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Just For Fun

The Love Lives of Fish and Humans

You might learn something about romance

By Jennifer Allford, '84 BA

February 12, 2021 •

This Valentine’s Day, as you express the depth of your love to your special someone, you may want to take a moment to also ponder the depth of the fish tank. You might be surprised to find out that we have a few things in common with fish in the romance department.

Let’s dive in with Pete Hurd , professor of psychology in the Faculty of Science, who confesses to spending “way too much of my working day thinking about the emotional lives of fish.”

Hurd studies behaviour, personality and genetics in both humans and cichlid fish. His lab looks at the links between environmental influences, genes, hormones, brain and behaviour. As such, he is expertly poised to comment on those aspects of romance we have in common with fish. After all, as Hurd says, “We are just fish that think too much.”

1: Do fish love their mates and families?

Hurd and his colleagues have studied species of cichlid fish that breed in monogamous pairs. “And I’m convinced these fish love their mates and love their kids,” he says. “They look after each other for months on end, better than dogs look after their pups.”

Hurd says some of the fish he has studied “hate everyone else outside of that family group. They’re territorial or they’re nasty.” Other closely related cichlid species have extended pack structures, and Hurd compares them to wolves. “They’ve got their mate and their kids and they’ve got these friends that they trust to help them raise their kids,” he says. Fish outside this group are neighbours, strangers and rivals. “This blows me away that there’s a fish with a brain that’s slightly larger than the head of a pin and it has friends that it trusts to look after the kids!”

2: But is it just hormones that cement love and hate in fish and humans?

“This is one of those things that people who study hormones and behaviour are always struggling with, this idea that people have hormones like marionette strings,” Hurd says. It may be the other way around. Our thoughts change hormone levels more than hormones change thoughts and behaviour, he says. For example, there are hormones involved in being happy, but we can’t just dose somebody with that hormone to induce happiness. “And there are hormones involved in love, but if we just give people that hormone, it also makes them gullible, or maybe it makes them more xenophobic.”

The same chemicals, neurotransmitters and hormones involved in love are also attached to having a nemesis. Hurd’s group looked at differences between cichlid species without a strong social group and compared them to the species that had friends and an extended social structure. “We found differences in the fish version of oxytocin,” he says. This is a hormone deeply involved in regulating an individual’s social behaviour , but it’s also involved in xenophobia and gullibility.

Hurd says research shows that administering the same hormone to a human as a nasal spray makes them more trusting and gullible — the downsides of being too loving. The xenophobia that comes with oxytocin is what enables fish, or humans, to recognize a nemesis. “So, the love bit doesn’t seem to be separable from other bits of social life,” he says. “It’s a two-edged sword.”

To Hurd, love isn’t unique or separable from everything else in our emotional lives. “Neither are the hormones, neurotransmitters and brain structures that are associated with love.”

3: Why do we — humans and fish — fall in love?

Hurd has four reasons why fish fall in love. “Two are related to evolutionary history and are a bit harder to apply to humans,” he says. But two reasons can be applied to fish and people. The first has to do with genes, hormones and neurons: the machinery of what goes on in the brain. The second is the function of whether it serves the organism to fall in love.

As a biological process, love is important because we need to reproduce. “Evolutionary history has handed us that mechanism,” Hurd says. “We descended from a long, long line of individuals, all of whom, under whatever circumstances, managed to reproduce.” He says the commitment to raise offspring to adulthood is “a huge investment” requiring the ability to form and stick with a commitment. “And that kind of a commitment is shaped by evolutionary history.”

4: Do we fully understand love?

“Biologists understand something about why animals pair up and breed and then form lifelong alliances,” Hurd says. But animals can also sneak around on their mates and sometimes abandon their offspring. “I don’t know that neurobiology has any deeper understanding of love than really good novelists have. I would say that love is still a mystery.”

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