Animal Attraction

In a previous episode of Nature Minute we talked about porcupine love. With Valentine’s Day right around the corner it’s time to revisit the subject.

In the human world, success is usually measured in money and power. In the natural world, success is measured by passing on genes to a new generation. Darwin proposed evolution as natural selection by survival of the fittest. Those best equipped to survive their environment will have the most offspring, in theory.

There are two ways in nature to ensure that your offspring will survive to produce offspring of their, furthering your own genes. The first is a high reproductive rate (fecundity) with little to no parental care. The second is lower fecundity with a high rate of parental care.

Some examples of high fecundity animals are insects, which lay thousands of eggs, and mice, which may have multiple litters of a dozen or more in a single year. Surviving mouselings reach sexual maturity at a very early age and have babies that are older than their aunts and uncles. Many plants fall into this category also. Think of how many wishes you’ve made with dandelion seeds. Or if you are like me, think of how many mornings you woke up to a yard full of dandelions that weren’t there the night before.

Lower fecundity breeders are typically larger than high fecundity breeders (this is a general rule, but there are exceptions of course). We fall into this category, along with whales and elephants. We all have a relatively long gestation period (40 weeks for people, 20 months for elephants) and births are commonly single. Sexual maturity takes years to reach and mothers do an excellent job of caring for their young.

Just as there are two ways of breeding, there are also two ways of breeding- monogamy and promiscuity. Monogamy is what we think of in human relationships, a pair mating for life. Bald eagles and barn owls are monogamous.

Promiscuity can be either male or female. Male promiscuity is very common in the natural world (and humans too). A successful male has many offspring, but why should he limit himself to a single female? In these situations, frequently a dominant male will have a harem of females to mate with. Elk and bison are great examples. Going back to a previous Nature Minute on the elk rut, we learned that young males will challenge the older dominant male for the right to mate.

Elk rut, photo by Tom Bartel

Female promiscuity is way to confuse males. In some species, a male will kill any young that are not his own. He wants his own genes, and not someone else’s, to be passed on in perpetuity. To counter infanticide, in some species the female will take multiple mates. Since no one is really sure who the father is, all males assume fatherhood and are unlikely to kill any young since it very well could be their own. It is even possible for all of them to be the father. Bees, hedge sparrows, and garter snake females will all take multiple mates.

In the human world, typically a boy will ask a girl out on a date. Females hold all the power. The same is true in the animal world in many cases. Males will put on a courtship display or perform a courtship ritual, hoping to catch the attention of a lucky lady. Prairie chickens have a lek, which is similar to a middle school dance, but the stakes are higher. Boys on one side, girls on the other. The males strut their stuff and the females pick out their favorites. After it’s over, they all go back to their home territories. Usually there is some desirable trait that females are looking for that demonstrates the male’s fitness (as is “survival of the fittest”, not like a fitness test in gym class). It can be brightly colored feathers, awesome dance moves, the loudest croaking, huge antlers, or any number of other things. The male with the best traits gets to pass those on to the next generation through his genes.

Greater prairie chicken lek, photo by Adrian Binns

So what did we learn today? When it comes to love, people are still pretty much animals. It’s ladies’ choice, and the guys really don’t care as long as she says yes.