Genetic study finds the brain is most similar to — testicles?

AVEIRO, Portugal — For men who spend too much time thinking about the opposite sex, they are often accused of “thinking with the wrong head.” Ironically, a new study reveals when it comes to the human brain, the organ it shares the most in common with are actually the testicles.

Researchers in Portugal say the brain and a man’s nether regions have a remarkable number of genetic similarities. Oddly enough, this isn’t the first time scientists have suspected that the brain and the testis have more in common than it would seem. In fact, a previous study discovered sperm quality can positively affect intelligence in men.

In this report, a team from the University of Aveiro examined the proteins in 33 different tissue types. Those included samples from the heart, intestine, cervix, ovaries, and placenta.

“Surprisingly, human brain and testis have the highest number of common proteins, compared with other human body tissues,” researchers explain in the journal Royal Society Open Biology.

Not only are these two regions similar, they’re practically identical! The study finds the human brain consists of 14,315 different proteins, while the testis consists of 15,687. After comparing the two tissues, study authors found they have a staggering 13,442 proteins in common. Researchers also took a closer look at the different genes throughout the body and discovered these two are even similar there as well.

“A large-scale analysis of the expression of 33,689 genes in 15 human tissues revealed that human brain and testis shared the greatest similarity in gene expression,” the team writes.

Brain, testicles even have the same barrier to keep them healthy

Although the brain spends its day hard at work thinking, and the testicles sit around waiting for sex, researchers note both have extremely high energy demands. Due to these energy requirements, both are very vulnerable to oxidative stress — the imbalance of free radicals and antioxidants in the body which can damage cells and tissue.

To defend against this, the study finds both areas have created their own blood barrier to keep out harmful substances. In the case of the blood-brain barrier, this protective layer prevents toxic elements from reaching brain tissue. For the blood-testis barrier, this shield is a vital component of male fertility.

As for how the brain and the “balls” became so much alike, study authors suspect a process called speciation had something to do with it. Simply put, this is the process by which new species form during evolution. Researchers believe the same pressures of natural selection that created modern day humans in the first place also helped to shape how the brain and testis evolved too.

“This is an underexplored topic, and the connection between these tissues needs to be clarified, which could help to understand the dysfunctions affecting brain and testis,” researchers note.

Also, for women who may be thinking this is just a male oddity, researchers find female brains share this ball-like quality too.