Nature, nurture, and evolution:

A discussion of the significance of genetics and evolution for understanding human behavior

Senior Seminar in Neural and Behavioral Sciences
Bryn Mawr and Haverford Colleges, Spring, 2002

Session 2: Paradigmatic Cases and Methodological Considerations
(Readings and Web Links)

Name:  Rebecca Roth
Subject:  Human Behavior
Date:  2002-02-10 16:21:32
Message Id:  892

How much do genes account for individual differences between us? To explore human behavior one needs to look at the relationship and interaction between genes and the environment. We need a greater understanding of how the environment actually affects our genes, leading to the great diversity of human behavior.

According to Chapter 18, gene-environment correlation occurs when people with high genetic values for a trait experience environments with high values for that trait. Chapter 5 spoke about how the ALDH-2 polymorphism shows how genes can relate to behavior . It says that the ALDH2 allele appears to lower the risk for the development of alcohol related problems. This shows that genes operating elsewhere in the body can influence behavior. Everyone has probably heard the saying, “I just have bad genes” when trying to explain a certain action or behavior. We know that genetics influences the likelihood that we may get certain disorders or exhibit certain traits.

From reading the article on the neurobiology of cricket song, I learned that cricket song has a genetically determined component. Studying animal behavior is learning how simple behaviors lead to more complex behaviors. The field of animal behavior looks at understanding the causes, functions, development, and evolution of behavior. The development of behavior is concerned with the ways in which behavior changes over the lifetime of an animal. The evolution of behavior is concerned with origins of behavior patterns and how these change over generations of animals. There are hopes that in understanding animal behavior we can better learn from our own behavior. For instance, giving flies jet lag turned out to have direct implications for understanding circadian rhythm in mammals, even humans.

Why is behavior so difficult to understand? Our behavior not only reflects our general well being, but also how well we relate to our environment. Some organisms are capable of evolving, while others are not. Why is it that some organisms don’t evolve? And have those organisms that evolved, evolved to be adaptable rather than requiring continuing evolution to specialize?

Our mental condition is part of a complex interplay between our biology and our environment. There have been brain structures identified and chemistry which are shown to control behavior. The discovery of brain chemicals (ex: endorphins) leads to an understanding of how behavior can also be a biochemical event. Genetic research leads to identification of certain genes that seem tied to behaviors. Medicines and drugs are produced which also affect and or alter our behavior. There are also scanning devices which show mapping of brain functions. We have only begun to identify the genes that control the molecules of the brain. We can learn about behavior from previous studies and cases. There will always be more advancements.

Name:  Huma
Subject:  Reliable studies?
Date:  2002-02-13 18:49:11
Message Id:  966
I’m not sure that I can produce a formula for identifying observations of genetic/evolutionary considerations that are relevant and ones that are not. In reading Young’s article on circadian rhythms, I was impressed by the body changes that occur within a 24-hour period. Also, the article on tetrachromats raised important questions about the plasticity of the brain and it’s adaptability to significant changes in genes. These signify valid and relevant evolutionary influences on behavior, as do the studies on supertasters. These studies can provide information on the human body, somewhat like an owner’s manual explaining what the body is doing or how it works. Furthermore, it can provide helpful advice for maintaining our “machinery”. The knowledge of supertasters could be an excellent ways of dealing with obesity, and to reduce an affinity for high-fat/high-sweet foods. This could result in decreasing diabetes and cardiovascular disease. Ideally we would want to extract applicable information from these studies and better our lives.

We must, however, beware of issues such as the tongue-rolling phenomenon which is unlikely to be inherited; yet this notion has permeated society. There is a danger in ascribing too many traits to genetics that may not be determined or even influenced by genes.

This leads me to the studies that I find irrelevant. While, reading through the various articles from 2001 on the BG news Home Page, I was fascinated and found it difficult to stop reading. I had a strange feeling that I was being sucked into addictive pop bio/psych studies. Most of them were neither conclusive nor significant, but I read them because they were fun and told a great story. One stated that a propensity to get divorced could be found in ones DNA (because monozygotic twins are more likely to have similar patterns of divorce). Another stated, “Researchers suspect that the Chinese love of gambling may also have a genetic component and are keen to begin blood tests on local gambling addicts.” One observation was that 30% of anorexics were born in June. I don’t find these observations to be reliable, as they cannot factor out environmental influences on behavior, but I can’t disregard the correlations either. Regardless of the quality/reliability of research that occurs, people enjoy reading these studies because it gives them something to explain/blame their behavior on. For complex human behaviors and matters of choice there is much more going on than a one-to-one contingency between genes and behavior. Though genes can be identified for things like PKU, downs syndrome, and colorblindness, these behaviors do not generally involve societal pressures, constructs, or reinforcements.

