换句话说 贫困是可以遗传的Intergeneration inheritance of poverty 通过慢性压力改变神经传导通路 压力让人变蠢 亦 让人早死早超生。然而遗憾的是 这项correlation study只在浅层面confirm了大多数layman的常识 ，并未深层探讨serotonin等其他neurotransmitter水平与慢性压力维持的关系 譬如并未探究serotonin 在消除stressor作用的效能。
THAT the children of the poor underachieve in later life, and thus remain poor themselves, is one of the enduring problems of society. Sociologists have studied and described it. Socialists have tried to abolish it by dictatorship and central planning. Liberals have preferred democracy and opportunity. But nobody has truly understood what causes it. Until, perhaps, now.
The crucial breakthrough was made three years ago, when Martha Farah of the University of Pennsylvania showed that the working memories of children who have been raised in poverty have smaller capacities than those of middle-class children. Working memory is the ability to hold bits of information in the brain for current use—the digits of a phone number, for example. It is crucial for comprehending languages, for reading and for solving problems. Entry into the working memory is also a prerequisite for something to be learnt permanently as part of declarative memory—the stuff a person knows explicitly, like the dates of famous battles, rather than what he knows implicitly, like how to ride a bicycle.
Since Dr Farah’s discovery, Gary Evans and Michelle Schamberg of Cornell University have studied the phenomenon in more detail. As they report in this week’s Proceedings of the National Academy of Sciences, they have found that the reduced capacity of the memories of the poor is almost certainly the result of stress affecting the way that childish brains develop.
Dr Evans’s and Dr Schamberg’s volunteers were 195 participants in a long-term sociological and medical study that Dr Evans is carrying out in New York state. At the time, the participants were 17 years old. All are white, and the numbers of men and women are about equal.
Stress in the city
The capacity of a 17-year-old’s working memory was also correlated with allostatic load. Those who had spent their whole lives in poverty could hold an average of 8.5 items in their memory at any time. Those brought up in a middle-class family could manage 9.4, and those whose economic and social experiences had been mixed were in the middle.
These two correlations do not by themselves prove that chronic stress damages the memory, but Dr Evans and Dr Schamberg then applied a statistical technique called hierarchical regression to the results. They were able to use this to remove the effect of allostatic load on the relationship between poverty and memory discovered originally by Dr Farah. When they did so, that relationship disappeared. In other words, the diminution of memory in the poorer members of their study was entirely explained by stress, rather than by any more general aspect of poverty.
以上两项关联性本身并不能证明周期性压力对记忆力有损害， 但Evans和Schamberg博士又用了一项叫做等级复原的统计方法来研究结果，可用它消除Farah博士原先发现的非稳态荷载对贫穷与记忆力之间关系的影响， 结果发现这一关系确实没有了，换句话也就是说，他们的研究对象中穷人记忆力差完全是因为压力，与其它抽象层面无关。
To confirm this result, the researchers also looked at characteristics such as each participant’s birthweight, his mother’s age when she gave birth, the mother’s level of education and her marital status, all of which differ, on average, between the poor and the middle classes. None of these characteristics had any effect. Nor did a mother’s own stress levels.
That stress, and stress alone, is responsible for damaging the working memories of poor children thus looks like a strong hypothesis. It is also backed up by work done on both people and laboratory animals, which shows that stress changes the activity of neurotransmitters, the chemicals that carry signals from one nerve cell to another in the brain. Stress also suppresses the generation of new nerve cells in the brain, and causes the “remodelling” of existing ones. Most significantly of all, it shrinks the volume of the prefrontal cortex and the hippocampus. These are the parts of the brain most closely associated with working memory.
Children with stressed lives, then, find it harder to learn. Put pejoratively, they are stupider. It is not surprising that they do less well at school, end up poor as adults and often visit the same circumstances on their own children.
Dr Evans’s and Dr Schamberg’s study does not examine the nature of the stress that the children of the poor are exposed to, but it is now well established that poor adults live stressful lives, and not just for the obvious reason that poverty brings uncertainty about the future. The main reason poor people are stressed is that they are at the bottom of the social heap as well as the financial one.
Sir Michael Marmot, of University College London, and his intellectual successors have shown repeatedly that people at the bottom of social hierarchies experience much more stress in their daily lives than those at the top—and suffer the consequences in their health. Even quite young children are socially sensitive beings and aware of such things.
So, it may not be necessary to look any further than their place in the pecking order to explain what Dr Evans and Dr Schamberg have discovered in their research into the children of the poor. The Bible says, “the poor you will always have with you.” Dr Evans and Dr Schamberg may have provided an important part of the explanation why.