mate economics

Lately, I've been reading a lot about women's mate preferences. Professional reasons, I assure you. One of the more intriguing methodologies I've come across has used economic principles, like minimum standards and diminishing marginal returns, to examine people's priorities in mate characteristics. The central issue at hand is sex-differences.

Briefly, evolutionary psychologists have proposed that (heterosexual) men and women tend to value different things in romantic partners because of their reproductive value. These differences emerge based on the asymmetric costs of sex. In our species, like most mammalian, females get pregnant. Therefore, women have to be particularly careful about mating situations since there's the possibility of internal fertilization. Remind yourself that we're talking evolutionary history here, and how our ancestral environment shaped the design of our respective male and female brains. Thus, any reference to reliable contraception (such as the pill) is irrelevant. Robert Triver's parental investment theory predicts, specifically,that the sex making the largest investment in lactation, nurturing and protecting offspring (women, in our case) will be more discriminating in mating - and the sex that invests less in offspring (men) will compete for access to the higher investing sex.

Sex differences in mating strategies and preferences are particularly visible in species like the elephant seal, where there is a vast sex disparity in parental investment. Males compete (vigorously) for access to reproductive females, and females choose to mate only with the most dominant males. Females, in effect, are "choosing" nothing more than the genetic quality of their mate, since he'll have absolutely nothing to do with parental care.

Humans, admittedly, are a different story. We're defined by intense bi-parental care of our offspring, due in large part to our extended childhood and period of vulnerability - which in turn exists because our massive brain needs time to develop and acquire boatloads of information. Thus, we might expect sex-differences in mating strategies and preferences to be less extreme in our species - and they are. But don't doubt that they still exists. Men cheat more than women, crave a wider variety of sexual partners, and tend to be less discriminating. For example, if you ask men and women what's the likelihood that they'd have sex with someone they've known for 1 year... or 1 month... or 1 week... or 1 hour... you get data like these:

(cool data presented in a shitty graph)

A positive number on the y-axis indicates a positive inclination to have sex, so it's interesting to look at where the lines cross the x-axis for both men and women. For women, it's around 6 months. For men, it's around 1 week. Now, admittedly, these data were collected approximately 20 years ago and some might argue that "things have changed, man! Women hook up ALL the time, now." Bullshit. If anything, recent evidence suggests that college women are having less sex nowadays than they did 10 years ago, even if they are engaging in more non-commital make-out sessions with boys in the back of the bar/party/van/etc.

When it comes to specific mate preferences, or what we look for in members of the opposite sex, we're all pretty choosy. Neither men nor women (some fools notwithstanding) mate indiscriminately. But there's still the question of what we prioritize. What traits do we particularly value in our partners? And here we will find some interesting sex differences that again can readily be explained by evolutionary theory.

Briefly, men tend to place greater importance on physical attractiveness than women do. This largely has to due with cues of youth and reproductive fertility. Women, in contrast, tend to place greater importance on resources than men. "Resources" in this context can mean many things - it could mean actual wealth, for example, or traits that help one acquire wealth (such as industriousness, intelligence, social status, etc.). This largely has to do with finding a mate that can help support the family and offspring survival outside of immediate investments, like breastfeeding. Our ancestors survived, and successfully passed on their genes, because of this reciprocal cooperation and division of labor.

If you ask men and women to rank a list of traits that they value in marriage partners, you'll get something like this (from Buss & Barnes, 1986):

(click for larger image)

Men and women agree that "kindness and understanding" are vital. There is no sex difference there, or with an appreciation for intelligence, creativity, and health. However, three items stand out on this list: 1) physical attractiveness, 2) college graduate, and 3) good earning capacity. Each of these shows a strong sex difference in how men and women ranked their importance. Can you guess who ranked each one higher?

