The Tunnel Hill Bike Trail runs from Harrisburg to Karnak, Illinois along an abandoned railroad line. South of Tunnel Hill, the trail crosses a valley by means of the Breeden Trestle, which is shown in these photographs.
Saturday, November 28, 2009
Tunnel Hill, Johnson County, Illinois
I wanted to create action shots of Tim as he emerged from this tunnel under a highway on the Tunnel Hill Bike Trail. In continuous shooting mode, my Canon Powershot A590 will take 1.4 shots per second. I failed to switch to continuous shooting mode in time and was only able to get off a single shot as he left the tunnel.
Evidence about the Causes of Race Differences in Cognitive Ability
In 2005, two academic psychologists, J. Philippe Rushton and Arthur R. Jensen, wrote a survey of social science research on whether race differences in IQ result from environmental factors, genetics, or a combination of the two. The survey was published in the American Psychological Association's journal, Psychology, Public Policy and Law. East Asians, whites, black Americans, and sub-Saharan Africans have average IQ scores, in order, of about 106, 100, 85, and 70. The variation in the averages is an uncontroversial fact. The cause of the variation is debated. (Important caveat: The variation tells you nothing about the intelligence of a particular individual. 15-20% of black Americans have an IQ higher than the white average.)
The mainstream view in the social sciences, which can be called the blank slate model, claims that the genes responsible for cognitive ability are evenly distributed among all human population groups. This view denies that any part of the group differences in IQ is due to genes. The alternative view, called the hereditarian model, says that group differences and individual differences at least in part reflect different distributions of the genes responsible for cognitive ability.
To reconcile the assumption of human equality with the fact that the races have different IQ averages, social scientists have relied on three theories. They argue that the racial variation in IQ is due to cultural bias in the tests, that it results from differing levels of effort made by test takers, or that some aspect of the environments of low scoring groups depresses their IQ. In the survey, Rushton and Jensen show that these theories cannot account for all the variation in IQ and that the variation must therefore be due in part to genetics.
I. The pattern of IQ scores cannot be due to cultural bias.
The cultural bias theory has been undermined by research using Raven's Progressive Matrices ("RPM"), which are culture-neutral tests in which the subject selects the missing element in a pattern of geometric shapes. Scores on RPM show the same racial pattern as as other IQ tests. The racial differences on RPM can't be due to cultural bias since the matrices are culture-free.
Further, if IQ tests were biased, the tests would underpredict blacks' grade point averages in school and performance on the job. But multiple studies have shown that IQ tests have equal predictive validity for blacks and whites.
II. The pattern of IQ scores cannot be due to variation in the effort made by different races.
Researchers have used tests of reaction time to analyze whether people of different races make the same effort on IQ tests. Reaction time is negatively correlated with IQ: the smarter you are, the faster you can react to a prompt and the faster you can solve a puzzle. The reaction time data follows the racial same pattern as average IQ scores, with sub-Saharan Africans averaging the longest reaction times (lower intelligence) and East Asians averaging the shortest (higher intelligence). Although Africans have the slowest reaction times, they demonstrate faster finger movements on the tests. This data cannot be reconciled with the hypothesis that people of African descent make less of an effort than whites and Asians.
The hypothesis that race differences in IQ result from different levels of effort also conflicts with scores on forward and backward digit span. On these tests, the subject has to repeat a series of single digit numbers in the same order they are read to him or in the opposite order. Repeating the digits backwards is more of a test of raw cognitive ability, whereas digits-forward is a test of short term memory. The subject's score is the largest number of digits he can repeat without error on two consecutive trials. The difference between the average score for blacks and whites on digits-backward is twice as great as the difference on digits-forward. The test of pure cognitive horsepower produces a larger racial gap than the test of short term memory. This difference can't be explained by cultural bias or lack of effort. (It is confirmation of Spearman's hypothesis that the more a test measures raw cognitive ability (or g), the greater will be the difference in two racial groups' scores on the test.)
The mainstream view in the social sciences, which can be called the blank slate model, claims that the genes responsible for cognitive ability are evenly distributed among all human population groups. This view denies that any part of the group differences in IQ is due to genes. The alternative view, called the hereditarian model, says that group differences and individual differences at least in part reflect different distributions of the genes responsible for cognitive ability.
To reconcile the assumption of human equality with the fact that the races have different IQ averages, social scientists have relied on three theories. They argue that the racial variation in IQ is due to cultural bias in the tests, that it results from differing levels of effort made by test takers, or that some aspect of the environments of low scoring groups depresses their IQ. In the survey, Rushton and Jensen show that these theories cannot account for all the variation in IQ and that the variation must therefore be due in part to genetics.
I. The pattern of IQ scores cannot be due to cultural bias.
The cultural bias theory has been undermined by research using Raven's Progressive Matrices ("RPM"), which are culture-neutral tests in which the subject selects the missing element in a pattern of geometric shapes. Scores on RPM show the same racial pattern as as other IQ tests. The racial differences on RPM can't be due to cultural bias since the matrices are culture-free.
Further, if IQ tests were biased, the tests would underpredict blacks' grade point averages in school and performance on the job. But multiple studies have shown that IQ tests have equal predictive validity for blacks and whites.
II. The pattern of IQ scores cannot be due to variation in the effort made by different races.
Researchers have used tests of reaction time to analyze whether people of different races make the same effort on IQ tests. Reaction time is negatively correlated with IQ: the smarter you are, the faster you can react to a prompt and the faster you can solve a puzzle. The reaction time data follows the racial same pattern as average IQ scores, with sub-Saharan Africans averaging the longest reaction times (lower intelligence) and East Asians averaging the shortest (higher intelligence). Although Africans have the slowest reaction times, they demonstrate faster finger movements on the tests. This data cannot be reconciled with the hypothesis that people of African descent make less of an effort than whites and Asians.
The hypothesis that race differences in IQ result from different levels of effort also conflicts with scores on forward and backward digit span. On these tests, the subject has to repeat a series of single digit numbers in the same order they are read to him or in the opposite order. Repeating the digits backwards is more of a test of raw cognitive ability, whereas digits-forward is a test of short term memory. The subject's score is the largest number of digits he can repeat without error on two consecutive trials. The difference between the average score for blacks and whites on digits-backward is twice as great as the difference on digits-forward. The test of pure cognitive horsepower produces a larger racial gap than the test of short term memory. This difference can't be explained by cultural bias or lack of effort. (It is confirmation of Spearman's hypothesis that the more a test measures raw cognitive ability (or g), the greater will be the difference in two racial groups' scores on the test.)
III. The pattern of IQ scores cannot be due to different environments.
After refuting the idea that race differences in IQ reflect varying levels of effort or cultural bias, Rushton and Jensen review several categories of evidence that shed light on whether the differences can be pinned entirely on the environment, or whether genetics must also play a role. The conventional wisdom in the West holds that people of sub-Saharan African descent show depressed IQ scores because of poverty, a culture that undervalues education, or other harmful environmental influences. Egalitarians make an analogy to corn seeds. Corn seeds in normal soil will produce plants of normal height, while the same seeds produce stunted plants in a deprived environment.
Several categories of evidence show that environmental differences cannot account for all the racial variation in IQ. First, the IQ gap remains even when consideration is limited to blacks from privileged backgrounds. Black Americans with high socioeconomic status have lower average IQ scores and lower SAT scores than white Americans from the lowest socioeconomic backgrounds.
The Minnesota Transracial Adoption Study looked at black children, mixed race children, and white children who were adopted by upper middle class white parents. The IQ of the adoptees was measured at ages 7 and 17 and compared to the IQ of the nonadopted white children of the parents in the study.
The blank slate model assumes that some aspect of the black environment is depressing black IQ. In the study, the harmful black environment had been replaced with an upper middle class white environment, which should eliminate or reduce the harmful effects of the black environment. However, when the subjects' IQ was measured at age 17, the mean IQ of the black adoptees was the same as the mean IQ for all blacks in Minnesota (89). The mixed race adoptees had an average IQ of 99 (which was intermediate between the mean for blacks and whites). The averages for the black and mixed race children were below the average IQ of the white adoptees (106) and the average of the nonadopted white children (109). The blank slate model is unable to explain why the racial variation remains even after the black environment has been completely replaced with a white environment.
