December 8, 2005

About bat brains and bat testicles.

Their size is inversely proportional, and related to the sexual promiscuity of the female. Female monogamy correlates with a large brain for the male, which is the opposite of what the scientists predicted. Is it more interesting that the big-brained bat-male's sexual partner is monogamous or that a bunch of scientists speculated that promiscuity would evolve along with bigger brains? I'm more interested in human behavior, so I tend to focus on the scientists, guys who are probably proud of their big brains, and I can't help speculating that they are attracted the idea that women at their evolutionary level will be promiscuous.

(Link found via a comment on this post.)

21 comments:

Jacques Cuze said...

Pitnick and his colleagues had predicted that, in species with promiscuous females, males would require bigger brains in order avoid being cuckolded. So they were surprised to find the opposite: “Perhaps monogamy is more neurologically demanding.”

Stupid article or stupid hypothesis? How about in a species with promiscuous females, males need to be promiscuous as well as thus need bigger testes to produce more sperm.

The article mentions nothing about the monogamy of the males.

Did the scientists control for promiscuity of the male bats?

Eli Blake said...

Actually, the pertinent question would be how the size of the brain relates to the size of the pituitary gland and the hypothalamus (very likely a direct correlation).

Now I read the wrong prediction this way:

It has long been known that in monogamous animals, courtship skills are more important in the male than fighting skills, while the reverse is true in polygamous animals. Apparently the assumption was made somewhere that developing a strategy to win a fight would require more mental capacity than developing a strategy to win a mate.

And I can see how a bunch of fuddy duddy old male scientists (I know quite a few) would develop such a hypothesis, but I would suggest that it is not so much that they think they are Casanova, but rather that they are romantically challenged (women aren't easy to classify scientifically).

Eli Blake said...

quxxo:

That is why I mentioned the hypothalamus and the pituitary gland, which ultimately regulate both the amount and direction of sexual desire and the production of sperm. Large testicles has nothing to do with it.

Ann Althouse said...

Eli: Yeah, I'm picturing the guys not getting women and developing the hypothesis that they are just so damned ahead of the curve brain-wise that the promiscuous women have just not arrived yet. Oh, the pain of being ultra-evolved!

Pooh said...

Ann, tell me about it...Well, I now appear to have a ready made excuse for extended bachelorhood. Sweet!

Oh wait, I just broke the "no-sex life talk" rule. It's getting so hard to follow what can and can't be said anymore.

Jacques Cuze said...

Related: The Theory Of Incompetent Design. (Via Kos)

So is there intelligence in the design?
Yes! No, no there isn't. The thing that perhaps is closest to all of us is our own skeleton, and there are certainly all kinds of stupidity in our design. No self-respecting engineering student would make the kinds of dumb mistakes that are built into us.
All of our pelvises slope forward for convenient knuckle-dragging, like all the other great apes. And the only reason you stand erect is because of this incredible sharp bend at the base of your spine, which is either evolution's way of modifying something or else it's just a design that would flunk a first-year engineering student.
Look at the teeth in your mouth. Basically, most of us have too many teeth for the size of our mouth. Well, is this evolution flattening a mammalian muzzle and jamming it into a face or is it a design that couldn't count accurately above 20?
Look at the bones in your face. They're the same as the other mammals' but they're just squashed and contorted by jamming the jaw into a face with your brain expanding over it, so the potential drainage system in there is so convoluted that no plumber would admit to having done it!
So is this evolution or is this plain stupid design?

John(classic) said...

"The article mentions nothing about the monogamy of the males.

Did the scientists control for promiscuity of the male bats?"

----------
Brief mention in the article:

"Male fidelity appeared to have no influence over testes or brain size."

Jacques Cuze said...

You're right, thank you.

John(classic) said...

"How about in a species with promiscuous females, males need to be promiscuous as well as thus need bigger testes to produce more sperm."

On the whole? One pteropine Casanova could support a lot of adulterous females.

Slocum said...

I'm more interested in human behavior, so I tend to focus on the scientists, guys who are probably proud of their big brains, and I can't help speculating that they are attracted the idea that women at their evolutionary level will be promiscuous.

My sense has been that females of the human species tend to be more enamored with our promiscuous 'relatives'. A lot of academic feminists seem to love those wildly promiscuous Bonobos.

Jacques Cuze said...

On the whole? One pteropine Casanova could support a lot of adulterous females.

According to Darwin, I want *my* sperm in the next female. Not that he's judgmental, but he says YOU will be a failure in your species if YOUR sperm isn't in that female.

John(classic) said...

"According to Darwin, I want *my* sperm in the next female. Not that he's judgmental, but he says YOU will be a failure in your species if YOUR sperm isn't in that female."
==========
Is that necessarily true (as a specific conclusion from Darwain, or as a more general conclusion from evolution)?


If an individual's purpose in life is to see that his genes prosper, that could be done either by fertilizing a lot of females, or by fertilizing a very few and seeing that the female and the offspring have a high probability of survival. In other words, monogamy may be a tool for increasing the chances of survival of one's genes.

Might be a much better chance than practices such as that of some jellyfish, which I recently learned are hermaphrodites who simultaneously release sperm and eggs in a sort of huge jellyfish mass orgy.

Jacques Cuze said...

I believe Darwin insisted that YOU are (an evolutionary) failure if YOUR genes don't propagate. But I don't know.

I believe what you are referring to is evolutionary altruism:

The Evolution of Altruism

Despite the overwhelming success Darwin’s theory has had in explaining a wide variety of natural phenomena, great debate continues over the theory’s application in explaining the evolution of an aspect of animal behavior known as altruism.

