There is so much animals can teach us about who we are and who we have always been, especially in regard to our love lives. Whenever I ponder human behaviour, I try to consider the biological reasons for why the behaviour may have evolved over time. In these posts, I discuss my thoughts on these matters.

Bat research is fascinating

my research project on sperm competition in bats

/0 Comments/in , /by

Hi folks – long time, no blog!

I have written before about the relationship between testes size and brain size in micro bats (aka echolocating, insect-eating bats as opposed to fruit or nectar eating bats). Many of you have also emailed me information about the scientific study that was published in 2006 by research team Pitnick et al. that first demonstrated this relationship. Thank you very much for that and in exchange I thought I might give you a bit of an update on what I am in the middle of doing to further our understanding of the brain-testes relationship in bats.

For my masters degree I am looking at whether or not there are any differences in the brain volume of male and female micro bats. I have been wondering if there might be ever since reading about Pitnick et al.’s study. My thinking was that if there is, indeed, some sort of inverse relationship in bats between brain size and testes size whereby the two metabolically expensive organs trade off against each other then it stands to reason that perhaps females could have larger brains than males since they don’t have testes competing with their brains for dominance in the body. At least, I thought, this might be the case in species where males have very small brains due to their enormous testes which hog all the body’s resources.

My study is fairly small in scale but I am hoping that it will still prove interesting. I am comparing averages of male and female brain volumes in 9 Australian micro bat species – some that have mating structures where females are promiscuous and some where females are loyal to a single mate (a dominant male harem leader). To do this we are CT scanning a collection of skulls and then using computer technology to create 3D models of the brains as a way to ascertain volume.

Here’s a picture of the first skull we scanned. It makes me laugh every time I look at it – such a big machine to scan such a tiny object (that little spot on the blue towel is the skull):
going through the CT scanner

And here is a model I am putting together of that same skull. It needs work but it’s still pretty cool:
model of a bat skull - in progress!

Interestingly, the factor that influences testes size in micro bats in female sexual behaviour. When females are highly promiscuous and take many sexual partners the males tend to have much larger testes than species where females are loyal to a single mate. It is assumed that the large testes trait develops in species where females are promiscuous because there is greater competition among sperm for access to the eggs in these individuals and so those males with more sperm available tend to be selected for over time. It is similar to how if you are really keen to win a meat raffle you will buy more tickets.

The same relationship between female promiscuity and testes size occurs in primates, including humans and for that matter, basically all animals. You can look at most any wild animal and get a good idea of the level of female promiscuity by looking at the testicles of the males. The difference with bats is that because bats weigh very little (as little as 2 grams!!) and have an extremely tight energy budget they cannot afford to have both heavy brains and heavy testes and so they trade one tissue type against the other.

Pitnick and his colleagues in their landmark study originally predicted that the opposite relationship would occur – ie that large brains would equal large testicles. They postulated that species with promiscuous females would have larger brains as a way for the males to avoid being cuckolded. They were surprised when they discovered that the opposite was true and remarked that “perhaps monogamy is more neurologically demanding.” I think many of us would attest to the truth of this statement!

If my study shows that there are any size differences in male and female bat brains as a function of testes size it may potentially mean that female promiscuity is a force strong enough to influence male intelligence in a measurable way. An intriguing notion but at this stage very much a theoretical one.

*Sidenote: the boys on the construction sites where I have been working have heard me talk about animal testicles so much that they have become terrified I’m going to show up at their bedroom door one day with my calipers! Actually that’s not completely true .. some have actually volunteered for the job! .. all in the name of science, right? 😉

** Oh and yes the bat in the picture above is alive! It was just very very cold because I pulled it from a tree which had just been buldozed on a construction site in the very early hours of a winter morning.

Size matters – and if it didn’t, you’d be smaller

/3 Comments/in , /by

Does size matter? It’s the age old question. Some say that it’s the ‘motion of the ocean’ that matters while others have pointed out that ‘they don’t make small dildos’. Still others have pointed out that, actually, they do make small dildos! If you ask me, I’ll tell you that size does matter. But I’m not just speaking of pers

onal preference, here. The question of whether or not length and/or girth is important becomes obvious if you look, as I always do, to the animal kingdom.

Male humans, you see, have penises far larger than any of the other primate species around the world. Even Silverback gorillas, as massive as they are, only manage to achieve erections of about 1.5 inches. Many theories have been put forward for why humans have such large dingdongs. Originally they wondered if a big penis might have evolved to make insemination easier but that didn’t make sense since the less endowed primates are just as good at breeding as we are. They then thought a big wang might be useful in male/male competition (aka showing off) but then they realized that most indigenous cultures have coverings over their genitals so that didn’t seem like a good explanation either. They then wondered if a big cock might have evolved to help us to perform some of the more adventurous kama sutra style position that many of us are quite partial to but that also didn’t make sense because orangutans, chimps, bonobos and many other primates are into all the same crazy shit that we are – and then some!

