While a poor environment can have an impact on intelligence, the variations of intelligence in humans in a primarily inherited trait.  It's inheritance is not as strong at height, for instance, but most studies suggest that genetics makes 70% of the difference.  This suggests that the powerful worldwide trend of the most intelligent to have far fewer children that average is having a strong and negative impact on the future of human society.  Unfortunately, no one seems to care.

Smart Kids Cortical Thickness Develops Longer: In a study of 306 children and teenagers without psychiatric or neurological disorders, brain scans demonstrated that the brightest children with IQs of 121-149 experienced rapidly cortical thickening from ages 7 to 12 before thinning to near normal levels while average children had their cortical thickness peak at age 8 and to a lesser extent before declining to standard levels.  The thickening in the bright children was most prominent in the prefrontal cortex, the primary area for analytical thinking. Shaw P, et al, NIMH, Bethesda.  Nature 3/30/06.  Previous research has shown that the development of many neurons is typical of childhood and that the pruning of the neurons to smaller numbers for adult life is part of the process for developing the complex patterns necessary for human intelligence.

Academic Female Professors Don't Have Children: In a study of Mary Ann Mason of the University of California, Berkeley, it was found that 50% of tenured female professors in the sciences and 62% in the humanities are childless as well as 30% and 39% of male professors. (Reported in New Scientist 4/8/06). Ed: This is a huge loss for the future of our nation, since it is absolutely certain that genetics plays a big role in intelligence.  Our university system is destroying the future of our society for short-term gain.  These rates, both male and female, are much higher than society in general, although large percentages of doctorate degree graduates outside of academia are also childless.  Even those who have children, usually have just one or two and very rarely more than two.  Genes connected with success in higher education are being rapidly lost forever.

Verbal Reasoning Largely a Genetic Trait: Whole-population estimates using twins from unique mental surveys in Scotland of 1st June 1932 and 4th June 1947 administered the same validated verbal reasoning test to almost everyone born in 1921 or 1936 and attending school in Scotland found 1089 twin pairs. A mixture distribution was used to estimate genetic and environmental components of verbal reasoning variation by maximum likelihood. There were consistent heritability (approximately 0.70) and shared environment (approximately 0.21) estimates. The estimates did not change substantially when additional quantitative traits (height and weight) were added in a multivariate analysis. Large, consistent estimates of the heritability of cognitive ability in two entire populations of 11-year-old twins from Scottish mental surveys of 1932 and 1947. Benyamin B, et al. University of Edinburgh, UK. Behav Genetics 2005 Sep;35(5):525-34.

Impoverished Environment May Play a Role: In a study of IQ scores in 7-year-old twins from the National Collaborative Perinatal Project, in "impoverished" families, 60% of the variance in IQ was accounted for by the shared environment, and the contribution of genes is close to zero; in middle class "affluent" families, the result is almost exactly the reverse. Socioeconomic status modifies heritability of IQ in young children. Turkheimer E, Haley A, et al. University of Virginia, Charlottesville. Psychol Sci. 2003 Nov;14(6):623-8. Ed: This study is highly unusual in finding no genetic contribution in low-income families. While its hypothesis sounds reasonable, even low income Americans are much better nourished and have much better health than previous generations except for a higher rate of maternal substance abuse.  Even schools are much better funded with the lowest student/teacher ratio in modern American history and also low by international standards. Obviously, its findings need to be replicated by independent researchers. The researchers choice of wording suggested that they may have had a political bias independent of their research data.

Prion Protein M129V Polymorphism Accounted for 2.7% IQ Variation: Correlations between general intelligence (g) and brain volume are about 0.40, and is largely due to genetic factors. Methionine at codon 129 in the prion protein is associated with white matter reduction in healthy volunteers and schizophrenic patients. This study of 335 community-based healthy Germans found the M129V polymorphism associated with Full Scale IQ (genotype: P=0.013; allele: P=0.005). The genotype accounted for 2.7% of the total variability in Full Scale IQ (partial eta2=0.027). M129V variation in the prion protein may influence cognitive performance. Rujescu D, Hartmann AM, et al. Ludwig-Maximilians-University, Munich, Germany. Mol Psychiatry. 2003 Nov;8(11):937-41.

SNAP-25 Gene Variance Accounted for 3.4% of Performance IQ: The synaptosomal-associated protein of 25 kDa (SNAP-25) gene plays an integral role in synaptic transmission. Recent studies have suggested a possible involvement of SNAP-25 in learning and memory. The SNAP-25 gene lies in a linkage area implicated in intelligence. In two independent family-based Dutch samples of 391 (mean age 12.4 years) and 276 (mean age 37.3 years) subjects, researchers genotyped 12 single-nucleotide polymorphisms (SNPs) in the SNAP-25 gene on 20p12-20p11.2. A strong association was found between three SNPs in the SNAP-25 gene and intelligence. The strongest, replicated association was found between SNP rs363050 and performance IQ (PIQ), where the A allele was associated with an increase of 2.84 PIQ points (P=0.0002). Variance in this SNP accounts for 3.4% of the phenotypic variance in PIQ. The SNAP-25 gene is associated with cognitive ability: evidence from a family-based study in two independent Dutch cohorts. Gosso MF, et al. Vrije Universiteit, Amsterdam, The Netherlands. . Mol Psychiatry 2006 Sep;11(9):878-86.

Dysbindin-1 Gene Linked to Intelligence: The gene for dysbindin-1 (DTNBP1) is located at 6p and has been implicated in schizophrenia. The same 6p has been associated with intelligence. In a study of DTNBP1 genotype and general cognitive ability (g) in two independent cohorts, including 213 patients with schizophrenia or schizo-affective disorder and 126 healthy volunteers, DTNBP1 genetic variation influenced human intelligence. Genetic variation in DTNBP1 influences general cognitive ability. Burdick KF, et al. Albert Einstein College of Medicine, Glen Oaks, NY 11004, USA. . Hum Mol Genet 2006 May 15;15(10):1563-8.

Genetics Strong for IQ and for Height; Environment Minor Factor: In a study of height and IQ in 209 Dutch twin pairs at the ages of 5, 7, 10 and 12 years, 208 twin pairs at 16 and 18 years of age and 567 twin pairs and their siblings in adulthood, the heritability of height was high in all cohorts and across all ages (a2 = 0.93 - 0.96). In adulthood, heritability was also high for full-scale IQ (FSIQ: a2 = 0.83-0.84) and somewhat lower for verbal IQ (VIQ: a2 = 0.66-0.84). In early childhood, the heritability was lower, and common environmental factors had a substantial effect on FSIQ and VIQ. A positive association of height and IQ was found in early childhood and adolescence. In adulthood, a correlation was found between height and FSIQ in young adulthood and between height and VIQ in middle age. All correlations could be ascribed to genetic factors influencing both height and IQ. Thus, these results show that the association between height and IQ should not be directly regarded as evidence for childhood living conditions affecting IQ, but the effect of genetic factors affecting independently or interacting with environmental factors should be considered as well. Genetic contributions to the association between height and intelligence: Evidence from Dutch twin data from childhood to middle age. Silventoinen K, et al. University of Helsinki, Finland. Genes Brain Behav 2006 Nov;5(8):585-95.

Genetics Strong for Intelligence in Two Nationwide Scottish Twin Studies: The Scottish Mental Surveys of 1932 (SMS1932) and 1947 (SMS1947) administered the same validated verbal reasoning test to almost everyone born in 1921 or 1936 and attending school in Scotland. There were 572 twin pairs from the SMS1932, and 517 pairs from the SMS1947. Researchers found consistent heritability (approximately 0.70) and shared environment (approximately 0.21) estimates. The estimates did not change substantially when additional quantitative traits (height and weight) were added in a multivariate analysis. Large, consistent estimates of the heritability of cognitive ability in two entire populations of 11-year-old twins from Scottish mental surveys of 1932 and 1947. Benyamin B, et al. University of Edinburgh, UK. Behav Genet 2005 Sep;35(5):525-34.

Genetic Importance Doesn't Decrease with Age: The differentiation hypothesis in cognitive development states that cognitive abilities become progressively more independent as children grow older. Studies of phenotypic development in children have generally failed to support the hypothesis. This study of 6 psychometric measures of verbal and nonverbal cognitive abilities in 209 Dutch twin pairs at ages 5, 7, and 10 years found little evidence for the differentiation hypothesis. Stability in subtest performance is due mainly to genetic influences. The shared environment contribution to phenotypic stability is small. The unique environment contributes to age-specific variance only. A twin study of differentiation of cognitive abilities in childhood. Rietveld MJ, Dolan CV, et al. Amsterdam, The Netherlands. Behav Genet. 2003 Jul;33(4):367-81.

Intelligence Dropping in Thailand: The IQ level of Thai children aged 6-12 had dropped when the 1997 survey findings were compared with the 2002 figures, Bangkok Post 12/04. In 1997 the average IQ of Thai children was 96.5 in Bangkok, 92.3 in the central region, 87.9 in the northern part. In 2002, the figures were 94.6 in Bangkok, 88.8 in the central region and 84.2 in the North. The setback in the children's IQ levels were blamed on their parents' income levels, professions and educational backgrounds. Xinhua. http://english.people.com.cn/200412/08/eng20041208_166596.html

4 SNPs Associated with Mild Mental Impairment: Mild mental impairment (MMI) represents the low extreme of the quantitative trait of general intelligence and is highly heritable. Using SNP-MaP (SNP Microarrays and Pooling), we have identified four loci associated with MMI. These four loci have been replicated in two SNP-MaP studies and verified by individual genotyping. The two SNP-MaP studies conducted were a case-control comparison (n = 515 and n = 1028, respectively) and a low versus high general intelligence extremes group comparison (n = 503 and n = 505, respectively). Twelve loci showing the largest significant differences in both SNP-MaP studies were individually genotyped on 6154 children. Of the four loci positively associated with MMI, the minor allele of each conferred the greater risk for MMI. Although each SNP accounts for a small amount of variance, their effects are additive and they can be combined in a 'SNP set' that can be used as a genetic risk index for MMI in behavioral genomic analyses. SNPs, microarrays and pooled DNA: identification of four loci associated with mild mental impairment in a sample of 6000 children. Butcher LM, Meaburn E, et al. Institute of Psychiatry, London, UK. . Hum Mol Genet. 2005 May 15;14(10):1315-25.

Cholecystokinin A Receptor Gene Mutations Linked to Slightly Lower IQs: In a study of cholecystokinin A receptor (CCKAR) genotypes and intelligence in 2251 Japanese adults ages 40-79, the CCKAR gene promoter polymorphisms A-81G and G-128T were determined. Intelligence was assessed by Japanese Wechsler Adult Intelligence Scales - Revised Short Forms (JWAIS-R SF). The average IQ levels of the wild-type allele and the mutation allele at nucleotide -128 were 103.4 and 101.6, respectively (p=0.008). The difference in IQ for A-81G was also significant (p=0.011): IQs of 103.6 with the wild-type allele and 102.0  with the mutation. Cholecystokinin A receptor gene promoter polymorphism and intelligence. Shimokata H, Ando F, et al. National Institute for Longevity Sciences, Obu Aichi, Japan. . Ann Epidemiol. 2005 Mar;15(3):196-201.

Interleukin-6 Genetic Variation Increased in Lower Functioning Premees: The pro-inflammatory cytokine IL-6 may be neurocytopathogenic, and elevated levels are associated with impaired neurological outcome among children born prematurely. The rare C (rather than G) variant at position -572 in the IL-6 gene is associated with an increased IL-6 synthetic response. In 113 prematurely born native British children, intellectual performance (median, interquartile range) at 2 years was worse in the 10 carriers of the C allele than for those with GG genotype: Griffiths Developmental Quotient: C allele, 92.4 vs. 100.9, p = 0.002; General Cognitive Ability: C allele, 88.0 vs. 103.0, p = 0.037; Movement ABC score: C allele 8.3 vs. 4.0, p = 0.081. Variation in the interleukin-6 gene is associated with impaired cognitive development in children born prematurely: a preliminary study. Harding D, et al. University of Bristol, Bristol, UK. . Pediatr Res 2005 Jul;58(1):117-20

KLOTHO Gene Variants May Affect Intelligence: In a study of the influence of a variation in the KLOTHO gene on cognitive ability at age 11 and age 79 in 464 people from the Lothian Birth Cohort 1921 (LBC1921), and at age 11 and age 64 in 451 people in the Aberdeen Birth Cohort 1936 (ABC1936), in the LBC1921, people with the KLOTHO V/V genotype had lower verbal reasoning ability at age 11 and age 79, and lower non-verbal reasoning at age 79, than those with the F/F genotype, or heterozygotes. In this sample, KLOTHO V allele status accounted for about 2% of the variance in life-long traits related to verbal and non-verbal reasoning, but not to age-related cognitive change. These results were not replicated in the ABC1936 sample. KLOTHO genotype and cognitive ability in childhood and old age in the same individuals. Deary IJ, Harris SE, et al. University of Edinburgh, UK. . Neurosci Lett. 2005 Apr 11;378(1):22-7.

Genetics Accounts for the Large Majority of Variance in Intelligence in Modern Australia: In a study of 256 monozygotic twin pairs and 326 dizygotic twin pairs ages 15-18 when achievement tested, and 15-22 when IQ tested, univariate analysis indicated a heritability for the QCST of 0.72. Adjustment to this estimate due to truncate selection (downward adjustment) and positive phenotypic assortative mating (upward adjustment) suggested a heritability of 0.76 The findings suggest that individual variation in QCST performance is largely due to genetic factors and that common environmental effects may be substantially accounted for by phenotypic assortative mating. The genetic basis of academic achievement on the Queensland Core Skills Test and its shared genetic variance with IQ. Wainwright MA, Wright MJ, et al. Queensland Institute of Medical Research, Brisbane, Australia. .

Genetics Primary Determinant of Intelligence: Genetic influences on brain morphology and IQ are well studied. A variety of sophisticated brain-mapping approaches relating genetic influences on brain structure and intelligence establishes a regional distribution for this relationship that is consistent with behavioral studies. These have proven complex cortical patterns associated with measures of cognitive ability. A measure of cognitive ability, known as g, has been shown highly heritable across many studies. These genetic links are partly mediated by brain structure that is likewise under strong genetic control. Other factors, such as the environment, obviously play a role, but the predominant determinant appears to genetic. Genetics of Brain Structure and Intelligence. Toga AW, Thompson PM. University of California, Los Angeles. . Annu Rev Neurosci. 2004 Jun 30

Females Do Less Well on Most Standardized Tests, But Better in School: Since 1972, females consistently have scored lower than males on the SAT, in both the verbal and math sections of the test, with girls falling behind boys in math by as many as 61 points. In 1996, the average combined SAT score of boys was still 39 points higher than that of girls, a pattern that persisted within every racial and ethnic group. There also are disparities in the PSAT, used for college scholarships, and the ACT, used for college admissions, as well as most examinations for admission to professional and graduate school. The SAT, which is designed to be an indicator of first–year college performance, underpredicts females' performance: while young women score lower than young men on the SATs, they earn higher grades when matched for the same courses in all subjects in their first year in college.