The Instigator
Pro (for)
3 Points
The Contender
Con (against)
0 Points

Nature vs. Nurture: "Rationality"

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Voting Style: Open Point System: 7 Point
Started: 7/24/2012 Category: Science
Updated: 6 years ago Status: Post Voting Period
Viewed: 6,228 times Debate No: 24859
Debate Rounds (4)
Comments (1)
Votes (1)




Resolution: Pro will argue that, on balance, environment is more important than genes in the development of rationality. Con will argue for the opposite position.


Rationality: The combination of intelligence and conscientiousness.

Intelligence: "the ability to learn or understand, or to deal with new or trying situations and/or the ability to apply knowledge to manipulate one's environment, or to think abstractly as measured by objective criteria (as tests.)" Here:

Conscientiousness: "the extent to which a person is organized, careful, self-disciplined, and responsible." Here:


1) Round 1 is acceptance.

2) Round 2 is opening arguments.

3) Round 3 is rebuttals.

4) Round 4 is final rebuttals, no new evidence/arguments.

5) No trolling, lawyering, or semantics.

I hope that this resolution may come to be agreed upon as the satisfactory one, and look forward to my opponent's acceptance.


Debate Round No. 1


I thank my opponent for his acceptance and his willingness to debate such a fascinating topic with me.

Pro Case

C1: The Flynn Effect. [1][2]

Over the past 60 years or so, the average I.Q. score has steadily risen in the modern countries where it has been tracked. The increase has been so rapid that we have had to periodically update the standards of what constitutes an "average" score (~100.) Each generation has seen an increase of between 5 and 25 general I.Q. points.

It is useful to immediately note that there is a distinction made, however, between something called "fluid intelligence" and something else, called "crystallized intelligence." Essentially, "fluid" intelligence is the ability to reason independently of any previously existing knowledge, in order to solve abstract problems. Each generation has, on average, experienced a 15 point rise in "fluid" I.Q. for the past 60 years. On the other hand, "crystallized" intelligence is the aggregate of our knowledge in specific areas, and the level of skill we have in applying that information. Each generation has, on average, experienced a 9 point increase in "crystallized" intelligence.

This is counterintuitive. We might think that, with the passing of each generation, their main advantage would be in having a more detailed and advanced pool of knowledge to draw on, and to learn from. This is partially true, apparently. However, the increase in abstract problem-solving ability is surprisingly more significant. I account for it by one, or both, of two factors: 1) Educational systems have improved the manner in which they teach children how to think on their own, and more importantly, 2) Our everyday environment has become increasingly abstract, complex, and fast-paced. What cannot explain these changes is any inheritable genetic factors, because the timeframe is simply too brief.

My favored explanation agrees with that of Flynn, who "favors environmental factors," and who Restak indirectly quotes as saying that, "The direct effect of genes on I.Q. accounts for only 36% of I.Q. variance, with environmental differences making up the remaining 64%..."

C2: Neuroplasticity. [1][3][4][5]

For quite some time brain researchers thought that the brain was static. They believed that it was as unchangeable as skin color, height, or eye color. Recently, however, that trend has been broken and research increasingly finds evidence that the brain is a dynamic, adaptive organ that "wires" and rewires itself in response to our habits and environment.

This process is referred to as "neuroplasticity." It follows two fundamental rules, worded very rhythmically as, 1) "Use it, or lose it," and 2) "Cells that fire together, wire together,"

1) Use it or lose it:

The maximum number of neurons our brain will ever have is achieved at the end of our most critical period of brain development, the 2nd trimester of our gestation period. By the time we are born, this number has already decreased. A newborn, however, still has significantly more neurons than an adult. In infancy, as the number of neurons drops, the number of connections between neurons -- synapses -- increases.

A synapse is literally a physical manifestation of learning. The infant immediately starts using its high neuronal potential to "make connections" (i.e. learn) about its new environment. It logically follows that if an infant's environment provides more opportunities for learning and positive stimulation, then that particular infant will carry more of those synapses out of infancy with them. And if they continue to live in a stimulating environment, and/or maintain cognitively challenging habits, then they will probably avoid much of the full 40% loss, by adulthood, of synaptic connections that people experience on average.

