We can learn a lot about human sexuality by studying humans; however, it is important to keep in mind that humans are just one animal species among the millions of species with whom we share our planet. To fully understand human sexuality, we must therefore examine it against the broad context of animal reproduction in general. In other words, the stories told to youngsters about the birds and the bees are far more germane and relevant than the people telling them might care to admit. Let’s take a look at some of the many ways that life on this fantastic planet keeps itself going from generation to generation.
If animals could talk, most any animal you asked would tell you that human sexuality is more than a little aberrant by their standards. As I just said above, fully appreciating just how different human sexuality is requires setting aside our human-centric thinking to look at humans as just another animal among all animals. Only 3% of mammals are monogamous and this percentage plummets when one considers the many millions of animal species in the world. This one trait alone places humans far beyond the +/-2 standard deviations from the mean that is generally considered to be the “normal” range for statistical purposes.
Comparing multiple sexual behaviors only increases the abnormality of human sexuality. Human females have evolved concealed ovulation, are sexually receptive at all times during their cycles and experience menopause (cessation of fertility long before death). Most human copulation occurs horizontally with the male on top of and facing the female (missionary position). We wear clothes, which cover up our built-in sexual signals while at the same time wearing cosmetics such as makeup and perfume to enhance our sex appeal. Our sex normally takes place in private. We have recreational sex; in fact, we have most of our sex for the sheer fun of it with no intention of reproducing. Modern technology has even allowed us to prevent conception from taking place. Any one of these is an oddity among animals and no species besides homo sapient possesses our truly unique package of sexual traits.
Why?
The best way to answer this question is to see how natural selection works followed by a look at some of the many reproductive strategies animals use. We’ll then look at some of the pressures facing human men and women and the lengths humans and animals will go to reproduce. This will provide the foundation we need to narrow our focus toward humans in the coming weeks.
No Looking Back
Human sexuality has been evolving for millions of years and most closely resembles a combination of chimpanzee and bonobo sexuality plus some additional, uniquely human traits. From how human eggs get fertilized to nursing infants and unequal parental investments, evolution has come too far down this particular path for it to change direction or backtrack, barring both some compelling reason to change and plenty of time to make that change. Put another way, I hope you like your evolved sexual traits because those are the sexual traits you’re stuck with.
Why Sex?
All joking aside, sex is a costly, messy affair. It would be much easier to reproduce asexually like bacteria. Imagine being able to reproduce at will by simply splitting yourself in two. Mutations introduced by imperfect gene copying and either encouraged or suppressed by environmental factors drives evolution of the species. No more dating, courtship, sex, morning-after blues, child rearing, marriage, divorce, nothing. Asexual reproduction is simplicity itself. It makes sense for simple organisms that may not live long enough to have a reasonable chance of finding a suitable mate.
Complex organisms such as humans and most animals benefit from sexual reproduction because it creates genetic diversity, particularly when long life spans are involved because this limits opportunities for mutation and evolution. Humans tend to be strongly attracted to people whose genotypes are very different than their own, the more different the better. Mixing these disparate genotypes can give the child a stronger immune system, which helps the child pass on its genes and continue the parents’ genetic legacy. At least that’s how it works in theory. Environmental factors and changes can snuff out an otherwise promising genetic lineage while creating conditions for a previously undesirable lineage to flourish. Those individuals best suited to current environmental conditions have more children. Remember that the ultimate point of life is to reproduce.
Sexual reproduction also creates conflict because what’s in each parent’s genetic interests is often contradictory. The battle of the sexes is a very real phenomenon that exists for very good reasons, as we saw in a previous article. This conflict may seem awful, particularly in the heat of the moment, but it serves a strong evolutionary purpose: Those best able to mitigate or resolve their conflicts enjoy increased reproductive potential. It there comes as no surprise that humans couples who have devised mutually agreeable conflict-resolution strategies and/or who have similar ways of responding to various situations tend to remain together the longest. Even so, sexual reproduction in humans favors males who court many females, who respond by being highly selective. This explains (among many other things) why women placing personal ads seeking to meet men can usually count on receiving far more responses than men who place ads seeking women.
Natural Selection
Life exists to beget life. Natural selection therefore favors adaptations that improve the odds of successful reproduction, defined here as both having more children and helping those children survive to have children of their own. These adaptations can be physical, such as breasts that mimic buttocks and thus serve as sexual signals. They can also be mental and/or psychological. For example, the average human would be hard pressed to recognize individual penguins in a huge Antarctic flock let alone tell which chick belongs to which parent. You can bet your bottom dollar that penguins can recognize each other and discern their young in a penguin crowd just like humans can spot a familiar face in a human crowd. I can’t imagine any species whose children require parental care lacking the ability to recognize individuals because that would lead to parents raising just any child, a clear no-no in evolutionary terms under most circumstances.
