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A Wilder View: A look at why some animals mate for life

swan
Posted at 11:40 AM, Feb 15, 2023
and last updated 2023-02-15 13:40:57-05

MISSOULA - With love in the air, we're going to explore a mystery of the animal kingdom — why do some animals mate for life?

People are quick to tie the knot, but many animals say they’d rather not. In the animal kingdom, mating for life is a rarity. Only 3% of the over 5,000 mammal species are reported to mate for life.

The most commonly cited examples include beavers, wolves, gibbons, and prairie voles. But, recent DNA studies have shown that even species once considered monogamous — such as wolves and gibbons — may actually have multiple partners in their lifetime.

Staying faithful can be a challenge for many animals. They have biological urges to spread their genes and seek the best father for their young. And, mating for life can be costly as it requires animals to put all their reproductive investment in one mate.

An estimated 90% of all birds are socially monogamous meaning they find mates to raise babies with but still engage in the occasional fling. Take these lovebirds for example -- swans, once considered the epitome of mating for life, are known to cheat and abandon their mates.

This raises questions about why promiscuity is tolerated, despite the supposed commitment to monogamy.

One theory is that females find a mate that is a good provider, but they are attracted to other males who offer superior genes or control of resources. While male animals may be promiscuous for increased reproductive success.

Some scientists believe monogamy evolved in species where reproductive success is higher through pair bonding than promiscuity, to allow both parents to care for their young. Black vultures' parents incubate eggs and feed their fledglings, which results in happier babies. This holds true for people too, where children take a long time to mature.

However, some theories about the evolution of monogamy being based on fatherly caregiving are countered by the fact that males in some monogamous species do not help care for their young. Even though mating for life among wildlife is rare there are still a few gems out there, prairie voles are one of the few true species that provide scientists with valuable insights into the biology of mating for life.

Male prairie voles will prefer to mate exclusively with the first female they mate with and will even attack other females. This behavior has been linked to certain neurotransmitters, such as dopamine, which is also implicated in drug addiction in humans.

The receptors are also similar to those found in people and our close relatives' bonobos — which display empathy and strong social bonds, while they are not found in less empathetic, aggressive chimpanzees. These results suggest that these receptors may impact social structure among different species and explain individual variation in attitudes towards commitment.

The combination of genetic and environmental factors influences the reproductive behavior of each species, making every species that practices monogamy unique. While scientists are starting to uncover the biology behind certain animals staying loyal to their partners, the true reason for mating for life in the animal kingdom remains mostly a mystery.