So, what sort of scientist is James Rilling, who teaches a course called The Anthropology of Fatherhood, at Emory? Well, according to the comments about him on RateMyProfessors.com "he's interested in the subject, he can be funny, and he's nice. I recommend this class", although he does appear to rely heavily on multiple-choice tests and rote learning.
Ten years ago, he was one of the team that found the brain has areas connected with altruistic behaviour. This was a useful piece of science because it explained the paradox that humans sometimes behave in ways that benefit others and not themselves. I'm less convinced by his more recent experiment. That there is a connection between testicles and fatherhood has been known for millennia. But that involvement is usually very brief relative to the time spent being a father.
Rilling obviously has a gift for media-friendly research. This latest one has been a boon for headline writers from: "Aw, nuts! Nurturing dads have smaller testicles, study shows" to "When size matters" and "Do you have the balls?"
But ultimately this is bad science at its worst. The small sample size alone is probably enough to invalidate the result. Rilling examined just 70 fathers for his study, which used MRI to gain its crucial data, by the way. The study also shows only correlation and, as real scientists repeatedly try to explain to non-scientists - sequence does not mean consequence.
This was the mistake made by the rooster who, having noted that every time he crowed the sun came up, drew the conclusion that he was responsible for the sunrise.
The speed with which the story made its way around the world demonstrates how happy we are to be distracted by an attention-getting snippet that even if it were true, would contribute nothing to our understanding of people and how we behave.
Because, more than anything else, the experiment raises the question: So what? What does this dubious result tell us that can be of any practical use? Ladies, carry your calipers with you?
The "result" merely reinforces stereotypes about manliness and parenting. The implication - never at any point spelled out - is that if you are a nurturing father you are less of a man than someone who is not involved. And that is not the modern reality.
Most of the fathers I know are trying hard to be good at the job, especially the nurturing side. They need support and encouragement, not someone telling them their behaviour is merely a consequence of their physiology.