This is a quantity game; parents who can have the most offspring are theoretically the ones who are best suited to their current environment. Any change in the environment could strip a given set of genes of its favored status and replace it with a different set. Extinction occurs when insufficient numbers of individuals with any sets of genetic traits exist to repopulate the species. How exactly parents manage to have the most possible children is wide open to question- and therein lie the seeds of parental conflict. Please review my article on conflict in the home for more details.
Natural selection chooses among currently available options. Two parents represent two sets of genetic traits, or options and their child represents a third trait that combines the first two. This is the menu open to natural selection. Two parents won’t create a child with completely different genetic material, meaning that natural selection cannot simply invent a new option any more than patrons at most restaurants can’t cook their own food or invent special dishes.
I must take a short detour to explain that words such as choose and invent usually imply deliberate, conscious action. Applied to natural selection, these words can imply the presence of an unseen super-intellect, which can be referred to as a god or super-intellect. I don’t necessarily mean to imply this because no conscious action, blueprint, or designer may be necessary for natural selection to occur in at least some if not most or even all cases. For example, the mix of parental genes inside a child could predispose it to store extra body fat. If the environment cools, then this child and anyone else with a similar trait may be better able to survive and have children of their own. If the climate warms, then this child and others like it may be unable to survive long enough to reproduce. This “choice” may be an example of natural selection with no guiding intellect or design behind it. Then again, it could be proof positive that some super-intellect (God) is indeed real, As for “invention”, imperfections in gene copying can introduce mutations, or changes in the child’s genes that are not present in the parents’ genes. Imagine transcribing a letter and omitting or misspelling a word. That is completely different than writing a completely new letter from scratch without trying to faithfully copy the original.
Reproductive Strategies
Let’s take a look at some of the many ways animals reproduce.
No Contact
Many female fish lay eggs directly into the water, whereupon the male releases a cloud of sperm. There is no actual contact between the mates. This works well because many of the shapes best suited for various underwater environments may not lend themselves to actual coitus. Some fish species guard their eggs and protect the hatched young while others swim away leaving the eggs to their fate. It makes little sense to guard a large clutch of eggs where the sheer numbers all but guarantee successful reproduction. On the other hand, fish who lay fewer eggs and/or whose eggs have longer gestation periods may gain by hanging around to protect their offspring. The basic formula is simple: Investing energy in any one egg that results in less protection for other eggs and lower resulting odds of reproduction makes no sense. Remember, evolution is a numbers game.
Single Queen
Ants, bees and termites have a unique caste system where sterile workers tend to the young, grow food (ants and termites were the world’s first farmers) and keep the colony clean and maintained. Soldiers, also sterile, guard the colony and invade other colonies. Fertile males mate with a queen who then establishes a new colony, settles down (she will never move again after this) and starts cranking out eggs. Eliminating reproductive issues from most of the population provides an absolutely loyal and efficient workforce that in turn helps ensure the great number of births and survivors, a few of whom will go on to become fertile males or queens. Eggs and queens are carefully guarded and the young fed and raised.
Polygyny
Animals who give birth to live offspring may benefit from polygyny where one male maintains a harem of several females. This benefits the females since they don’t have to worry about rival male advances, giving them more time to look after their young. Their reproductive ability is not slowed down by sharing the male since they may only give birth to one child at a time (such as walruses). Dominant males win more mates and thus an increased opportunity to pass on their genetic material. Battles for supremacy tend to go to the largest males, so the pressure is on males to grow as large as possible. Male walruses can weigh twice as much as females and possibly even more. The average size of a harem depends on the ratio of male/female size. Human males are larger and approximately 20% heavier than human females. Humans are therefore at least mildly polygynous by nature. We’ll return to this topic in a future article.
Serial Monogamy
Most birds form pair bonds for a single season, although some do mate for life. Eggs and chicks are extremely vulnerable to both environmental factors like temperature and predators. One parent must therefore guard the nest at all times while the other finds food for the brood. Some species have both parents taking turns on the nest while other birds have well-designated gender roles. Chicks generally become mature enough to no longer need constant watching after one season, so it makes little sense to limit one’s reproductive potential by sticking around too long.
It may be to one parent’s advantage to pass the child rearing buck to the other parent and go off to reproduce some more. The parent with the most invested in the outcome (typically the female) has a harder time shirking its duty. This may leave males free to leave the nest ostensibly on a hunting run and simply mate with another female, who is then committed to raising the chick. Birds can’t abort their eggs, unlike human fetuses.
Monogamy
Parents who both invest heavily their children may benefit from monogamy. Human babies are born helpless and remain more or less helpless for a long time- over two decades once one factors in a potential college education. A human child can spend between 1/4 and 1/3 of its life preparing for adulthood- a fraction that may be relatively constant throughout our evolutionary history as life spans increased along with the complexity of education. Children with only one parent face a significantly higher risk of starvation and predation, particularly when that parent is a mother who is not as well suited for fighting off enemies as the father. Thus, if the father wants to see his children grow to reproduce and bear grandchildren, he’d better be by the mother’s side doing his part.
