David Barash and Judith Lipton (Image: Yoav Altman)

New Scientist caught up with husband-and-wife writing team David Barash and Judith Eve Lipton to discuss their latest book, Strange Bedfellows: The surprising connection between sex, evolution and monogamy. We ask them what we can learn about monogamy from other species, and how writing a book about monogamy affected their own marriage.

Your last book, The Myth of Monogamy (W. H. Freeman, 2001) talked about the rarity of monogamy in nature. What made you decide to write another book on the subject?

David: Intellectual honesty or a scientific balancing of the scales if you will. Myth of Monogamy was looking at the glass half empty, at the problems that biology poses for monogamy, but we were aware that monogamy, for all its difficulties, does happen. It happens in animals, it happens in humans. We didn’t want to give the impression that it’s impossible.


Judith: There were both scientific and personal reasons. We thought it was important to point out that the promiscuous behaviour we were describing in ducks, for example, doesn’t necessarily hold for people. David and I have been married and monogamous since 1977.

There are different kinds of monogamy – for instance, there’s a tapeworm that has only one partner until it dies. That’s extremely unusual, but there are other forms of monogamy that are more common, like us! We were each married before and have had other sexual partners, but have been monogamous in our own marriage.

Strange Bedfellows is dedicated to David’s parents who were married for 64 years. They were joined at the hip; they had only spent a total of 3 nights apart until his father developed colon cancer and was in the hospital.

David: It is not an advice book as such, but the issue of advice looms not too far in the background. There are people who want to be monogamous but worry that it may be impossible. To some extent the book is written for those people.

So is monogamy “unnatural”?

Judith: Monogamy is rather like playing the violin. Doing it well is difficult and takes a lot of work, but it’s not impossible. And some people would argue it has real social value.

David: We can’t ever totally transcend our biology. If playing the violin was totally beyond our biological capabilities, it just couldn’t happen. The same goes for monogamy. In order to be monogamous one has to be willing to swim upstream against certain biological impulses, but there is also a biological push in favour of monogamy, especially when it comes to parenting.

Judith: Also when it comes to ageing. People are living longer than ever now, and as you grow past the age of courtship and mating, into the age of disability, picking up prescriptions and dealing with Medicare, sexual diversity is less important and having a good buddy is more important.

The way we look at mating changes when we think about people who are becoming more infirm and less motivated by fresh partners. The miracle of monogamy is the potential for long-term cooperative friendships that transcend mating desires.

David: We have horses here – you can hear them neighing in the background. This morning Judy fed them and tonight I will, and our collaboration is what it allows us to keep horses. That’s true in the animal world as well. In many cases of natural monogamy, part of the payoff has to do, not just with old age or parenting, but with maintaining stuff.

Judith: That’s why beavers are interesting. They are mostly monogamous because they share a lot of work, between making their dams and doing collaborative housekeeping.

David: There are other beavers who would love to take advantage of the work they put in. So, by having cooperative long-lasting relationships between adults, they can do value-added estate planning to maintain and defend their stuff against others.

Is that kind of monogamous setup more or less effective than the strategies of species like ants or bees, who work as a whole colony to protect their resources?

David: It works differently for different species. In ant colonies, the queen is the only one who reproduces and an individual worker is not disadvantaged when someone else does the reproducing.

For humans and other mammals, it’s not in our interest to let someone else do the reproducing. So one way to do it is to be monogamous. And if you’re monogamous, you’re paying a price by sacrificing other reproductive opportunities.

Judith: In the 1960s scientists began to ask, why do bees cooperate? And it came down to a matter of sharing genes at a level that’s very different than mammals and other insects.

The study of the social insect triggered the gene’s-eye view of evolution. You can’t really say the bees are not monogamous, because only the queen flies up and mates, and all her sisters don’t mate because it’s not in their advantage genetically.

David: In the book we have lots of examples of other monogamous animals, like the beavers and the Malagasy jumping rat, who have good reasons for being monogamous that are not altruistic. It’s just that, given their biology, they do best by being part of a committed pair.

We’re trying to make a case that, although there is much in biology that works against monogamy, there’s also much that works in favour of it. We as humans are not doomed or destined to one extreme or the other; there’s a lot of room for human choice.

