Lindsey: I'm Dr. Lindsey Doe.  This is Sexplanations and we have a sibling channel called Nature League.  The host, Brit Garner, is here to tell me and you about the evolution of orgasms.  Hi, Brit.

Brit: Hello.  I am so excited to be here.  Thank you so much for thinking this up and I'm really pumped to talk about this.  I'm a PhD student in wildlife biology.  On Nature League, we talk about life on Earth and why it's awesome. 

(Intro)

Brit: What are some of the common hypotheses that you have heard or know of?

Lindsey: That it--what is it called when, it's like a tail, that it no longer has a purpose, that it's evolutionarily just disappeared?

Brit: Yeah, vestigial.  Sometimes we use that, yep.

Lindsey: Yeah, the clitoris, that it's like, an undeveloped penis that has al of the erogenous tissue and the ability to have an orgasm but is just an aside or that it does increase the fertility of the female because if she has an orgasm then she's more likely to have contractions and draw the seminal fluid in with the sperm in it.

Brit: Right, and all of those seem legit anatomically, but there's still something a little bit missing because it was looking at humans and so this team two years ago, what was really cool, in 2016, came out with a paper where they said, alright, that's cool.  These hypotheses have been on the table, but if we go back and look at what organismal female orgasms potentially did way earlier on in the mammal lineage.

Lindsey: This is so exciting.  I'm so excited.

Brit: I know!  The phrase 'mammal lineage' gets me very excited too, don't you worry.  I'm thrilled about it.  So they looked back and what winds up coming into play is actually ovulation.  It just so happens that there are a couple of different ways that mammals ovulate.  One of them is environmental, so there's some kind of a cue, a lot of times photo periods, so the period of light in a day or in a season, and that triggers--

Lindsey: I'm so excited.

Brit: Right?  So and that's like, completely mind-blowing that the eye picking up an amount of light makes an ovary release an egg, like, like, that's amazing, how tied in we are to our environment, and so you have that for certain species that need to do it seasonally, something like that.  Also mammals have something called induced or partner induced ovulation, and this actually comes from the act of copulation.

Lindsey: Cats.

Brit: Totally.  

Lindsey: Okay.

Brit: You're good, man.  She's good.  What's cool though is actually thinking about why something like cats--so this partner induced ovulation, we see actually in North American predators that have really wide ranges.  Well, if you have really wide ranges, not as likely to find a reproductive partner.  A lot of home ranges and especially cats behaviorally, a little more solitary, so if you were cued by the environment, it's possible that there wouldn't be a mate and you're like, dang it.  

Lindsey: Yeah, yeah, yeah.

Brit: So instead, the ovulation occurs because of the act, which makes sense if you're that kind of a species.

Lindsey: So if you don't know, domestic cats at least, have spikes on the penis that go into a vagina and can scrape the vaginal walls so that it stimulates ovulation.

Brit: Tell me more.  It's delightful.  

Lindsey: Is that all cats?

Brit: Pretty sure.  I don't know if the barbing is exactly the same in larger species, but for sure we see even in larger cats, so like I was saying, North American carnivores, so thinking about like, a mountain lion or a cougar, absolutely it's that.  It's that act of copulation that is, that is triggering and inducing the ovulation.

Lindsey: (cat sound)

Brit: Just like that.  That's actually scientifically accurate.  It's what it sounds like.  Ovulation.  (cat screech)

Lindsey: You're horrible.  Why are you tearing my vagina apart.  

Brit: Pretty much, and they're like, ovulation, you're welcome.  So environmental and induced, or partner-induced or copulation-induced, and then you might be thinking, well, I don't do either of those and that's true, because primate lineage, so us and other primates, not all primates but most do something called spontaneous ovulation, meaning that nothing is inducing it, like, it's not an environmental cue.  It winds up being a cycle, so with humans, we talk about the, you know, an ovulation cycle, a menstrual cycle.  So this is a really kind of unique thing in mammals, particularly primates, and so that is now where this research team looked and said, okay, if we want to get to the bottom of this, we want to look at which happened first in evolutionary time.  Yeah, and so like, which, like, which one of these was earlier on, and one way to do that is to look at older groups of species, so getting out of mammal town and heading in and looking, yeah, mammal town, TM, and it turns out environmental cues for ovulation, we see in fish and also some amphibians, so that's a way earlier version, if you will.  So then the question mark was alright, so then which one came first, was it the copulation-induced or was it the spontaneous?  So they decided, let's figure out some traits that we can kind of define and say, yep, that's orgasm.  So in this study, the way that they said, we're gonna look at and cue in and say, yes, that is a, again, chromosomal female orgasm, was neuroendocrine reflexes, so the brain is the neuro part and endocrine is the hormones and reflex being you responding to something.  In this particular case, they looked at two specific hormones.  What they found that was the most common to look at was prolactin and also oxytocin.  Yeah!

