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)大腦體積的第一次跳躍式增長發(fā)生在3千9百萬年前。那時，齒鯨亞目(該目包括海豚、齒鯨、抹香鯨、喙鯨等成員)從古鯨亞目中分離出來，而其中的一些成員，特別是現(xiàn)代海豚的祖先，體型減小，大腦體積增大。與此同時，海豚的大腦有了回聲定位的能力.因此,溝通能力的提升也很有可能與大腦體積的增大相關。

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1千5百萬年前,(海豚的)大腦又經歷了一次突然的進化.馬里諾和她的同事推測，社交環(huán)境的改變-特別是海豚生活方式的改變,很可能是造成這次進化的原因。比如，海豚越是需要溝通以利生存，它們的大腦就越會朝著這個方向進化。

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."
回過頭來說，現(xiàn)如今，與體型相近的動物相比，海豚的大腦要上大5倍.馬里諾說，“人類大腦是同體型動物的7倍--(和海豚的相比)差別并不是很大。”

She concluded, "Essentially, the brains of primates and cetaceans arrived at the same cognitive space while evolving along quite different paths."
她總結說，“靈長類動物和鯨類的大腦的認知能力基本上處在同一是水平，只是進化方式截然不同?！?/p>

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