Brigham Young and 21 of his wives.
Evolutionary fitness is one of the most important concepts in Darwinian evolution. Essentially, fitness can be regarded as a measure of how much of an individual’s genes are passed on to the next generation. More specifically, the higher proportion of the next generation that is comprised of your genes, the more fit, evolutionarily, you are.
Fitness: A short example
For example, say I have one copy of a particular version of a gene: Gene X. No one else in my population of 100 individuals has it. Since we all have two copies of every gene, the frequency of Gene X can be regarded as 1 out of 200. Let’s assume that I pass on Gene X to four of my children in the next generation of 100 individuals for this population. Gene X has now increased from 1 out of 200 to 4 out of 200. Since the frequency of Gene X increased from the first to the second generation, Gene X can be regarded as a gene of higher evolutionary fitness.
Maximizing Your Fitness
Okay, now that we’ve reviewed fitness as the measure for evolutionary success, it begs the question: how can I maximize my evolutionary success? Answer: have as many children as possible (who will survive to one day themselves reproduce). This way, your genes will constitute a higher proportion of the future generations of gene pools.
An obvious limitation to the number of children a person can have is childbirth itself. Nine months, a painful delivery, and then years of caring for the child requires a huge investment in resources. Moreover, women might be viewed as a “limiting step” in this process (I hope I don’t get shot for that one). In particular, mating with only one women would surely slow a man down if his main goal was to produce as many offspring as possible.
Polygamy: Evolutionarily Advantageous
Joseph Smith Jr. was on to something when he founded the Church of the Latter Day Saints. Specifically, his many, many, many wives made him highly successful (from a Darwinian standpoint), although he publicly condemned the practice. By some accounts he may have had 20 children with his multiple wives. While the privilege of polygamy had previously only been reserved for the highest of alpha males (like the one and only Genghis Khan, to whom a large proportion of China can claim some relation), Smith had labored to include multiple wives in the doctrine of his faith. Simply join his church and you become an evolutionary celebrity. To this day, there are many living in Utah who can claim some relation to Joseph Smith Jr.
Divorce/Second Marriages: The Compromise in the name of Monogamy
Let’s assume (or believe) that all human actions are still driven by primal evolutionary urges. Having multiple wives surely fits this bill since it allows for greater evolutionary fitness. However, polygamy is outlawed in western culture, so outside of those who practice it underground, it is not a reliable option for men who wish to increase their fitness.
For men, the divorce/second marriage life route allows for more than one family, more than one wife, just not at the same time. By Darwinian standards, those who get divorced and remarry are actually more successful than those who are monogamous their whole lives (assuming that they have more children). Men who get divorced and remarry will be passing on a higher proportion of genetic material into the next generation.
Let’s take this argument a step further. What if the behavior: “Get divorced, remarry” has a genetic factor that predisposes a man to engaging in this behavior. If this behavior results in higher fitness (higher % of genes passed on by those who exhibit the behavior), then one might argue that a higher proportion of men in the next generation will have genes that predispose them to get divorced. By this logic, if divorce is an activity that makes men more fit (evolutionarily), then we can expect to see divorce rates rise in future generations!
Is Maximizing Our Darwinian Fitness our True Goal in Life?
This question gets to the heart of our discussion. Is maximizing the number of children we have our major goal in life? For some species, yes. For humans, no. Our sentience seems to have made us immune to many of the evolutionary pressures that drive other animals’ behaviors. For example, if having your own genes passed on in your children was so important, then why is adoption so popular? Also, why do many couples elect to not have children ever? These actions seem to be at odds with the idea of evolutionary fitness, yet many members of our species engage in them.
Finally, if maximizing evolutionary fitness was really the ultimate goal in life, then why wouldn’t all men (and women) go around the world donating sperm (and eggs) to all of the banks they can find. I can think of no quicker way to maximize the number of genetic offspring you have. Hopefully, no one does that because it would be kind of creepy.