Declining brain size/domesticity.

[gcol]

This article appeared in the UK times today.

It interested me for several reasons:

 

1. Genetic changes caused by conditioning & training.

 

2. Possible reason why the female brain is smaller than the male.

 

3. Human brain size actually declining irrespective of sex.

 

4. possibility of an evolutionary trend we may not find welcoming.

The ideas raised seem to relate to several past and present threads, not sure which one to put it in.

 

Comments, observations?

 

Please read all before replying, even if chosing only one aspect for response.

 

Why is a woman's brain smaller than a man's? Maybe because she's a fox

Science Notebook by Terence Kealey

 

WHY DO WOMEN have smaller brains than men? Male brains weigh around 1.25kg; female brains weigh on average 100g less.

One possible answer comes from an unexpected study of foxes. In 1959 Dmitri Belyaev, a Russian geneticist, launched a long-term experiment to tame foxes. Starting with a population of caged wild animals, he selected from each generation the puppies who were friendliest (or, initially, least hostile) to humans, breeding only from them.

 

After 35 generations he produced animals that had been transformed from the usual snarling fearfulness of wild foxes into animals that were similar to domestic dogs. The tamed foxes wagged their tails, whined for affection, were submissive, barked like dogs and their ears flopped. As Darwin said: “Not a single domestic animal can be named which has not in some country drooping ears.” Belyaev seems to have concertinaed all this into 50 years when it took 10,000 years to domesticate wolves as dogs.

 

And the tame foxes’ brains were smaller. Domestic animals generally do have small brains. On average, domestic dog, cat, sheep and pig brains weigh 25 per cent less than those of wild animals. The mechanism remains a mystery. A recent study by Elena Jazin and her colleagues from Uppsala University in Sweden, published in Current Biology, reported that of 30,000 brain genes about 40 showed differences between tame and wild foxes. All we do know is that blood levels of stress hormones are lower in tame than wild animals and that brain levels of anti-stress hormones are higher.

 

But would it be dangerous to suppose that women’s brains are smaller than men’s because, over the millennia, we men have been selecting friendly women with whom to breed? And that therefore we have domesticated them? And that they, in turn, have selected assertive men? Interestingly, human skulls of both sexes have been shrinking over the past few tens of thousands of years, suggesting that as human beings have been increasingly domesticated, so they have shrunk their brains — without losing the gender difference.

 

One force that drives up brain size is social interaction. It was Robert Trivers, the biologist, who showed in his 1985 book, Social Evolution, that there is a direct correlation between the size of a species’ brain, the size of its social groups and the degree of social interaction between the animals of the group. Men and women inhabit different social spheres, and though women may enjoy deeper social interactions than men, it is probably men who, as tribal leaders, have experienced wider social interactions over evolutionary time.

 

In any event, small brain size seems to optimise emotional intelligence. In a paper published last month in Current Biology, Brian Hare and his colleagues at Harvard University showed that domesticated foxes were better than wild foxes at reading human social cues. For example, domesticated foxes instinctively understand a person’s intention when he or she points at an object and they investigate it. Social intelligence, therefore, seems to be increased when fearfulness and stress are lowered by selective breeding for tameness. Certainly our border terrier at home, Rusty, is uncanny in his ability to understand our intentions (when he wants to).

 

And then there is body size. Irrespective of other factors, there is a direct correlation between the size of an animal’s body and its brain. We human beings have haremic tendencies, so women are smaller than men. So their brains are too.

 

Does any of this matter? A recent paper in the British Journal of Psychology by Paul Irwing, of the University of Manchester, and Richard Lynn, of the University of Ulster, claims that more men have very high IQs than women do. But IQ tests remain so controversial and so subject to cultural factors that we will need another half century before fully understanding them. Not only that, we also simply do not know enough about our brains to draw safe conclusions from any of these observations.

 

But what I do know is that such speculations are dangerous in the academic world. Lawrence Summers, the President of Harvard, lost his job when he conjectured that women might not scale the same intellectual heights as men, so for me to continue this theme might be perilous.

 

The author is the Vice-Chancellor of the University of Buckingham.

