马克博士也观察了其它有蹄动物，比如鹿。
Dr Bracke also looked at other hoofed animals, such as deer.
但更重要的是，马克博士提出猪此种行为演变形成于猪最古老祖先。
But more fundamentally, Dr Bracke suggests the behaviour could have evolved in pigs' most ancient relatives.
“猪的遗传基因与一些特别爱水的动物有关，如河马和鲸。”马克博士说道。
"Pigs are genetically related to particularly water-loving animals such as hippos and whales," Dr Bracke said.
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