2) Cells that fire together, wire together:

Another paradigm shift in neuroscience has lead to the revelation that people who practice distinct skills have distinctive brains. In other words, a neuroscientist can tell the brain of a musician from that of a circus juggler. Both activities, by the way, that they would recommend to improve your brain's performance, and increase neuroplasticity (i.e. the ability to make new connections.) As another example, they have also found distinctive changes in the brains of meditators, which highly correlate with the number of years practiced. Meditators, especially experienced ones, it is especially worthy of noting here, are masters of conscientiousness.

The most interesting and recent development in this area is a study conducted that demonstrated that, for one thing, the I.Q. of individual teenagers can vary (it can go up or down) by as much as 20 points in four years. For another, it demonstrated that these changes can happen in both verbal and non-verbal intelligences. And finally, it demonstrated that specific changes in verbal I.Q. were associated with changes in the verbal circuitry of the brain, while changes in non-verbal I.Q. were associated with the non-verbal movement circuitry of the brain. It is unlikely that these specific, physical brain changes were predestined by the genes, and therefore it can be concluded that they were probably a result of changing environmental influences in the children who did experience the biggest changes in I.Q.

C3: Early education improves I.Q. and success later. [6][7]

The "Abecedarian" project intervened in the lives of low-income families, putting half of their babies into high-quality day care programs. The study reported that these children were four times more likely to graduate college (23% v. 6%) than the controls, they were more likely to have consistent employment (75% v. 53%), and less likely to use public assistance.

Norway extended their compulsory middle school attendance by two years in 1955. What they found was a 3.7 point increase in I.Q. for each additional year of school. Taken together with the abecedarian study, this strongly suggests that both I.Q. and conscientiousness can be significantly affected by positive environmental influences. And that the earlier, the better.

C4: Nature vs. Nurture: There can be only one! Well, almost... [8][9]

A study of the genes of surviving elderly Scottish people, aged 65 and older, who had taken I.Q. tests at age 11, has been carried out along with a re-testing of the group. The study used advanced genetic testing, referred to as genome-wide complex-trait analysis, to determine the influence of genes on lifelong cognitive change. The study's conclusion is that genes account for 24% of I.Q. variability across a person's lifetime. Therefore, about 76% of the changes in our I.Q. can be accounted for by environmental influences, which means that the smarter we are about selecting that environment, the smarter we are likely to become.

[1]Restak, Richard. Think Smart: A Neuroscientist's Prescription for Improving Your Brain's Performance. New York: Penguin, 2009. Print.

[3]Doidge, Norman. The Brain That Changes Itself. New York: Penguin, 2007. Print.



==Pro’s Case==
Pro explains the Flynn effect by citing better education and a more intellectually stimulating environment, but fails to provide any evidence for these claims. More likely, it is the result of having less malnutrition and disease, both of which can stunt development—this is also why average height has increased over time. [3] This would explain why the Flynn effect has stopped, and perhaps even reversed, in recent years—because those things are no longer an issue in the developed world. [4] [5] This stagnation cannot be explained by Pro’s explanation of the Flynn effect—has our education system declined and the world become less stimulating over the past few decades? So while environmental factors may have played a large role in the past, when we were much poorer, they don’t anymore.

If Pro’s claim about the environmental influences on child brain development were correct, surely there would be some evidence of it in twin and adoption studies. But there isn’t. [1] [2] Why, if this sort of environmental influence is so important, are the IQs of twins raised by different families pretty much the same as twins raised together?

Pro claims that meditating physically changes people’s brains, as does practicing other skills like music and juggling. But this proves nothing. Practicing something makes you better at that specific thing, but that isn’t the same as improving intelligence or conscientiousness. Pro claims that meditators are “masters of conscientiousness”—but provides no evidence of this claim. This sort of claim requires proof, not just intuitive appeal. Even if you accept that meditation can improve conscientiousness, you’d need some sort of scientific study to measure the effect, to show whether it is a large or small effect.

