Single-parent Kids Do Best

    Single mums are better at raising their kids than two parents 一 at least in the bird world. Mother zebra finches¹ 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 factors² such as hunting and food supply. With two parents around, there"s always a conflict of interests³，which can have a detrimental effect on the quality of the offspring.

    In evolutionary terms⁴，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 it"s normal for parents to try to pass the buck⁵ to each other. But Ian Hartley from the UniversityofLancasterand his team wondered how families solve this conflict, and how the conflict itself affects the offspring.

    To find oiit⁶，they measured how much effort zebra finch parents put into raising their babies. They compared single 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 two — supposedly 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 it"s 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 thought to affect the quality of care,given to offspring, says zoologist Rebecca Kilner atCambridgeUniversity, 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 Hartley"s 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 female"s 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.

词汇：

evolutionary / ˌi:vəˈlu:ʃənri/adj.进化的

ecological / ˌi:kəˈlɒdʒɪkl/adj.生态的

detrimental / ˌdetrɪˈmentl/adj.有害的 

offspring/ "ɒfsprɪŋ/n. (单复数同形）儿女，子孙，后代.

experimental / ɪkˌsperɪˈmentl/adj.实验的， 根据实验的 

empirically / ɪm"pɪrɪklɪ/adv.以经验为根据地

clutch / klʌtʃ/n. 一次产的或孵的卵   

reproductive/ ˌri:prəˈdʌktɪv/adj. 生殖的

注释：

1.zebra finch:斑胸草雀，一种澳大利亚小鸟，它有黑白色条纹，而且是受欢迎的笼养鸟。

2.family conflict is as important an evolutionary driving force as ecological factors:家庭冲突是与 生态因素同样重要的进化推动力。

3.a conflict of interests：(双亲之间的）利益冲突

4.in evolutionary terms：从进化的角度讲。in. ?. terms, in terms of…：从……方面来讲；就……而言。例如：It has been a terrible year in terms of business.就生意而论，这是很糟糕的一年。

5.pass the buck (to)：推卸责任，把为难的事推给另！|人0 例如：Bus companies are just passing the buck by saying their drivers are responsible for delays.公交公司说司机应该对误点的事负责，这只是在推卸责任。

6.to find out：这是一个承上的短语,从逻辑上讲，它的宾语应该是:how families solve this conflict, and how the conflict itself affects the offspring。

According to Hartley, which of the following is NOT influenced by sexual conflict?

A:The evolution of the offspring"s behaviour B:The look of the offspring"s faces C:The number of eggs produced by one offspring at a time D:The offspring"s body size

Single-parent Kids Do Best