Must Sex Lead to Death?

Never heard of the dasykaluta?  The phascogale?  Don’t be surprised.  Small marsupials rarely get favorable media attention. Look at how we treat mice.

But these otherwise insubstantial, arthropod ingesting (that includes roaches) rodents deserve our interest and perhaps our piteous respect. For they show the lengths evolution can go to keep a species going . In this case, the wholesale obliteration of all marsupial males.

Immediately following  frenzied sex.

The Problem

The insects that these small marsupials live on swarm and increase in number at very specific times of year.  Your food source gets really plentiful, but only for a short short period.

The Solution

What biologists like to call “female led” evolutionary reproductive cycles.  The mating season is brief.  Sometimes, through the intervention of biological clocks, it consists of just 24 hours.  For the whole year.

Reproduce that day or nothing.  Talk about pressure.

And the females have the option during these marathon communal orgies  to mate with any male they choose.  Which they do, repeatedly.

The first result – massive sperm competition.  Those most capable of getting there first and foremost get their genes reproduced.  The rest will never see or know any offspring.

Yet they won’t anyway.  At the end of the session, phase 2 takes place – all the males die off.

Suicidal Reproduction

Semelparity is the term used to define reproduction followed by suicide.  Though most of us might think the term was invented for kinky science fiction novels or Marvel Comics calendars, it’s fairly common practice on earth.  It is especially popular with fish.  We just don’t think of it as happening to our fellow mammals.

But once these males have engaged in their biologically clocked, environmentally conditioned and evolutionarily prescribed mating frenzy, they drop dead.

How? It’s actually a bit complicated, but steroid levels – major stress hormones – surge to remarkably high states.  Effectively, the brakes come off.  Partially as a result, testosterone levels reach heights pop producers term  “off the charts.”

What’s the end result of superhigh steroid and testosterone levels?  The phrase used is “immune collapse.” Reproduction over, the males just fall apart, experiencing a quick, collective end.

The females of course all stick around.   Parenting gets done by Mom.  Alone.

Why Is Suicidal Reproduction So Effective?

The food supply is constrained.  When it appears, so does sex and reproduction – really quickly.  Everybody competes. And the competition is out in the open – literally. The females can get to know all the males they want, and remain very unconcerned about what happens to them afterwards. The winners really win.

It’s the kind of scenario some entrepreneurial economists might find proper and just in specific human circumstances – except for twinges of regret from some  male commentators.  But then again, human males perhaps overrate sex.  Plenty of species have the capacity to reproduce asexually – especially when there are famines around.

What Does This Semelparity Say About Evolution?

Life on earth is extraordinarily varied and adaptive.  What counts is that the species survives – anything that’s thrown at it.

Individual don’t matter much.  In many ways, they hardly matter at all.

What counts is keeping diverse genes in the population.

What Does This Say About Stress?

Several things.  That too many stress hormones can kill you – sometimes rapidly.  In human examples, twenty five year olds left without food alone at sea may experience heart attacks and watch their hair turn white – overnight.  Pushing the pedal and reaching for extremes may work on the species level, but it’s hell on individuals.

Second, it’s obvious that for some mammals there is such a thing as too much testosterone.

The human story of testosterone is quite different.  Fans of the multibillion dollar testosterone “replacement market” should take note.

We don’t know the long term effect of all those extra sex hormones.  And we certainly must look at single hormones in context.  It’s become pretty obvious over the last few years that looking at testosterone levels in human males and females – without considering estrogen, often produced from testosterone – is like trying to understand a language with the  vowels stripped out.

These are complicated systems.  How they interact is what counts.  As to how most of all that really works,  we only have a couple of clues.

Pity the Poor Mammals

Biology is  inevitably highly inventive.  Life on earth is violent, nasty, brutish and short.  Getting the best genes to survive unknown adversities may explain the importance we ascribe to human sex.  That’s particularly true when we look at “sexiness” – and why the bad girls and bad boys are so devastatingly attractive.

Sex and death – they really do go together.
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