IQ can vary a lot during childhood, but still has substantial genetic influence—probably around .45 heritability. [6] And then environmental influences disappear after adolescence. Note that this doesn’t mean that a good environment can raise IQ during childhood, and then that raised IQ sticks after you become an adult. You revert to your genetic potential whether your family environment raised or lowered your IQ during childhood—this is shown by twin studies. During their childhood, twins raised apart may have had very different IQs—but once they became adults, such changes disappeared, and their IQs converged, going back to a .76 correlation. [2] Since environment is, at most, only slightly more important than genes during childhood, and much less important than genes during adulthood (in which we spend most of our lives), genes are, on balance, more important than environment for intelligence.

If the results of this program were really caused by changing environmental factors, then surely such benefits would show up in other early intervention programs, like Head Start. But according to the Department of Health and Human Services, “Once the children enter school there is little difference between the scores of Head Start and control children. . . Findings for the individual cognitive measures—intelligence, readiness and achievement—reflect the same trends as the global measure. . . By the end of the second year there are no educationally meaningful differences on any of the measures.” [7]

The differences in IQ in the Abecedarian Project emerged at 6 months of age—1.6 months after the mean entrance age of 4.4 months—then stayed constant during the rest of the program’s intervention, until age 5, and beyond. [8]

Which seems more likely—that the Abecedarian project caused permanent IQ differences, while other early intervention programs couldn’t, after just 1.6 months in the program, and then was unable to make more improvements during the next several years of the program, or that the two groups had genetic differences in IQ before the program?

The variability over a person’s lifetime is different from the variability between people. This is an important distinction. The study Pro cites is about how much a person’s intelligence changes over their life. Imagine that there are only 4 genes that affect IQ. People with the A gene have an average IQ of 115, and people with the B gene have an average IQ of 85. People with the C gene have a slightly wider IQ variance over their life, and people with the D gene have a slightly narrower IQ variance over their life. People have either AC, AD, BC, or BD.
Imagine that environment can affect your IQ 5 points over your lifetime. Since the C and D genes affect the change over a lifetime so little, environment can play a larger role in the change over a person’s lifetime than genes, even if it plays a small role overall. Supporting this is the fact that people’s IQ doesn’t change very much over their lifetime.

==My Case==
C1: Heritability of IQ
By adulthood, adopted siblings aren’t more similar in IQ than any 2 random strangers picked from the population. [1] The correlation of IQ between identical twins raised together is .86, compared to .76 for identical twins raised apart. [2]

C2: Heritability of Conscientiousness
The heritability of conscientiousness is estimated to be .18-.49. [10] The effect of shared environment (family environment) is negligible, and ‘unique environment’ accounts for the rest. [10]

C3: Shared Environment vs. Unique Environment
‘Shared environment’ is what most people mean by ‘nurture.’ It is everything adopted siblings living in the same home would have in common—parents, school, socioeconomic status, neighborhood, etc. ‘Unique environment’ is everything that isn’t genes or shared environment—which means that it doesn’t imply environmental influence.

The burden of proof is on Pro to show that ‘unique environment’ means environmental influences. I contend that for traits like conscientiousness, much of ‘unique environment’ is individual choice. Much of how responsible and careful you are isn’t ‘determined’ by outside influences, but rather is just something you choose to be. I challenge Pro to provide a specific part of an environment that he thinks accounts for ‘unique environment.’ All of the environmental influences he has named so far are part of ‘shared environment’—which has little measured effect.

[1] Bouchard TJ (April 1998). "Genetic and environmental influences on adult intelligence and special mental abilities". Hum. Biol. 70 (2): 257–79.
[2] Scarr S. 1997. Behavior genetic and socialization theories of intelligence: truce and reconciliation. In R. J. Sternberg & E. Grigorenko (Ed.), Intelligence, Heredity, and Environment (pp. 3-41).
[4] Cotton, S. M.; Kiely, P. M.; Crewther, D. P.; Thomson,, B.; Laycock, R.; Crewther, S. G. (2005). "A normative and reliability study for the Raven's Colored Progressive Matrices for primary school aged children in Australia". Personality and Individual Differences 39: 647–660.
[5] Sundet, J.; Barlaug, D.; Torjussen, T. (2004). Intelligence 32 (4): 349–362.
[6] Neisser, U.; Boodoo, G.; Bouchard, T. J. , J.; Boykin, A. W.; Brody, N.; Ceci, S. J.; Halpern, D. F.; Loehlin, J. C. et al. (1996). "Intelligence: Knowns and Unknowns". American Psychologist 51: 77.
[7] Ruth McKey et al., “The Impact of Head Start on Children, Families, and Communities,” U.S. Department of Health and Human Services, HHS 85–31193, June 1985. p8-11.
[8] Spitz, “Some Questions about the Results of the Abecedarian Early Intervention Project Cited by the APA Task Force on Intelligence,” p.72.
[9] Spitz, “Does the Carolina Abecedarian Early Intervention Project Prevent Sociocultural Mental Retardation?”: pp.228–229
Debate Round No. 2


