The Hidden Cost of Compromise in Animal Pairs

Contrary to popular belief, nature includes many monogamous species that remain faithful to a partner for long periods, sometimes even for life.

Beyond humans, animals such as wolves, porcupines, hammerhead sharks, bald eagles, sunbirds and many others maintain long term pair bonds.
However, recent research suggests that many females find themselves paired with males who are less attractive or below average in quality.

The study also found that settling for a partner who is not sufficiently attractive increases stress levels among females.
Among monogamous pairs, very few animals end up with a perfect partner, since statistically the most desirable individuals are often already taken. Research conducted over recent decades shows that females adopt several subtle strategies to improve their reproductive success.

One such strategy involves mating with stronger males in order to enhance the genetic quality of their offspring. The study focused on pairs of Gouldian finches, a species divided into two types based on head color, red headed and black headed.

Red headed males tend to be more aggressive and less suited to family life, as they invest less in caring for their young. In one experiment, female finches were allowed to choose their preferred partners. In another, fifty red headed females were randomly paired with males of both types.

When females were matched with males whose head color matched their own, eggs were laid nearly a month earlier than in pairs with mismatched colors. In addition, males with different head coloring caused stress levels in females that were three to four times higher than in matched pairs.

Researchers believe these findings may also apply to humans. Stress caused by a lack of attraction to a partner could influence how long it takes to conceive and the number of children a woman eventually has.

A certain degree of genetic var
iation is necessary to avoid inbreeding, but too much variation can trigger rejection. The most successful pairs, according to the study, were those that remained together and functioned well. The findings challenge the long held assumption that monogamous relationships are inherently happy.