职称英语2015综合类考试阅读理解精选文章(2)

　　单亲幼儿最出色

　　单亲母亲在抚养孩子方面比双亲要好至少在鸟的世界是这样的。母斑胸草雀必须在努力工作并且亲自抚养较少的鸟，但是她们抚养的雄性后代更有吸引力，更容易得到配偶。

　　这个发现显示家庭冲突是与捕食和食物提供方式这样的生态因素同样重要的进化推动力。身边有双亲就总有利益冲突，这会对后代的质量产生的害的影响。

　　从进化的角度讲，在动物界，任何一个父亲或母亲的最佳策略是让他人来照顾后代，这样，他们就可以集中精力再次繁殖后代了。所以父母之间很自然就出现了相互推卸的责任的现象。但是兰卡斯特大学的IanHartley及他的工作组想知道家庭是如何解决这个冲突的，以及冲突本身是如何影响后代的。

　　为了找到答案他们衡量斑胸草雀抚养它们的子女花了多少力气。他们监控每个母亲或父亲采集的食物量，以及移动或增加小鸟，因此每对草雀养4只小鸟，每只单身母雀养两只假定这是相同的工作量。通过这些方法他们对单身母雀和成对草雀做了比较。

　　但是他们发现单身母雀比与配偶共同抚养后代的母雀多付出25%。如果公雀太懒的话，为了避免筋疲力尽，有配偶的母雀并不十分努力工作。这样做的后果就是后代付出代价。Hartley说：后代要为这种冲突付出某些代价。

　　这种代价不是表现在身材和体重的锐减，而是表现在他们对异性有多大吸引力上。当小鸟长大后，研究者通过提供给雌性她们所选择的伴侣的方法检验雄性后代的健康情况。那些由单身母亲扶养大的雄性比由父母抚养大的雄性更多地被选中。

　　研究鸟类父母冲突的剑桥大学动词学家rebeccaKilner说，很久以来人们就认为两性之间的冲突会影响对后代的照顾。但是试验证据并不充分，这个突破主要是以经验来显示这种影响的。

　　Kilner说更为令人惊讶的是Hartley说这种冲突可能会严重影响行为的进化、窝卵数目甚至外表。Hartley说：人们并没真正确定这种联系。人们通常认为雌性的繁殖策略受捕食和食物提供方式的影响。Kilner说父母之间的冲突现在也应该被考虑在内了。

　　Single-parent Kids Do Best

　　Single mums are better at raising their kids than two parentsat least in the bird world. Mother zebra finches have to work harder and raise fewer chicks on their own, but they also produce more attractive sons who are more likely to get a mate.

　　The finding shows that family conflict is as important an evolutionary driving force as ecological factors such as hunting and food supply. With two parents around, theres always a conflict of interests, which can have a detrimental effect on the quality of the offspring.

　　In evolutionary terms, the best strategy for any parent in the animal world is to find someone else to care for their offspring, so they can concentrate on breeding again. so its normal for parents to try to pass the buck to each other. But Ian Hartley from the University of Lancaster and his team wondered how families solve this conflict, and how the conflict itself affects the offspring.

　　To find out, they measured how much effort zebra finch parents put into raising their babies. They compared ingle females with pairs, by monitoring the amount of food each parent collected, and removing or adding chicks so that each pair of birds was raising four chicks, and each single mum had twosupposedly the same amount of work.

　　But single mums, they found, put in about 25 per cent more effort than females rearing with their mate. To avoid being exploited, mothers with a partner hold back from working too hard if the father is being lazy, and its the chicks that pay the price. The offspring suffer some of the cost of this conflict, says Hartley.

　　The cost does not show in any obvious decrease in size or weight, but in how attractive they are to the opposite sex. When the chicks were mature, the researchers tested the fitness of the male offspring by offering females their choice of partner. Those males reared by single mums were chosen more often than those from two-parent families.

　　Sexual conflict has long been tough to affect the quality of care given to offspring, says zoologist Rebecca Kilner at Cambridge University, who works on conflict of parents in birds. But the experimental evidence is not great. The breakthrough here is showing it empirically.

　　More surprising, says Kilner, is Hartleys statement that conflict may be a strong influence on the evolution of behaviour, clutch size and even appearance. People have not really made that link, says Hartley. A females reproductive strategy is usually thought to be affected by hunting and food supply. Kilner says conflict of parents should now be taken into account as well.