When asked which human organ shares the most similarities with your brain, most would tend to point towards the gut, which is often referred to as the 'second brain' because of its large number of neuronal connections it.
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But according to a study conducted by researchers from the University of Aveiro in Portugal and the University of Birmingham in the United Kingdom and published on Wednesday 2 June in the journal Open Biology, there are also surprising similarities between your brains... and your testicles.
Brain and testicles, with unexpected similarities
This in itself is not really a surprise: previous research had already pointed to possible links between intelligence and sperm quality, or between aspermia and psychological disorders, as noted by the Science Alert website.
As part of this study, the researchers compared the proteins of cells from 33 body organs. The result was that the brain and the testicles have 13 442 proteins in common, more than any other organ observed.
As these proteins play a role in the development and cellular communication of both organs, the researchers went further in their analysis and found other similarities: the brain and the testicles are both very energy-intensive organs, one because of the cognitive tasks it has to perform, the other for the continuous production of sperms.
The two organs, isolated from the rest of the body by the blood-brain barrier and the blood-testicular barrier respectively, also function quite similarly. Neurons, like testicular cells, engage in exocytosis, a process by which the cell releases large biomolecules through its membrane. This allows brain cells to communicate with each other, and sperm cells to fertilise an egg.
The speciation process involved?
But why do the brain and testicles have so much in common? Researchers suspect that the cause of these similarities is the involvement of both organs in the speciation process, the evolutionary phenomenon by which new living species are formed from common ancestors.
The researchers point to 60 genes unique to humans, many of which are found in the brain and testes.
The higher expression levels in the cerebral cortex and testes suggest that these genes may contribute to phenotypic features exclusive to humans, such as enhanced cognitive abilities.
