Why Some Animals Are Monogamous – but not Higgs the cat.
Hi Higgs here. We at Lightning Rod noticed a couple of interesting new scientific papers on the evolution of monogamy. I volunteered to take on the science of monogamy because I think you humans are a little too close to the issue to see it as objectively as I can.
Higgs: Monogamy fascinates human beings – so much so that a surprising number of scientists are devoted to studying who practices it and why. I suspect it's because you want desperately to understand yourselves. We cats are driven to mate in a promiscuous fashion, but human mating behavior varies in the extreme with some remaining faithful to partners and others trying to mate with as many other humans as possible.
IMHO the first thing we must to do understand monogamy is to resist the urge to judge. I've observed that humans tend to look down their noses at those they deem more or less promiscuous than themselves – labeling people as "sluts" on one end of the spectrum and "losers" on the other. Please refrain from this kind of thinking and you will open your mind to something new.
In nature, Darwinian processes determine faithfulness or lack thereof. Monogamy is much more common in birds than in mammals and in many cases the father bird helps incubate eggs and get food for the hatchlings. In emperor penguins it's the dad who sits on the egg through the frigid Antarctic winter.
But these penguins and a number of other monogamous birds don't necessarily mate for life. They may switch mates when a new breeding season rolls around. DNA paternity testing shows that many bird couples engage in "extra pair copulation" - a behavior pattern commonly referred to by humans as cheating.
Mammals are less likely to be monogamous at all. Even allowing cheating or some level of divorce, fewer than 10 percent of mammals engage in monogamous mating. But many scientists, being mammals themselves, hope to gain some self-understanding from this monogamous minority.
One of the most important studies on mammalian mating came to light in the 1990s. It involved two related species of little rodents called voles. There were monogamous prairie voles and promiscuous meadow voles.
Researchers realized that this huge difference in vole behavior seemed to come down to the way they responded to two hormones – vasopressin and oxytocin. Both animals made these hormones but the prairie voles had many more receptors – molecules that bind to these hormones and allow them to have an effect.
And so the scientists designed an ingenious experiment. They took the promiscuous meadow voles and added oxytocin and vasopressin receptors to their brains. The result – the once promiscuous voles now behaved just like their monogamous cousins.
That study showed that monogamy in animals can come down to physiology, which is in turn driven by evolution – ultimately coming down to what suits the selfish needs of selfish genes as they jockey for the chance to proliferate. And it doesn't take much of a change in an animals' physiology to switch behavior, which helps explain why monogamy seems to have spring up independently in dozens of different species of mammals.
More recently, scientists have been trying to figure out which environmental conditions tend to correlate with monogamy, and which may trigger its evolution.
In one study published this summer, scientists examined the evolutionary history of 230 different primates and another looked more broadly at more than 2000 different mammals. The mammal study didn't include humans while the primate study did, and apparently classified your species as both monogamous and not monogamous.
One group concluded that spreading out of females into very diverse territories preceded a shift to monogamy. Under those conditions, males would have more surviving offspring if they stayed put than if they wandered off and left their original mates open to other males.
The other study's authors concluded that the one behavior that always preceded monogamy was infanticide by rival males. They suggested that males became monogamous because it allowed them to protect their offspring.
The authors of these studies were quoted far and wide saying it's difficult to extend the findings to human beings. But there are other clues that do speak to human monogamy, as we learned talking to Duke University biologist Michael Platt. He said that humans are complicated because their behavior can be motivated by a tangled yarn ball of nature and culture.
As Dr. Platt explained, physiology holds clues to an animal's natural mating tendencies. One of the hallmarks of monogamous mammals is lack of visible sex differences. Many monogamous monkeys are identical in shape and size and color. That tendency can apply to birds as well – The famously devoted emperor penguins are so alike that biologists have trouble telling males from females.
And male reproductive organs can be adapted for a more monogamous or promiscuous life, he said. When females mate with multiple males during a single fertile cycle, they set up what biologists call "sperm competition". In chimps, for example, females may mate with 8 males in less than an hour, and this situation favors males with very high sperm counts, and large testicles.
Gorillas face no such pressure in their mating system. They have to fight with other males in order to get access to females, but once that happens, their sperm don't have to compete.
Human testicles are not as big as those on chimps but they're bigger than they would need to be if we were truly monogamous animals.
I had good sized testicles for an 12-pound animal. On my very first check-up, the veterinarian asked if I'd been neutered. Nobody knew. The vet lifted my tail and exclaimed, "Oh, he is definitely NOT neutered." Then I fell asleep and my testicles got lost. They haven't been seen since.
But I digress. The important thing here is that by withholding judgment and applying science, humans and cats can learn a lot by considering ourselves in the context of other mammals. Humans tend to resist thinking of themselves as animals. But as the famous biologist Theodosius Dobzhansky once wrote, "Nothing in Biology Makes Sense Except in the Light of Evolution".
Thank you for letting me express my views. – Higgs.