Pro Case:

C1: Con is correct to say that I should have supported my speculation with evidence, so I admit that those specific points are no longer as relevant. However, he then claims that the Flynn effect was most likely caused by improved nutrition and medicine, which is probably true, but clearly supports the idea that environmental influences have a large impact on the expression of intelligence.

With that being said, our education system has declined, in the United States at least;

"Over the past 30 years, one country after another has surpassed us in the proportion of their entering workforce with the equivalent of a high school diploma, and many more are on the verge of doing so. Thirty years ago, the United States could lay claim to having 30 percent of the world’s population of college students. Today that proportion has fallen to 14 percent and is continuing to fall.

While our international counterparts are increasingly getting more education, their young people are getting a better education as well. American students place anywhere from the middle to the bottom of the pack in [student] the advanced industrial nations."

-2006 Report by the National Center on Education and the Economy’s New Commission on the Skills of the American Workforce. [1]

And, on the other side of Con's response, he is right that the environment hasn't become less stimulating. To the contrary, it has become too stimulating in many ways. Mainly through the increasing ubiquity of "smart" technology and Internet-use.

Greenfield writes, "Already, it's pretty clear that the screen-based, two dimensional world that so many teenagers - and a growing number of adults - choose to inhabit is producing changes in behaviour. Attention spans are shorter, personal communication skills are reduced and there's a marked reduction in the ability to think abstractly." [2]

Also, Richtel reports that, "Scientists say juggling e-mail, phone calls and other incoming information can change how people think and behave. They say our ability to focus is being undermined by bursts of information." Also, that, "While many people say multitasking makes them more productive, research shows otherwise. Heavy multitaskers actually have more trouble focusing and shutting out irrelevant information, scientists say, and they experience more stress." [3]

So Con's claim that environmental factors don't play a large role anymore is demonstrably false. They are probably more relevant than ever.

C2: Con makes a basic implementation assumption here that isn't necessarily correct. Simply because twin studies and neuroplasticity research both exist doesn't imply that they would have been combined yet, as the latter is much newer than the former, and twin studies take time.

To answer his question about the similarity of MZ twins raised apart, consider a pair of twins who are both slightly taller than average. How much more likely is it that they would both be matched to an environment where they were encouraged to play basketball? It would clearly be much more likely than in the case of a pair of twins slightly shorter than average. This goes for IQ as well, with the difference being that IQ can be, and is, increased or decreased by environmental factors such a study habits, or lack thereof. People with even slight genetic advantages or disadvantages tend to be matched to environments where those tendencies are reinforced. [4]

Con here ignores the fact that my evidence showed large, short-term changes in I.Q. to be associated with specific brain changes that likely developed from specific changes in individual environments.

Moreover, meditation has been demonstrated to improve attention, focus, stress management, impulse control and self-awareness, even in relatively inexperienced meditators. These clearly relate to the definition of conscientiousness. [5]

Physical exercise has been demonstrated to produce similar effects, as well as enhancing overall brain function. [5][6]

Also, studies have shown specific, brain-training tasks to improve unrelated measures of fluid intelligence. [7]

C3: Con makes another implementation assumption here, since what proof does he have that Head Start employs the same techniques as the abecedarian project? Furthermore, his argument is somewhat of a strawman, as I never cited the abecedarian I.Q.s, but only their later-life success rates as measured by college graduation, employment rate, and use of public assistance.

I did cite the improved I.Q.s of Norwegian schoolchildren from increased education, which weren't measured until they were 19, 3-5 years after the extra school, which shows that the improvements lasted, and which Con never addressed.

