It’s not necessarily something you might think about often, the shape of a person’s thumb. For me it has always been one of the first things I notice. All throughout school I would scour my classrooms for anyone with opposable appendages that were out of the ordinary.
Have you ever seen an “orange” thumb?
Six-year-old me didn’t care so much for how she was different, all she knew was that some people at school had an “orange” thumb, like her, and others had “banana” thumbs. It was only years later that I found others with “orange” thumbs and began to wonder, why are my thumbs so strange?
Well, it turns out that I was born with a condition called brachydactyly type D (or BDD). Sometimes also called the stub thumb, it’s where the end bones of both of my thumbs are about half the size of a normal thumb’s, and the nail beds are wide. It’s also the most common form of brachydactyly – about 3% of the world’s population have the condition.
What does having a stub thumb mean?
Well, back when fortune tellers started practicing palmistry it also meant that you were accused of having a temper and being callous, earning the name “murderer’s thumbs.” Which is pretty cool, unless you were accused of a crime because of it.
As far as modern science has found, it’s actually a harmless mutation (if you count out the teasing endured in school), and doesn’t serve any evolutionary purpose. Or relate to a person’s temperament. BDD is just… kind of weird.
For me, my odd thumb means that I can find some ordinary tasks difficult. Tapping out a message on my phone? I have to type with my index finger because the pad of my thumb is the size of 2×3 of the letter keys on a large keyboard. Holding a bowling ball? It’s like trying to fit into your jeans after Christmas.
A couple of weeks ago when was trying to use an electric carver to cut a roast. It required a button on the underside and one of the top of the handle to be held at the same time. Pretty easy to do right? No complicated manoeuvres or novel length manuals. Turns out my thumb was just a little too short to be able to reach both.
Why do people have brachydactyly?
Well, brachydactyly is what is called an autosomal allele – it’s a gene variation that only occurs on chromosomes (the things that contain our DNA) which are sex chromosomes (the ones that vary between the sexes). This means that the allele can be inherited or mutated regardless of a child’s gender. However, there is a bit difference between sexes with slightly more observed cases occurring in females. One or more of the bones in a person’s fingers (or toes) is about half the length it would usually be, causing anything between minor inconvenience to requiring surgery to improve function of the hand.
Maybe the next time you find your mind wondering sitting in a public space, have a look around – not every thumb is what you might expect.