Lindsey: Bonding, right, of course.

Brit: So in this specific study, they said, cool, let's go ahead and define that female orgasm as this reflex of prolactin and oxytocin and then they looked across species and wound up finding that almost all of the organisms that they looked at in these trees were more likely to have this induced ovulation and that wound up correlating to where the clitoris actually is in relationship to the vaginal orifice.

Lindsey: Okay.  There's so much going on right now.

Brit: I know.

Lindsey: Alright, so you've got a tree.

Brit: Yeah.

Lindsey: That is mapping out all these different mammals.

Brit: Yep, and we call that a phylogeny, so a phylogenetic tree is showing the relationships and histories of different species.

Lindsey: Okay.

Brit: Totally.  

Lindsey: And you're looking at their hormones and you're specifically suggesting that it would be prolactin and oxytocin that are going to change throughout this tree to help us indicate whether or not these orgasms are induced like cats.

Brit: Totally.

Lindsey: Whether they're spontaneous or cyclical like human beings.

Brit: Yeah, exactly, and these primates, and so we're, we have that tree exactly and then we make a second phylogenetic tree.

Lindsey: Okay.

Brit: That instead of showing that trait, it is showing a trait specifically where the clitoris is anatomically.

Lindsey: What.

Brit: Compared to the vaginal orifice.

Lindsey: Okay and.

Brit: And it almost lines up perfectly that the clitoris being away from, instead of inside or right on the edge of the vaginal orifice, almost lines up one to one with the spontaneous or cyclical ovulators.

Lindsey: What!  

Brit: Yeah.  Which tells us that the clitoris, if it anatomically is basically right there, either inside or right along the vaginal orifice, for these species who are induced by copulation to ovulate, of course it plays the role, right?  This female orgasm, with clitoral, that tissue, anatomically, is doing the thing.  Helping ovulation do it, and then when it moved away anatomically over time, it was only afforded to do that because evolutionarily speaking, we kind of figured out how to have this whole like, cycle thing instead of just being induced.

Lindsey: Wait, wait, wait, so you're saying that in organisms that have induced ovulation, the clitoris is closer to the vagina or even within it.

Brit: Yep.

Lindsey: Than organisms like us that have cyclical ovulation.

Brit: Yeah.

Lindsey: So even though I think my clitoris is really close to my vagina, it's actually much further than other species.

Brit: It's like miles away.  Are you kidding me?  Like that inch is like evolutionary miles.  

Lindsey: And you're saying also that the reason why it has been afforded the possibility to separate more is because my body, over evolutionary time, has figured out a way to run on a cycle rather than--

Brit: Totally.  

Lindsey: Penis spikes.

Brit: Being induced.  Yeah, cycles, penis spikes, you know.  Trade offs in the balance of life here.

Lindsey: Yeah, seriously.  I'm trying to think like, what's better, menstrual cramps or penis spikes.  

Brit: And so the conclusions of this paper are like, look, if you get a little bit out of this anthropocentric or human-centric approach to this question and really just look at the lineage of mammals, you see that the older trait was having not only environmental, it was definitely older for ovulation, but that induced ovulation is the older ancestral trait and then over time, only this weird group, these weirdos that are called primates, have not only this different way of ovulation but it also lines up with their anatomy, which is just form and function, nothing like it.  Anatomy and physiology is one of the coolest ways to demonstrate evolution and change over time.  I mean, just like, how wild is that, that there's actually a correlation between where the clitoris is in relation to the vaginal orifice and the kind of ovulation you have?  That's so cool.

Lindsey: I know, so doesn't that mean that it will just like, keep going and then like.

Brit: It'll be here in like, 20 generations, probably like, at nipple.  Oh!

Lindsey: I'm hoping it's going to be on the neck.

Brit: Yeah, but if it was like, next to nipples, you should get two for one.  There's just like, three pleasure zones within eight inches.  That's not bad.  That's efficient is what that is.  Efficiency, Lindsey, efficiency.

Lindsey: This is what makes you so cool.  So if you want to check out more about Brit's mind, how it works, and how much she knows in terms of nature as a whole, Nature League.  youtube.com/natureleague.  Brit, thank you so much for teaching us.

Brit: Thank you, Lindsey.  This has been awesome.

Both: Stay curious.

(Credits/Endscreen)