Judith: Sexual choices really are sexual choices. There is no biological determinism. Monogamy is hard: it’s easier to be sloppy in relationships, to not read the fine print or to follow your heart and fall in bed with people that turn out to be less high-quality than you thought the night before. But they are choices, and that’s where intellect and understanding come in. Sex education should really include a discussion about adultery, monogamy and mating strategies.

David: As an evolutionary biologist, I know there’s an increasing acceptance in the public of the role of evolution in human behaviour. There are some holdouts, particularly in the social sciences, but it’s more accepted in the public. And it’s about time.

But at the same time there’s a tendency for people to grab a small part of the answer and take it as a whole answer. We want to counter the tendency to think that biology is destiny with regard to monogamy – instead of “the devil made me do it”, now it’s “evolution made me do it”.

Evolution does incline us to look at other attractive potential sexual partners – that means you’re a healthy mammal. But we are arguing against the notion that one is totally at the mercy of biology.

People tend to think of females as more inclined to monogamy than males. Is that true?

David: In most species females are not as strictly monogamous as biologists used to think.

Judith: It’s not that females are inclined to monogamy, but that they are inclined to be more choosy; to go for quality rather than quantity. If you take a male to a red light district in Bangkok or Amsterdam and give a day pass, saying “have as much sex as you want” they would think “great!”

Females wouldn’t – they don’t go to red light districts, they don’t pay for sex, there’s nothing equivalent in the prostitution industry. There’s not one society where females pay for sex on a regular basis.

David: And there’s not a society on earth where males don’t!

Judith: Females go to bed with males because they want resources. Men bring them flowers, provide big incomes, provide big territories. Women look for handsome, genetically healthy males who provide good resources. Men look for young fertile women with a waist-to-hip ratio of .72. Males are lookers; females are calculators.

What species are the most monogamous?

David: There’s an invertebrate called Diplozoon paradoxum, which is a worm that lives in the gills of fish. The male and female worms meet in adolescence and their bodies literally fuse together. They remain monogamous their whole lives – but they don’t have a choice!

The California mouse is pretty monogamous, as are the Malagasy jumping rat and the fat-tailed lemur. And beavers.

Judith: Newlyweds shouldn’t be given images of swans because swans aren’t monogamous. They should get images of Malagasy rats or fat-tailed lemurs!

What about penguins? After March of the Penguins, the Christian right was holding penguins up as the supreme model for monogamous relationships.

David: Emperor penguins remain monogamous during a given mating season but then they move on.

Judith: They are serial monogamists, not lifetime monogamists.

David: I don’t think the religious right would be enthusiastic about people dissolving their relationships after every offspring.

Judith: I think the Emperor penguins deserve to mix and match after all that swimming – they work so hard!

Did researching and writing a book about monogamy together teach you anything about your own marriage? Did it affect your relationship?

Judith: I think it was a good thing for our relationship, and it might be my favourite book that we’ve written together.

We were working on the book while I was 3,000 miles away in Costa Rica. We’re not used to being apart, so it was interesting to be writing about monogamy when we were actually experiencing being apart for the first time in so many years.

For me the experience was interesting because it showed some of the downsides of monogamy, in that there’s a co-dependency – you get used to your partner so much. For me, being away heightened both the benefits and the difficulties of monogamy because it was lonely.

David: The main reason Judy was in Costa Rica was she really hates the cold weather we get up here in Seattle, and I’m not that crazy about the weather they’ve got in the tropics – plus I have to be here to teach. So we have inclinations to be different.

How do you manage those differences in a monogamous relationship? One way of doing it is by letting each other have some flexibility.

Judith: I’ve met a lot of people who are exploring being sexually monogamous but living apart for extended periods of time, so that the relationship doesn’t get in the way of other kinds of non-sexual adventures. Now that we have Skype and webcams and things, maybe monogamous relationships will become much more flexible, allowing the partners to be individuals and not suffocating one another.

For instance, David climbed Mount Kilimanjaro. That’s the last thing I’d want to do! We allow each other exploratory room but it doesn’t violate the constraints.

Maybe flexible monogamy is the key to helping people maintain monogamous relationships. Humans have a flexibility in our social systems that no other animals have. I think there are ways for people to have happier, more honest, more stable relationships, by understanding biology and then developing strategies for growth and support.