This is all well and good, but isn't how mate-choice works in the real world. We deal with people who are amalgamations of many traits, a combination of physically stunning but none-too-bright, or brilliant and rich but cruel. What do we do in these situations? Well, we prioritize. We weigh costs and benefits, and depending on what we're looking for at that moment in our life, we make (imperfect) decisions. Herein lies the brilliance of the economic mate-choice model, introduced by Normal Li and Doug Kenrick.

You have 20 "mate-dollars" to spend on a potential sexual partner. This is only going to be a one-night stand and you'll never see this person again. You can distribute this money across a number of traits, including physical attractiveness, kindness, intelligence, and so on. Where do you put your money? What do you value most highly?

Perhaps not surprisingly, when phrased like this - with a relatively small budget and a casual sex scenario - both men and women put a lot of money into looks (66% of budget for men, 54% for women).

But now, let's say, you're shopping for a marriage partner... a soul mate. What will you invest in? Will you really put that $15 into attractiveness, when you're sacrificing intelligence, amicability, and empathy? Well, if you're a man, you're more likely to (actually, men put about 1/3 of their budget into looks, even for a long-term partner - compared to 25% for women).

(from Li & Kenrick, 2006)

A clever model. Social psychology can sometimes leave a bad taste in my mouth, because it's based so heavily on self-report data and is often atheoretical. But I admit to liking evolutionary-minded analyses like these, which demonstrate (in many ways) what we've long suspected: men and women are different. But the valuable lesson here is that they're different for a reason, and that reason isn't as simple or dull as "culture taught them to be so."

LHC is Cthulhu

First paragraph from Lovecraft's The Call of Cthulhu (1928)...

"The most merciful thing in the world, I think, is the inability of the human mind to correlate all its contents. We live on a placid island of ignorance in the midst of black seas of infinity, and it was not meant that we should voyage far. The sciences, each straining in its own direction, have hitherto harmed us little; but some day the piecing together of dissociated knowledge will open up such terrifying vistas of reality, and of our frightful position therein, that we shall either go mad from the revelation or flee from the light into the peace and safety of a new dark age."

Of course, he may be referring to the Great Old Ones, dreaming in R'lyeh until they wake and destroy us all (see Cloverfield).

Cthulhu fhtagn!

But might not the "terrifying vistas of reality" also be these trauma-inducing images from the Hubble?

Oh mighty crab nebula, I worship thee

Or the tentacled limbs of the Large Hadron Collider, and the dark mysteries it will reveal?

asymmetric tail-wagging

This is old news by today's standards... but lately I've been thinking about it some more, after watching Fenris wag his tail when Aili or I come home or when he meets another dog.

In the April 24, 2007 New York Times, there was a Science Times article on asymmetric tail-wagging. Some Italian scientists hypothesized that dogs may possess hemispheric asymmetries in the neural regulation of their emotional/motivational responses. The valence hypothesis argues that the left hemisphere of the brain is more specialized for processing positive emotions (e.g. joy, safety, attachment), while the right hemisphere regulates more negative emotions (e.g. fear, anger).

I should note at the outset that I have never been a particularly big fan of hemispheric asymmetries - or rather, how they become distorted and exaggerated for public consumption. By and large, neuroscientists don't have a firm understanding of the various differences between the hemispheres. There are some "known" lateralizations:

1. language processing is biased towards the left hemisphere
2. spatial ability is biased towards the right
3. the left hemisphere regulates somatosensation (touch) and motor control on the right side of the body, and vice-versa: the principle of contralateral control

But I cringe when I hear people say things like, "she's a right brain person - so emotional and artistic." First off, this assumes that because there are functional and structural differences between the hemispheres, there will also be significant differences between individual people in hemispheric dominance. This may or may not be the case. It is possible that Larry has better spatial ability than Moe because his right hemispheric spatial centers are more broadly developed (or distributed), due to either genetic or environmental influences. But this is a big assumption. Correlating individual differences in behavior & personality with individual differences in brain structure (a la phrenology) is not something that most neuroscientists focus their attention on.

Second, there's this thing called the corpus callosum, a dense collection of axons that connect the two hemispheres and allow them to fluidly communicate with one another. This means that most complex cognitive functions are mediated by both hemispheres. Even when it comes to language processing, the right hemisphere makes significant contributions (especially if you're left-handed and/or female). "Left brain" and "right brain" are misnomers. Such terms are really only applicable when referring to those wacky split-brain patients.

All this is not to say that hemispheric asymmetries don't exist. There are hundreds of empirical demonstrations, perhaps the most convincing being the aforementioned split-brain studies conducted by Gazzaniga and his students. I recall learning about these experiments during my junior year in college, at the same time I was taking a course in metaphysics from Derek Parfit. He had us read all these crazy thought experiments on "identity"... So, you're on Earth and some engineers first scan and then destroy your entire brain and body. They recreate you, cell by cell, on the Moon using that scanned blue-print. Is this Moon version still "you"? The emerging materialist in me would scream (silently, from the back of the lecture hall) "Yes!" And then Derek would throw that mind-blowing loop in: what if the engineers fucked up and didn't destroy your Earth copy but still created your Moon copy? Which version is actually "you"? Are they both "you"? Is that possible, given how personal identity is? Which individual's consciousness would you occupy? When you opened your eyes after the operation, would you see Earth's green fields or the desolate lunar landscape?

So here I am going through some weird existential identity crisis, and then my cognitive neuroscience professor starts telling me that if you cut your corpus callosum, you will actually have two identities within yourself. One hemisphere might have you reach out your right arm to hug your wife, while the other hemisphere is having your left hand grab a knife. Or something less dramatic, but you get the point. Why would our brain be designed this way?

Of course, there is a strong engineering advantage to this kind of specialization: division of labor. It is likely that lateralization evolved because individuals with more specialized hemispheres were better able to juggle multiple cognitive tasks at once, be more likely to survive and eventually reproduce. Turns out that hominids aren't the only ones with these kinds of design characteristics. On to the actual experiment...

Quaranta A, Siniscalchi M, Vallortigara G (2007). Asymmetric tail-wagging responses by dogs to different emotive stimuli. Current Biology, 17: R199-201.

The experimenters placed test dogs in an apparatus that allowed them to present controlled stimuli and concurrently measure tail-wagging responses. The stimuli used were: the dog's owner, an unknown person, an unfamiliar dog, and a cat. The specific tail-wagging variable the authors were interested in was wagging angle. This was assessed using the following method:

"Tail wagging scores associated with the different stimuli were analyzed from video-recordings. Positions of the tail were scored every 10 seconds by superimposition on the computer screen of a cursor on the long axis of the body: the maximum extents of the particular tail wag occurring at each 10 second interval was recorded. Using single frames from video recording two angles were identified with respect to the maximum excursion of the tail to the right and to the left side of the dog's body (Figure 1). Tail wagging angles were obtained with reference to the axes formed by the midline of the dog's pelvis — the segment extending lengthwise through the dog's hips, drawn from the largest points as seen from above; dotted line in Figure 1 — and the axes perpendicular to it. Tail wagging angles were evaluated by the segment that extended lengthwise through the base and the tip of the tail, considering the tip of the sacral spine as 180° and the base of the tail as 0° (as in Figure 1). Minimal movements of the tail, within a range of maximum 3° overall, which were plausibly not correlated to wagging, were discarded."

The results?

• When dogs were shown their owner or an unknown person, they exhibited a right-sided bias in amplitude. In other words, their tail swung farther and more extremely to the right than to the left (as shown in the image above: compare an 85 degree swing to the right versus a 70 degree swing to the left). This more intense wag to the right in indicative of greater left hemisphere involvement. The left hemisphere, according to the valence hypothesis, is associated with more positive emotions. So, when a dog wags more intensely to the right, they are expressing joy/attachment/love/etc.
• In contrast, when subjects were shown an unfamiliar dog, they exhibited a significant left-sided bias in tail-wagging. This is indicative of right hemisphere dominance and negative emotional valence. A dog wagging its tail more intensely to the left is expressing anxiety/threat assessment/etc.
• The cat condition provoked minimal tail-wagging, but interestingly enough, a slight right-sided bias.

