Social Question

lillycoyote's avatar

What are the current and/or prevailing theories regarding the evolution of left-handedness in humans?

Asked by lillycoyote (24835points) July 2nd, 2010

I don’t really have more details. The question seems pretty straight forward, at least to me.

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41 Answers

Coloma's avatar

Some say left handedness is a stroke of genius others say it’s a birth trauma. lol

I’m a southpaw and fit the profile for creative right brained type. lol

I know that there is some evidence that older mothers produce a higher rate of lefties. 40 and over…but my mother was 34.

Great question…I’ll do some research.

lillycoyote's avatar

@Coloma Interesting. My father was a lefty and couldn’t have been more left brained. A chemist, though he was an extremely creative, though systematic, problem solver; but I saw that as a left brained trait. I look forward to seeing what you find. I have, sadly, had to resign myself to the fact that my inner evolutionary biologist, though curious, eager and relatively intelligent, is really no match for actual evolutionary biology. :-)

charliecompany34's avatar

my wife is left-handed. she is very social and can just about talk to anybody on the planet. dont get me wrong: she knows where home is and is happily married, but total strangers are always affected by her no matter the situation. i am happy to be married to a left-handed woman.

my dad is left-handed too. he has the same outgoing personality. left-handed people are so approachable. you just love to be around them but dont know exactly why…

Coloma's avatar

@charliecompany34

Hah…funny…and true, I am always rambling on with perfect strangers..I do have a knack for being very approachable and making others feel at ease. That’s a cool theory you have there. ;-)

charliecompany34's avatar

@Coloma i know, right? i mean left-handed people always seem to be treated like aliens but they really are pivotal people. i love my left-handed wife. she makes a room light up when she enters.

AmWiser's avatar

The POTUS is left handed.
I know it doesn’t have anything to do with the question. Just thought I would throw that in:D.

lillycoyote's avatar

footnote: please, continue your discussion, I am enjoying it, that’s why I always ask my questions in the social section, but just to let everyone and anyone know, if anyone out there wants to answer the question I actually asked, please feel free. :-)

lillycoyote's avatar

@Coloma LOL. We were commenting simultaneously. I was wondering if anyone was going to actually answer my question at the same moment you were actually answering my question. Carry, on folks, this is your thread as much as it is mine.

lillycoyote's avatar

@Coloma Your link didn’t quite work but I found the page you were linking to. Thanks.

Coloma's avatar

@lillycoyote

I just noticed that…okay…good. ;-)

Coloma's avatar

Maybe something just went awry and us lefties should have been born Parrots. lololol

lillycoyote's avatar

@Coloma It’s a good site. I just entered “left-handedness” in their search menu and it came up. Figured since it was call “libraryindex.com” that might just work. Funny thing about libraries. You can just look stuff up. :-) I don’t know what causes that but sometimes I will link to what seems to be a specific page on a site and end up with a link to their home page. Happens all the time.

lillycoyote's avatar

@Coloma I think it’s just that parrots are politically moderate, naturally adept at diplomacy and consensus and find the idea of right or left “wingedness,” any sort of ideological extremism to be distasteful. They are much more enlightened than humans.

Coloma's avatar

@lillycoyote

Beyond a doubt,I wasthinking much more simplistically, that they are babbley wonders too. lol

dpworkin's avatar

There are no theories of the evolution of handedness. There are theories of hemispheric dominance, or “lateralism” You can look them up on PubMed. There are thousands of papers.

Coloma's avatar

Yes there are…the link I posted speaks of a genetic mutation theory in the evolutionary development of right handedness. Note the title of the article.

MissAusten's avatar

I don’t have an answer, but think it’s a very interesting question. I never thought of handedness in evolutionary terms.

My husband and one of my sons are both lefties. My husband is an extremely talented artist. He’s also very socially adept. My son is six, and we’re still wondering what he is. ;)

dpworkin's avatar

I beg your pardon, @Coloma, there do indeed seem to be two people who think handedness is genetic, but they disagree with one another.

Coloma's avatar

@dpworkin

Hahaha..well..that makes sense! lol

Coloma's avatar

@MissAusten

That’s pretty cool that your son inherited ( it seems ) his fathers left handedness. I only had one child, she is right handed like her father. I was the only lefty in my entire family as far as anyone living knew.

I was also the only blue eyed blonde in recorded history…I’m thinkin’ the milkman and my mom sipped out of the same straw. lololol

dpworkin's avatar

I remain unconvinced that we are talking about a heritable phenomenon.

Coloma's avatar

2 lefties in the same family….sort of stacks the deck at least in @MissAusten ‘s circumstance I think.

Who knows…who cares…it’s just fun to share and ponder.

lillycoyote's avatar

Thus Spoke Dpworkin. He has written a simple, yet surprisingly eloquent and persuasive declarative sentence: “There are no theories of the evolution of handedness.” Case closed. I suggest we all move on and begin reading the “thousands of papers” he recommends.

dpworkin's avatar

Anecdote is not data, and there are meaningless statistical clusters of everything.