I’m most confused about how to distinguish studies that have relevant genetic/evolutionary considerations and those that don’t. So far, I’ve looked at them on a case-by-case basis, without a finite set of rules to dictate what is a valid line of research and what isn’t.

Name:  ingrid
Subject:  thoughts?
Date:  2002-02-13 21:19:43
Message Id:  967
One of my major concerns with the article on finding Madame Tetrachromat was the amount of surprise conveyed. Isn't the whole concept of evolution founded on the idea of change and mutation? After watching my season 3 boxset of the X-files with friends recently, I've come to wonder why mutation is such a big deal. In the biological writings for this week (and links from sites linked) there is an extrapolation on the genesis of sensory perception. For instance, a cell that was sensitive to light had an advantage and was able to leave well lit areas (to avoid drying up). Then once light sensitivity was selected for, perhaps type of light (colour) was. And then maybe cells that were able to detect motion, next shapes, then distance. Think about the leap from an uncovered eye (w/o cornea) to a covered eye (w/cornea) and how that helped depth perception. That is a major mutation. A film to cover the eye that appears. My point is that if an eye can appear, why can't an extra colour? Why not ESP? Certainly some sensitivity to the brain waves of others would be an evolutionary advantage.

The fascinating thing though, was the wondering as to whether the brain would be able to processes this new colour? Would it be able to make a new channel. I do see the distinction and think it's amazing, however I don't see why it would seem so baffling and so much like a miracle.

And a fun question. Is 'sweet' for us 'sweet' for a mouse? Wouldn't it have to do (evolution wise) in a comparison of function? More like sweet being attractive and sour being aversve. Would sugar actually be sweet to a mouse, or would wheat be sweet for a mouse? And because of this, would the chemicals (that bind to the receptors in a mouses mouth and brain to indicate something attractive is on the tongue) be responsive to the same (EXACT) chemicals that trigger our own? For that's the assumption that these tests make, since they're looking for the same chemicals. I'm not sure if this is a valid question, I was just wondering if they can make these assumptions of 'taste'.

Name:  Elizabeth Olson
Subject:  NBS #2
Date:  2002-02-13 21:58:28
Message Id:  968
There are a number of types of evidence that can be used to support the hypothesis that a particular behavior has a genetic or evolutionary basis. In terms of genetic considerations, one methodology is doing twin studies (as in the tongue-rolling reading)and/or adoption studies in order to statistically determine heritability, the proportion of phenotypic variance attributable to genetic variance. In order to determine which specific genes are involved in producing the phenotype, one can do linkage studies (which identify the location of a gene based on family pedigrees and known genetic markers), and association studies (which identify genes by comparing the genotypes of a large group of people affected by the phenotype). In terms of evolutionary considerations, the typical methodology is to propose a problem humans faced in our evolutionary history, propose a mechanism for dealing with that problem, make hypotheses based on that mechanism, and then test to see whether the predicted behavior is exhibited in current populations (this is Toobey and Cosmides' usual strategy). The conclusions are strengthened if the pattern is found cross-culturally (e.g. most of Buss' studies)and/or if it can be demonstrated in non-human primates. (Also, if the pattern is found in human infants, this can support an evolutionary explanation of behavior, but failure to find the pattern does not necessarily support the idea that the behavior does not have an evolutionary basis).

In terms of genetic evidence, linkage and association studies allow you to determine the location of the gene and potentially the sequence of that gene, while heritability studies do not. Heritability studies have the benefit of being much simpler, less expensive, and requiring less equipment, but they are based on a number of potentially faulty assumptions (e.g. that the environmental contribution to the phenotype is the same for MZ vs. DZ twins or that adoption occurs through random placement). In general, especially in terms of evolutionary evidence, the claim that a given trait has an evolutionary or genetic basis is strengthened when multiple observations corroborate the same finding.

It is important to keep in mind that the finding that a behavior has a genetic basis can mean a number of things; the finding that a trait has a genetic basis does not mean that the environmental influence is irrelevant. A number of factors (incomplete penetrance, variable expressivity, etc. etc.) leave the door open for enormous environmental influences on the genetically constrained phenotype.

One question/ uncertainty I have about my answers stems from the Molecular Neurobiology class that I'm taking at Haverford. We have spent the past couple of days going over embryonic development. As I've been thinking about our often incredulous take on one gene's ability to influence a complex behavior, I've been wondering whether some of that incredulity stems from our incomplete/ inadequate appreciation for how the development of the nervous system unfolds. It seems to me that especially if a gene had an effect very early in development, it could have global and complex consequences.

