It has always raised questions about why the male gonads (testicles, nuts, balls) hang outside the body in a precarious unprotected sack.  Considering their importance to reproduction, they sit outside the body, fully exposed to the elements.  It seems counter-intuitive at times.  On top of that, there is great debate on whether they were ‘designed’ that way or ‘evolved’ that way.  As a sex educator, I won’t digress into the design/evolve debate despite sometimes using the word ‘designed.’ However, at the start of this post, let me be clear that the word ‘designed’ is used synonymously with ‘purpose’ because at the heart of a sex educator is the desire to educate people on the purpose of their bodies, specifically around sexual health.

Were they designed or evolved to be this way?

But suppose you are interested in the hypothesis surrounding the ‘design/evolve’ debate.  In that case, the leading one proposes that the descent of testicles in humans and in many other mammals evolved to provide a situation specific to the activation of sperm.  This poses the question, if reproduction was of paramount importance, why did something considered vital to reproduction end up outside the body, vulnerable to damage?

For 60 years, there has been debate and studies on the adaptive significance of the scrotum.  The leading interpretation is that the scrotum descended outside the body to provide a cold environment for optimal spermatogenesis.  In fact, in 1978, a researcher named Bedford argued that the epididymis, located inside the testicle, functions much like a cold storage unit for sperm.  He claimed that the epididymis forced the evolution of the descent of the testicles outside the body. 

For most mammals, we know that the formation and storage of viable sperm require testicles to be maintained below body temperature.  In addition, it has been proven that the maintenance of viable sperm requires temperature below body temperature.  So, for sperm to form, grow, and mature, it needs a temperature roughly 2-4 degrees below general body temperature.

Even the anatomy of the testicles aims to help with temperature maintenance.  The cremaster muscles hug the testicle and spermatic cord and are shaped like a teardrop.  When the cremaster muscles contract, they pull the testicles closer to the body.  When they relax, the testicles drop away from the body.  So, when you feel cold or the outside temperature drops below the ideal temperature for sperm viability, the cremaster muscles contract and draw the testicles closer to your body to keep them warm.  When you feel hot, the cremaster muscles relax and drop the testicles away from your body to help keep them cool. 

Those cremaster muscles also work as a protective mechanism for the testicles.  During arousal and intercourse having a pair of testicles hanging really low increases the risk of damage.  Again, blunt force trauma comes to mind.  To minimise this, the cremaster muscles contract and pull the testicles close to the body during sexual arousal.  Kind of think of it as tucking themselves up behind the penis for protection during thrusting.

Another element of design/evolution/purpose is the skin thickness of the scrotum.  Scrotum skin is thin to promote heat dissipation.  In addition, how the arteries and veins are positioned provides additional cooling/heating advantages for the testicles.  Even how one testicle usually hangs lower than the other is said to increase the surface area of the scrotum for heat dissipation or cooling.

Why are they so sensitive?

If you ask any man that has been kicked ‘in the nuts, ‘ they will tell you that it is a pain like no other.  It brings them to their knees, takes the breath out of them, tears to their eyes.  It is widely known that it is the most vulnerable part of their body.  And, how often are we told that the most effortless self-defense mechanism is to kick them in the balls?

So, why are they so sensitive?  Well, the easiest way to be protective of something is to make it incredibly painful if they are hurt, right?  That age-old motto “you’ll only do it once to be a quick learner” rings true in this scenario.  The testicles are chock full of nerves, all with different purposes.  Some help regulate temperature, some help pull them out of harm’s way, and some are purely there to make you want to hurl your guts up if they get hurt.  All those nerves have neural pathways that track backward into your body towards your stomach.  This is why when your testicles get hurt, you feel that pain deep within your abdomen. 

It does beg the question of why ‘grab life by the balls’ means to seize the day and be mature in a given situation or problem.  In fact, grabbing the balls will stop any man in his tracks, and I’m sure most men will say their life stops temporarily and flashes before their eyes.