It was from the book “Sperm Wars” (you can find it on Amazon) and the following article from Keep The Doctor Away (a British online medical journal):
Evolutionary ‘Sperm Competition’ Discovered
13/02/2007
Some breaking news, just in time for Valentine’s Day: Researchers have identified something called ‘sperm competition,’ evolved by men to ensure a genetic future in spite of the possibility of infidelity by their partner.
Natural selection is generally thought of as something that happens prior to – and in fact leads to - the Big Event. We are attracted, for example, to physical features that tell us our partner is healthy and will give us a fighting chance to carry on our genetic lineage.
But a new article in the February issue of Current Directions in Psychological Science suggests that the human male has evolved ways to pass on his genes after the Big Bang as well, a phenomenon dubbed “sperm competition.”
In their article, Todd Shackelford and Aaron Goetz at Florida Atlantic University describe this as “the inevitable consequence of males competing for fertilizations.”
For a monogamous species, sperm competition may seem beside the point. But according to the authors, extra curricular copulations (i.e. affairs) appear to be a significant part of our ancestral history and could, evolutionarily speaking, spell disaster. A man whose partner engages in some off-sides dalliances may be unwittingly investing his resources – food, protection, credit rating – in a genetically unrelated offspring.
Competition may even affect sperm count, say the authors. The more time men spend away from their partners (time that their partners could have spent giving other males genetic opportunities), the number of sperm in their ejaculate increases upon their next copulation.
The authors even took the liberty of constructing artificial phalluses, which they found actually removed an ejaculate-like substance from an artificial vagina. This could indicate that the penis acts as a ‘squeegee’ to remove an interloper’s calling card.
But according to the authors, sperm competition is not just biology: sexual partners report that men thrust more deeply and quickly following allegations of infidelity, possibly bungling the aspirations of rival sperm. The same periods of separation that increase a man’s sperm count may also help to explain the increasingly lustful feelings men develop after long periods apart from their mate. That is, the human male may want to copulate as soon as possible as insurance against possible womb-stealing by a genetic rival.
The authors compare sexual adaptation to a Cold War phenomenon: “Sexual conflict between males and females,” Shackelford and Goetz describe, “produces a co-evolutionary arms race between the sexes,” in which an advantage gained by one gender leads to counter-adaptations in the other.
They speculate that research may move beyond male adaptations to, for example, see if females have developed biological or behavioural mechanisms to increase retention of sperm from men with the most favourable genes. But that’s for another Valentine’s Day.
If anybody wants to double-check the original article, here is the link below: