Detecting genetic disorders with 3d face scans September 16, 2007Posted by Johan in Abnormal Psychology, AI, Applied, Behavioural Genetics, Developmental Psychology, Face Perception.
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Following on from last week’s post on smile measuring software, The Scotsman (via Gizmodo) reports on the work by Hammond and colleagues at UCL, who are developing 3d face scans as a quick, inexpensive alternative to genetic testing. This is not as crazy as it sounds at first since it is known that in a number of congenital conditions, the hallmark behavioural, physiological or cognitive deficits are also (conveniently) accompanied by characteristic appearances. The classic example of this is Down syndrome, which you need no software to recognise. More examples appear in the figure above, where you can compare the characteristic appearances of various conditions to the unaffected face in the middle.
Hammond’s software can be used to identify 30 congenital conditions, ranging from Williams syndrome (a sure topic of a future post) to Autism, according to the Scotsman. I know of no facial characteristics of autism, so I would take that part of the story with a grain of salt. The system claims an accuracy rate of over 90 percent, which is not conclusive, but certainly good enough to inform a decision to carry out genetic tests that are. The UCL press release gives some more information about how the software works:
The new method compares a child’s face to similarly aged groups of individuals with known conditions and selects which condition looks the most similar. In order to do this, collections of 3D face images of children and adults with the same genetic condition had to be gathered, as well as controls or individuals with no known genetic condition.
It really is too bad that the software uses 3d images – those cameras are neither cheap nor ubiquitous, which somewhat defeats the point of using this software as an affordable alternative to (or initial screening for) genetic testing. I can’t help but wonder if it wouldn’t be possible to achieve similar accuracy using normal portraits. If you can tell how much someone is smiling in a photo, you should be able to pick up on that extra chromosome…
Big brother knows best? Maybe not June 24, 2007Posted by Johan in Behavioural Genetics, Developmental Psychology, Rants.
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As a big brother, it is tempting to accept the conclusions that Kristensen and Bjerkedal (2007) draw in their recent article in Science. According to these researchers, IQ is associated with birth order, more specifically social birth order. This measure was created by looking at families where the oldest sibling had died, thus leaving what was biologically the middle child as the “social big brother” (note that the IQ data comes from army conscripts, so all the tested siblings were male). Kristensen and Bjerkedal found that even in these families, the older surviving sibling tended to have a slightly higher IQ than the younger sibling, as the figure below shows.
Note that differing ages is not a factor here, since all siblings were tested at the same age. Kristensen and Bjerkedal argue that this supports a social interpretation of the IQ difference in terms of the family environment, rather than a biological account based on the notion that the first-born might have experienced a better pre-natal environment.
This story has made the rounds both in the news and in blogs, and generally there is surprisingly little criticism. I think Kristensen and Bjerkedal fail to consider an alternative explanation for their results.
Consider the factors that go into deciding whether you want to have another child or not. It is likely that you will consider your experiences with the child or children you already have. Parents who are not as satisfied with their current child or children are less likely to have another child, and this is likely to work the same way when deciding to have child number two, three, and on.
Note that I’m assuming here that parents will pick up on a child’s IQ and that this trait will express itself relatively early on, before the parents decide whether to have another child. So the data for the non-smart first-borns aren’t represented accurately in this analysis, since their parents didn’t have more kids as often.
But here’s the catch: each time you procreate, your chances of hitting the jackpot (ie, all Smart Kids) decreases. This follows from basic probability: if the chance of having one Smart Kid with your genes is x, the chance of having two Smart Kids (x²) must be smaller, and the chance of all Smart Kids continues to decline in this fashion. You’re playing with the same chromosomes each time, so it’s reasonable to assume that the probability is constant.
So if the parents consider their luck before deciding to have another kid, and if they count their luck in the number of Smart Kids, you would expect IQ to drop off as it does in the figure above. Parents who have a first Smart Kid are more likely to have a second child, and parents who have two Smart Kids are more likely to have a third. But with each new child, the chance of the jackpot (all Smart Kids) declines.
To summarise: The parents’ decision to have more children is determined in part by the IQ of the existing children, which means that more intelligent children are also more likely to have younger siblings. But conversely, this selection won’t operate on the youngest child, and will operate to a lesser extent on middle children.
With this account of the data, there is nothing particularly surprising about Kristensen and Bjerkedal’s essential finding that the social big brother (ie, the middle sibling) is smarter than the third sibling. You would expect this, given the interaction between the genetic lottery and the parental choice to procreate.
Let me refute one criticism that could be raised against this account: You might think that the younger siblings in families where the first-born died should have about the same IQ as the younger siblings in families where the first-born didn’t die. This is not the case, as a comparison between the black and the green dots in the figure above shows.
Before you conclude anything from that, look in the supplements for the article. You will find that Kristensen and Bjerkedal restricted their dead first-born sample to cases where the first-born was stillborn, or had died before the age of 1. So maybe the first-born simply wasn’t alive for long enough for the parents to base their further procreation decisions on the smartness of this kid. If this is true, the same parental decision-making process that would normally be based on the first-born is now based on the second-born: Smart Kids are more likely to get younger siblings, while not so Smart Kids are less likely to have younger siblings.
It’s worth emphasising that these are subtle effects. The difference in this study was around 3 points (M=100), so while my discussion of Smart Kids and not so Smart Kids above may sound categorical, I’m only trying to make my point salient. Even if my little theory above is correct, IQ is likely to only play a small role in whether parents choose to procreate or not – otherwise, we would see larger effect sizes in studies such as this one.
If nothing else, I think this study highlights the issue of effect sizes in psychology. Is an IQ difference of 3 points worth discussing? What is the relevance of such a small effect? Can it form the basis of policy changes, or advice to parents? Surely not. I’m not even sure if it has theoretical relevance – surely there are factors out there that explain a bigger part of the IQ variability, and where the exact underlying causes are equally unknown. Yet, this study is treated as if it is hugely important. Look at the quotes below from the New York Times, for instance:
Three points on an I.Q. test, experts said, amount to a slight edge that could be meaningful for someone teetering between an A and a B, for instance, or even possibly between admission to an elite liberal-arts college and the state university, some experts said. They said the results are likely to prompt more intensive study into the family dynamics behind such differences.
“I consider this study the most important publication to come out in this field in 70 years; it’s a dream come true,” said Frank J. Sulloway, a psychologist at the Institute of Personality and Social Research at the University of California in Berkeley.
The edge between liberal-arts college or state university? The most important study in the field for the past 70 years? Don’t believe the hype.
Kristensen, P., Bjerkedal, T. (2007). Explaining the Relation Between Birth Order and Intelligence. Science, 316, 1717.
Light blogging: Obesity and personal responsibility May 30, 2007Posted by Johan in Behavioural Genetics.
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While most societies have become increasingly acceptant of the idea that people are not strictly personally responsible for addictions such as alcoholism, or psychological conditions like anorexia nervosa, one condition where the blame remains firmly on the shoulders of the individual is obesity.
This is likely to change in the future, as more and more people become obese. At some point, this minority will become large enough to affect the public debate more than it has so far. But at present, the popular notion is that obesity is caused by excessive eating and poor exercise (which is strictly speaking true), and that everyone should be equally able to behave accordingly (which is improbable).
The video below is a good example.
In Swedish media, this story has been reported with the angle that the mother is feeding her daughter copious amounts of food, and now the nice doctors have taken the child away to control her eating in a way that the mother did not. The only write-up I’ve found in English is from some Croatian news site. Conveniently, it matches the Swedish write-up word for word, so the original story is most likely from Reuters or AP.
When I saw the video, my initial reaction was – “ah, so that’s that Prader-Willi syndrome looks like.” Prader-Willi is a genetic condition (see the page on OMIM) caused by a number of gene deletions on chromosome 15 of the paternal gene.
It would be relatively easy to understand Prader-Willi if it produced obesity by slowing metabolism, so that a normal intake of food caused obesity, or through movement disorders that make it difficult to get enough movement into your day. Instead, the chief characteristic of Prader-Willi is insatiable hunger. People with this condition live through their days as though they are starving. A quote from a case study illustrates the point:
[...] The worst problem, though, was her appetite. She ate everything she could and never seemed satisfied. At first her parents were so pleased to see her finally gaining weight that they gave her food whenever she asked for it. But after a while it was clear that she was becoming obese. A specialist diagnosed her condition and told her parents that they would have to strictly limit Carrie’s food intake. Because of her weak muscles and low metabolic rate, she needed only 1200 calories per day to maintain a normal weight. But Carrie was constantly looking for food. She would raid the refrigerator until her parents installed a lock on it and on the cabinets where they put food. They had to be careful of how the disposed of leftover food, vegetable peels, or meat trimmings because Carrie would raid the garbage can and eat them. (Carlson, 2007, p. 395)
I think a lot of people have a common-sense understanding of behaviour where automatic processes are biological or genetic and cannot be controlled, while controlled behaviours such as eating are necessarily controllable, and thus reflect the individual’s shortcomings in self control. Prader-Willi syndrom is a striking example of how wrong this dichotomy is. Individuals with this condition experience such a strong drive for food that they simply cannot control themselves.
