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Dog Brains Have Unexpectedly Grown Larger, Scientists Discover
Dog brains are much smaller than wolf brains, but new research suggests modern breeding efforts have somewhat increased their relative size.
Compared to ancient dogs, modern breeds that developed in the past 150 years possess larger skulls compared to their body size. Yet scientists still don't know why.
Numerous studies have shown that domesticating wild animals – like dogs, fish, pigs, cattle, sheep, rabbits, and cats – dramatically shrinks their relative brain size.
Scientists think this is a response to a reduced need for brain power when it comes to survival.
But researchers discovered something unexpected when comparing the skulls of 159 dog breeds, including some wolves.
While the size of a wolf's brain is 24 percent larger than that of a similarly sized dog, the more that a dog breed differed from a wolf, genetically speaking, the larger their brain.
The findings suggest that while dog domestication thousands of years ago might have initially shrunk parts of the dog brain – like those related to mate choice, predators, or hunting – modern breeding has triggered some modest cognitive growth in the past century and a half.
But how?
"Different dog breeds live in varying levels of social complexity and perform complex tasks, which likely require a larger brain capacity," says evolutionary biologist Niclas Kolm from Stockholm University in Sweden.
So Kolm and his colleagues hypothesized that some dogs, bred by humans for more complex tasks like herding or sports, would have larger relative brains.
That was not the case. Instead, the only factor that seemed to impact the relative brain size of modern dog breeds was how different their genes were compared to wolves – not the function of the breed, its litter size, or its life expectancy.
In fact, researchers could not find any difference in relative brain size in the breeds laid out by the American Kennel Club.
Past studies found that individual dogs' absolute brain size plays a role in their memory and self-control, but this doesn't seem to be a strong enough force to influence their overall breed's relative brain size.
The findings are supported by other recent research, which also suggests the behavior certain dogs are bred for is not evident in their genetic makeup.
"Perhaps the more complex social environment, urbanization, and adaptation to more rules and expectations have caused this change, affecting all modern breeds," speculates ethologist Enikő Kubinyi from Eötvös Loránd University in Hungary.
This falls in line with the social brain hypothesis – the idea that large brains can evolve to suit more complex social environments.
Previous research, for example, has found that dogs more closely related to wolves are worse at communicating with humans.
To learn more about how ancient and modern dog brains differ from wolves, the team suggests future research should compare the size of different brain regions.
Perhaps then scientists can figure out what impact we've had on dog brains and behavior.
注释：
urbanization: n
表示" 都市化；城市化"，means "the condition of being urbanized"，如：Urbanization in Spain is distinctly correlated with a fall in reproductive rate. 西班牙都市化进程的加快很明显和该国的出生率下降有关。
ethologist: n
表示"生态学研究者, 行为研究者"，means "a zoologist who studies the behavior of animals in their natural habitats"，如：The groundbreaking study in this area was conducted by the human ethologist Irenaus Eibi-Eibsfeldt. 在这个领域，人类行为学家IrenausEibi－Eibsfeldt进行了开拓性的研究。
中文简要说明：
科学家发现，与古代狗相比，在过去 150 年间发展的现代犬种，脑容量明显增大。科学家们仍然不知道为什么，推测可能与现代社会更复杂有关。
科学警报(Science Alert)报导，狗是从狼驯化而来，狗的体型明显小于狼，因此狗的大脑也就比狼的大脑来的小；但是新的研究表明，比起古代的狗，现在的狗在一定程度上出现明显的脑容量增加。
这有点不寻常，因为大量研究表明，人类把野生动物驯化成家畜或是宠物后，比如狗、鱼、猪、牛、羊、兔子和猫，相对脑容量都会出现显著缩小；科学家认为，这是因为习惯人类环境后，生存所需要的脑力就会减少，这是「不必活得那么辛苦」的代价。
但是研究人员却发现，狗似乎有点不同。在比较包括一些狼在内的 159种犬只的头骨时，发现狗的脑容量是「大、缩小、再增大」的过程。
虽然狼的大脑比同样体格的狗大了24%，但从基因上讲，狗的品种与狼的差异越大，它们的大脑就越大。
研究结果表明，几千年前狗驯化的过程中，出现脑部缩小的情况，可能某些部分功能比较不需要，比如与择偶、捕食者或狩猎有关的部分。但现代育种的新品种犬种，在过去一个半世纪以来，又出现脑容量再次增大的现象。
瑞典斯德哥尔摩大学的演化生物学家柯尔姆( Niclas Kolm)说：「现代不同品种的狗，生活在不同层次的社会，会被要求执行复杂的任务，或许需要更大的脑容量。」
柯林姆和他的同事原本假设，特殊任务的狗，比如牧羊犬、猎犬，会比其他犬种有更大脑的容量。但事实并非如此，所有的现代犬的脑容量都有增加，不只限于特殊品种。 究人员还发现，基因与狼差异愈大的狗，脑容量反而愈大。
匈牙利罗兰大学(Eötvös Loránd)的动物行为学家阿尼柯( Enikő Kubinyi)推测：「也许现代这种更复杂的社会环境、城市化，以及人类对狗狗提出更多的规则和期望，导致了这种变化，影响了所有的现代犬种。」
这符合社会大脑假说，现代人与狗狗的互动其实相当复杂，狗狗已被证实能听的懂主人所说的命令与字汇，而不是勉强猜测。所以狗狗可以被训练成搜救与缉物。大脑必须进化到适应更复杂的社会环境。
为了更多地了解古代和现代狗，其大脑与狼有何不同，研究团队未来的研究，将会比较不同地区犬种的脑容量大小，也许科学家们就可以弄清楚，我们对狗的互动，对牠们的大脑和行为产生了什么影响。
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