Why do some animals stay monogamous?

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1. The less popular option

Monogamy – where individuals remain faithful to a single partner – is relatively rare in the animal world. It occurs in less than 5% of non-human mammals. In primates, that increases to around 15%.

Pair bonds are more common among bird species – but thanks to DNA technology, we now know that most of these supposedly monogamous couples are, in fact, fooling around. Even those apparent paragons of virtue, swans, cheat. True monogamy is now thought to occur in only around 30% of all bird species.

So if monogamy is infrequent in the wild, why do some animals stick together? Meet some of the most faithful couples in the animal kingdom – some of which are same-sex couples – and find out what the perks of monogamy may be.

2. CLICKABLE: The power couple

An African wild dog pack is a discrete social unit that travels, hunts and rests together. They have a strong social structure that supports the monogamous alpha pair. Click on the labels below to find out more about this pack's structure.

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3. The monogamy molecule

Oxytocin – sometimes called the 'love' molecule – is a hormone that also acts as a neurotransmitter promoting bonding behaviours in mammals.

Cuddly tamarins have more oxytocin

Cuddling, grooming and sex are a big part of a tamarin couple’s life. Partners with a high level of oxytocin perform more cuddling, grooming and sex, while those with low levels of oxytocin spend less time on such relationship-building activities. Receptors for oxytocin can be found in the brain's reward centre and it’s thought that these create a sense of pleasure as close bonds are formed during monogamous relationships.

What about us?

Oxytocin works in a similar way in humans. Whilst it won't single-handedly make you fall in love with someone, it does seem to strengthen bonds, including those formed in monogamous relationships. A study found that if oxytocin is administered to men who are then shown pictures of their partner, this stimulates the reward centre in the brain, thereby increasing the attractiveness of the partner and helping to keep men faithful.

4. CLICKABLE: What about same-sex couples?

Faithful same-sex couples exist in the animal kingdom, hinting that monogamy is about much more than just sex. Can you identify which same sex-couples are monogamous from the examples below?

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Images: Getty and Animals in Love, BBC One, 2015

5. Can you call it love?

Liz Bonnin meets Prof Kurt Kotrschal to ask whether animal couples might be experiencing something akin love.

Liz Bonnin interviews Prof Kurt Kotrschal. (Animals in Love, BBC One, 2015)

The story of Tariq and Judith is a very romantic one. These two geese formed an extremely close bond. When Judith disappeared in a storm, Tariq behaved in a way that could only be described as grief-stricken. Judith unexpectedly returned a year later and the pair have been together ever since. Is it possible for greylag geese to experience emotions as strong as those we call love?

6. Monogamy's advantages

What do you think are the perks of sticking together for these animal couples?

Offspring survival

A cotton-top tamarin couple sharing childcare duties.

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Offspring survival

YES

A study, which analysed 230 species of primates, suggested that protecting the kids is a great benefit of monogamy.

Parenting skills

Tariq and Judith – a very faithful pair of greylag geese that have been together for over eight years.

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Parenting skills

YES

In some species, like barnacle geese, an added advantage is that long-term partners who get to know each other well become better at caring for their young.

Genetic diversity

Non-alpha African wild dogs in a pack are often siblings.

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Genetic diversity

NO

Monogamous parents don't 'spread' their genes as much, so offspring have less genetic diversity than in a polygamous society.

Defending turf

A pair of siamang gibbons singing their haunting daily duet.

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Defending turf

YES

Defending a territory and its resources is one of the main reasons gibbons are monogamous. Gibbon couples perform beautiful duets, staking claim to their turf.