While I have no idea if the girl in the video above has Prader-Willi, I think this is a far more likely explanations than some kind of force-feeding instigated by the mother (note how the child asks for popcorn at one point in the video). Much like how schizophrenia and autism used to be blamed on the parents before the genetic underpinnings became understood, parents of Prader-Willi face constant derogation every time they show their face in public, because the obvious interpretation is that they are over-feeding their child.
In a sense, it’s true that parents are responsible for their children. But as the case study I cited above shows, these parents face a task that is almost impossible. Apart from the sheer physical difficult in preventing all access to food in a modern society, it must be emotionally straining to be unable to give your child food even though they feel as though they are starving.
While the very existence of a large increase in obesity worldwide suggests environmental rather than genetic influences, it’s clear that modern-day access to food is something that people are able to cope with to different extents. In a way it’s ironic that the features of obesity – binge eating, pre-occupations with food – must have been adaptive at one point in our history. When access to food is not always guaranteed, those who are able to make the most of opportunities to eat, who show the greatest interest in locating food, and who are able to metabolise the food efficiently will be more successful.
Still, the same false dichotomy between uncontrollable biological factors and controllable behavioural factors are used by many obese individuals too. Obesity acceptance groups usually emphasise biological factors such as metabolism, perhaps because they realise that these factors are more likely to elicit sympathy. But as Prader-Willi shows, sheer appetite can have a genetic component also.
Carlson, N.R. (2007). The Physiology of Behavior. London: Pearson.
Inheritance of Environmental Influences? April 18, 2007Posted by Johan in Behavioural Genetics.
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One of the basic tenets of the theory of evolution through natural selection is that learned behaviours are not inherited. A recent study by Lindqvist et al (2007) suggests that this rule has exceptions.
Lindqvist et al (2007) raised two breeds of chickens under stressful or non-stressful conditions. Stress was induced by randomly turning on and off the light, which is very disturbing to chickens since many of their behaviours are tied to the day-night cycle (e.g., they do not feed in darkness). From the eggs produced by these two groups, a sample was raised under identical, non-stressful conditions.
To test the effects of the stressful environment, the parents in the two groups and their offspring performed a maze learning test. Additionally, the offspring were tested for their ability to compete with each other for access to food.
The behavioural results indicated that stressed chickens in the parental generation needed more trials to solve the maze test. This in itself is not surprising – it merely shows that the stressful environment did affect the parental generation. Among the offspring, there was no significant difference between chickens with stressed and nonstressed parents. However, with some statistical trickery (testing differences in the cumulative proportion of birds that solved the test after each trial), a significant difference emerged for one of the chicken breeds. No significant differences emerged for the competition task, or for the other breed.
So it would seem that for one breed, the stress carried over, presumably due to changes in gene expression carrying over to the next generation. Lindqvist et al (2007) carried out some genetic analyses to investigate this possibility, and appear to have found some evidence to support this. Unfortunately, my understanding of genetics is not strong enough to give you a decent review of this part of the paper.
This study has been cited in more than one Swedish newspaper as evidence that “disproves” Darwin’s theory. I very much doubt that. First, unexpected results from a single study need to be confirmed. Secondly, the significant difference between the two groups that this paper hinges on had to be literally squeezed out of the data.
Given the interpretation that Lindqvist et al (2007) give their data (ie that changes in gene expression were transmitted across generations), I see a problem with their design: The stressful environment may have damaged the hens’ eggs or general egg-production. The eggs were only taken out of the stressful environment once they had been laid, of course, so while the chicken were then raised in a non-stressful environment, the prenatal environment may not have been equivalent for the two groups. However, one finding that speaks against this criticism is the lack of a significant difference between the hatchability of the eggs from the two groups. Any negative changes in the prenatal environment should affect hatchability, presumably.
I find this paper fascinating, but at the same time it is outside my subject area, so I want to end with a disclaimer: I don’t know as much about this subject as I do about my normal topics. If someone with a better grasp of genetics blogs this story I’ll be sure to update this post with links.
Lindqvist, C., Janczak, A.M., Nätt, D., Baranowska, I., Lindqvist, N., Wichman, A., Lundeberg, J., Lindberg, J., Torjesen, P.A., & Jensen, P. (2007). Transmission of Stress-Induced Learning Impairment and Associated Brain Gene Expression from Parents to Offspring in Chickens. PLoS ONE, 4, 1-7.