Today I want to talk to you about monogamy.
On what it is, why some animals do it, and how common it is in the wild.
One of the animals I'm going to be talking about in this video is humans
but listen to me very carefully
ARE YOU LISTENING?
I am not, I repeat NOT, giving relationship advice in this video.
[Intro]
Now, you've heard of monogamy
and you probably have a pretty good idea of what it is
but I'm going to hit you with some definitions just in case.
[reads]
Sometimes that period is a single breeding season; sometimes it's for an animal's entire adult life.
and also scattered throughout the animal kingdom we see examples of social monogamy.
That's what happens when
[reads]
There are not a lot of socially monogamous animals
There are some insects, a hand full of fish, a whole bunch of bird species, a few mammals,
and even a parasitic flat worm.
The diversity of species that practice social monogamy
leads us to believe that instead of having some kind of common socially monogamous ancestor,
they all sort of arrived at this strategy each individually.
I should also mention the obvious here:
Uh, monogamy is not the only game in town.
[reads]
When it's the man that's doing the extracurricular partnering it's called polygyny
which is like "many wives"
and when it's female it's polyandry
or "many men"
and when it's both male and female partners it's called plygynandry.
And let's not forget good old fashion promiscuity
which is basically
[reads]
it can talk into the sack.
but back to monogamy.
you'll notice that before I was referring to social monogamy.
this is a delicate way of saying that
this pair, by all outward appearances,
shares recourse and works together and only has sex with each other.
this isn't necessarily the same thing as sexual monogamy
which means that these two are seriously only having sex with each other EVER. SERIOUSLY.
Sexual monogamy is actually pretty rare
because even between socially monogomous animals
there's a lot of what's called extra pair copulations going on.
This is a fairly recent discovery actually
where we've been using DNA analysis to catch these extra pair copulaitons red handed.
because, apparently, if you're going to want to do some extra pair copulation
you're going to want to be a little sneaky about it.
Let's look at some examples.
Birds are a good place to start
because monogamy makes a lot of sense if you are a bird.
In fact, 90% of bird species are socially monogamous
at least within the breeding season and many go beyond breeding season.
This is something only 3% of mammals can claim.
The reason birds like monogamy is because they lay eggs
and egs require a lot of sitting on
and when these eggs hatch the baby birds need to be fed almost constantly
and they're taught to fly and also got to be protected from predators
Being bird parents is frickin' complicated!
So, for a lot of birds, being a so called bonded pair makes a lot of sense
making it possible for both parents to ensure their genes get passsed on
in a healthy happy offspring without starving to death
or having some kind of stress induced aneurysm.
For a long long time scientists assumed that these socially monogamous bird species
were also sexually monogamous.
Take, for example, the dunnock
A cute little brown sparrow that lives in English hedge rows.
A Victorian naturalist, the Reverend F.O. Morris,
was so impressed by these birds' seeming devotion to each other
their "humble behavior" and their "drab and sober dress" that
he often recommended his parishioners emulate their snooze-festival of an existence.
It wasn't until the 1990s, through DNA analysis,
that scientists realized that the dunnock has some of the naughtiest sex in England.
It turns out the dunnocks paired up just like the Reverend observed, however
the female dunnock then turns around and encourages other males to invade her male's territory
once the other male gets to her, she takes him behind a shrub
does a little tail-spinny-grindy dance and he can't handle it
so male number two .... does the deed.
Then male number two goes off to find her a nice juicy worm
feeling quite pleased with himself.
In the mean time, the alpha male, or male number one,
has gotten the feeling that something's not quite right on the home front
Well, he goes over to his lady and pecks at her private parts until she ejects
the sperm packet that male number two left
and then alpha male must assert his dominance and so he mates with her again
and this can happen all over and over again about a hundred times per day ;
I don't think that the Reverend would have approved.
So why would Mrs. Dunnock cuckold alpha male like this?
Well, it's to say why animals do anything
but one reason is that she now has two males bringing her juicy worms
and even, potentially, two males to help her raise her children
though one of them has to be kind of sneaky about it.
and in fact if you do paternity tests on all the little baby dunnocks in a dunnock nest,
turns out often several daddies involved in one nest.
So, social monogamy even among the birds
turns out to be a lot less monogamous and a lot more social than anyone ever thought.
Even swans, until recently considered the paragon of avian monogamy
because they mate for life,
upon closer inspection get divorced a lot more often than scientists ever gave them credit for.
and though they might not be as permiscuous as Mrs. Dunnock,
they do their fair share of mating outside of their bonds.
And so, the distinction between social monogamy and sexual monogamy becomes quite clear
It's not cheating if you don't get caught by a scientist.
Of course there are a few real deal sexually monogamous species out there.
There are beavers and there are the Californian mice
and the malagasy giant jumping rat.
They remain faithful throughout their entire lives
either because it helps them fight off predators,
or establish a giant territory,
or raise scads and scads of giant jumping rat offspring,
it's also worth noting all of these animals are extremely territorial
so there's not a lot of opportunities for promiscuity, but still.
And now to answer the question you've been asking yourself this entire episode,
What about humans? Aren't we monogamous?
Weeeeeeeeeeeeeeeell not strictly speaking
I mean if a zoologist came down from another planet
looked at us they would say
"Human kind: mildly polygamous, you know kind of socially monogamous,
but occasionally engaging in extra pair copulations."
Monogamy is possible! Even potentially advantageous for humans
but our genes say that for a long time polygyny, or the practice of men
mating with multiple, like a set group, of women
was very much the norm for a very long time in our history.
Studies are showing that polygyny may have become popular with the early humans
because women actually, on average, pass along more of their genes to their offspring
and even though mongamy is more popular with humans than it once was,
a lot of modern societies still engage in some forms of polygamy.
And it's true that very few American men these days take multiple wives,
but over the course of their life times, men tend to father more children with multiple women
than women with multiple men.
You can call this whatever you like,
but anthropologists call it effective polygamy.
Another reason that our ancient ancestors might have been less interested in monogamy
is that monogamy is hard to pull off.
It takes an animal with an enormous brain and big ol' cerebral cortex
to figure out how to do it.
because monogamy requires us to not only know what we want but also
to figure out what out mate wants and provide for that want
that is not our own on a day to day basis.
It also takes a huge amount of brain power no only to figure out if a mate is fertile, but also
if it will be a good mate in the long term. If it will not only be able to produce offspring
but take care of them takes a lot of calculating so monogamy's difficult for stupider animals
But we are not stupider!
and it could be in fact that monogamy has been on of the driving forces for making human kind smarter.
For making us more human.
Some scientist have gotten as far as to speculate that our super sophisticated social intelligence
that our ability to navigate tricky social situations and maintain our status within complicated social groups
was made possible by the ultra challenging task of how to make monogamy work for us.
So while monogamy might not be normal
it might not be the strictly natural state for humans,
it can be argued that most of the great things that we do as humans aren't natural
Playing the violin, sending people to space, making really awesome YouTube videos.
None of those things are natural, but they're awesome.
We do these and thousands of other things every day that go against our instincts because our
giant cerebral cortexs are telling us that it's worth it.
Thank you for watching this SciShow infusion. Like good little scientists, our citations are in the description.
If you would like to read more about sex practices of various animals including humans
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