它们是一代又一代选择性繁殖和杂交的产物。
They are the product of generations of selective breeding and hybridisation.
科学家们研究过一些品种后表示牛的基因组显示出这种有选择性繁殖的迹象。
Scientists examined several breeds and say the cattle genome appears to show evidence of this selective reproduction.
其原因之一可能因为牛是通过选择性繁殖的方式来提高牛奶的蛋白质含量（乳品生产者所期望的品质）的。
One reason this may be so frequently found is because cows have been selectively bred this way to increase the protein content of the cow-milk (a quality desired by dairy producers). 9
过去的实验告诉我们通过选择性的繁殖促使生成后代具有更好的学习能力是比较容易的，比如大鼠，蜜蜂，以及研究者钟爱的果蝇。
Past experiments have demonstrated that it is relatively easy through selective breeding to make rats, honey bees and—that great favourite of researchers—fruit flies a lot better at learning.
某些鸟类从每组完成蜕皮您就可以开始您的选择性配对繁殖。
As certain birds from each group complete molting you can start your selective pairing for breeding.
“在M-K地区的动物有更多选择性，”派克说，“它允许动物使用一种以上的策略来谋生，这或许对长期的生存和繁殖是重要的。”
"Animals in the M-K still have a lot of options, " Parker says. "It allows animals to use more than one strategy to make a living, which may be important for long-term survival and reproduction.
“在M-K地区的动物有更多选择性，”派克说，“它允许动物使用一种以上的策略来谋生，这或许对长期的生存和繁殖是重要的。”
"Animals in the M-K still have a lot of options, " Parker says. "It allows animals to use more than one strategy to make a living, which may be important for long-term survival and reproduction.
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