北极熊是唯一完全肉食性的熊。

Polar bears are the only completely carnivorous bears.

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一影响力的书拥护这一观点，那就是迈克尔·波伦的《杂食性的困境》，书中开头问：“我们晚餐吃什么？”

An influential book espousing this view, Michael Pollan's "The Omnivore's Dilemma", starts by asking: "What should we have for dinner?"

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为了将温度的重要性孤立来看，他们只研究雌鸟的喙长，并将生活在不同气候但拥有相似食性的鸟类进行对比。

They isolated the importance of temperature by studying only female beak length and comparing species with similar diets living in different climates.

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Then going from a plant based diet to a diet that included meat.

人类的饮食由植食性发展为含肉类的饮食

耶鲁公开课 - 关于食物的心理学、生物学和政治学课程节选