⇐ Introduction |
Asparagus urine ⇒
Table of Contents
Genetics of arm folding
Summary
Some people fold their arms with the right arm on top, and some with the left. You may have heard that the way you fold your arms is a genetic trait, that folding with your right arm on top is dominant. That's not true! Scientists have studied families and twins, and it's clear that genetics doesn't have much influence on how you fold your arms. Don't be suspicious if your family includes two left-on-top parents and a right-on-top child, and if you're a teacher, don't use arm folding as an example when you're teaching genetics.
Are there just two kinds of arm folders?
Fold your arms and look down at them; you either have your right forearm on top (R) or your left forearm on top (L). Now fold your arms the other way. For many people, it feels really weird to fold their arms the "wrong" way. I fold my arms with left on top, and when I force myself to fold with right on top, it just feels wrong and uncomfortable. For this reason, most of the people who have studied arm folding have just asked their subjects to fold their arms, then recorded which was on top. They have assumed that there are two kinds of people, L people who always fold with left on top, and R people who always fold with right on top.
A few studies have mentioned a small fraction of people who have no preference, but Sharma and Nath (1971) are the only researchers I'm aware of who carefully studied how consistent the preference is. They told people to cross their arms three times in one day, waited three days, had them cross their arms three more times, waited three more days, and repeated the count. They did this without telling the subjects that they were studying the consistency of arm folding. Of the 110 people they looked at, only 47% crossed their arms the same way all 9 times. This means that there aren't just two kinds of people, L and R; there are a lot of people who will cross their arms either way.
Unfortunately, almost all of the arm-folding studies published after Sharma and Nath (1971) failed to cite them and continued to assume that people were either L or R. I don't know if this is because later authors were unaware of the paper (it was in a well-known journal, so they should have seen it if they wanted to be arm-folding experts), or if they thought there was something wrong with the study (it seems pretty rigorous to me).
Arm folding and handedness
You're probably wondering, is the way you fold your arms related to whether you're right- or left-handed? Most studies (Wiener 1932, Reiss and Reiss 1998, Mohr et al. 2006, many other studies) have not found any relationship, but Tran et al. (2014) collected a large sample size (over 12,000 people) and found that 38% of righthanded people and 57% of lefthanded people were R folders. (It takes a large sample size to get enough left-handed people.) As in most studies, Tran et al. (2014) just had people fold their arms once, ignoring the results of Sharma and Nath (1971).
Many of the studies of arm folding have looked for differences in arm-folding preference between sexes, and associations of arm folding and hand clasping, and they've found that any relationships are weak and inconsistent.
Family studies
Wiener (1932) was the first to examine the genetic basis of arm folding by comparing parents and offspring, with the following results:
| Parents | R offspring | L offspring | Percent R |
|---|---|---|---|
| R×R | 31 | 50 | 38% |
| R×L | 81 | 99 | 45% |
| L×L | 58 | 70 | 45% |
Each of the three kinds of matings has about the same proportion of R and L offspring, so Weiner (1932) concluded that there is no genetic basis for arm folding preference. If arm folding was a simple genetic trait with R dominant, two L parents could not have an R child; instead, close to half of the children of L×L matings are R. So in 1932, it was clear that arm folding was not a simple genetic trait and shouldn't be used as an example in genetics classes.
For some reason, people kept doing family studies of arm folding, so that Reiss and Reiss (1998) were able to summarize the numbers from 12 studies:
| Parents | R offspring | L offspring | percent R |
|---|---|---|---|
| R×R | 731 | 672 | 52% |
| R×L | 1230 | 1497 | 45% |
| L×L | 629 | 1038 | 38% |
There is some association between parents and offspring, in that R×R parents have a higher proportion of R offspring than do L×L parents. But all studies have found many R offspring of L×L parents and many L offspring of R×R parents, so even if there is some genetic influence on arm folding, it is not a simple one-locus, two-allele genetic trait.
For many of the traits I disuss in these pages, an initial study, based on a small amount of data, was fairly consistent with the trait being a simple genetic trait; only after further studies were done did it become clear that this wasn't true. For arm folding, none of the scientific papers I've seen make any claim that arm folding is a simple genetic trait, with R dominant over L; I have no idea where some textbook authors got this completely wrong idea.
Twin studies
Reiss and Reiss (1998) summarized the results of two twin studies, which gave nearly identical results. About half of the pairs of monozygotic (identical) twins consist of one R twin and one L twin, and the same is true for dizygotic twins. If arm folding was determined solely by genetics, then identical twins would be identical, of course. This is further evidence that other things besides genetics (something in the environment, or just random chance) influence arm folding.
| Monozygotic | Dizygotic | |
|---|---|---|
| Both R | 48 | 12 |
| Both L | 80 | 49 |
| R + L | 109 | 78 |
Further research
I can't think of any reason to do more research on the genetics of arm folding, but there are some interesting questions that could be answered fairly easily. There are still people publishing papers that use arm folding as an example of "laterality" (difference between right and left), so it might be worthwhile for someone to do another study like Sharma and Nath (1971) to see how consistent people's arm-folding is; it would be a fun and easy classrooom project. And a large, careful study of arm folding and handedness, following up on Tran et al. (2014) but using multiple observations of arm folding as in Sharma and Nath (1971), might be mildly interesting.
Off the top of my head, here are some other questions about arm folding. For people who have a strong preference, is there an anatomical difference between their arms that makes one method of folding more comfortable? Do babies and toddlers have a preference, or does it develop later in life? If people with a strong preference force themselves to cross their arms the wrong way, does it eventually get equally comfortable?
Mohr et al. (2003) found that R arm folders who clasp their hands with left thumb on top have significantly more "magical ideation" than the other three arm folding/hand clasping combinations. And Zang et al. (2008) reported that R high school students did significantly better than L on exams in four out of six subjects. Any relation between arm folding and brain function seems pretty unlikely to me, but I suppose someone should follow up on these.
References
Mohr, C., G. Thut, T. Landis, and P. Brugger, 2003. Hand, arms, and minds: Interaction between posture and thought. Journal of Experimental and Clinical Neuropsychology 25: 1000-1010.
Mohr, C., G. Thut, T. Landis, and P. Brugger. 2006. Arm folding, hand clasping, and Luria's concept of "latent left-handedness." Laterality 11: 15-32.
Reiss, M., H.-A. Freye, and G. Reiss. 1997. Functional importance of hand clasping and arm folding. Perceptual and motor skills 85: 1209-1210.
Reiss, M., and G. Reiss. 1998. Arm-folding in families: A review of literature and some new data. Psychologia 41: 81-87.
Sharma, A., and S. Nath. 1971. Standardisation in the recording of arm-folding types. Human heredity 21: 509-515.
Tran, U.S., I. Koller, I.W. Nader, J. Pietschnig, A.H.E. Schild, S. Stieger, E. L. Zeilinger, and M. Voracek. 2014. Lateral preferences for hand clasping and arm folding are associated with handedness in two large-sample latent variable analyses. Laterality 19: 602-614.
Wiener, A.S. 1932. Observations on the manner of clasping the hands and folding the arms. American Naturalist 66: 365-370.
Zang, Z., Z. Han, and Y. Zang. 2008. Effects of hand clasping and arm folding on academic performance. Neural regeneration research 8: 914-917.
Go to John McDonald's home page
This page was last revised October 26, 2026. ©2026 by John H. McDonald. Content is available under the Creative Commons Attribution-Noncommercial license.