It is no coincidence that human sexual signals and behaviors evolved to fit this exact scenario. Why do women conceal ovulation and why are they sexually receptive throughout their entire fertility cycles (unlike chimpanzees and bonobos who do neither)? Because sex is fun. It has to be in order to motivate us to try and reproduce as much as possible. A person’s body responds in exactly the same manner whether the sex is procreationally or recreationally intended. The male gets to enjoy sex all the time and thus has little need to seek satisfaction elsewhere. The female get to enjoy sex all the time while protecting her enormous investment that begins with eggs that are roughly 1,000,000 times the size of sperm. and continues through a risky pregnancy, nursing and carrying the baby.
Polyandry
One female with more than one male (as seen in the movie Paint Your Wagon) conveys significant advantages for the female because she enjoys increased protection and a more reliable food supply. It does nothing, however, to help her reproduce more rapidly or nurse more than 1-2 infants at once. All of the males who did not sire the child lose the great game of life (passing on the almighty DNA) because they are helping another male’s genes succeed at their own expense. Which brings me to…
Cuckoldry
Any animal, humans included, that can sire a child and then get another individual to raise it as its own has won the evolutionary lottery because it gets to pass on its genetic material without doing any of the work. The cuckold (animal raising the other child as its own) is at a double loss because it is both not passing on its own genes and working as if it was. Cuckoldry occurs far more often than one might think, even among humans.
Don’t confuse cuckoldry (raising someone else’s genes thinking they’re your own) and adoption (deliberately raising someone else’s genes, which also occurs surprisingly often, including with me). Both of these are also distinct from relatives helping in child care because by doing they are helping pass on at least some of their own genes.
Incest
I’ve already mentioned that humans tend to be most strongly attracted to people whose genotypes are the opposite of their own. Does your significant other have a unique scent that makes you weak at the knees? You’re smelling her or his opposite genotype and your body is telling you this mating has a strong likelihood of producing the kind of robust offspring that would be well able to reproduce in its own turn.
If partnering with someone of the opposite genotype is good, then it stands to reason that mating with someone of a similar genotype is bad. The people with the closest genotypes are our blood relatives: siblings, parents, uncles and aunts, cousins, etc. Incest (sexual relations with blood relatives) carries a heightened risk of birth defects, mental retardation, etc. Small wonder that most (if not all) animals, humans included, have a built-in taboo against committing incest.
Our built-in incest taboo is so strong that it can even extend to non-relatives who were raised near us as children. A survey of over 2,700 Israeli marriages turned up only 13 (just under half a percent) from children raised in the same kibbutz- and all of these children had moved in after age 6. A prepubescent human is not ready for sex, but she or he already knows who not to mate with.
Internal vs. External Fertilization
Fish that simply release eggs and sperm into the water (as well as other animals that fertilize their eggs externally) have invested roughly equally in the reproduction process. Internal fertilization requires a large up-front investment on the mother’s part in the form of specialized structures (genitalia) that allow mating and insemination to occur. Animals that give live birth (as opposed to birds that lay fertilized eggs) require extensive specialized organs including genitalia, uterus and placenta.
External fertilization gives both parents an equal opportunity to either ditch the other to watch the offspring or even to be cuckolded. Female animals that either lay fertilized eggs or give birth to live offspring can be absolutely certain that they are, in fact, the mother with rare exception. Ensuring paternal certainty is another consideration altogether, one that in humans has almost all societies to adopt complex laws designed to ensure marital fidelity and even premarital virginity, particularly of females.
Mixed Strategies
Internal fertilization sets up the inherently unequal investments I’ve previously described, making males more likely to have to pitch in because it’s almost impossible for the female to raise the young solo. Humans are an extreme example because our children remain helpless after weaning but even that isn’t enough to completely level the playing field nor to completely align the parents’ interests (as evidenced by human males being larger than women). The man, like some male birds, will be tempted to let his eye- and more- wander somewhat. Polygyny and deception can work, as we’ll see in a future article, because the fraud may not be discovered in time. This mostly-monogamous-with-occasional-side-trips approach is called a mixed reproductive strategy. It can work but it’s a pretty risky gamble.
I hate to say this, ladies, but this fundamental male drive won’t disappear any time soon. It would be wonderful if all fathers stuck by their mates and devoted themselves wholeheartedly to one family and one set of children. The problem is that natural variances in temperament would produce men who were more likely to cheat. These men would have more offspring, who would eventually crowd out their faithful brethren. Evolution is a numbers game. Period.