What are we to make of this? Well, before I swallow this whole, I'd really like to see a detailed explanation of how the canine brain regulates muscular control in the generation of a tail-wag. The issue here, as Dr. Davidson in the NY Times piece points out, is that the dog tail lies along the midline of the body. How does contralateral control of musculature apply to a limb that isn't asymmetric?

Hmmm... google search in progress...

"The canine tail usually consists of between six and 23 highly mobile vertebrae.These vertebrae are enclosed by a versatile musculature that make the various segments, especially the tip, capable of finely graded movements that lift the tail, move it from side to side, or draw it down toward the anus or between the hind legs. The caudal muscles lie on the lumbar vertebrae, sacrum (in the lower back region) and tail vertebrae. The muscles insert on the tail/caudal vertebrae exclusively. The muscles are attached to the tail vertebrae by tendons. The most posterior tendons attach to the last tail vertebrae. Part of the musculature is formed from muscles associated with the rectum, the anus and the pelvic diaphragm. Four to seven paired nerves serve the tail muscles. These muscles have many tendons that insert from the fifth or sixth caudal vertebra, then onto the next vertebra, and so on to the end of the tail."

So I suppose that the left hemisphere (motor cortex) controls muscles on the right side of the tail that can pull it in that direction. And the right hemisphere controls muscles on the left side of the tail that pull it in the other direction.

A final note: there is also evidence that our facial musculature exhibits a slight lateralization when we make emotional expressions. Happier emotions, exemplified by smiling, are expressed more strongly in the right side of our face. Negative emotions show a left-bias. It is possible that when we meet someone we have conflicted feelings about (we enjoy their company but find them slightly annoying), these emotions play out in a lateralized fashion on our face.

Might all this be partly responsible for the notion of left as sinister?

monkey-controlled robot destroys los angeles

This story was printed today in the New York Times science section: "Monkey's thoughts propel robot, a step that may help humans." I'm always on the lookout for anything neuroscience-related that seems to fuck with our notion of what's science fact and what's science fiction, and this one certainly fits the bill. As I understand it, the scientists implanted some recording electrodes into the motor cortex of a monkey, somehow translated this code of electrical activity into a set of instructions for a robot (?) such that when the monkey walked, the robot walked in a similar fashion. This, by itself, is pretty impressive. But the experimenters were also able to get the monkey to make the robot walk by using only its thoughts (and some clever operant conditioning), even when it wasn't walking on the treadmill. Here's a schematic that will help you make sense of what I just said (and visit the link for full details):


I am actually astounded by this. I really had no idea we, as a scientific community, had the knowledge necessary to make this possible. There are a couple of issues here that really stand out and beg for further information:

1. Where exactly in the motor cortex were these electrodes? It sounds like the team was trying to capture the neural code of not movement itself, but motor-planning. That's premotor cortex, rather than primary motor cortex. Premotor cortex is also where you find lots of mirror neurons, which fire when an animal either does something or watches another animal engage in the same behavior.

2. How the hell did they translate this neural code into a set of motor instructions for the robot? Quoting from the article:

"The video and brain cell activity were then combined and translated into a format that a computer could read. This format is able to predict with 90 percent accuracy all permutations of Idoya’s leg movements three to four seconds before the movement takes place."

Ummm, ok, but... what? FP/MC, got any thoughts here? Cracking the neural code in this fashion is perhaps the defining problem in computational neuroscience, and it seems like these guys have done it (at least with motion). Am I just naive to what's going on in my field? (probably)

If you're wondering why you'd even want to do something like this, well... I'm a little disappointed by your lack of imagination. Besides the eventuality described in the title of this post, you could use this technology to 1) provide people who are paralyzed with robotic helpers, 2) control robotic movements in dangerous environments (e.g. mining delithium crystals on asteroids), 3) play a much cooler version of Team Fortress 2.