Life is a continuous struggle – is there anyone who’d disagree? Life is a race, a race of the fittest to survive as Herbert Spencer observed 150 years ago after reading Charles Darwin’s “On the Origin of Species” opus. And it starts with the sperm. In most animal species the male gametes, also known as spermatozoa or spermatozoons, vastly outnumber the eggs and often the ratio is millions to one. It is therefore only an incredibly tiny percentage of sperm that are successful and meet, enter, and fuse with the egg cell nucleus to start a new individual.
In mammals the sperm’s goal, the egg cell, is usually quite a distance away and the race is on as soon as the sperm are released into the female genital tract. Little is known if there isn’t perhaps already some kind of selection prior to the sperm being released, but once on its way the steeplechase with physical and chemical hurdles to overcome has begun. The female makes it real hard for the little sperm to reach their goal. As with all races there are tactics and foul play. The fastest sperm expend a great deal of energy, but are not necessarily the toughest and longest-lived. The slowest, on the other hand, which always form a considerable component of the sperm’s total volume, are often malformed and abnormal either morphologically or physiologically. Why the female makes it so hard for the sperm is, of course, her way to make sure that her egg gets the best possible suitor.
As if they realized they had no chance of coming first, some sperm soon ‘give up’, cluster together and form a barrier, known as the ‘sperm plug’, which makes it harder for a second or third batch of sperm (possibly even from a different male) to make its way up to the egg. In other words, they “sacrifice” themselves to make sure that at least one of their batch (the fastest away) can get to the egg first. They “trip up” and interfere with sperm that enters the genital tract later and the term “kamikaze sperm” has aptly been coined for them by the Irish psychologist P.G. Hepper. The opposite strategy, namely a gigantic and powerful sperm cell, itself incapable of fertilizing an egg, but carrying the tinier and weaker spermatozoans to their target like an airplane carrier the fighter planes to the combat zone, operates in certain species of snails – but then again, snails have such an unusual sex-life anyway and often do things a bit differently that they deserve having their own blog sometime.
But what about humans? The sperm of human males contains more abnormal and malformed sperm than one encounters in almost any other mammal. This could mean only one thing (or could it?): the huge number of kamikaze sperm are designed to make sure that another man’s sperm does not reach and fertilize the egg – an anti-cuckoldry device suggesting it evolved out of widespread promiscuity. But stop: the huge number of abnormal sperm could be an indication of the exact opposite, namely ancestral monogamy. Since in a monogamous relationship there is no great need to have 100% fit and fast sperm, a large number of abnormal sperm can be tolerated. After all, there is no competition and thus no need to be faster, stronger, and longer lived than a competitor’s sperm. For a male in a monogamous relationship to get it right sometime and to propagate his own genes, there are ample opportunities. And so, there you are: human faithfulness “on the block” and some food for thought. It’s your choice which theory to accept.
© Dr V.B. Meyer-Rochow and http://www.bioforthebiobuff.wordpress.com, 2017.
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