The first jump in brain size happened 39 million years ago, when odontocetes (members of an order that includes dolphins, toothed whales, sperm whales, beaked whales and porpoises) diverged from their ancestral Archaeoceti group. When this split occurred, body sizes for some decreased and brain sizes increased, especially in the ancestors of modern dolphins. This coincided with the emergence of echolocation, so improved communication skills likely were tied to the brain size boost.
(海豚的)大脑体积的第一次跳跃式增长发生在3千9百万年前。那时，齿鲸亚目(该目包括海豚、齿鲸、抹香鲸、喙鲸等成员)从古鲸亚目中分离出来，而其中的一些成员，特别是现代海豚的祖先，体型减小，大脑体积增大。与此同时，海豚的大脑有了回声定位的能力.因此,沟通能力的提升也很有可能与大脑体积的增大相关。

Fifteen million years ago yet another brain growth spurt happened. Marino and her colleagues speculate that changes in social ecology-essentially the dolphin's social lifestyle-probably contributed to the process. For example, the more a dolphin needed to communicate, benefiting its survival, the more its brain evolved to permit that interaction.
而1千5百万年前,(海豚的)大脑又经历了一次突然的进化.马里诺和她的同事推测，社交环境的改变-特别是海豚生活方式的改变,很可能是造成这次进化的原因。比如，海豚越是需要沟通以利生存，它们的大脑就越会朝着这个方向进化。

Moving to the present, dolphins have brains that are about "five times larger for their body size when compared to another animal of similar size," Marino said. "In humans, the measure is seven times larger-not a huge difference."
回过头来说，现如今，与体型相近的动物相比，海豚的大脑要上大5倍.马里诺说，“人类大脑是同体型动物的7倍--(和海豚的相比)差别并不是很大。”

She concluded, "Essentially, the brains of primates and cetaceans arrived at the same cognitive space while evolving along quite different paths."
她总结说，“灵长类动物和鲸类的大脑的认知能力基本上处在同一是水平，只是进化方式截然不同。”

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