职称英语2015综合类考试阅读理解精选文章(2)_职称英语阅读理解

职称英语2015综合类考试阅读理解精选文章(2)

　　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.