Name:  caroline
Subject:  this week
Date:  2002-02-13 22:18:34
Message Id:  970
One major indicator of there being a genetic or evolutionary component is consistency of behavior. When a particular action can be standardized across populations or even species that can be taken as evidence for some innate mechanism. A potential complication in relying on gross observations for identifying behavioral trajectories is that they don't allow for distinguishing among the more subtle underpinnings. Of course, it is possible now to do more detailed inquiries into the precise genetic links. This method of observation has behind it the strength of science; however the tendency for correlations to become entrenched as causation should be recognized and resisted. Despite this word of caution, research into the genetic bases of behavior has been vital in understanding the progression of some conditions. Where one gene has been definitively connected to a particular behavior or state of being, the manipulation thereof has been greatly facilitated. Even saying that one gene equals one behavior does not provide the complete picture. The evolutionary explanations of behavior that we invoke rely on the requirements of antiquated social structures. The concerns of our ancestors seem primitive in comparison to what we face today. But the fact remains that our genetic structure evolved to meet those now obsolete needs, and sufficient time has not yet passed to allow that structure to have further evolved to such a degree. Keeping that in mind, it is important to temper too strong a dependence on genetic and evolutionary explanations of behavior with an understanding that the environmental context also plays a role. This may especially be the case where the genetic explanation cannot be reduced to a single gene. The relevance of a more contextual approach to behavior is enhanced when considered against the previously acknowledged weaknesses of the evolutionary approach. Getting back to my first point, identifying a behavior from any perspective will entail the observation of patterns. Establishing some consistency of action will be evidence enough that some causal mechanism is at work. It then becomes our job to isolate what that mechanism is. As is typically the case, allowing for some mix of genetic, evolutionary, and environmental causes will likely prove most fruitful.
Name:  Caitlin Costello
Date:  2002-02-14 01:05:24
Message Id:  976
Reading the article that exposed the fraud of the tongue-rolling gene made me a little upset that I'd been lied to all these years, because I definitely remember learning that there was a single gene for the trait, and nothing I could do to overcome the flat-tongued destiny prescribed by my deficient alleles. It also got me thinking about how we come to accept things as "fact" in the psychological/scientific world. When I was in intro psych, it seemed like there was a lot of "truth" in psychology, phenomena that were so well established that they did not have to be qualified with "some studies have shown...", e.g. I will do better on a test if I sit in the same seat as I did in lecture, I inappropriately attribute other people's behavior to internal causes, and it will take me a long time to say green when it is printed in red. But since then it has become clear that we never actually "know" anything in psych--we're always just building on the body of evidence that suggests it.
Now maybe these findings weren't presented in the textbook in as "factal" a matter as I remember and the qualifications have been lost to my nostalgia for the good old days when things made sense, footnotes I ignored, or retrospective memory bias (if that really even exists; seems like you can't trust anything anymore), but it seems like by the time these phenomena are described in an intro textbook and specific studies are no longer cited, they are well enough established that we pretty much accept them as true. But how many studies have to corroborate the same findings for this to happen? Is it a beyond a resonable doubt kind of thing, or more a preponderance of evidence (i'm thinking the O.J. criminal/civil trial...)?

Admittedly, it's different for behavioral phenomena like coding specificity than for possible genetic coding like tongue-rolling--behavioral phenomena, which are by definition described population norms, can certainly exist without every person behaving that way, whereas a gene "for" a trait is something we could conceivably physically find and would potentially affect people in a more black-and-white way. But it's still a relevant consideration to determining if something has a genetic influence. In what percentage of MZ vs. DZ twins does a trait have to co-occur to convince us of a genetic component? In how many cultures do people have to behave similarly to indicate an evolutionary mechanism?

I think this issue is particularly interesting in relation to evolution, and there are several obstacles to our being able to effectively use and evaluate evolutionary theories of behavior. One, which Liz and Ingrid brought up, is that we don't have a thorough enough understanding of neurological development and what happens on the cellular level to assess the feasibility of explanations involving genetic mutations and the scope of genetic influence on behavior. Another is that our personal frame of reference is in decades, not millions of years--we can't really know what might be possible in the time frame under which evolution works, or how it would look through the many generations. In a way, we both can't think small enough and can't think big enough to make sense of evolutionary theories.