Altruism is the deliberate sacrifice of a portion of an individual’s reproductive capacity in order to increase that of another. This reproductive capacity is more often described as an individual’s genetic fitness, and is precisely defined as the contribution an individual makes to the gene pool of succeeding generations relative to the contributions of other individuals within a population. Thus, an altruist is defined as an individual who decreases his own genetic fitness to increase the fitness of another. The concept of altruism is best understood through example: an African wild dog voluntarily “babysitting” the pups of a pack, while the pack’s hunters search for food ; a bird giving an alarm call to warn others of an approaching hawk, and thus drawing attention to itself in the process ; a man jumping into a swimming pool to save a drowning stranger. While these acts obviously require different levels of sacrifice on the part of the altruist, on average we can expect all of them to decrease his number of expected offspring.

This is where the paradox of altruism arises. If, by definition, altruism reduces an individual’s fitness, we should expect Darwin’s natural selection to select against the altruistic trait and eventually reduce its representation within a population to zero. Even if a population existed that contained only altruists from the beginning, it would be vulnerable to subversion from within, whereby a single, mutant selfish individual could exploit the altruistic tendencies of his neighbors and eventually drive the altruistic trait to extinction.

Although the problem of altruism was largely ignored by early evolutionary theory, over the past several decades it has risen to become a central issue in the debate over the level at which natural selection operates - whether that be the level of the gene, individual, kin group, or even an entire population. Numerous theories have been proposed to explain this phenomenon, several of which are discussed bellow.


More at the link, including mathematical goodness.

John(classic) said...

quxxo-

Actually I meant something different.

Suppose a gander. He has two alternative ways of giving his genes a high probability of propagation. He can fertilise as many geese as possible, or he can fertilise one goose, and provide aid to her and their goslings so that the goslings survival is more likely.

Note that the goose has different impetuses. To her it matters not that the goslings are the progeny of a particular gander, only that he thinks they are and provides protection. Indeed over successive pregnancies her genes' propagation would probably best be served by cuckoldery--combining her genes with a wider gene pool while still obtaining protection from the gander would be a very profitable strategy for her genes if she could get away with it..

As the complexity of organism increases, the investment by the father in protection and child rearing may become quite substantial . An error by the father in which female and progeny he invests resources in can become very expensive for the propagation of his genes. A jellyfish, on the other hand, need not worry about wolves, migration,the scarcity of tasty antelopes, or dance lessons.

Which brings us to virginity rings. Might these be a way for a female to advertise her desirability by saying "I am not already pregnant. My children will have your genes. You can invest resources with confidence"?

Unconsciously, of course.

Jacques Cuze said...

As the complexity of organism increases, the investment by the father in protection and child rearing may become quite substantial. An error by the father in which female ... he invests resources in can become very expensive for the propagation of his genes

Oh man, don't I know it!

reader_iam said...

Huge jellyfish mass orgy.
Huge jellyfish mass orgy.
Huge jellyfish mass orgy.


Could that explain the invasion of the Japan, S. Korean, and Chinese fishing waters by gigantic jellyfish (6 feet wide and weighing 450 pounds, with countless poisonous tentacles)?

Shudder.

Ann has her issues with squirrels.

I, with jellyfish (freakin' freaks).

Ugh.

reader_iam said...

Fascinatin' discussion here, otherwise ...

(No offense, johnclassic. It's my problem, not yours.)

John(classic) said...

reader_iam said
Could that explain the invasion of the Japan, S. Korean, and Chinese fishing waters by gigantic jellyfish (6 feet wide and weighing 450 pounds, with countless poisonous tentacles)?

=============
Could explain a lot about government too..

peter hoh said...

It's kind of like what John Roberts had to say about judges and umpires. Scientists get to measure the bats and balls, but they don't get to swing.

Bruce Hayden said...

Originally, I didn't think that the authors made their point that well. But rereading the article, I think they do.

The thing is that species, for the most part, are in equalibrium (I think that humans fairly recently went out of equalibrium). That means that a balance is struck between all sorts of competing requirements, including, as the authors suggest here, energy consumption.

So, in different species we see different strategies. In some, the males compete for the females, and in others, they just stand in line. The former would seem to prefer brains over testes, and the later the reverse, with their sperm doing the competition.

I think the result logical, and therefore, find the scientists original alternative hypothesis to have been the questionable element.

But I think that their problem was in looking at it from a cuckhold point of view. What they didn't explain, and may have been critical here, is how the males in the different species competed for the females, if indeed they did.

In some species with promiscuous females, there is not that much overt competition among males. Rather, they let their sperm compete for them. Some of our (pygmy?) chimp relatives are that way. Everyone screwing everyone, male or female. Or, dogs and house cats, which seem to be fairly indiscriminate, with the females likely to be inseminated by multiple males (for multiple births).

Getting back to Ann's question, I don't think that it would be valid to extrapolate between bats and humans here. Our testes size is commensurate with mild female promiscuousness. Maybe 75% or so of kids born belong to the putative father. This, of course, ranges significanty depending on the relevant societal norms.

I think instead of looking at this as smart male versus dumb female, it is better to look at this as smart male versus dumb male. But the reason that this would not necessarily translate to humans is that our females have an incentive to be smart too - to keep the males happy so they will stick around and help raise the kids. Not so with most other species.

So, no, I don't think that the scientists were tying smart and promiscuous together. Esp. since the level of human male and female promiscuity is fairly well known.

Mary said...

I think there should be a "Best Comment" for the year award.

peter hoh, 10.36. Topically funny!