Finally someone wondered

if female choice might have been involved but this was dismissed almost immediately after a few studies showed that women don’t really like looking at penises. This isn’t surprising considering what a huge epic fail playgirl magazine was!

So if women don’t even like to look at penises could female selection really be involved in the evolution of the huge human wang? Well as Meredith Small points out in her book ‘Female Choices: Sexual behavior of female primates‘ .. and as what virtually all women already understand .. a woman doesn’t have to love the sight of a cock to appreciate how it feels. Hence it is entirely possible and indeed very likely that the reason men have such large penises is that women enjoy them so much that over time they mated more often with these big boys than with the little smokeys and essentially bred the big cock gene into the species. Women, therefore, are amazing designers. Not just of fashion and homes but of men – and their penises!

Of course female don’t’ always have choice over who they mate with. There are arranged marriages and tribal system where a dominant male type character has rights to females and of course there has always rape. Also women will also make mate choices based on things other than cock size (shocking, I know). But generally speaking it can definitely be argued (and I do) that there have been enough women choosing mates based on their cock size over the last few thousand years to increase the size of human penis beyond what would ever be necessary on a purely functional basis.

So does size matter? Of course it does .. but don’t worry. You’re already doing way better than almost any other primate on Earth.

If you enjoyed this you might also enjoy my post on primate testicles …

The biology of why guys are obsessed with lesbians

/0 Comments/in , , /by

From gay to straight and everything in between, there is an enormous amount of sexual inclinations out there and every last scintillating one of them is natural. There is not one mating system that humans have thought of that an animal did not think of first. Sex is, after all, an animal act.

The obsession so many men have with lesbians, though, has always perplexed me. Lesbian porn, in particularly, is baffling. It’s not really made for lesbians; it’s made for straight men. They love it so much that they regularly destroy their monthly internet download limits in their pursuit of it, and for what? As Susan from “Coupling” pointed out, “it’s a whole area of sex with nothing for them to do”.

Women don’t seem to share this obsession with homosexual behaviour in the opposite sex. Sure, we love our gay boys but you don’t see us crawling under the covers with a rabbit, an iPad, and some gay male porn. It just doesn’t do for us what it does for them. Why is that? Well, once again I suspect it has to do with our evolution.

Female koalas will mount one another when there is a hunky male around

Homosexual behaviour has been documented in over 1500 species and well-studied in about 500. More often than not this “homosexual” behaviour has to do with female/female interactions rather than male/male interactions (although there are plenty of documented accounts of those as well). The most common female/female sexual interactions that you see don’t seem to be inspired by a genuine attraction of a female to another female as much as its a way to for the females to signal to the males that they are ready to be mated. Females are not fertile all the time so homosexual behaviour is one way that they can signal to males when they are. Its comparable to girls making out with each other in night clubs as a way to get the attention of men. Males don’t need to use this same technique to signal to us when they are ready to mate because they are always ready to mate. They don’t have cycles of fertility like we girls do.

Cows are one of these species famous for lesbian behaviour. The girls will regularly mount one another when they are in heat which researchers think is partly to do with their peaking oestrogen levels (which make them feel uncontrollably sexual) and partly to do with their needing a way to signal to the males that they are fertile. My research advisor at the University of Queensland is studying this same behaviour in koalas. Captive female koalas will mount one another when there is a male koala around but, interestingly, not if they are left alone. Sometimes they will reject the advances of the male, though, and continue on with the lesbian escapade. Why this happens is a biological mystery.

Because of this way that many female animals will display homosexual behaviour when they are in heat or otherwise ready to mate, male animals seem to be forever on the lookout for signs of girl-on-girl action. With this in mind, it makes perfect sense that a man would get a rise out of watching lesbians in action. There must be some ancient, primal, instinctual thing happening in men (most of them, anyway) that recognises female homosexual behaviour as a sign of female fertility and mating-readiness.

Let it be known, though, that while it appears that many female animals act homosexual as a way to attract males, there are plenty of truly homosexual female animals who don’t seem to be, in any way, seeking male attention by way of their behaviour. The classic example is the swan family. Swans are known for being exceptionally loyal in terms of mate choice. Swan couples generally stay together for life and it is not uncommon for them to choose a mate of the same sex. Probably the most famous lesbian swan couple lives in Boston Public Garden but there have been many others documented elsewhere.

Photo credit

The biology of why guys are obsessed with threesomes

/in , /by

Threesomes. Every man’s fantasy. Personally I’ve never seen the appeal but then again, I’m not a man. I’ve always found it interesting that even though a lot of women have participated in threesomes, very rarely are they participating in a two men/one woman arrangement. It’s almost always two women with one man. Why is that? My guess is that it has to do with our evolution.