The hereditarian model can explain these results. They are due to racial differences in the distribution of genes responsible for cognitive ability. When the black environment is replaced by the white environment, average black IQ will still be below the white average because the two populations don't have the same set of genes that affect cognitive ability.
Regression to the mean in IQ bears out the hereditarian view and further undercuts the blank slate model. Regression to the mean refers to the fact that the children of geniuses will tend to be less intelligent than their parents because the parents on average won't pass on all the genes that are responsible for their exceptional minds. On the other hand, the children of people who are of below average intelligence will tend to be smarter than their parents because the parents won't pass on all the genes responsible for their cognitive deficiency. "For any trait, scores should move toward the average for the population."
Genetic theory predicts that the children of black Americans will regress toward the black IQ average of 85 and the children of white Americans will regress toward the white IQ average of 100. Studies have confirmed the prediction. When white and black students were matched at an IQ of 120, the siblings of the black students had an average IQ of 100 and and the siblings of the white students had an IQ of 110. If the blank slate model is correct that environment is causing the variation in IQ, the siblings of the black students with an IQ of 120 also ought to have an IQ of 120, and there is no reason for them to have a significantly lower average IQ than the siblings of the white children. The blank slate model cannot explain this data. Genetic theory can.
Studies have shown that, as people age, the effect of shared genes on IQ gets stronger, while the effect of shared environments on IQ gets weaker. The correlation in the IQ of siblings who are raised apart rises from 0.24 in childhood to 0.49 in adulthood. The correlation in the IQ of unrelated people who are raised together drops from 0.24 in childhood to 0.01 in adulthood. Since environmental effects weaken and genetic effects get stronger over time, environmental differences are unlikely to account for the variation observed in the average IQ of adult blacks and whites.
The blank slate model cannot account for the positive relationship between IQ and head size, and the positive relationship between IQ and the volume of gray matter in the frontal cortex. The average head size for East Asians, whites, and Africans follows the same pattern as their IQ scores, with East Asians largest, blacks smallest, and whites intermediate. However, when whites and blacks are matched for true-score IQ, the difference in average cranial circumferences drops to zero. This data suggests that the race difference in IQ is due to brain physiology. Proponents of the blank slate model have not offered a theory to explain how environmental differences could result in average differences in head size.
Finally, the testing data related to mixed race individuals contradicts environmental explanations for the racial pattern in IQ. On average, mixed race individuals have IQ scores that are intermediate between the mean scores for unmixed populations. This outcome is consistent with the genetic hypothesis, since mixed race individuals would have some genes associated with the black average and some genes associated with the white average, leading to an IQ score that is intermediate between the averages for unmixed populations.
IV. Conclusion
The blank slate model cannot account for the transracial adoption studies, the discrepancy between the IQ of low socioeconomic status whites and high socioeconomic status blacks, the head size data, or the data on regression toward the mean. The available evidence refutes the notion that the racial pattern in IQ is due solely to the environment, culturally biased tests, or lack of effort, which means that genetics must be responsible for part of the racial variation in IQ.
After refuting the idea that race differences in IQ reflect varying levels of effort or cultural bias, Rushton and Jensen review several categories of evidence that shed light on whether the differences can be pinned entirely on the environment, or whether genetics must also play a role. The conventional wisdom in the West holds that people of sub-Saharan African descent show depressed IQ scores because of poverty, a culture that undervalues education, or other harmful environmental influences. Egalitarians make an analogy to corn seeds. Corn seeds in normal soil will produce plants of normal height, while the same seeds produce stunted plants in a deprived environment.
Several categories of evidence show that environmental differences cannot account for all the racial variation in IQ. First, the IQ gap remains even when consideration is limited to blacks from privileged backgrounds. Black Americans with high socioeconomic status have lower average IQ scores and lower SAT scores than white Americans from the lowest socioeconomic backgrounds.
The Minnesota Transracial Adoption Study looked at black children, mixed race children, and white children who were adopted by upper middle class white parents. The IQ of the adoptees was measured at ages 7 and 17 and compared to the IQ of the nonadopted white children of the parents in the study.
The blank slate model assumes that some aspect of the black environment is depressing black IQ. In the study, the harmful black environment had been replaced with an upper middle class white environment, which should eliminate or reduce the harmful effects of the black environment. However, when the subjects' IQ was measured at age 17, the mean IQ of the black adoptees was the same as the mean IQ for all blacks in Minnesota (89). The mixed race adoptees had an average IQ of 99 (which was intermediate between the mean for blacks and whites). The averages for the black and mixed race children were below the average IQ of the white adoptees (106) and the average of the nonadopted white children (109). The blank slate model is unable to explain why the racial variation remains even after the black environment has been completely replaced with a white environment.
The hereditarian model can explain these results. They are due to racial differences in the distribution of genes responsible for cognitive ability. When the black environment is replaced by the white environment, average black IQ will still be below the white average because the two populations don't have the same set of genes that affect cognitive ability.
Regression to the mean in IQ bears out the hereditarian view and further undercuts the blank slate model. Regression to the mean refers to the fact that the children of geniuses will tend to be less intelligent than their parents because the parents on average won't pass on all the genes that are responsible for their exceptional minds. On the other hand, the children of people who are of below average intelligence will tend to be smarter than their parents because the parents won't pass on all the genes responsible for their cognitive deficiency. "For any trait, scores should move toward the average for the population."
Genetic theory predicts that the children of black Americans will regress toward the black IQ average of 85 and the children of white Americans will regress toward the white IQ average of 100. Studies have confirmed the prediction. When white and black students were matched at an IQ of 120, the siblings of the black students had an average IQ of 100 and and the siblings of the white students had an IQ of 110. If the blank slate model is correct that environment is causing the variation in IQ, the siblings of the black students with an IQ of 120 also ought to have an IQ of 120, and there is no reason for them to have a significantly lower average IQ than the siblings of the white children. The blank slate model cannot explain this data. Genetic theory can.
Studies have shown that, as people age, the effect of shared genes on IQ gets stronger, while the effect of shared environments on IQ gets weaker. The correlation in the IQ of siblings who are raised apart rises from 0.24 in childhood to 0.49 in adulthood. The correlation in the IQ of unrelated people who are raised together drops from 0.24 in childhood to 0.01 in adulthood. Since environmental effects weaken and genetic effects get stronger over time, environmental differences are unlikely to account for the variation observed in the average IQ of adult blacks and whites.
The blank slate model cannot account for the positive relationship between IQ and head size, and the positive relationship between IQ and the volume of gray matter in the frontal cortex. The average head size for East Asians, whites, and Africans follows the same pattern as their IQ scores, with East Asians largest, blacks smallest, and whites intermediate. However, when whites and blacks are matched for true-score IQ, the difference in average cranial circumferences drops to zero. This data suggests that the race difference in IQ is due to brain physiology. Proponents of the blank slate model have not offered a theory to explain how environmental differences could result in average differences in head size.
Finally, the testing data related to mixed race individuals contradicts environmental explanations for the racial pattern in IQ. On average, mixed race individuals have IQ scores that are intermediate between the mean scores for unmixed populations. This outcome is consistent with the genetic hypothesis, since mixed race individuals would have some genes associated with the black average and some genes associated with the white average, leading to an IQ score that is intermediate between the averages for unmixed populations.
IV. Conclusion
The blank slate model cannot account for the transracial adoption studies, the discrepancy between the IQ of low socioeconomic status whites and high socioeconomic status blacks, the head size data, or the data on regression toward the mean. The available evidence refutes the notion that the racial pattern in IQ is due solely to the environment, culturally biased tests, or lack of effort, which means that genetics must be responsible for part of the racial variation in IQ.
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