C4: Con is right that there is a difference between the variability between oneself and others. However, I argue that what matters to anyone is the relative amounts to which their own intelligence is affected by their genes and by their environment. Clearly this study demonstrated that the latter leaves a lot of room to work with in terms of changing one's own I.Q.

Con's punnet square is simply wrong. If IQ had 4 genes, there would be 64 genotypes. Perhaps he meant 4 alleles, but that would still be 16 genotypes, not 4. Either way, intelligence is a multifactorial trait influenced by many genes, along with the environment.

To address his point though, for one thing, I.Q. can change by much more than 8 points, as much as 20 points or so in a short timeframe, as I have already demonstrated. Second, the Scottish study also showed that the I.Q.s in old age correlated to the I.Q.s in youth by a factor of only about 0.62. This shows that they are related, of course, but also shows that they can, and do, change much more than Con implies. Especially when you consider that the first tests were done at age 11, when the children were already past their most neuroplastic, early-life stage. [4][8]

Con Case:

R1: Traditional twin studies are based on correlations, which do not equal the level of causation, and estimations of heritability, which are not totally reliable, nor are they supported by direct, biological evidence. Conversely, Deary performed another study which tracked specific genes in order to discover the genetic variance of IQ between people. His conclusion? The genetic variance of IQ is between 40-50%. Which means that environmental variance is between 50-60%, and that it is, on balance, more important in 'determining' IQ. [9][10]

R2: Con's own numbers here, along with my evidence that traits that comprise conscientiousness can be neurologically-altered, show that on balance, it is influenced more by environment than by genes.

R3: For one, if Con wanted me to only argue for one type of "environment," he should have clarified that before the debate began. Second, I agree with him that "unique" environment is mostly personal choice regarding activities, habits, etc. Third, my own case, however, has shown that shared environment does have measurable effects on IQ. Finally, a dual example for his request is the prevalence of technology.

[4]Restak, Richard. Think Smart: A Neuroscientist's Prescription for Improving Your Brain's Performance. New York: Penguin, 2009. Print.
[9]Cummings, Michael. Human Heredity: Principles and Issues. 9th ed. Belmont: Cengage, 2009. Print.



==Pro’s Case==
Pro argues that the education system has declined, and that now, environments are too stimulating. While I think that our education system isn’t actually declining, but just declining relative to other countries, it is irrelevant. Surely, we can agree that whatever the overall state of education in the United States, it is good in some schools and bad in others. And yet, twin studies find that shared environment—which would include which school your parents send you—doesn’t matter that much. If schools were important, then family environment would certainly matter, because it affects what school you’re sent to. Same with how “stimulating” an environment is—surely, some family environments in the U.S. are more or less stimulating than others.

Pro concedes my explanation of the Flynn effect—and while this shows that environmental influences used to have a significant impact, they no longer do, which is why the Flynn effect has stopped.

Pro argues that people with a genetically higher IQ might seek out environments that raise their IQ even further—presumably educational resources. But if this were the case, surely shared environment would have a closer relationship with IQ. Shared environment includes what school a person goes to, what opportunities their parents provide for them—and this appears to have very little effect. For twins, their IQs are correlated at .86 when they’re raised together, compared to .76 raised apart. It’s plausible that these factors Pro mentions are responsible for that .1 difference. High IQ twins raised together might both benefit from their parents sending them to a good school, while twins raised apart might be sent to different educational environments. But if such things were more important than genetics, it would show up in shared environment—being self-directed toward education isn’t the only way your education is affected, your parents play an important role. If ‘study habits’ were relevant, then shared environment would be relevant—parents have a significant effect on study habits.

I do not ignore Pro’s evidence about high IQ variance during childhood—I merely point out that such changes are temporary. If a stimulating environment raises your IQ as a child, then it goes back down once you’re an adult.

Exercise and meditation may help people, but showing that isn’t enough—Pro have to also show that the effect is significant relative to the effect of genes.

Pro cites an article about a study showing that brain training tasks can improve fluid intelligence, but this study has been debunked. It only used 1 test of fluid intelligence, and the control and experimental groups were different in an important way—the experimental group had to come in regularly for training, while the control group just went home and did whatever in between tests. [1] The experimental group may have had more motivation than the control group. A new study, using the same brain-training techniques, but with 8 intelligence tests and better controls, found no evidence that this brain training has any effect. [2]

The higher IQs explain the other things Pro mentions—IQ is associated with all of those things. If one group had a genetically higher IQ than the other, then there’s no evidence that the intervention had any effect.

