The thumb: stout, fleshy, comprised of a pair of phalanges. Along with tears, one of the things that distinguishes us as human. Useful for hitchhiking, expressing satisfaction (or lack thereof) in a movie, condemning a downed gladiator to death, and swiping and tap-tapping on smartphone screens.
Therein, a problem. For while the thumb, viewed in aggregate, is not growing, the mobile phone most certainly is. Later this week, Apple will unveil the iPhone 5, which is likely to include a screen measuring four inches corner to corner—half an inch longer than the display on the current model. But Apple is just playing catch-up. Already HTC makes a phone, the One X, with 4.7 inches of pixelated real estate; the Galaxy Note, from Samsung, boasts a preposterous 5.3 inches. Is it all getting to be more than the average thumb can handle?
Related query: How big is the average human thumb, anyway? Depends, as with so many things, on whom you ask. In 1931, Montague Francis Ashley-Montagu, the eminent British anthropologist, measured the first-digit phalanges of 61 contemporaries, including a fellow Brit, an Australian, an African, and a Pacific Islander. The mean thumb length, he concluded, is two inches.
Sixty years later, Thomas M. Greiner, a researcher for the U.S. Army—Anthropology Branch, Behavioral Sciences Division, Soldier Science Directorate—conducted his own thumb study on 2,307 service members. Unlike Ashley-Montagu, Grenier measured from the tip all the way down to the proximal flexion crease of the metacarpophalangeal joint—what a layman might call the crotch of the thumb. Correspondingly, he came up with larger figures: An average thumb length of 2.74 inches in men and 2.49 in women.
In 2008, Vimala Balakrishnan and Paul H.P. Yeow of Malaysia’s Multimedia University published a paper titled “A Study of the Effect of Thumb Sizes on Mobile Phone Texting Satisfaction.” One hundred and ten users were surveyed. The verdict: Those with big mitts have a tougher time than phone users whose digits are dainty. But their research looked at just one phone function and, more important, took place four years ago, when tiny handsets like the Motorola PEBL were more popular.
Over to Ben Bederson, a professor of computer science at the University of Maryland and a co-author of “Target Size Study for One-Handed Thumb Use on Small Touchscreen Devices.” As phones get taller, he predicts, the short-of-thumb may find themselves more vulnerable to frustration. “If you have a small hand, you’re going to have a harder time reaching that top button.”
Thus a conclusion is reached: In the future, the advantage will go to people with thumbs long enough to place each far-flung touchscreen button within their range (à la Bederson). But since the keyboards that appear for typing out texts and e-mails are not expected to expand that much with overall screen size, the ideal thumb will also be svelte (à la Balakrishnan). It will be an Olympic volleyball player of a thumb, in other words. Those not so blessed will fall into another category. The supersize smartphone in your palm will gleam, but you may find yourself all thumbs when you go to use it.