm.nih.gov/16953958/).

This phenomenon appears across many countries. Younger students in a grade often perform slightly worse academically and are more likely to be diagnosed with attention disorders, partly because they are simply less mature than their classmates.

Once again, this is not astrology. But it is how institutional structure x date of birth can affect you.

Conclusion

Look, if someone believes astrology is divinely inspired, I don’t expect two-pages and a handful of hyperlinks to studies they probably did not click on to change their mind. I expect them to call me a Capricorn and suggest crystals.

But I also know a lot of astrology and tarot lovers who don’t take it seriously, and who would find the information above fascinating. After all, many of the greatest scientists of all time understood the world in paradox. V.S. Ramachandran, for example, views religion and science as distinct, believes in both despite contradictions. I do too, minus astrology.

Timing of birth matters. And that is more fascinating to me than horoscopes.

It’s not zodiac symbols, it’s institutions. And a bit of biology. But, again, that biology is due to enviromental factors, and I have never heard a New Ageist / Hippie ask me if I was born in the Northern or Southern hemisphere.

More important than astrological sign is IQ average. Sadly, IQ scores have been declining in many countries, suggesting people may actually be getting less capable of complex reasoning on average. This equates to more people buying into astrology and bad politics. Which is depressing. But at least it has evidence.