You can engineer a prairie vole to become monogamous when it's naturally polygamous.

We've separated the males from the females.

If there's a male mosquito that you release, and if there's a female around, that male will find the female.

Meet the hermaphrodites.

She always knows where he is, and she doesn't have to be monogamous, because some of these females come up with multiple males attached.

The gourd is a feminine aspect the stick is a male.

If they don't find a female, then they'll die anyway.

It's the females, I think, that lay the eggs, and then the males fertilize them.

I have three dogs. One is male and the other two are female.

And the second is a phenomenon that males are very, very good at finding females.

This final commitment of yourself, your ships, of all of us to fight at sea, when did you decide?

So the males will go out, they'll look for females, they'll mate. If they mate successfully, then no offspring.

Specifically, it's male fireflies who are all flashing in perfect time together, in perfect synchrony, to reinforce a message to the females.

So here's a typical situation, male meets female, lots of offspring.

And these two males are fighting, they do it by bouncing their butts together, which is an interesting concept. Now, here's a male on the left and a female on the right, and the male has managed to split his coloration so the female only always sees the kinder gentler squid in him.

My favorite being, Cheese crumbs spread before a pair of copulating rats will distract the female, but not the male.

This is one of my favorite ones here, where they have rabbit breeding, so males choose the lucky rabbit.

Down below here, we see calls made by both males and females that also carry over very long ranges.

And if this is a female, she'll immediately mate with a male and off she goes because time is very short.

When you're floating in a vast sea, with little control over who you may meet, it can pay to play both sides of the field.

So when you develop a cancerous cell in your breast, aromatase converts androgens into estrogens, and that estrogen turns on or promotes the growth of that cancer so that it turns into a tumor and spreads.

So, now we believe that the different shape of the lure is how the male recognizes the female in the anglerfish world, because many of these males are what are known as dwarf males.

And as a result, these exposed males lose their testosterone, they're chemically castrated, and they're subsequently feminized because now they're making the female hormone.

In fact, more genetic profiling told us that this tumor in Jonas actually probably first arose from the cells of a female Tasmanian devil and Jonas was clearly a male.

But what atrazine does is it turns on an enzyme, the machinery if you will, aromatase, that converts testosterone into estrogen.

It was Derry's biggest win of the campaign and perfect preparation for the showdown with Cork.

The tigress...

And she?

It can move from a fertilized egg to a spat, which is when they're floating through the water, and when they're ready to attach onto another oyster, to an adult male oyster or female oyster, in a number of weeks.

To overcome her?

Now one dude in lab was even able to reactivate memories of female mice in male mice, which rumor has it is a pleasurable experience.

Third Female

So the large baleen whales will produce long, beautiful songs, which are used in reproductive advertisement for male and females, both to find one another and to select a mate.

So if we can tell the gender of the shark before we sample it, we can tell the geneticist this was taken from a male or a female.

If you put more sterile males out into the environment, then the females are more likely to find a sterile male than a fertile one, and you will bring that population down.

Ganswindt, the director of Mammal Institute of University of Pretoria, said that these two little lions born on August 25 were a female lion and a male lion. They were pretty healthy and quite normal.

She'll holler on me.

There's a hind. There's a doe.

As Darwin did not believe that pure aesthetics would guide female peacocks and lions in their choice of mating partners, he had to find a rational reason for females preference for males with hindering characteristics. The very fact, he reasoned, that these features make life harder signals to prospective partners that individuals who can do reasonably well with them have an especially good genetic set up and are thus likely to produce strong offspring.

Those females, they're not trying to.

It's only the female mosquito that will actually bite you.

It's just the female.

In recent studies that we've published, we've shown that some of these animals when they're exposed to atrazine, some of the males grow up and completely become females.

There's only 8,000 basking shark females in the world?

Now if this signal is used for males and females to find each other for mating and they're dispersed, imagine the impact this could have on the recovery of endangered populations.