Our brains have more in common with the testicles than you ever wanted to know
This charming saying about men thinking with their lower regions has taken on new meaning. A new study has found many disturbing similarities between men’s brains and the bowels of their scrotum.
“The brain and testes have the highest number of common proteins, compared to other tissues in the human body,” a team led by biomedical scientist Bárbara Matos of the University of Aveiro in Portugal. writes in his new journal.
While the brain has a very complex role – controlling our bodies, receiving and interpreting signals from the sensory organs, not to mention all of our thoughts and feelings, the human testes only have two main functions – the production of sperm and hormones. (Although many of us should be forgiven for attributing these gonads to our own thoughts and feelings as well.)
Previous studies have suggested that there are links between sexual dysfunction and brain disorders, and even between intelligence and sperm quality. Of course, such links don’t mean much on their own, but now the team of researchers from Portugal and the UK have found an explanation for their existence.
They compared proteins from 33 types of tissues, including the heart, intestine, cervix, ovaries and placenta, and found that the testes and the brain share 13,442 proteins in common. This is corroborated by gene expression studies showing that these two distantly located organs share the highest number of genes among all organs in the body.
Taking a closer look at the shared proteins most highly expressed in these tissues, Matos and his colleagues found that they are primarily involved in tissue development and cellular communication. These shared proteins make sense when you consider how similar the two tissues are in many ways, the team explains.
Both the brain and the testes are hungry for energy to fuel very demanding processes like thinking and producing millions of tiny sperm a day. So both organs have specialized cells to support the hard-working neurons in the brain and the germ cells in the testes – to keep them well nourished and physically comfortable.
Also, although they are cells with very different purposes, neurons function in many ways in the same way as sperm. Both cells have important tasks of moving things from inside themselves to their outside environment – a process called exocytosis.
This is how brain cells transmit neurotransmitters to each other. In semen, the same process is used to release important fertilization factors.
In neurons, exocytosis is also involved in the growth of their small branched arms, collectively called neurites (dendrites and axons), while in the sperm, this process allows its bowels to fuse with an egg.
“It is an under-explored subject, and the link between these tissues needs to be clarified, which could help to understand the dysfunctions affecting the brain and the testes”, the team wrote.
These findings raise many questions, the most obvious being how did two such disparate organs come to share so much in common? Researchers suspect this is because they are both heavily influenced by the process of speciation.
Just as animals separated by millions of years of evolution and which evolved half a world away from each other can develop the same traits, so do different tissue groups within the human body.
For example, unlike most other animals, koalas have confusing fingerprints similar to ours – thanks to the obvious selection pressure exerted by our need (well, that of our primate ancestors) to seize the trees – despite 70 million years evolution between us. This process is called convergent evolution.
In this case, the researchers propose that the same selection pressures involved in maintaining species distinct from each other can be imposed on the two organs, causing them to evolve in a convergent fashion. They point to 60 genes encoding proteins, unique to humans, many of which are found in the brain and testes.
“The highest expression levels in the cerebral cortex and testes suggest that these genes may contribute phenotypic characteristics exclusive to humans, such as improved cognitive abilities,” the team wrote.
While testicular owners might not be so thrilled with these biological disclosures, the rest of us might be inclined to think that it makes a lot of sense. But before we go too far, this finding means that female brains share these similarities with bullets as well.
Their research has been published in Royal Society of Open Biology.