cricket

The following is a portion of Kachana's recent post at the Baptist Board:

Which-handedness is associated with linguistic ability, left or right? Or is it the fact that there's a preference at all in species, that makes that species more inclined to linguistic ability?

I would have asked you this on the Baptist Board, but was afraid I'd get a BB boob-whacking since this treads dangerously close to the dreaded banned topic of ~~evolution~~. (shhhh!)

(If anyone else other than Kachana knows about handedness, feel free to enlighten me. :-)

Sauron

Perhaps language is such a specialized process, that handedness represents an evolutionary method of "load-balancing" the mental work required to support it. Hemispheric specialization would be a way for humans to perfect language ability, but with the side-effect that one side of hte body would become preferential or dominant.

And of course, this dominance is transverse: left-handed people are dominant in the right hemisphere of the brain, and vice-versa.

One way to test this theory would be to compare the language abilities of ambidextrous people to the abilities of people who were strongly right- or left-handed.

It would also be interesting to see the real-time neural activity maps of right-handed and left-handed people, who were engaged in highly linguistic actvities. Which areas of the brain were highly active, vs. less active, might vary in right handed, vs. left handed people.

Cricket, check your private messages, please.

Godless Dave

Agh, I have a linguistics degree, I should know this but I don't!

I'll try to dig through my old textbooks over the weekend. But I would be leery of this claim, since I believe some other mammals have been observed to favor one side or the other.

The one thing I do know is that language function is located in the left hemisphere (in Broca's and Wernick's areas) in all right handed people, and about half of left handed people. Or so they taught me 12 years ago.

The Lone Ranger

"Handedness" long predates any "linguistic" abilities.

Many trilobite fossils show damage from predator attacks that took place during the trilobites' lifetimes. When the pattern of which side of the trilobites' bodies were struck by the predators is analyzed, it shows that the trilobites tended to dodge in one direction or the other. (Some species tended to dodge to the left, while others tended to dodge to the right.)

That a great many modern (and ancient) animals tend(ed) to favor one side of the body over the other is well established. It has been theorized that a tendency to show "handedness" is favored by selection. The hypothesis works something like this: If all the animals in a given population tend to favor one side (say the right), then predators will quickly "learn" to predict their prey's escape behavior. However, if most animals of a given species favor one side, while a substantial minority favors the other side there is no way for predators to reliably predict which way the animal will attempt to dodge an attack. (Apparently, a ratio of about 90/10 is more difficult for predators to adapt to than would be a 50/50 ratio.)

*****

On the other hand, human speech is highly complex, and a good deal of the human brain is devoted to the production of speech. It has been theorized that lateralization of the brain (which has little to do with "handedness") may have been an adaptation to make speech generation and recognition more efficient, by allowing one half of the brain to become more specialized for the task.

Cheers,

Michael

lpetrich

Actually, 50/50 would be the most difficult case to adapt to, since one would be wrong the largest fraction of the time no matter what one chose.

And this happens not only with prey, but also with predators. In Lake Tanganyika, there are certain cichlid fish that are adapted to eating the scales off of other fish. They eat from either the left side or the right side of the victim fish; there are equal numbers of left-side and right-side scale eaters, for the reason I've stated.

If there were lots of left-side eaters, the victim fish would become selected to turning rightward, thus making their left sides difficult to reach. This produces opportunities for right-side mutants, which proliferate until the victim fish is not selected for turning in either direction.

URL: <a href="http://jinrui.zool.kyoto-u.ac.jp/ChimpHome/Mahale/Fish.html" target="_blank">http://jinrui.zool.kyoto-u.ac.jp/ChimpHome/Mahale/Fish.html</a>

The Lone Ranger

lpetrich:


It has been a few years since I read the paper regarding "handedness" in prey, so I may not be remembering it entirely accurately.

As best I recall, the authors claimed that in more or less solitary prey animals, a ratio of roughly 90/10 seemed most stable. If all the prey animals tended to dodge in one direction, it would obviously be easy for predators to adapt to the prey animals' evasion behavior. On the other hand, if half the prey animals turn in one direction while half turn in the other, predators obviously cannot hope to predict which direction a given prey animal will turn in. In this case, the best strategy for a predator is to attack from directly in front of or directly behind the prey animal, and react appropriately as it attempts to dodge.

If most of the prey animals tend to dodge in one direction, while a few dodge in the opposite direction, the predators will naturally tend to attack from the side toward which they "expect" the prey to dodge. This gives the "oddball" prey animals a distinct advantage, since they'll dodge in the opposite direction that the predators expect them to. It would seem that the "oddball" behavior would therefore become more common, but if it does, the predators adopt a "attack from directly in front or directly behind" strategy and so negate the advantage of being an "oddball".

Anyway, the authors concluded that for more or less solitary animals, something like a 90/10 ratio of "handedness" was most advantageous for predator avoidance.

For schooling/flocking animals, the story is very different. In this case, either a 100/0 or better yet, a 50/50 ratio is advantageous. If all the animals in a flock/school tend to dodge in the same direction, they retain the advantages of flocking behavior. Under this circumstance, it would be disastrous for an animal to turn in the opposite direction of its conspecifics, since it would thereby isolate itself from the flock/school, and so be an easy target for an attacking predator.

The best strategy for animals that tend to school would be a 50/50 turning ratio. If, when a predator attacks, half the animals turn in one direction while half turn in the other, the flock/school immediately splits in half. Not only does this make it impossible for a predator to predict which way any given animal will dodge, but the predator will also lose precious time while it "decides" which half of the flock/school to pursue.

Cheers,

Michael

copernicus

What we know is that injuries to Broca's and Wernicke's areas cause different types of aphasia. Damage to Broca's area disrupts grammatical functions, but damage to Wernicke's area disrupts semantic functions. It isn't at all clear what it means to say that linguistic ability is "located" in these areas. Maybe they are just important to the organization of linguistic information that is stored elsewhere.

Prepubescent individuals seem able to relocate linguistic function in different areas--e.g. to the right side--when these areas are damaged. Adults are much less likely than children to recover language function when they suffer brain damage to linguistic "areas".

We have long known that linguistic function is associated with specific areas of one side of the brain, but I have never heard that linguistic ability was somehow associated with "handedness" in individuals. We do not really understand the way in which human language evolved. All animals have "call" systems--equivalent to universal noises humans make to express emotions: crying (sorrow), screaming (fear), laughter (amusement), growls (threat), shouts (pain), etc. Birdsongs are an additional mechanism of communication for those species, much like human language is different from the animal/human "call systems". there can be a variety of dialects within some bird species. Maybe human speech is related to the same function in birds, or maybe the similarities are just coincidental.

RufusAtticus

Short post for now. I got a lot of catching up to do because I just got back from a conference on the evolution of language.

There is a theory that a gesture-based proto-language preceded speech. There have also been studies which showed that speech can become labored if a person's hands are bound. There definately appears to be natural associations between manual gestures and vocal speech.

-RvFvS

[ April 01, 2002: Message edited by: RufusAtticus ]</p>