[mattbimbo]

i once read an article along the lines that women in the countryside have higher prolactin levels compared to women who live in a city. also glucocorticoid levels are higher for people living in cities compared to the those in the country and glucocorticoids counteract prolactin. the net result of this was that women in the city had smaller breasts on average compared to women in the country. i don't know whether the paper was a one off, or part of a serious line of research, but the antagonistic effects of GCs on prolactin are well recognised.

 

i looked at the papers by elena Jazins and brian hare, mentioned above, and it seems that the genetic and hormonal differences between wolfs and domesticated dogs are small. however i couldn't find any mention of why smaller brain sizes contribute more to emotional intelligence. i was under the impression this had to with the activity of the hypothalamus, and is independent of brain size. can anyone help me out with a reference or two here?

[mattbimbo]

perhaps the most significant result of all this research comparing the effects of domestication on the brain is that animals can have the same/similar emotional intelligence that humans have?

[gcol]

Interestingly, human skulls of both sexes have been shrinking over the past few tens of thousands of years, suggesting that as human beings have been increasingly domesticated, so they have shrunk their brains

 

 

This was the part of the article that particularly sparked my interest. There seems to be a popular conception that human evolution is measured by thinking capacity, going hand-in-hand with increasing brain size. This quote throws some doubt on that, suggesting that adapting to a society where interpersonal skills are more important than jungle survival skills, less brain power is required, and evolution is responding appropriately

[mattbimbo]

good point. relying on others for answers or getting information form others perhaps puts less burden on ourselves.

 

or maybe smallness equates with efficiency?

[mattbimbo]

and did you know this?

 

from the above link

This behaviour indicates that it could be the value of information, rather than the constraint of brain size, that has influenced the evolution of teaching.

[gcol]

Matt Bimbo:

 

1. Your last two posts suggest to me that learning by rote and example requires less brainpower. Modern education requires much rote learning to tick the boxes of the norms of the education system, (memory) and less original thinking. Mainstream education may however .have always been like this, and not just a modern trend.

 

2. Have we, as a species, trained ouselves to be more domesticated, and evolution is cementing this change. I hope this is not a sort of self-reinforcing genetic closed loop. If so, I smell the possible beginning of an evolutionary dead end.

 

3. If the brain is actually decreasing, it may only be the part required for "jungle survival". This part may be shrinking, the social interraction part expanding but at a slower rate, giving an overall reduction.

[mattbimbo]

perhaps. i have always considered modern schooling an act of domestication.

fortunately many learn to rebel and undo their schooling. but now you are making me worry about the brains of our teachers? do they get smaller as they give more rote teaching.

 

does "jungle survival" include warlike behaviour?

[swansont]

2. Possible reason why the female brain is smaller than the male.

 

 

The quote from the article mentions sexual dimorphism (not by name, though). What it doesn't do is quantify if that accounts for all of the difference in brain mass.

[mattbimbo]

this thread has got me thinking of a quote by ML King

"If we do not learn to live together as friends, we will die apart as fools"

 

maybe this should be rewritten in light of gcol's thoughts? sinice by living together we will die as fools.

[gcol]

this thread has got me thinking of a quote by ML King

"If we do not learn to live together as friends' date=' we will die apart as fools"

maybe this should be rewritten in light of gcol's thoughts? sinice by living together we will die as fools.[/quote']

 

Very deep, that, is it similar to suggesting that social peace and harmony breeds atrophy? I remember that theme being explored frequently in fiction, where a peaceful and easygoing race has been easy prey to an outside threat.

 

Mattbimbo:

does "jungle survival" include warlike behaviour?

 

Regretably, I suppose it must.

 

Swansont:

The quote from the article mentions sexual dimorphism (not by name, though). What it doesn't do is quantify if that accounts for all of the difference in brain mass.

 

With extreme cowardice, I am going to steer clear of that one!

 

Mattbimbo:

but now you are making me worry about the brains of our teachers? do they get smaller as they give more rote teaching

 

If I were a teacher, I would send you hate mail. But as I am not, that raised a real chuckle.

--------------------------------------

This article did raise several issues. It will be interesting to see which, if any, prompt the most thoughts.

[swansont]

Swansont:

 

With extreme cowardice' date=' I am going to steer clear of that one!

