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Single-parent kids do best
Single mums are better at raising their kids than two parents – at 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 findings shows that family conflict is as important an evolutionary driving force as ecological factors such as hunting and food supply. With two parents around, there’s 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 it’s 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 family 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 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 mum had two – supposedly the same amount of work.
But single mums, they found, put in about 25 percent more effort than females rearing with their mate. To avoid being exploited, mothers with a partner hold back from working too hard if their father is being lazy, and it’s the chicks that pay the price. “The offspring suffer some of the cost their conflict,” says Hartley.
The cost does not show in any obvious decease 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 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 Hartley’s statement that conflict may be a strong influence on the evolution of behavior, 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.
1. With which of the following statements would the author probably agree?
A. single mums produce stronger sons
B. single mums do not produce daughters
C. two-parent families produce less attractive children
D. two-parent families produce more beautiful offspring

2. According to the passage, in what way does family conflict affect the quality of the offspring?
A. the young males get less care
B. the young females will decrease in weight
C. the offspring will become lazy fathers or mothers in the future
D. the offspring will not get mature easily

3. What is the relationship between paragraph 4 and paragraph 5?
A. cause and effect
B. experiment and result
C. problem and solution
D. topic and comment

4. According to Hartley, which of the following NOT influenced by sexual conflict?
A. the evolution of the offspring’s behavior
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

5. According to the passage, people believe that a female’s reproductive strategy is influenced by
A. an evolutionary driving force
B. a conflict of interests
C. ecological factors
D. the quality of the offspring

答案及解析：
1． 文章标题分析：
Single-parent（单亲） kids do best