The Norwegian study does show that education can have an effect, but I don’t think it shows a permanent effect. The measure was done 3 years after the schooling ended—the gains could have faded out since then. This is supported by the fact that people reach their peak intelligence at 26, not 19. [3] If schooling was a relevant causal factor, it would have also shown up in twin and adoption studies. The quality of schooling in America is very different depending on where you live—and yet, adopted siblings aren’t more similar to each other in IQ than any 2 random people, and twins raised together aren’t much more similar than twins raised apart.

Again, I concede that IQ may change quite a bit because of environment during childhood. But then it goes back to your genetic potential and stays there. Con’s evidence does not contradict this—in fact, it supports my conclusion. My theory would expect childhood intelligence to be different from adult intelligence, because the effects of family environment fade out.

==My Case==
Since we haven’t found all of the genes responsible for intelligence, it would be impossible to find out exactly how much IQ is genetically determined using the kind of study Pro cites. That’s why we use twin studies. Pro fails to provide a substantive criticism of twin studies—saying correlation is not causation is not enough, you have to provide a more plausible theory of causation that explains the correlation. Surely IQ doesn’t cause genes—but what explains the correlation then, if not that genes cause IQ?

No, it shows that conscientiousness is more influenced by ‘something other than genes/family environment’ than genes. This is not necessarily environment.

I am not asking Pro to argue for “only one type of environment.” He can cite any environmental influence he wants—as long as it’s actually an environmental influence. I would like Pro to cite a definition of ‘environment’ that includes the choices of the person in question.

A school (or parents) instilling values in the child that makes them more conscientious—teaching responsibility, for example. This is an environmental influence. A person choosing to save money rather than spend it as soon as they get it? This is not an environmental influence—and yet, it would be included under ‘unique environment’ because ‘unique environment' simply means ‘not genes or family environment.’ Identical twins raised in the exact same environment could still make different choices—have different levels of conscientiousness. For IQ, this doesn’t really apply, but conscientiousness is just how responsible and self-disciplined someone is—something people can choose to change regardless of their genes or environment.

[3] McArdle, John J.; Ferrer-Caja, Emilio; Hamagami, Fumiaki; Woodcock, Richard W. (2002). "Comparative longitudinal structural analyses of the growth and decline of multiple intellectual abilities over the life span.". Developmental Psychology 38 (1): 115–42.
Debate Round No. 3


Pro Case:

Con claims that the decline in education is irrelevant because it's only a relative decline. This simply can't be true. The way we value education is precisely how it is doing as compared to other educational systems, past or present. For example, we know we're worse off now because we were better off before. And, we know we're not doing that well now because most advanced nations are doing better. Obviously, some schools will be better than others within the country, but even the overall state of education in the U.S. has been relatively outmatched by the overall states of other nations. There are certain countries with much more intensive school programs that do better than the U.S. on tests of IQ.

I used "stimulating" as an oversimplification for describing the addictive nature of media-based technology and the adverse, drug-like effects it is being demonstrated to have on the human brain and mind in a growing body of research. This, for one thing, cannot be cast aside as impact-less or unimportant, as the effects are quite significant (they're physical and behavioral), and the scope of those affected is only going to grow. Second, it is a perfect example of a "shared" environment that is also a "unique" environment, as the Internet, cell-phone networks, and even cable television are a sort of shared environment, whereas the interaction of each individual with their devices and programs is a unique environment. So clearly, both "shared" and "unique" environments (put together they might simply be called "experience") still have substantial effects on IQ.

Con is right that both being self-directed toward education and parent-directed toward education are important environmental (i.e. experiential) factors in affecting IQ. However, that was my argument. It is much more likely that a person with a slight, inherited advantage in IQ will be both self-motivated and parent-motivated to do well in school, thus reinforcing their advantage. Conversely, someone with a slight, inherited disadvantage in IQ will be less motivated to do well in school academically, and their parents might encourage success in sports or some other activity. This can explain why twins correlate on their IQs even when separated.