Coloma's avatar

@dpworkin

Not everything HAS to be dredged out of some hardcore database.

We all know your extreme attachment to data, good for you.

BUT…some of us just want to discuss, have fun…PLAY with a question.

Sheesh…I can’t imagine what talking to you at a party would be like. lol

dpworkin's avatar

I have an attachment to data in threads on Fluther, which is an Answer Service, and depends upon the accuracy of the people who post. That has nothing to do with what I’m like or who I am, or what I do at parties.

Dr_Lawrence's avatar

Here is the content of @Coloma link:

Genetics and Evolution – Theories About The Evolution of Handedness

One characteristic that distinguishes humans from other primates is the fact that the overwhelming majority (90%) are right-handed. With the exception of parrots, which show a similar population bias for right-footedness, other animals appear to have more balanced proportions of hand or foot preferences. In “The Genetics and Evolution of Handedness” (Psychological Review, vol. 104, no. 4, 1997), Michael Corballis proposed that at some time during human evolution a mutation produced a “dextral” allele (D), strongly predisposing humans to right-handedness. Corballis speculated that the trait was additive—that is, it was also influenced by other genes that supported the bias toward right-handedness—and that the D allele, with a slight heterozygotic advantage, was probably spread and generalized to the population quite quickly. This inheritance would explain the relatively unchanged proportions of right- and left-handed people in the population. Corballis hypothesized that this unique human allele may have arisen in Africa between 150,000 and 200,000 years ago.

Gregory Jones and Maryanne Martin presented a somewhat different mechanism of the inheritance of handedness in “A Note on Corballis (1997) and the Genetics and Evolution of Handedness: Developing a Unified Distributional Model from the Sex-Chromosomes Gene Hypothesis” (Psychological Review, vol. 107, no. 1, 2000). The researchers proposed that, rather than transmission of handedness based on the fitness of the genotype, the handedness gene may be located on the sex chromosomes. Their model presumed that left-handedness is genetically recessive, with low penetrance (the allele is present but not expressed) and with a genetic variation located on the X chromosome. Jones and Martin concluded that the chance of being left-handed is recessive rather than additive as assumed by Corvallis and asserted that the distribution of left-handedness is consistent with that which would be expected for a recessive X-linked gene with low phenotypic penetrance.

dpworkin's avatar

Translation: they don’t know.

Coloma's avatar

@ Addendum:

It’s also the social section so we don’t HAVE to know anything for certain.

lillycoyote's avatar

@dpworkin That’s simply one article, one study, not exhaustive.

Response moderated (Personal Attack)
Response moderated (Off-Topic)
dpworkin's avatar

Why the ad hominem? If I say something wrong or stupid (which is quite likely) why not just attack what I said, instead of attacking me? Does it make you feel better?

lillycoyote's avatar

Because you didn’t actually say anything. You didn’t construct any sort of argument, you didn’t provide any sources You simply said: “There are no theories of the evolution of handedness,” which, as a matter of fact, is simply not true, as though your simply declaring it to be so, made it so. There are theories regarding the evolution of handedness. Theories that either make a case for it or make a case against it. And the reference to “thousands of articles.” Well, thank you very much, that wasn’t really helpful at all. You are smart and knowledgeable, @dpworkin, you should be able to do better than that. Not be so patronizing, that’s what made me cranky.

dpworkin's avatar

I was in error. BFD.

Response moderated (Personal Attack)
augustlan's avatar

[mod says] Flame off folks. There’s no need to make this personal.

MissAusten's avatar

@Coloma and @dpworkin Whichever theory is correct, no one may every know. Family stories are anecdotal, but I find it interesting that my husband’s family does have a lot of lefties. His grandfather was left-handed, so is one of his aunts. He is, our son is. It may just be a big coincidence, or it may be genetic. Whatever it is, it’s interesting.

My son, my husband, my husband’s sister and their father are also all allergic to penicillin. When my son had an allergic reaction to penicillin, the doctor told me the allergy isn’t hereditary. I am skeptical, just because it seems like too big of a coincidence to be, well, a coincidence. Another doctor told me such allergies sometimes do run in families. Who the heck knows.

Coloma's avatar

@MissAusten

Yes, who knows…it’s the interesting part, that interests me. lol

If temprament and other traits can be inherited I see no reason to discount possibility just because no substantial evidence exists.

I have often been in the 1–5% bracket.

Okay..sooo, 99% of others don’t have this particular reaction or experience…well SOMEBODY has to be the 1%. lol

My old cat was in the 4% of cats that could not tolerate a certain medication, the vets insisted his reaction wasn’t due to the drugs…bullshit…good thing I am a seeker and pro-active, had I taken their word at face value he would have been dead much sooner than he was.

Who knows…maybe your family has flipped the switch on left handed inheritance.
The switch has to get flipped at one point or another. haha

everephebe's avatar

grrrr huff huff grrrrr

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