In the Dark

My thumbs can bend backwards about 90 degrees, a property known as distal hyperextensibility or, less formally, ‘hitchhiker’s thumb’.

I don’t know of any particular advantage or disadvantage of having bendy thumbs, although it does make holding a clarinet or soprano saxophone a little awkward, as the thumbs are used to support the instrument when it is played. The only useful thing I can think of is the comedy value of seeing people freak out when they see the bendy thumbs in action.

I don’t think this ‘condition’ has been studied very much, but I am given to understand that somewhere between 15 and 30% of the population has bendy thumbs. The property is inherited and is commonly believed to be controlled by a single gene with two alleles, one for ‘straight’ and one for ‘bendy’ ; the one expressing bendiness being recessive explains why straight thumbs are more common. I now realise, however, that this is not the case. For one thing, it seems that thumb bendiness is not a simple binary property. That also makes it difficult to define it for statistical purposes: what angle of bend do you choose to classify a thumb as bendy?

I also have blue eyes, which is another recessive trait, but it has been known for some time that eye colour is not controlled by a single gene.

This entry was posted on July 22, 2018 at 12:16 pm and is filed under Biographical with tags Distal Hyperextensibility, Hitchhiker's Thumb, Thumbs. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.