It's obviously difficult, if not impossible, to describe the relative impact on IQ and conscientiousness from meditation and exercise at this time. The studies didn't measure IQ in any of them, let alone study their genes. They look more at behavior, brain structure, and health. Suffice to say that these types of behaviors may or may not change your genetic potential, but they certainly help you express it maximally.

As for the large IQ changes associated with brain changes, Pro presents no evidence to support his claim that these can't last. And as for the improved fluid IQ, some studies have "debunked" it while others have replicated it. I would say the jury is still out.

Con's alternate explanation for the abecedarians is plausible, but how likely is it considering that the improved group was taken randomly out of another group of low-income children, and that the remainder of that group served as the controls and did much worse on these measures of lifelong achievement? The group that did 4 times better in graduation just happened to have higher IQs in the first place, is what Con appears to be arguing. Con has no evidence of this, so I think the better explanation is that intervention did help.

As for the Norwegians, even if the improvement did fade, hat would suggest an even larger improvement than the measurement, which was a significant improvement of 4 IQ point per extra year of education. It's unlikely that IQ accelerates at that rate naturally when rising to its peak at 26. The problem with twin/adoption studies shows itself here as well. Regardless of which shared environment you're in, your genetic tendencies usually tend to be reinforced by appropriate unique environments, whether its due to motivation from others or yourself.C4:Con's response is simply not what the research concluded. It concluded that the genetic variance of one's own IQ was 24% across the whole lifetime, or a very large portion of it (11-79.) So the fact that IQs are somewhat similar, but also somewhat different, at the end of that period doesn't lend itself more to either case, but Deary's conclusion about the genetic variance does.

Con Case:

Deary is very careful in his approach and I wouldn't think that he would put forward such numbers unless he had taken measures to work Con's concerns into his conclusions. This is probably why he somewhat widely described the genetic variance of IQ between individuals as between 40-50%. My criticism of twin studies isn't concerned about the method0logy per se, even though it doesn't actually take information about specific genes into account, but about the misled conclusions it's responsible for in the public mind. Saying correlation is not equal to causation is important, because if all you do is cite .70 or .80 correlation for twins, it leads people to thinking that IQ is 70% or 80% genetic, when the more detailed research (Deary) shows that this is probably a large overestimation. The main problem is that IQ, like education earlier, is a trait valued on a relative basis. What makes the IQ of a genius special, or a mentally-disabled person unfortunate, is the difference between it and the average. These differences are what we call variance, and Deary's research has made the best scientific attempt so far at estimating the causes of these differences. His best hypotheses so far are that the variance between individuals is 40-50% genetic, meaning 50-60% is experiential (all of the controversial types of 'environments" combined), while the variance within an individual lifetime is only 24% genetic, meaning 76% is environmental (i.e. experiential.) Thus, the problem with trying to analyze IQ in terms of similarities is that it's a relative trait whose differences are more important, and since these differences are mostly caused by external, as opposed to inherited, factors then the "environment" affects it more than genes.

Con here says the differences in conscientiousness are caused mostly by whatever is not genes or shared environment, which is generally described as "unique" environment, but what I would call individual experience. And I would argue that this is, as for intelligence, the determining factor in most of the differences.

I apologize to my opponent if we've had a bit of a misunderstanding, but my interpretation of "nurture" and "environment" is essentially everything that is not genes. i.e. experience. This is what I am and have been trying to prove is more important than inheritance in 'determining' IQ. I'm sorry if he judged me as having a similar outlook on these words as most people, and if I have not been clear enough. However, this is clearly what Deary means when he says that the rest of the variance between IQ that he has not accounted for with genetics is probably due to "environmental influences." Therefore his evidence, along with the growing neuroscientific research into brain changes associated with behavioral and performance changes associated with all sorts of specific activities, and the obvious benefits of optimizing certain kinds of shared environmental influences, is sufficient to demonstrate that in the case of rationality, nurture edges out nature and beats it.


==Pro's Case==
Pro completely ignores my argument about the differing quality of schools within the U.S.—“ Surely, we can agree that whatever the overall state of education in the United States, it is good in some schools and bad in others. And yet, twin studies find that shared environment—which would include which school your parents send you—doesn’t matter that much. If schools were important, then family environment would certainly matter, because it affects what school you’re sent to.”

