Sex Drive and Contraceptives
Evolution’s primary mechanism for ensuring procreation in humans has always been sex drive. The higher the drive, the more likely humans would have been to procreate.
This changed with the arrival of contraceptives. In societies where they’ve been easily available and widely used for decades, a massive environmental change has taken place.
In such societies now, an extraordinary sex drive no longer confers an evolutionary advantage to those thus endowed, since it doesn’t necessarily result in more offspring than a moderate one. At the same time, milder sex drive will not be penalized by natural selection (it will not be selected against), since it won’t necessarily lead to fewer children.
The consequence of this might be that sex drive will diminish. It will not disappear, as of course it will still be necessary for humans to engage in sex. But it will taper until a new optimum is reached. Perhaps something like the enjoyment we derive from eating. Having an orgasm when biting into an apple would not increase our Darwinian fitness (it would in fact be detrimental), thus there’s no reason for it to evolve. Evolution has optimized the level of enjoyment we experience when eating, so that it’s exactly what’s required: with less pleasure we’d be at risk of being malnourished, and more pleasure would not translate into better nourishment and health; thus there’s no mechanism, no “justification”, for it to increase further.
Why would something that’s already evolved taper under different selection pressures if it’s not causing any harm? Even if our sex drive were not at all costly to the organism in some way, it would taper. The reason is that keeping such a fine-tuned or precise mechanism necessitates a rather singular configuration, as opposed to one less well calibrated for the purpose. In other words, the right phenotypic “structure” for the intense sex drive and pleasure still predominant in humans is perfectly “designed and assembled” for it to operate that way. Thus, random mutations are far more likely to diminish its efficacy than to reinforce or enhance it. This has of course always been the case. The difference is that now, thanks to the widespread availability and use of contraceptives, such mutations will not be selected against (until a new optimal level is established, as mentioned above). To reiterate, they will not be selected against because a couple with moderate sex drive is not likely to have, on that account alone, fewer children than a couple with a very strong one. And thus gradually a less intense sex drive, coupled with less intense sexual pleasure, will become more prevalent in the population.
But people will continue to have different numbers of children, and so evolution will not rest. Now other traits may become relevant in our differential fitness. Assuming such traits to be at least partly genetic, they will tend to be selected for and eventually predominate in future generations. These are traits that would make people more “immune” to birth control, such as, for example, improper handling of contraceptives or negligence in their consistent use, a strong desire to have children, or religious beliefs. Also, whatever traits are selected as new key differentiating factors in the number of children people have, will tend to intensify over the generations.
As people become increasingly “resistant” to birth control, sex drive could again, depending on the circumstances, become a key differentiator in the number of their offspring, in which case it would tend to increase again. For example, let’s suppose that carelessness in the use of contraceptives (which would be related to conscientiousness, one of the Big Five personality traits, all substantially heritable) ends up conferring the biggest evolutionary advantage and begins to prevail in the population. It would be like going back to an era when no birth control existed, an era in which varying sex drive would again play a key role in the varying numbers of children people have.
This hypothesis shows how our culture and behavior can influence our evolution by creating new selective pressures (the use of contraceptives altering the genetic makeup of future generations). It also assumes a nearly inescapable genetic influence on our behavior. Some prominent thinkers believe that there’s nothing inescapable about it. For example, Richard Dawkins and Steven Pinker propose that our use of contraceptives illustrates our capacity to override the urges of our genes.
Dawkins — The Selfish Gene (30th Anniversary edition):
We, that is our brains, are separate and independent enough from our genes to rebel against them. As already noted, we do so in a small way every time we use contraception. There is no reason why we should not rebel in a large way, too.
Pinker— How the Mind Works:
Well into my procreating years I am, so far, voluntarily childless . . . ignoring the solemn imperative to spread my genes. By Darwinian standards I am a horrible mistake . . . But I’m happy to be that way, and if my genes don’t like it, they can go jump in the lake.
I don’t think such a capacity really exists, and at any rate those examples are not persuasive, since our genes just haven’t had time yet to catch up with the new environment that contraceptives have brought about. A more suitable example would have been if they had stated that we can easily decide, for whatever reason, to wholly abstain from having sex — but of course that’s not the case.
Sam Harris has provided an equally uncompelling example of how we can override the imperatives of our genes:
If we were true Darwinians, every man’s deepest desire would be to continually donate sperm to sperm banks so that he could sire thousands of children for whom he’d have no further responsibility. If we really viewed the world from the perspective of our genes, no other answer to the question “How should we act in the world?” would seem more fitting.
Here Dawkins himself shows far more sense: