But let's unpack that sentence. We are talking about average differences among people and not about individuals.
Heritability "Heritability" is defined as the proportion of variance in a trait which is attributable to genetic variation within a defined population in a specific environment. The determination of many traits can be considered primarily genetic under similar environmental backgrounds. For example, a study found that adult height has a heritability estimated at 0.
For example, a twin study on the heritability of depression in men calculated it as 0. In fact, according to the concept of regression toward the meanparents whose IQ is at either extreme are more likely to produce offspring with IQ closer to the mean or average.
Heritability measures the proportion of variation in a trait that can be attributed to genes, and not the proportion of a trait caused by genes. Thus, if the environment relevant to a given trait changes in a way that affects all members of the population equally, the mean value of the trait will change without any change in its heritability because the variation or differences among individuals in the population will stay the same.
This has evidently happened for height: The value of heritability can change if the impact of environment or of genes in the population is substantially altered. The population in developing nations often has more diverse environments than in developed nations.
Today, this can be prevented by following a modified diet, resulting in a lowered heritability. A high heritability of a trait does not mean that environmental effects such as learning are not involved.
Vocabulary size, for example, is very substantially heritable and highly correlated with general intelligence although every word in an individual's vocabulary is learned. In a society in which plenty of words are available in everyone's environment, especially for individuals who are motivated to seek them out, the number of words that individuals actually learn depends to a considerable extent on their genetic predispositions and thus heritability is high.
Furthermore, there may be differences regarding the effects on the g-factor and on non-g factors, with g possibly being harder to affect and environmental interventions disproportionately affecting non-g factors. However, that the opposite occurs is well documented.
Heritability measures in infancy are as low as 0. In contrast, studies of other populations estimate an average heritability of 0. Environment and intelligence There are some family effects on the IQ of children, accounting for up to a quarter of the variance.
However, adoption studies show that by adulthood adoptive siblings aren't more similar in IQ than strangers,  while adult full siblings show an IQ correlation of 0. However, some studies of twins reared apart e. This shared family environment accounts for 0.
By late adolescence it is quite low zero in some studies. There is a similar effect for several other psychological traits. These studies have not looked into the effects of extreme environments such as in abusive families.
Knowns and Unknowns " states that there is no doubt that normal child development requires a certain minimum level of responsible care.
Severely deprived, neglectful, or abusive environments must have negative effects on a great many aspects of development, including intellectual aspects. Beyond that minimum, however, the role of family experience is in serious dispute.
There is no doubt that such variables as resources of the home and parents' use of language are correlated with children's IQ scores, but such correlations may be mediated by genetic as well as or instead of environmental factors.
But how much of that variance in IQ results from differences between families, as contrasted with the varying experiences of different children in the same family? Recent twin and adoption studies suggest that while the effect of the shared family environment is substantial in early childhood, it becomes quite small by late adolescence.
These findings suggest that differences in the life styles of families whatever their importance may be for many aspects of children's lives make little long-term difference for the skills measured by intelligence tests. Non-shared family environment and environment outside the family[ edit ] Although parents treat their children differently, such differential treatment explains only a small amount of non-shared environmental influence.
One suggestion is that children react differently to the same environment due to different genes. More likely influences may be the impact of peers and other experiences outside the family.
This factor may be one of the reasons why IQ score correlations between siblings decreases as they get older. Phenylketonuria is an example,  with publications demonstrating the capacity of phenylketonuria to produce a reduction of 10 IQ points on average.
Knowns and Unknowns" also stated that: Thus it is not yet clear whether these studies apply to the population as a whole.
It remains possible that, across the full range of income and ethnicity, between-family differences have more lasting consequences for psychometric intelligence.
The children's IQs initially averaged 77, putting them near retardation. Most were abused or neglected as infants, then shunted from one foster home or institution to the next.
Nine years later after adoption, when they were on average 14 years old, they retook the IQ tests, and all of them did better. The amount they improved was directly related to the adopting family's socioeconomic status. The average IQ scores of youngsters placed in well-to-do homes climbed more than 20 points, to Intelligence: Genetics, Genes, and Genomics Robert Plomin and Frank M.
Spinath King’s College London More is known about the genetics of intelligence than about any other trait, behavioral or .
Intelligence: Genetics, Genes, and Genomics Robert Plomin and Frank M. Spinath King’s College London More is known about the genetics of intelligence than about any other trait, behavioral or biological, To be able to address these issues, this article needs to assume.
Hundreds of new genes may underlie intelligence—but also autism and depression. By Ann Gibbons Jun. 25, , AM. Being smart is a double-edged sword. Intelligent people appear to live. Factors related to a child’s home environment and parenting, education and availability of learning resources, and nutrition, among others, all contribute to intelligence.
A person’s environment and genes influence each other, and it can be challenging to tease apart the effects of the environment from those of genetics.
Genes, an international, peer-reviewed Open Access journal. Special Issue "Eye Genetics and Therapies" In addition, artificial intelligence (AI) systems have been developed to identify medical diagnoses and treatable diseases using image-based deep learning.
Before taking that leap, we would have to understand the genes that contribute to intelligence. Some scientists are on the hunt for such “smart genes,” and their research has come under fire. The two biggest specters: that the work could support racist notions of biological differences, and that it could make those designer smart babies a reality.