Single mums are better at raising their kids than two parentsat 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 University of Lancaster and 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 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 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.
注釋：
1.zebra finch:斑胸草雀，一種澳大利亞小鳥，它有黑白色條紋，而且是受歡迎的籠養(yǎng)鳥。
2.family conflict is as important an evolutionary driving force as ecological factors:家庭沖突是與 生態(tài)因素同樣重要的進(jìn)化推動力。
3.a conflict of interests：(雙親之間的)利益沖突。
4.in evolutionary terms：從進(jìn)化的角度講。in.?.terms,in terms of…：從方面來講;就而言。例如：It has been a terrible year in terms of business.就生意而論，這是很糟糕的一年。
5.pass the buck (to)：推卸責(zé)任，把為難的事推給另!|人0 例如：Bus companies are just passing the buck by saying their drivers are responsible for delays.公交公司說司機應(yīng)該對誤點的事負(fù)責(zé)，這只是在推卸責(zé)任。
6.to find out：這是一個承上的短語,從邏輯上講，它的賓語應(yīng)該是:how families solve this conflict,and how the conflict itself affects the offspring。
譯文：
單親幼兒最出色
單身母親在撫養(yǎng)孩子方面比雙親要好——至少在鳥的世界是這樣的。母斑胸草雀必須要非常 努力地親自撫養(yǎng)較少的小鳥，但是她們撫養(yǎng)的雄性后代更有吸引力,更容易得到配偶。
這個發(fā)現(xiàn)顯示家庭沖突是與捕食和食物提供這樣的生態(tài)因素同樣重要的進(jìn)化推動力。身邊有 雙親就總會有利益沖突，這會對后代的質(zhì)量產(chǎn)生有害的影響。
從進(jìn)化的角度講，在動物界，任何一個父親或母親的策略是讓他人來照顧后代，這樣，他們 .就可以集中精力再次繁殖后代了。所以父母之間很自然就出現(xiàn)了相互推卸責(zé)任的現(xiàn)象。但是蘭卡 斯特大學(xué)的Ian Hartley及他的工作組想知道家庭是如何解決這個沖突的，以及沖突本身是如何影響 后代的。
為了找到答案，他們衡量斑胸草雀撫養(yǎng)它們的子女花了多少力氣。他們監(jiān)控每個母親或父親采 集的食物量,移動或增加小鳥，因此每對草雀養(yǎng)4只小鳥，每只單身母雀養(yǎng)兩只——假定這是相同的工作量。通過這些方法他們對單身母雀和成對草雀作了比較。
但是他們發(fā)現(xiàn)單身母雀比與配偶共同撫養(yǎng)后代的母雀多付出25%。如果公雀太懶的話，為了避免筋疲力盡，有配偶的母雀并不十分努力工作。這樣做的后果就是后代付出代價。Hartley說: “后代要為這種沖突付出一些代價�！�
這種代價不是表現(xiàn)在身材和體重的明顯減少，而是表現(xiàn)在它們對異性的吸引力上。當(dāng)小鳥長大 后，研究者通過提供給雌性它們所能選擇的伴侶的方法檢驗雄性后代的健康狀況。那些由單身母親撫養(yǎng)大的雄性比由父母撫養(yǎng)大的雄性更多地被選中。
研究鳥類父母沖突的劍橋大學(xué)動物學(xué)家Rebecca Kilner說，很久以來人們就認(rèn)為兩性之間的沖
突會影響對后代的照顧�！暗窃囼炞C據(jù)并不充分。這個突破主要是以經(jīng)驗來顯示這種影響的�！�
Kilner說，更令人驚訝的是Hartley說這種沖突可能會嚴(yán)重影響行為的進(jìn)化、窩卵數(shù)目，甚至外 表。Hartley說:“人們并沒真正確定這種聯(lián)系。”人們通常認(rèn)為雌性的繁殖策略受捕食和食物提供的 影響。Kilner說父母之間的沖突現(xiàn)在也應(yīng)該被考慮在內(nèi)了。
