What hand grip has to do with depression

As someone who loves to read across a wide variety of sciences there are two trends that I find concerning:

1. a) The increasing disinterest in science and even anti-science attitudes (as during the COVID pandemic)
2. b) The decreasing quality of science reporting and research itself

As a recent example for b) consider the following article about research that found that stronger grip strength is associated with lower rates of depression.

Physical strength may partially account for the sex difference in depression, study suggests

“We argue it is important to consider physical factors such as formidability (e.g. body size, upper body strength) that might shape interactions with social partners and thus also shape risk of depression—especially symptoms like suicidality, low interest, feeling down and feeling bad,” the researchers concluded. “As this replication study has shown… physical formidability might protect against depression, and sexual dimorphism in upper body strength (proxied here with grip strength) may partially account for the sex difference in depression.”

While I can somewhat relate to the study as a male with low grip strength and depression in my teenage years, I find the conclusion that lower grip strength could also account partially for higher depression rates in women highly illogical.

From the point of view of evolutionary psychology, it makes sense that stronger males would find it easier to achieve alpha positions and therefore have lower rates of depression. However, the same rules of intrasexual competition would not apply to females. So, the phenomenon that needs explaining here is why females who have lower grip strength have higher depression rates compared to females who have higher grip strength rather than males. What’s more, the researchers might have chosen any dimorphic trait to confirm their hypothesis, e.g. height. Shorter guys have higher rates of depression (surprised?). Women have higher rates of depression as they tend to be shorter than guys too. Apart from this not making any sense at all, it is also false: guys who are shorter OR taller than average have a higher risk for depression. Weird, right?

From: souce

In any case, if we want to find out if the grip strength - depression correlation is meaningful at all, we have to dig deeper here.  A 2008 study suggested that men with a smaller second digit compared to the fourth digit had higher levels of grip strength. Now, this is something that makes much more sense. A lower 2D:4D ratio is an indication of higher testosterone exposure in the womb which basically corresponds to a more masculinized physique and personality.

A high 2D:4D ratio also correlates with the Big 5 factor “agreeableness”. While we all know that women tend to be higher in agreeableness than men, this label is a bit unfair towards men and somewhat misleading. The ratio reflects fundamental personality traits that can be found in all cultures, even those that yield only two dimensions of personality:

Joseph Henrich in The WEIRDest People in the World (2020).

So, did the Tsimane' reveal the WEIRD-5 [=Big 5]? No, not even close. The Tsimane' data reveal only two dimensions of personality. No matter how you slice and dice the data, there’s just nothing like the WEIRD-5. Moreover, based on the clusters of characteristics associated with each of the Tsimane'’s two personality dimensions, neither matches up nicely with any of the WEIRD-5 dimensions [...] these dimensions capture the two primary routes to social success among the Tsimane', which can be described roughly as “interpersonal prosociality” and “industriousness.” The idea is that if you are Tsimane', you can either focus on working harder on the aforementioned productive activities and skills like hunting and weaving, or you can devote your time and mental efforts to building a richer network of social relationships.

From the point of view of evolutionary psychology, these two dimensions correspond to the caregiving (more female) profile and the provisioning (more masculine) profile, or  F(eeling)/T(hinking) in Jungian psychology.

From here on it shouldn't be so hard to understand why people with a lower grip strength have a higher risk for depression. In our highly competitive world, we value success more than prosociality, which can be easily seen in such phenomena that women are paid less than men, caregiving jobs (nursing, education, etc.) less valued than jobs that make more money, etc. Our modern work environment is more hostile towards women who are often torn between having children and being cut off from social life or a job that provides access to social life, but also more competition than women are often programmed for. Of course, this also affects men (even to a larger extent) who are F-types and are also often found in caregiving jobs like nursing and teaching.  Therefore, the correlation with depression is really about F-types, women and men. If this hypothesis is true, it would also be likely that T-type women have lower rates of depression.

Another study from 2007, analyzed how grip strength predicted body morphology (waist-to-hip (WHR)/shoulder-to-hip ratios (SHR), and 2D:4D), sexual behaviour/history, and aggression in men and women. The researchers found that men with higher grip strength tended to have larger shoulder-to-hip ratios (V-taper shape), more sexual encounters, and tended to be more aggressive, compared to those with less grip strength. This corresponds to the prior link to testosterone. What’s more

We investigated sex differences in shoulder to hip ratios (SHR) and waist to hip ratios (WHR), and their relationships to different features of sexual behavior. Males with high SHR and females with low WHR reported sexual intercourse at an earlier age, more sexual partners, more extra-pair copulations (EPC), and having engaged in more instances of intercourse with people who were involved in another relationship (i.e., having themselves been EPC partners). The predictive value of these morphological features was highly sex-specific.

What we are seeing here is called a high level of sexual dimorphism. What’s interesting to note is that this higher level of sexual dimorphism goes hand in hand with early puberty and higher sociosexuality, both signs of a fast life history strategy. A fast life history emphasises current over future reproduction and is characterised by fast growth, early maturation and high reproductive effort at the cost of elevated mortality. Now, this could be just part of naturally occurring variation or alternatively, it could be indicative of an environment in which a fast life history can be consistently found. I have argued that this is the case in nomadic pastoralism. The V-shaped body type (mesomorph) should therefore be most common in pastoralists, the endomorph in farmers and the ectomorph in hunter-gatherers.

 

Last but not least, there is hand shape. Masculine hands tend to be wider than female hands and therefore have a lower width to length ratio. In chiromancy (pseudoscience) four hand shapes are recognized.

We should be able to predict that the shapes towards the right should have a higher risk for depression. I think it is also, at least tentatively, possible to assign a different mode of subsistence to each hand shape:

Element	Dosha	MBTI	Evolutionary type
Earth	kapha	SJ	farmer
Fire	pitta	SP	herder
Air	vata (male)	NT	hunter
Water	female?	(N)F	gatherer

The long-palm, long-fingers water hand would make the most sense for gathering (picking fruits and storing them in your palm). I have not been able to find any research regarding hunter-gatherers and hand shape, but the few photos I have been able to find indeed indicate long delicate fingers (we typically associate with artists) and delicate wrists/ thin forearms, as well as typically ectomorph body types.  

This would predict that people who have “gatherer” hands, including men, would have the highest risk for depression. Our world is very much a farmer world, so hunters and pastoralists would also be at a higher risk for depression. We know from anthropology that both foragers and pastoralists tend to be much taller than farmers. This would explain why depression is more common among both shorter AND taller men. This could not be explained by standard evolutionary psychology, which would predict higher depression only for shorter men.

A lot of theories about physical traits and psychological traits have been discounted as pseudoscience (Ayurveda, Sheldon’s Somatotypes, etc.). However, if my hypothesis of four evolutionary types according to the mode of subsistence is correct, there will be many more correlations of body/mind found. For more information check out my book