Why Don’t We All Have Twelve Fingers Now?

The other day, someone asked me why humans haven’t evolved extra fingers to make it easier to use our smart phones and other new technology. We spend so much time interacting with this technology that having extra fingers to use for texting, scrolling, and other tasks would be quite useful. Why, then, don’t we have them?

To answer this question, we need to understand what it takes for a species to evolve. A species only evolves if a subgroup having a distinctive set of traits reproduces faster than the rest of the species over a long period of time. When this happens, the subgroup’s traits spread throughout the rest of the population, until all new members of the species have them. Darwin proposed that this occurs when the traits provide the subgroup with a reproductive advantage: for example, a finch having a smaller, pointed beak can gather food that finches with larger beaks can’t access. Today, biologists accept this mechanism as the primary way a species evolves, although there are other ways as well, such as genetic drift, where random variations in genes lead to lasting changes.

Knowing this, we can list what needs to happen for us to evolve those useful extra fingers:

  1. Some people must be born with extra fingers
  2. These people must reproduce more successfully than people with just 10 fingers
  3. This reproductive advantage must last until the trait spreads throughout the population

The first requirement is clearly met: about one of out every 500 live births will have at least one extra finger. That’s not extremely rare, but it’s also not very common: for comparison, Game 7 of the 2017 World Series had an attendance of 54,124 people, out of which we’d expect 27 people to have extra fingers (all else being equal). For the trait to spread, however, those people would need to reproduce more successfully than everyone else: that is, their offspring must have a better chance to reach reproductive maturity and successfully reproduce themselves than the offspring of people without the extra fingers. And while extra fingers could make it easier to use technology, it’s unlikely that this difference alone is enough to make that happen, especially for the hundreds of thousands of years it would take for the trait to spread to the rest of us.

If not extra fingers, then, what types of changes are we likely to see in our lifetimes? Our behavior is shaped by culture much more than biology, and culture can significantly change in relatively short periods of time. One such change is our increasing isolation from one another: the relative ease of travel, combined with cultural mandates to live as what 1960s counterculture would have called “our authentic selves” have made people less willing to connect with others just because of their accidental proximity. In today’s world, the ties of family and community are much less binding than at any point in recent history. Whatever one thinks of this, the impact will be as profound as walking upright, opposable thumbs, and brains that let us think one thing while claiming to believe another.