托福official61听力lecture1 The connection between neocortex size and social relationships in mammals原文解析+翻译音频

[00:00.00]Listen to part of a lecture in a sociology class.
[00:04.58]Sociology is really a cross disciplinary field. [00:09.07]We find that elements of biology, psychology, and other sciences often overlap as we study particular phenomena. [00:16.36]So let me introduce a concept from cognitive psychology. [00:20.72]Okay, let's say someone asks you to look at a list and memorize as many items on it as you can. [00:27.36]Most of us are able to remember, on average, seven items. [00:32.15]There are several variations of this memory test. [00:35.90]And the results consistently show that the human limit for short term memory is seven bits of Information. [00:42.83]This limit is called channel capacity. [00:46.43]Channel capacity is the amount of information that can be transmitted or received over a specific connection, like our brain and the channel capacity for our short-term memory. [00:58.49]It has some interesting real-life implications, like phone numbers. [01:02.80]Local numbers here in the United States all have seven digits, because the phone companies realized early on that longer numbers would lead to a lot more wrong numbers being dialed.
[01:14.94]But the idea of channel capacity doesn't apply just to our cognitive abilities. [01:20.37]It also affects our relationships with people around us. [01:24.79]Psychologists talk about sympathy groups. These are the people, close friends, family to whom we devote the most time. [01:33.37]We call or see them frequently, we think about them, worry about them. [01:37.46]And studies show for each of us, the size of that group is about 10 to 15 people. But why so small? [01:45.84]sure. Relationships take time and emotional energy. And most of us don't have unlimited amounts of either. [01:52.59]But what if there's another reason? what if it's our brain that setting the limit? [01:59.46]And in fact, there's evidence that indicates that our social channel capacity may actually be a function of our brain size, or more accurately, the size of our neocortex. [02:13.00]The neocortex is the frontal region in the brain of mammals that's associated with complex thought. [02:20.37]Primates have the largest neocortex is among mammals, but among different primate species, humans, apes, baboons, neocortex size varies. [02:31.55]A lot of theories have been proposed for these variations. [02:36.06]Like maybe it's related to the use of tools, but no theories ever seemed like a perfect explanation.
[02:42.80]Until the late 1990s, what an anthropologist named Robin Dunbar published an article about his studies of primates. [02:52.67]Dunbar theory is that if you look at any particular species of primate, you'll find that if it has a larger neocortex that it lives in a larger social group. [03:06.02]Take human beings, we have the largest neocortices and we have the largest number of social relationships. [03:14.90]So we've said that our sympathy group is 10 to 15 people. [03:19.85]What about our other relationships other than family and close friends, such as those that occur in the workplace will call these social groups as opposed to sympathy groups? [03:32.01]How many relationships can we handle there? [03:35.07]Those relationships aren't as involved, so we can handle more of them.
[03:39.94]But is there an upper limit? well, Dunbar says that there is, and he developed an equation to calculate it. [03:47.85]His equation depends on knowing the ratio between the size of the neocortex and the size of the whole brain. [03:56.18]That is of the whole brain, what percentage of it is taken up by the neocortex? [04:02.92]Once you know the average percentage for any particular species, the equation predicts the expected maximum social group size for that species. [04:14.07]For humans, that number seems to be about 150. [04:18.62]So according to Dunbar’s equation, our social groups probably won't number more than 150 people. [04:26.69]Now, Dunbar’s hypothesis isn't the kind of thing that's easy to confirm in a controlled experiment, but there is anecdotal evidence to support it. [04:37.54]As part of his research, Dunbar reviewed historical records for 21 different traditional hunter gatherer societies. [04:47.42]And those records showed that the average number of people in each village was just under 150, 148.4 to be exact. [04:59.07]Dunbar also worked with biologists to see if his hypothesis applies to other mammals besides primates. [05:07.02]When they looked at meat eating mammals, carnivores, they found that the ones with a larger neocortex also have a bigger social group. [05:16.60]And the number of individuals in that group is predicted by Dunbar’s equation supporting his hypothesis. [05:24.12]But when they looked at insectivores, mammals that eat insects, the results were inconsistent. [05:31.27]The data didn't disprove Dunbar’s hypothesis, but wasn't a nice, neat match like the carnivore studies, which isn't totally surprising. [05:40.56]Insectivores are hard to observe, since many of them only come out at night or they spend a lot of time underground. [05:48.37]So, we know a lot less about their social relationships.