Unit 8 Nature and Nurture
Twins, Genes, and Environment
十佳歌手策划案
Heredity or environment: which is stronger? The potentials which a person is born with determine in some way what he will do in life. Therefore heredity is fate, a kind of predestination. However, genes do not work in a vacuum; as soon as we begin considering the role that they play in the development of the individual, we e that there can be no development without the interacting environment. No characteristic is caud exclusively by either environment or genes.
The relative effects of heredity and environment are most clearly obrvable in identical twins. Most identical twins are raid together and are remarkably alike in both appearance and behavior. The cas demonstrate that individuals with the same genes, when raid in the same environment, will respond to it in much the same way. They do not indicate what would happen if the identical individuals were raid parately.
A number of studies have been made of identical twins raid apart. The twins who were the subjects of the studies lived in America, were raid in much the same physical environments, and experienced much the same nutritional histories. Therefore, as one might expect, they maintained the clost remblance to each other in physical appearance, height, and weight. Exceptions occurred when one twin had developed a rather vere illness and the other had not; but on the whole everyone is impresd by the great psychological and physical likeness that exist between identical twins, even tho who have been parated from infancy.
人文性In a study of nineteen ts of twins who had been parated from birth, investigators found that in approximately two thirds of the ts there were no more significant differences than existed among unparated pairs of twins. This strongly suggests the power of the genes and the limitation of the effect of environment. However, it must be remembered that, although the identical twins who were studied lived in different families far removed from each other, the environments in tho families were not, on the whole, substantially different. Usually every effort would be made to put each child in a home wit
h a background similar to that of its own family, and therefore it should not be surprising to find that the twins developed similarly. But in tho cas in which there had been a greater difference in the environments of the parated twins, the differences between the twins were more substantial. The following ca illustrates what happens to identical twins when they are brought up in contrasting environments.
简单的窗花怎么剪Gladys and Helen were born in a small Ohio town and were parated at about eighteen months of age. They did not meet again until they were twenty-eight years old. Helen had been adopted twice. Her first foster parents had proved to be unstable, and Helen had been returned to the orphanage after a couple of years; after veral months she was again adopted, by a farmer and his wife who lived in southeastern Michigan. This was her home for the next twenty-five years. Her cond foster-mother, though she had had few educational advantages herlf, was determined that Helen should receive a good education; Helen eventually graduated from college, taught school for twelve years, married at twenty-six, and had a daughter.
Gladys was adopted by a Canadian railroad conductor and his wife. When she was in the third grade, the family moved to a rather isolated part of the Canadian Rockies, where there were no schools, and Gladys' formal education came to an end, and was not resumed until the family moved to Ontario. She stayed at home and did houwork until she was venteen, and then went to work in a knitting mill. She went to Detroit at nineteen, got a job, and married when she was twenty-one.
Helen had been healthier than Gladys, in childhood and adulthood, but other than that, their environments had been very similar except for their educations. Their weight, height, hair color, and teeth were very similar. The differences that distinguished them were obviously associated with the different social lives they had led.
Helen was confident, graceful, made the most of her personal appearance, and showed considerable polish and ea in social relationships. Gladys was shy, lf-conscious, quiet and without charming or graceful manners. A scientist who studied them remarked, "As an advertiment for a college education the contrast between the two twins should be quite effective." 乐山大佛在哪
Considering the nature of their environmental experiences, the differences in Helen and Gladys are not surprising. Since psychological traits depend so much upon experience, it is to be expected that they will reflect it. On the other hand, traits that are not liable to be influenced by the environment are more likely to exhibit a high degree of similarity in identical twins. Important as they are, genes alone are never absolutely responsible for any trait. What we can do is t by the genes, but what we actually do is largely determined by the environment.
基因、环境与双胞胎
张能宝遗传与环境究竟哪一个影响更大呢？从某种程度上讲，一个人生来具有的潜力将决定他一生的作为。因此遗传即命运，是命中注定的东西。然而，基因并不是在真空中发挥作用的；一旦我们开始认识到基因在个人发展中所起的作用，我们就会明白，没有与其相互作用的环境，就不可能有任何个人的发展。没有一个特点是完全由环境或者完全由基因造成的。
向蜜鸟遗传和环境的相互影响在同卵双胞胎中最易观察到。大多数的同卵双胞胎是在一起抚养长
大的，因而无论在外表还是行为上都惊人的相像。这些实例说明，若在同样的环境中抚养长大，具有相同基因的个体就会以几乎同样的方式对环境做出反应。但这些例子并不能说明如果把这些同卵双胞胎分开抚养会发生什么情况。
对分开抚养的同卵双胞胎已进行了许多研究。被研究的这些双胞胎都生活在美国，成长的自然环境几乎相同，并且具有几乎相同的营养史。因而，正如所料，他们在外表、身高和体重上极其相似。但也有例外：一对双胞胎中的一个患了相当严重的疾病而另一个却没生病；但是总体而言，同卵双胞胎，甚至从婴儿时就分离的同卵双胞胎，在心理和身体上会如此相似，给每个人留下了深刻的印象。
在对从一出生就分离的19对双胞胎的研究中，研究者发现，其中约三分之二的双胞胎之间的差异与一起长大的双胞胎之间的差异一样不明显。这有力地说明了基因的影响力和环境作用的局限性。然而，必须记住的是，尽管被研究的同卵双胞胎生活在不同家庭里且相距甚远，但总体而言，那些家庭的环境基本上没有什么差异。人们通常都会千方百计地将每个孩子安置在和他自己原来的家庭背景相同的家庭里，因而发现这些双胞胎成长中有不少相似之处就不足为奇了。但是在那些分开抚养的双胞胎的生长环境有较大差异的实例中，
双胞胎之间的差异就很大了。下面的例子说明了在对比度很大的环境中成长的同卵双胞胎的情况。
格拉迪斯和海伦出生于俄亥俄州的一个小镇，在大约18个月大时被分开抚养。她们直到长白山天池在哪18慢羊羊简笔画岁才再次相遇。海伦被领养了两次。由于她最初的养父母靠不住，两年后海伦又被送回到孤儿院。过了几个月，她再一次被住在密歇根东南部的一对农场主夫妇领养。此后25年她一直住在那里。她的第二个仰慕尽管本身没受过什么教育，却下决心要让海伦得到良好的教育；海伦最终大学毕业，教了12年的书，26岁时结婚，并有了一个女儿。
