Apple Apple's new iPhone 5S has a fingerprint security detector, called Touch ID, which unlocks the phone only if it detects your fingerprint.

Immediately, people wanted to know — if someone chopped off your finger and stole your iPhone 5S, could they use the severed digit to unlock your phone? (The answer is no, apparently, but the question is even more ghoulish once you consider that its premise is that safeguarding the phone is more important than the finger.)

Of course, there's an even more crucial question that ought to be asked before you get to the iPhone 5S:

If someone — kidnappers, for instance — is going to chop off one of your fingers, which finger should you sacrifice? This actually happened to a British man kidnapped in Syria this year, so it's not simply a fanciful dilemma.

Many people get this wrong. They assume that the little finger, the pinky, is the one to say goodbye to.

The author and his mom on a very cold day, watching Liverpool F.C. Jim Edwards / BI I asked my mom, a retired doctor who practised surgical anesthesia for years in the Liverpool, U.K., area, which finger you give to the kidnappers. In terms of patients with actual severed fingers, she's seen a "couple of dozen fingers maybe, and an ear" in her career.

She says you want to give up the first finger on the hand you don't use for writing.

A lot of people think the first, pointing finger is the most important one they have. Wrong! Once it's gone, the other three compensate for it quite well. The second finger, for instance, is already pretty similar to the first finger.

The pinky is actually incredibly important, and it's a keeper. Basically, the reason humans have "opposable" thumbs — the springboard of our evolution from being just another ape — is that the thing doing the most opposing is the little finger.

According to the assistant chief of hand surgery at the NYU Hospital for Joint Diseases, the little finger does a disproportionate amount of gripping, while all the other guys are its helpers:

The other three digits—the index, the thumb and the middle finger—they fine tune where the tool goes. So if you have your little finger amputated, you're going to lose a significant amount of grip strength when holding everyday small objects. When you talk about utensils—like knives and forks—most of that stuff is fine manipulation rather than strength, so you're typically using the other three digits. You use the thumb, the index and the middle fingers in order to hold a spoon, or to hold a fork, or even to hold a pen and write things.

Take this test: Try doing pull-ups without using your little fingers, and then do the same without your first fingers, and you'll get an idea of how disabling it is to lose the pinky. A New York Times writer described the experience in 2008. It's not fun.

That raises a question: What if the kidnappers offer you the choice of losing a toe?

There's a bit of a debate here. My mom says that the little toe is analogous to the little finger, and as it is situated on the outside of your foot it does a disproportionate amount of work in maintaining your balance. The big toe, however, is obviously the strongest, and you need it to propel yourself while walking. "I'd probably go for third or fourth toe. You need the others for balance and for thrust," my mom reckons.

Scientific American took an optimistic view of the situation, and concluded that losing even a big toe isn't that disabling:

A nine-toed gait is less efficient, slower and shorter, but no less effective. "You're going to look choppier," Dugan says. Although running on fewer toes takes some getting used to, people can modify their style, train their muscles and practice balance exercises to compensate for a lost toe.

The importance of individual toes has actually been studied in some depth at Northwick Park Hospital in the U.K., and was the subject of a research paper by one of my mom's former colleagues at the Royal Liverpool Hospital, "The Importance Of The Toes In Walking."

The study ranks the toes, in order of the work they're doing. As you can see from this table, the big toe does ~30% of the job and the little toe does only ~9%. The pressure beneath them falls off in the order the toes are arranged on your foot:

The Journal of Bone And Joint Surgery

It's the same while you're just standing. The little toes are in use the least:

http://www.bjj.boneandjoint.org.uk/content/72-B/2/245.full.pdf

And when force while walking, rather than pressure from weight, is measured, the little toes are again the benchwarmers of the foot:

The Journal of Bone And Joint Surgery

What the paper doesn't investigate, however, is whether the little toes are doing a disproportionately large amount of the work relative to their size and strength, or if there are other consequences for losing them.

Rather than recommend a solid answer to the kidnapper dilemma, the authors chickened out when they wrote their conclusion:

The implication for clinical practice is that the toes play an important part in increasing the weight-bearing area during walking; every effort should be made to preserve their function.

This makes me think that perhaps my mom has nailed this one: The little toe is an extremity that's there for a reason, as is the big toe. So compromise and let them have No. 4.

To summarize: the first finger on the hand you don't use for writing is the least important finger, and the fourth toe on the foot you don't use to kick a soccer ball is probably your least important toe.