[/quote']

 

 

Why? It's a legitimate question. Dimorphism exists. What is the scaling facor of brain size with mass, and how much of the brain mass difference does this explain? If it explains all of it, then there is no need to search for any other effects, but since the author is searching for other effects, my massive brain tells me it is implied that dimorphism doesn't account for all of the difference. Or that it's really bad science going on, if there's no difference to explain and yet they're looking anyway.

 

(I don't understand why people are shy in pointing out that there are some physical difference between men and women. (and, vive le difference) And I don't understand the knee-jerk reaction that some have when facts are pointed out to them.)

[gcol]

Why? It's a legitimate question. Dimorphism exists. What is the scaling facor of brain size with mass' date=' and how much of the brain mass difference does this explain? If it explains all of it, then there is no need to search for any other effects, but since the author is searching for other effects, my massive brain tells me it is implied that dimorphism doesn't account for all of the difference. Or that it's really bad science going on, if there's no difference to explain and yet they're looking anyway.

 

(I don't understand why people are shy in pointing out that there are some physical difference between men and women. (and, vive le difference) And I don't understand the knee-jerk reaction that some have when facts are pointed out to them.)[/quote']

 

You are quite right, so let me get out of it another way:

I do not have the credentials and knowledge to add anything objective. I seem to remember at least two threads this year touching on dimorphism without that word actually being used. They were rather subjective. It raises shrill indignation from the distaff side. Letus see if a representative makes an appearance here........

[swansont]

You are quite right' date=' so let me get out of it another way:

I do not have the credentials and knowledge to add anything objective. I seem to remember at least two threads this year touching on dimorphism without that word actually being used. They were rather subjective. It raises shrill indignation from the distaff side. Letus see if a representative makes an appearance here........[/quote']

 

 

OK, fair enough. "I don't know" is a perfectly acceptable answer. (And, to my mind, preferable to avoiding the indignation, but that's me. I strongly object to ideology driving science)

[gcol]

Perhaps if domesticity is a factor that can be used irrespective of sex, (and in a matriarchal society it could just as easily be the male that exhibited a smaller brain), and demonstrated in domesticated animals where the process has been artificially speeded up, it could be examined without shrieks of subjective sexism? Or would that be too much of a cop-out?

[Skye]

I think in general body mass dimorphism is larger than brain mass dimorphism. Using the brain mass figures they gave, 1250cc is about 109% of 1150cc. The average US male is 86.1kg, which is about 116% of the average 74kg US female.

 

(The body masses are from here: http://www.cdc.gov/nchs/data/ad/ad347.pdf for 20+ y/o in 1999-2002)

[MM]

" Starting with a population of caged wild animals, he selected from each generation the puppies who were friendliest (or, initially, least hostile) to humans, breeding only from them."

 

If he's going make the correlation between small brain size from domestication why breed only the friendliest, where is the control group.

 

The control can't be the wild foxes since the one driving force for a brain is finding food.

[mattbimbo]

well it is a 'she' that did the breeding, scientifically and foxily.

 

the control ngroup consists of the wild foxes!

[mattbimbo]

i have had the chance to divulge some literature on sexual dimorphism.

there are many interesting differences. mens brains decilne in size with age, from 25y onwards, womens do not. intellect in mens brains is localised throughout the brain, in predominantly grey matter, while in women it is centrally localised and consists motsly of white matter.

[sunspot]

The overall observation of brain size decreasing with domestication and with culturalization (is that a word?) makes sense. The wild animal or the mountain man have to rely more on ingenuity for their survival. Adapting to a harsh and ever changing enivironment will require a lot more neural connections than rote learning within a comfortable fix environment.

 

Culture is very important, but it can create the irrational illusion of being more than one actually is. So many things are prefab, including what to think. The path of exploration may take a dozen prototypes but will build a wider range of adaptation than just learning the most popular accepted path. What is easier building a computer or learn to use money buy one? Which allows a greater rate of adaptation?

 

The idea of the brain shrinking and possibly becoming more centralized into the core emotional aspects of the brain, also makes sense. Rather than have to rely on logic and common sense to think through what we choose to believe, it is easier to rely more on an emotional perception, such as entertainment or prestige, to chose which ideas to call our own.