If the genetic advantage was slight and that slight advantage resulted in different experiences that then caused variance in IQ, then twin and adoption studies would not show what they show. If this were the case, children with different genetic parents adopted into the same family would be much more similar than they are. Their genetics would give them slight differences, but surely being raised in the same family would have some noticeable effect, if Pro’s argument was correct. Pro’s argument implies that slight genetic differences make these children seek out environments that are so radically different, and the parents treat their adopted children so radically differently, that their IQs don’t end up being correlated at all. This is absurd.

If these results can’t be measured, then they aren’t important to this debate. They could work—but then again, they could prove just as ineffective as ‘brain-training’ exercises.

I did provide evidence showing that IQ changes don’t last. There’s a lower correlation between twins IQs during childhood, when shared environment has a measurable effect, then the correlation goes back up when they’re adults, and the effect of shared environment drops to nothing.

The jury most certainly is not “still out” on the effects of ‘brain-training’ exercises. I showed why his single study was flawed, and provided a study that didn’t have those flaws that found that these exercises have no effect.

I do not think that the experimental group with the higher IQs “just happened” to have better graduation rates, I said that the higher IQs caused the higher graduation rates and other life outcomes. My point was that it is implausible that the intervention caused the higher IQs, since the difference showed up after 1.6 months and then stayed the same for the rest of the intervention.

I don’t understand Pro’s argument that “even if the improvement did fade, hat would suggest an even larger improvement than the measurement.” It most certainly would not—it would suggest no improvement if the higher IQs faded away.

Pro fails to address my argument. My point was that the part of the lifetime studied includes childhood. I conceded that environmental influences can cause a large amount of variance in childhood IQs, but then the environmental influence stops. This isn’t inconsistent with the study Pro cites.

==My Case==
I have no doubt that Deary’s work is careful, my concern is that I don’t see how he possibly could find the genetic influence of intelligence if we haven’t found all of the genes coding for intelligence yet. Pro is sure that he takes my concerns into account, but fails to explain how exactly he does so. Given that Pro failed to explain exactly why the heritability found by twin studies is wrong or how Deary accounted for the problems I mention, he has failed to meet his burden of proof.

See C3 about shared vs unique environment.

I asked Pro to delete the term 'acquired traits' from his definition of environment, because it would include everything that isn't genetics, during our previous attempt to do this debate that bugged out and had to be deleted. Pro says that by environment, he meant “everything that isn’t genetics, i.e. experience.” But my argument is that ‘experience’ isn’t the only possible non-genetic factor—there is personal choice. No reasonable definition of ‘environment’ includes free will. To repeat my argument from last round: “A school (or parents) instilling values in the child that makes them more conscientious—teaching responsibility, for example. This is an environmental influence. A person choosing to save money rather than spend it as soon as they get it? This is not an environmental influence—and yet, it would be included under ‘unique environment’ because ‘unique environment' simply means ‘not genes or family environment.’ Identical twins raised in the exact same environment could still make different choices—have different levels of conscientiousness.”

Pro argues that this is the way a source he cited meant 'unique environment' when talking about IQ--but this is irrelevant. I conceded that the 'unique environment' measured in IQ studies could be actual environmental influences, because you can't choose to have a higher IQ. My point was that conscientiousness is different, and could be chosen.
Debate Round No. 4
1 comment has been posted on this debate.
Posted by mark.marrocco 6 years ago
This is a challenge for LaissezFaire. If you are not LaissezFaire, do not take it. If you are LaissezFaire, and it still doesn't work for some reason or we still need to clarify anything, I'll have to do it tomorrow, because I'm sleepy now.
1 votes has been placed for this debate.
Vote Placed by frozen_eclipse 6 years ago
Agreed with before the debate:Vote Checkmark--0 points
Agreed with after the debate:Vote Checkmark--0 points
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Total points awarded:30 
Reasons for voting decision: Both cases were great. There is no doubt that genetics and environment are key factors to intellect etc.... Cons case did seem to evaluate a bit better but overall pros sources, logic and examples did convince me that environment is a bit more of a factor.