单选题
The term "g" (general intelligence) represents a
measure of overall cognitive ability across a variety of tests. It's not the
same as IQ but it does tend to correlate. Everyone agrees that "g" tends to run
in families. But is this down to genetics or to environmental
influences? However, no single gene has yet been conclusively
linked to intelligence. Rather it appears to be a case of complex interactions
on many levels between many different genes. Identical twins
have exactly the same genes, while non-identical twins share about half their
genes. Another feature of twins that makes them an ideal choice for studies is
that they tend to be raised in pretty much the same environment. If a particular
feature is the same in identical twins, but not in non-identical twins, then
chances are it's mainly genes that are controlling that feature.
So what do the twin studies show? Well, first degree relatives tend to
have "g" correlation of about 0.4～0.5. (Perfect correlation is 1; correlation of
0 means that the two things in question are totally unrelated). Identical twins
have a correlation of 0.85, while for non identical twins it's about 0.6. Which
suggests that genes play a very important role, but are not the only factor,
since if they were, the correlation between identical twins would be
1. Identical twins reared apart are almost as similar in "g"
scores as those reared together. Adopted children and their adoptive parents
have a "g" correlation of zero, while adopted children and their biological
parents tend to have the same correlations as any parent-child pair. So although
genes don't seem to be the only thing affecting intelligence, their effects seem
to be constant and apparently not overridden by environment.
Does heritability of intelligence alter over a lifetime? Remarkably, it appears
so. "g" heritability climbs gradually from 20% in babies to 40% in children,
peaking at 60% in adults. Why this should be is still a matter of speculation.
It's been suggested that as our cognitive abilities become more complex, new
genes may come into play that were not needed when brain functions were less
sophisticated. Or individuals may be drawn towards environments that fit with
their genetic makeup, as time goes by and genetic effects that started out small
in childhood build up together during adulthood.
单选题
All of the following statements about "g" are true EXCEPT ______.
A. "g" is to some extent inherited
B. "g" correlates with IQ
C. "g" can be attributed to a single gene
D. "g" is a measure of cognitive ability
【正确答案】
C
【答案解析】[解析] 文章第一段中有it tends to correlate，还有general intelligence tends to run in families和represents a measure of overall cognitive ability，从而说明选项A，B，D符合题意。第二段第一句的含义是：还没有确凿的证据表明某一种基因与智力相关，因此否定了选项C的合理性。
单选题
Identical twins are chosen as the subjects of the study because ______.
A. they have the same genes and live in the same environment
B. they have some genes linked to general intelligence
C. they have the same heritability of intelligence
D. they are alike in everything except for intelligence