Monogamy is on the decline, and we are to blame.
As the climate becomes increasingly unstable, so do the relationships of Earth’s most monogamous animal – the albatross.
The practice of monogamy is often thought of in relation to humans only. But monogamy isn’t something humans invented from a love for romance fuelled by jealous behaviour. In fact, our family of mammals are not even particularly monogamous. Around four percent of all mammal species are monogamous, in comparison more than 90% of bird species.
Rather than being something that was consciously constructed, monogamy evolved. Just like having opposable thumbs, the practice of pairing for life can increase the likelihood of passing on your genes, therefore conferring an evolutionary advantage. For example, it is believed that birds are generally monogamous due to the immense parental time investment needed to raise chicks. Imagine, to raise a baby bird you need to incubate eggs in a nest, simultaneously collecting food for yourself and later for them, all while fending off predators. One bird frankly could not do it. But in a paired relationship? Now you’re talking. Since paired birds are more likely to successfully pass on their genes, this trait would accumulate over generations leading to the evolution of monogamy.
Before we get too far, let’s put in a quick definition. When we think of monogamy in the animal kingdom, we tend to assume it is sexual monogamy (otherwise known as genetic monogamy), meaning a pair of animals that have eyes exclusively for one another. In sexual monogamy you do not, under any circumstance, mate with another individual. But there’s more than one way to be monogamous. The more common form of monogamy in the animal kingdom is called social monogamy, meaning the male and female mate, raise young together and spend time together – but they also mate with others outside of the pair. For humans we would call this an open relationship (turns out non-human animals are more “woke” than us).
Open or not, just like in humans, monogamous animals are prone to breaking up, a process that scientists have termed divorce. Divorce is said to have evolved alongside monogamy. It makes sense – if you pair with an unsuitable partner, you’ve really shot yourself in the foot when it comes to passing on your genes. Species need an opt-out system for the benefits of monogamous practice to shine.
Evolutionarily speaking, whether an individual stays with their partner or not comes down to a simple question of, if I stay with you, will you successfully help me pass on my genes? If you’re infertile, goodbye. If you are weak, goodbye. If you’re lazy and don’t bring home food regularly enough, goodbye.
Different species have evolved different divorce rates, i.e., the number of couples per 100 couples that part with their significant other. Species who inhabit inherently turbulent environmental conditions will have increased rates of divorce due to associated challenges finding food and shelter. Whereas species who live in abundance can focus on each other. It doesn’t matter that much if your partner is lazy, because there’s abundant food around.
Albatrosses demonstrate the epitomy of commitment. Their divorce rate is the lowest in the world, coming in at just under 4% (humans are at 40% for comparison). Due to their long lifespan, albatrosses can be together for around 70 years, even after regularly practicing long-distance, spending months away from each other. They have been observed to sleep with the head of one bird cosily pillowed against the breast of its mate. The life of the albatross is relatively simple, meaning they can focus on their love.
But all of this is changing.
Using data from 18 years of extensive observations, a team in Falkland Islands, off the coast of Argentina, looked at how divorce rates in albatrosses were impacted by environmental conditions.
The team found a strong correlation between years that had sea surface temperature that different significantly from the 30-year average, and an increase in divorce rate. This is where the crux of the conversation is, the tipping point, the tip of the iceberg (that’s melting while the polar bear stands on it). How could changing sea temperature affect the decision to stay or to leave your potential life-long partner?
It comes back to the question, “if I stay with you, will you successfully help me pass on my genes?”. Increases in sea temperature alter the availability of food. Higher temperatures make it difficult for organisms at the bottom of the food chain, like phytoplankton, to grow meaning that less food is available for animals further up the food chain, like seabirds.
Due to decreased abundance, albatrosses might take longer to find food and return home later than normal. In the waiting time, the partner may find a new mate that has already returned with plenty of food. Think, wives waiting for their partners to come home from fishing assuming their partner was lost at sea. Or, in years when food is harder to find, albatrosses may become injured or ill during their arduous search. An injured partner is not able to deliver to the best of their abilities on their marital agreement to help raise young. This also may lead to divorce. Yet another reason is the perception of laziness in their partner due to returning home with minimal food.
Why is this important?
Aside from the heart-breaking notion of Earth’s most monogamous species losing their passion for love, the increased break-ups may affect the entire population survival. Newformed couples are less successful at raising chicks, due to an inexperience with each other. With more new couples forming, we may see an increase in survival rate of chicks. Albatrosses are already listed as critically endangered.
If climate change increases divorce rates, this could reduce the number of new albatrosses making their way into the world, reducing the entire population size over time.