I also wonder how (or if) evolution is happening now. It seems that at least to some extent, we've "beaten" evolution--by doing things like making eyeglasses so the nearsighted don't all stumble off cliffs before puberty and thus allowing the genetically unfit to reproduce, we've greatly interfered with natural selection. Also, the way we think of evolution usually involves random mating at least within a certain geography, but that's hardly what happens, and hasn't for quite some time in human history--so how does that affect the evolution of the species? And "survival of the species" is hard to grasp from the perspective of the individual. Apparently the idea for the individual organism is to propagate its own genetic material--but how does this "incentive" influence our behavior? Maybe animals are operating under some kind of internal calculus whereby they will take a 25% chance of dying in order to save a cousin (or whatever), but humans are of course dealing with more complex issues.

One of the Behavioral Genetics articles said that animals who mate with animals they are genetically very different from have more offspring. But I think Buss says that we are attracted to people we look similar to because they are likely to have similar genetic makeups to our own. So which is more important, reproducing more or having our offspring resemble us genetically more? How do these relative considerations play out in animal behavior, much less human behavior, where sexual selection is a little more complicated than having sexy yet otherwise maladaptive peacock feathers. So are we "evolving" at all these days, or have our manipulations of the environment by now outweighed evolutionary effects? And what will all of this mean millions of years down the road when the evolution that may or may not be happening would have resulted in us all being tetrachromats?

To answer these questions would require, on my part, a better grasp of genetics and neurobiology, and on the scientific community's part, more agreement on how much evidence constitutes "fact". We also need a much longer lifespan to be able to think in an evolutionary manner. In the meantime, I think I'm going to go practice rolling my tongue, as it appears that there may be hope for me after all...

Name:  Niru Kumar
Date:  2002-02-14 01:21:27
Message Id:  977

Based on what we read, there seems to exist a lot of general uncertainty about common notions of human behavior inheritance. I think that the basic standard for evaluating it needs to be something objective. I think that observations need to imply something more than a statistical correlation. It is easy to amass statistics, without showing some actual mechanism for inheritance.

In cases were a gene can be identified that is correlated with the behavior, and if the expression of that gene can provide a causal relationship for the behavior, then and only then can we say that relevance exists. Twin studies can be very interesting and engrossing to read about, but I don't know if they are nearly enough to provide relevant information. They show the possibility of a genetic link, but don't actually provide a positive correlation.

The different levels of correlation seen definitely highlight the fact that because we cannot ascertain whether genetics is the key to human behavior, tha other factors are at play. The simple fact that we do twin studies shows that we try to eliminate environmental influences from our look at genetics. But, these influences probably have a significant impact on, at least, how our genes are expressed and how our brain pathways develop.

Name:  Mary Schlimme
Username:  Anonymous
Subject:  Session 2
Date:  2002-02-14 01:32:02
Message Id:  978
There are many observations that imply the relevance of genetic/evolutionary considerations when exploring human behavior that were discussed in this week’s readings. It is certainly important to consider the observations of animals so that we can better understand human behavior. For example, the research on fruit flies that found certain genes and proteins that seem to govern a circadian rhythm has been applied to understanding human behavior as well. By taking data from the genetically mutated flies and applying it to humans, we can better understand phenomena such as jet lag and narcolepsy and can possibly develop treatments for these conditions. The study of William’s Syndrome patients demonstrates the importance of studying genetics in humans. Most of these patients have a gene deletion in chromosome 7, which presumably causes the behavioral discrepancies. By studying the genetics of William’s Syndrome patients, we can explore the differences in the behavior and the behavior of people without the disorder in order to learn more about the factors that influence human behavior. Furthermore, by studying disorders with complex genetics (DCG) one can explore different areas of genetics that are believed to be working in a certain disorder in order to understand how the genetics affect behavior. For example, the study of Alzheimer’s Disease has currently lead researchers to believe that there are several possible events (and not one single cause) that can lead to the development of Alzheimer’s Disease. By understanding that these DCG are not solely determined by one particular event or genetic variable, one can appreciate the complexity involved in what determines human behavior. Finally, by comparing data found in twin and adoption studies (as discussed in Carey’s book) one can better understand how genetic and environmental factors relate to human behavior.

One significant difference of animal observations versus human observations is that one can perform many manipulations on animals that cannot be performed with humans. This can cause a problem because there are certain circumstances in which it is inappropriate to perform manipulations on people that are performed on animals, so one can only speculate that the observations seen in the animals would be similar in humans. However, researchers can use information gained from human data and apply it to animal research in order to investigate the underlying genetic influences on behavior. For example, in the case of Alzheimer’s Disease, researchers have been able to place alleles into mice and have found that these mice show plaques and tangles in the brain that are similar to those in patients with Alzheimer’s Disease. The researchers can then manipulate and test several variables that they are unable to test for in humans in order to better understand the behavior patterns of patients with Alzheimer’s.