You see, humans evolved to be essentially polygamous where one man would have 2, 3, or maybe even more wives depending on his social status and how good of a provider he was. Most indigenous societies around the world function this way and in a lot of ways promiscuity for a man and loyalty to a single partner for a woman makes perfect biological sense.

Our most primitive urge is to procreate and those that are the best procreators are the ones that pass their genes, most successfully, on. We are always, therefore, seeking to be the most effective procrators possible. The best way for men to be good procreators is to have many wives or sleep around a lot (especially if they are saving time by taking the girls 2 or 3 at a go!) Females, on the other hand, are limited in how many babies they can have and so our strategy is to do the best we can to make sure the babies we have stay alive. For women, polygamous life is just practical. With other women around, you have some help with the children and whatever work needs to be done. With them around nobody is ever left alone at home all day with a screaming infant and if you get sick and aren’t able to care for your little one, there is always someone else who can. For this reason I have always suspected that the loss of our tribes is felt most strongly by stay at home moms.

Our primal, polygamous nature is still very much a part of our genetics and its the reason why so many guys are hesitant to tie themselves to just one woman and why, to them, the idea of a threesome is just deliciously tantalising. And likewise, our polygamous nature where many females would have been loyal (for the most part) to a single man is why even those women that could easily attract the attention of a legion of men still generally idealise a romantic union with just one other person.

A lot of my friends are surprised when I tell them that I can really understand the thinking behind the women and also the man in the reality show, “Sister Wives” which centres around a polygamous family in Utah. I can understand how it must be nice for the women to have the company of one another and I respect the man for having an up-front polygamous marriage rather than pulling a Tiger Woods.

Some men are just like gorillas

Coincidently, gorillas are similar to our human ancestors and to the Sister Wives in the way that one male will have a harem of many loyal females.

photo credit: silverback

Men are competing for us even after they have cum and gone (sperm competition in bats and people)

/0 Comments/in , /by

It’s true – even after a man manages to woo us, fend of the competitors and get us into the sack, the job still aint done. At this point he basically just relays the responsibility onto his sperm who continue to compete in what reproductive biologists call a “sperm competition”. For sexually monogamous couples there are no sperm competitions but when a woman cheats on her partner or if she goes on some kind of unprotected Girls Gone Wild SOCal spring break, there can be stiff competition (pun sadly intended) for sperm.

I have just begun research into sperm competition for my master’s degree. I’m studying it in regards to bats. Bats have always been of fascination to me but it wasn’t until I started learning about their sexcapades that I decided to go into major student debt over it!

You see, because many species of bat live in gigantic social groups (sometimes numbering in the hundreds of thousands) there are near unlimited opportunities for them to sleep around (or “hang out” as we Gen-Y’ers call it ..hey maybe we get this term from the bats!). Most bats also don’t believe in monogamy. Only 12 of the over 1,200 species of bat are believed to be monogamous – and with a little genetic testing, I’m convinced it’s even less than that. They tend to live either polygamously or, more commonly, like baboons where any male can mate with any female with the exception of some direct family members. For bats, every day is a SOCal spring break! At least in the breeding season, anyway.

Even more ridiculous, female bats can distend their reproductive tracts to hold huge quantities of semen which they can keep alive in their bodies for up to 200 days!! All of this adds up to a situation where sperm are competing with each other like gang busters.

What happens, then, when the sperm have to compete so much is that natural selection favours males with larger balls (that produce more sperm) in the way that if you want to win a raffle you buy more tickets. Over time, then, bat balls have evolved to absolutely vulgar proportions! In one species, the Rafinesque’s big-eared bat, the combined testes weight is 8.4% of total body weight. That’s the equivalent of a 180lb man walking around with 20lb balls! IT’S INSANITY!!

The craziest part of it, too, is that because bats have to maintain low body weights in order to fly they can’t just carry around these gigantic balls without having to pay for it somewhere else and so not surprisingly – the brains take the hit. They have actually found that the larger the balls of a bat, the smaller the brain*.

I was just thinking about all of this in the shower (as you do) and realised how ridiculous it all is. I mean in an effort to be the winner of the sperm competition, testicles only think to do one thing: produce more sperm. Even if the end result makes them dumber. Does it never occur to them to produce quicker, faster, more efficient sperm and not have to sacrifice grey matter? Nope. Well, sometimes. Occassionally, rather than producing more sperm to win the sperm competition they’ll produce bigger sperm but this really isn’t much better.

And doesn’t this just sum up men perfectly?? I mean the male agenda is always about bigger, better, more. Women on the other hand, understand value. That’s why we produce one perfect, valuable, egg rather than a million crappy ones. Not to mention why we fantasize about one perfect partner instead of a threesome …

*This doesn’t apply to flying foxes

Photo credit