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Did a study find men growing beards or long hair have smaller testicles? No, that's not true: several tabloid newspapers misinterpreted the results of a joint study by the University of Western Australia and the University of Zurich about the relationship between the size of sexual ornaments and testes in primates and wrongly assumed it said something about the difference between individual humans.

The study was titled "Sexual ornaments but not weapons trade off against testes size in primates" (you can read it here) and it only compared testicle size and "sexual ornament" size between different species of primates, it did not look at that relationship within a single species. The paper even quotes two other studies finding the opposite relation within certain primate species (proboscis monkeys and mandrilss to be exact). It made no claims about differences between individual humans at all.

An example of the incorrect interpretation can be found in an article published by the Daily Mail on April 10, 2019 originally titled "Why men with beards and long hair have the smallest testicles" (archived here) which opened:

Researchers from the University of Western Australia found males quipped with physical ornaments - such as beards, manes or capes - tend to have smaller gonads.

Users on social media only saw this title, description and thumbnail:

Why men with beards and long hair have the smallest testicles

Researchers from the University of Western Australia found males quipped with physical ornaments - such as beards, manes or capes - tend to have smaller gonads.

The site later changed the title to "Why the 'showiest' males have the smallest testicles: Primates including humans only have enough energy to grow big testes OR an impressive beard or mane, study claims", which is somewhat less incorrect but the article still opens by making an incorrect claim about humans:

Men with longer hair and beards may have smaller testicles than those who struggle to grow facial hair, a study claims.

It found that humans, and more than one hundred other primates, face an evolutionary dilemma when it comes to their genitals.

Teams from the University of Western Australia, who carried out the research, say a male 'can be well-adorned or well-endowed, but it's hard to be both'.

Animals can either invest energy attracting females with impressive manes and beards or spend their energy growing larger gonads.

We contacted Prof. Dr. Stefan Lüpold of the Department of Evolutionary Biology and Environmental Studies at the University of Zurich, one of the authors of the original paper. He provided us with following statement:

Our study compared the expression of male badges of status and size of the testicles between different species of primates. Some species have large testicles for their body size but are not very ornate, while others have massive manes, capes or fleshy swellings but, in turn, relatively small testes. We did not compare relationships within individual species like humans. It would thus be wrong to jump to the conclusion that bearded men have smaller testes than shaved men. After all, testes do not grow when we shave. It is also important to realize that shaving a beard does not really change the fact that it keeps growing in the first place, so from an energetic standpoint, it hardly makes a difference.

In fact, it is even possible that relationships within individual species show the opposite, and this is not unusual for such comparative studies where average values of each species are compared. For example, as mentioned in our article, both proboscis monkeys and mandrills actually show the opposite trend to our overall findings, which highlights the fact that we should not use a between-species comparison to draw conclusions about the difference between individual human males or males of any other species.

Study co-author Dr. Cyril Grueter of the School of Human Sciences at the University of Western Australia emailed us this additional feedback:

We looked at correlations between natural ornamentation and testes size in a comparative study across 100 primate species (with hmans being one of those). So each species contributed two data points, one for testes size and one for ornamentation. We obviously can't jump to the conclusion that bearded men have smaller testes. No such within species measurements were taken. Claims that shaved men have smaller balls are complete nonsense.

The Daily Mail was far from the only site to incorrectly report on the study. Here are several other sites that also got this one wrong:

Blokes who can grow beards 'have smaller testicles than baby-faced peers'

Scientists found blokes can be 'well-adorned or well-endowed' - but not both MEN who can grow beards may have smaller balls than their baby-faced peers, scientists have claimed. New findings suggest blokes can be "well-adorned or well-endowed" - but not both. And they suggest it's because doing both takes too much energy.

'Showy' men with beards have the smallest testicles, study finds

Know a man with long hair and a beard? He's probably got small testicles, well, at least according to a new study. Researchers from the University of Western Australia and the University of Zurich have found that male primates can either be 'well adorned or well-endowed - but not both'.

Men with beards more likely to 'have smaller testicles than those without'

Men with bushy beards and long hair may have smaller testicles than their counterparts who struggle to grow facial hair, suggests a new study. This bold claim was made by a team from the University of Western Australia and the University of Zurich, who have studied the gonads of more than 100 different male primates as part of their research.

Males with beards have smaller testicles: study

Beards are the new Beamers. Even if you can't really judge a guy's manhood by his wheels, you just might be able to do so by his scruff: According to a new study, facial hair may also be a sign of small balls.

Study finds that men with larger beards have smaller testicles | JOE.co.uk

18 hours ago A new study undertaken by researchers at the University of Western Australia and the University of Zurich suggests males with 'showy' masculine attributes, such as beards, may have smaller testicles than other males.

Men With Beard And Long Hair Have The Smallest Testicles, Study Finds

by Mike Kennedy 1.6M Views Men with longer hair and beards may have smaller testicles than those who struggle to grow facial hair, a study claims. It found that humans, and more than a hundred other primates, face an evolutionary dilemma when it comes to their genitals.

It certainly takes balls to come up with such a hairy interpretation of a scientific study. To us this suggests the relationship between writing about scientific studies and actually reading them might be less strong than it should be.