Monday, February 17, 2014

Love comes in many forms

smart move there, big guy
gifts are one way to compete for mating rights
image: carilynn27
OK, so now that Valentine's Day is behind us, here's a little dirt on love.

Few animal species are, in fact, monogamous, that lifelong partnership with a single person – what many people would consider the ideal, "natural" family structure.

In less than 5% of mammal species do both males and females stay with one mate for life.

In some species, males have harems, in others, pairs shack up for a single breeding season, and in others, males and/or females cheat.

Each strategy can be successful for the animal to enhance his or her biological fitness by increasing the chance that he or she passes on genes to the next generation. Here's a fun explanation (love these!):

Video from MinuteEarth

So who IS monogamous?

Animals are monogamous when raising their young takes more care than the mother alone can provide, so the father pitches in to ensure the kids grow tall and strong. This might require helping to feed and guard the young from predators or even competing males.

they look cuddly, but in primates, monogamy may have evolved
as males stayed around to prevent outside males from killing
the young (which they do to then mate with an ovulating female)
photo: Audubon
Some scientists think that when females live spread apart from each other, such as in people, rather than in a group, males can't monopolize all of them, so they have to pick one to defend against competing guys. This way, they help to ensure that at least some of their genetic awesomeness continues into the next generation.

Here are 12 species (including humans) that are mainly monogamous, but the term is applied loosely, since genetic studies have shown that cheating occurs: some minority of bird eggs, for instance, belong to a different father than the one guarding the nest. Ooops.

As the video mentions, these "extra-pair copulations" may make biological fitness sense: they may help a bird ensure that his or her genes get passed on, in the event of disaster, like a flood or a predator, at his/her own nest, while keeping a single mate that will help raise the chicks for the entire breeding season.

Serial monogamy, in which the pair stays together for 1 breeding season, may help maintain genetic diversity by enabling different genetic combinations each year. In birds, once the chicks have fledged, the parents can go their separate ways to find food and recover from the exhaustion of chick-raising.

In nature, harems are groups of females that all mate with the same dominant male. The male is a Big Deal – he's large, aggressive, and, in cases where he must continuously defend his turf or his ladies, short-lived in his post.

the Big Guy gorilla will defend his harem of ladies and kids
but is otherwise pretty peaceful (even with us humans nearby)

the male impala (the guy with the long curved horns) keeps the ladies
by defending a territory with plenty of food (grass, shrubs, etc)

What about us?

Do these theories apply to people?  Uh, yes, actually.

Polygamy (having more than 1 spouse, of either sex) has been more common than monogamy among the many human societies over time. The word harem comes from the Middle East as a sacred place for women (the multiple partners of the single Man of the House plus their children).

You can see serial monogamy in the many divorces and broken engagements that occur each year, from which each person (hopefully) finds a new, exclusive partner. And surveys indicate that at least 15% but probably more married people in the US have committed adultery (this doesn't include cheating within engagements or other long-term relationships).

We humans are actually flexible, and we seem to both tolerate and thrive on different social structures: some sort of monogamy (one partner at a time, adultery, or open relationships all exist) has been more common in recent times. By its exclusive and stable nature, monogamy may allow the two partners to devote time to other pursuits (such as jogging or blogging) besides finding and defending a mate.

participants in this survey demonstrate the variety in human mating behavior
image credit: Karl Tate, LiveScience

An article on how many modern human societies reject polyamory (having more than one partner) points to the paradox that most people can imagine themselves having sex with a second partner yet live in mostly monogamous relationships and censure extra-pair encounters. Apparently, although many people are interested in additional partners, and some couples find happiness with swinging, the strong pressure from society and laws on people to promise monogamy is enough to hold them there. Until they split up, of course.

Read more

Carl Zimmer's New York Times article on newer theories of how monogamy developed in people

Slightly scientific, from Nature, on the evolution of sex and various mating systems, including monogamy

The more scholarly: Monogamy: an ambiguous concept

The way less scholarly: a variety of strange animal mating habits

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