Vocabulary
Directions: Scan the following passage and find the words which have roughly the same meanings as those given below. The number in the brackets after each word definition refers to the number of paragraph in which the target word is. 

1. We inherit genes, not traits. When we say that a boy got his brown eyes from his father, we really mean that he got the genes for brown eyes from his father. Every gene must develop in an environment, and the environment influences how that gene will develop. In the case of fruit flies, the vestigial(退化的)-wing characteristic will develop if the flies are raised at room temperature. If the flies are reared at about 92°F（33°C）, however, the wings will be almost normal.
2. In the final analysis, the question, “Which is more important, heredity or environment?” has no meaning. There can be no “heredity versus environment” situation: both factors, heredity and environment, must interact for an organism to develop.
3. Still, we can get some idea of the relative contributions of heredity and environment to certain traits. To do this, we must determine the genetic mechanism for a particular trait. We must also determine how much effect the environment can have on the trait. Neither of these determinations is easy, but for a few traits they have both been made.
4. In the case of Down’s syndrome, for example, we know that the presence of an extra number 21 chromosome sets limits on the development of the intelligence and largely determines certain other abnormal characteristics of the victim. Unfortunately, no amount of environmental manipulation can cause the victim’s intelligence to exceed a certain “subnormal” level. Thus we can say that in the development of the phenotype of a person with Down’s syndrome, heredity makes a relatively great contribution— by imposing severe limits.
5. But in most situations one can study, the role of the environment is very much in evidence. Identical human twins who have been reared apart show quite noticeable phenotypic differences, in personality and even in some physical characteristics.
6. The problem of assessing the relative contributions of heredity and environment to human intelligence is notoriously difficult and controversial. On the one hand, many studies have shown high correlations between the intelligence of individuals and their degree of “relatedness”. On the other hand, the many variables encountered in studies of this type make interpretation very difficult. But some studies have found correlations suggesting environmental factors influence intelligence more than genetic factors do. So the question of intelligence and inheritance is still very much up in the air. The problems and the controversy should not, however, obscure one basic fact: intelligence, like any other trait, depends on the interaction of both genetic and environmental factors.