In terms of what these observations imply for the importance of other factors, I like Carey’s lemonade analogy. Lemonade is a solution made of many parts and trying to name one part as the sole ingredient would be impossible. By applying this to behavior we find that behavior is complex and thus it is made up of several factors that can interact in statistically meaningful ways. I also think that Carey made an interesting point when he said that “environmental factors always contribute to individual difference in human behavior” since there has yet to be a perfect correlation for identical twins (who have identical DNA) on any behavioral measure. While this certainly seems appealing to me, I wonder about the validity of this statement – perhaps it is our means of measurement (which might not be perfect) that is causing us to obtain values that are close to but not equal to 1. This would then imply that there may be some things that are completely determined by something other than the environment (e.g. genetics) but we can’t observe them since our collection methods are insufficient. I’m not sure what the correct answer to this proposition is, and I’m not sure that we can solve it with our current methods, but perhaps we can move toward a less wrong answer.

Subject:  week 2
Date:  2002-02-14 02:08:02
Message Id:  980
Important observations that imply the relevance of genetic/evolutionary considerations for human behavior come especially from identical twin studies. Because the genetic make up of these individuals are the same, differences in their behavior cannot be attributed to genetics. Although certainty is never possible in correlational studies, matching behavior patterns in twins may be investigated as having a genetic basis. In this way, identical twins maybe a good starting off point in looking for gene/behavior links. Another possible way to observe genetic/evolutionary considerations for human behavior, maybe through animal knock out studies. Knocking out a particular gene allows the comparison of typical behavior with the working gene with the behavior seen if the gene is disabled. Any differences in behavior may be a result of the nonfunctional gene. Naturally occurring mutations in humans could be studied in a similar manner, like how Williams syndrome is studied. An important point to keep in mind when considering genetic basis of behavior is the difference between correlational and causal evidence. In the exciting age of the human genome project, it's hard not to be too eager to attribute behaviors to genes. Mistakes have already happened, like attributing tongue rolling to a simple inheritance. Identical twin studies gave evidence against this assumption which was published in 1952. However, in high school biology in 1996 I learned that tongue rolling was a simple inherited trait. Correlating genes to behavior already has a high potential to lead discrimination we cannot afford to make mistakes when it comes to attributing alcoholism or violent behavior to genes. It is not quite such a big deal for tongue rolling still to be believed as genetically determined, but imagine the consequences of a more serious behavior problem being misdiagnosed to the genes.
Name:  Rebecca Roth
Subject:  Questions
Date:  2002-02-14 14:38:17
Message Id:  988

Specific parenting behaviors can influence child outcomes (ex:Authoritative parents). However, wouldn't it be hard to tell if it is genetics that affecting the child's social interactions and personality or it is the environment in which the child grew up? Or a combination of both?

Also, this isn't relating to behavior--but what about when you to a different climate or location, (ex:down south)--you notice more people with blonde hair than up north. Also, more people up north have curly hair than down south. Why is that? Would the people who have curly hair now, have curly hair if they were born in a place where there is almost no curly haired people? Is it really genetics that determines this or is environment having a role as well?

Name:  hiro :)
Date:  2002-02-19 23:50:34
Message Id:  1091
ok, i'm late posting this comment about behavioral genetics because i was sick and almost dead last week...

my question is: how do behavioral genetics account for the changes in an individual's behavior over time?

i was facinated to know that there is a sweet taste gene because i love sweets. however, i have realized that i never really liked very sweet food before. now, i love it and i eat more sweets. how has my behavior changed over time? was i programed to change my food preference in such a way because of the genes i have? since genes direct very complicated events, such as programed cell death, i belive that genes can become active at a scheduled point during my physical development and produce proteins to alter the numbers or sensitivity of the taste receptors. or, maybe not the genes but the environmental factors caused the change. maybe the high stress level at college caused me to consume high sugar/calorie food, and what kind of genes for food preference i had didn't really matter. as liz has mentioned, twin studies can be applied in order to test these possibilities. (now, here's another question, which is a little off the topic: do genetics account for how people deal with stress? not everyone responds to stress with higher consumption of sugar.)

the change in one's behavior over time can be said about near-sightedness, too. i believe that near-sightedness is inherited as a dominant trait. so, in this case, the genes are responsible for the shape change of the eye balls. but, do these genes program/determine the timing of the development of near-sightedness? or do they simply increase one's suceptability to the change (meaning that the person may not develop near-sightedness, depending on the environmental factors)? i have also heard that sons of a near-sighted person develop worse eyesight than the same person's daughters. how can the sex difference be explained in terms of behavioral genetics?

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