Sexual Cannibalism
If you’re a man, imagine having sex with a woman. As you finish, you experience an uncontrollable urge to lean down and offer yourself to your mate, who proceeds to kill and eat you, perhaps while you’re still ejaculating. If you’re a woman, imagine feeling uncontrollably hungry, so hungry that you start eating your mate while still having sex. It’s OK to be freaked out and a little disgusted at this visual. After all, you’re human. This scenario makes no sense to you because your life span is measured in decades, giving you plenty of time to find food. Besides, killing the male during sex makes it awfully hard for the mother to raise her child and reduces the child’s chances of survival.
Now put yourself in the position of an insect (such as some species of mantis). Your life span is measured in days. After sex, the mother lays a bunch of eggs and flies off to die, leaving the eggs to fend for themselves. There is no need for parental involvement beyond copulation and egg laying. The short life span makes potential mates a rare commodity, meaning you’d best do it with the first candidate who happens along. Producing and laying eggs consumes a lot of energy, particularly when your reproductive strategy involves laying as many eggs as possible in the ultimate numbers-game hope that a precious few will survive.
Life exists for the purpose of begetting the next generation. If you’re the father, your entire reason for being ends the moment you finish mating. Remaining alive would be a waste of resources and nature wastes nothing. If you’re the mother, then you need a big meal to gather the energy you’ll need to put into growing all those eggs. Flying around trying to find food consumes precious energy in the same way that every failed hunt increase a predator’s risk of starvation. You need a big meal and the big male you just gone mating with has no more reason to live. Seen in this light, not eating your mate becomes the foolish choice.
If you think this sounds cruel, consider that the only reason you’re alive to read this article is because plants and animals died to give you nutrition. All life requires death in order to continue, from organic compounds released by decomposing corpses that feed plants to the antelope that feeds a tiger. Nature does not care for any individual in the slightest; it cares for the species as a whole, meaning that it cares for the genes. You, dear reader, are little more than a mobile laboratory built for the sole purpose of mixing and remixing DNA and ensuring your unique mixture lives to mix again. Everything else is fluff, as far as dear old Mother Nature is concerned. That includes you reading this article.
This holds true even if you never actually have children. The best moments of your life will happen when you are with someone in a pair-bonded relationship as I am with Jennifer. And just what are you doing in said relationship? Why, you’re going through the reproductive motions, of course!
Productivity
The average human woman can produce somewhere between 10 (breast-fed) and 30 (bottle-fed) children in a lifetime despite having about 400 available eggs, because she can’t incubate or breast-feed more than one uterus load of 1-2 (usually) children at once. Meanwhile, the man is ready at a moment’s notice and can theoretically sire thousands of children. Staying around to help raise the kids puts a serious crimp in his style, as I just noted above. The exception is when he can be positive that the children he raising are his genetic legacy. Cuckoldry is a real risk for human fathers. Human mothers have zero risk of cuckoldry. If the baby came out of a woman’s body, it’s hers. The joy of this certainty may at times be tempered by her utter inability to hand off caring for her children.
Vasopressin
Prairie voles (microtus ochrogaster) are small rodents that resemble mice with small ears and rotund bodies. They are roughly the size of small to medium rats. What makes this particular species of vole noteworthy is its human-like mating habits, right down to the nominal monogamy (mostly monogamous with occasional side action). Males guard their mates and young, fetch food, clean the burrow and more. They do this thanks to vasopressin, a hormone that increases both aggression and fathering instincts. The more vasopressin, the more faithful the male vole is likely to be.
Humans also have vasopressin. Early experiments seem to indicate that vasopressin in human males may perform the same functions. A surge of vasopressin during sex seems to enhance pair-bonding while also triggering aggression towards other males. This jealousy causes the male to attempt to keep other males away from his woman while being very devoted to her. I can’t help wondering if any relationship exists between excessive vasopressin and domestic abuse.
Rolling The Dice
Your head may still be reeling from what you just read about sexual cannibalism and how it’s just one more example of the reproduction imperative. Sexual cannibalism may be relatively rare, but consider that starving animals will routinely choose sex over food when given the choice. Deliberately pushing an animal to the brink of starvation and then giving it a choice between sex and food strikes me as a particularly awful experiment but it does prove my point about the absolutely central role that reproduction plays in all of our lives.
Let’s look at sex in the context of all we’ve discussed so far. Sex is expensive (and I don’t just mean fancy dinners and jewelry)! It consumes a lot of energy. It consumes a lot of time that could go toward finding food. Humans normally mate lying down, making them easy targets for roaming predators. Sex can even trigger heart attacks and other health issues. Fighting over sex and mates can be injurious or even fatal. Sex isn’t cheap. Then again, human sex is a lot cheaper than, say, mantis sex.
Rate This Post:
Did you like this article? Submit it to your favorite social bookmarking sites:
Comments:
1 Comment Already
Pingback & Trackback
Sorry, you must register to leave comments.