Which body parts do humans not need?

Our bodies are like museums of evolution. We walk on two legs because a common ancestor evolved to do so millions of years ago. And, like any showroom, we house organs and functions that have outlived their original purpose. 

Take the appendix, for example. Once a heavyweight in digesting a plant-heavy diet, it was dismissed by evolutionary scientist Charles Darwin, who wrongly decided that it was no longer necessary due to dietary shifts. Wisdom teeth helped early humans gnaw through raw roots and tough meats, but today, they’re little more than an expensive dental complication since our food is more processed. Even goosebumps—once a handy way to fluff up body hair for warmth or protect against predators—are now seen as little more than a fleeting moment of aesthetic drama.

So why do most of us still have these body parts and functions? 

It’s likely because they aren’t causing us any harm, explained Matthew Ravosa, the director of the Center for Functional Anatomy and Evolution at Johns Hopkins University School of Medicine. Even though they may not present an advantage, the lack of disadvantage reduces the natural selection pressures that typically eliminate traits within a population.

Some of these features have been co-opted or repurposed for a different function due to evolutionary changes in environment, behavior, or selective pressures. “The appendix is a good example of that,” added Ravosa. 

[ Related: Could we ever regrow our adult teeth? ]

Once considered vestigial, the appendix may play an essential role in gut health, helping the immune system fight pathogens. It contains a high concentration of immune tissue and houses beneficial bacteria that repopulate the gut microbiome after an illness or antibiotic use. This understanding has challenged the long-held belief that the appendix is a redundant organ. 

“Sometimes redundancy has a way of showing up under certain conditions; they’re not truly redundant,” said Michael Snyder, director of the Snyder Lab at Stanford University. “Going back to the appendix, it’s been suggested that it does have a use.” 

It’s not well understood what’s truly vestigial and what body parts may still be functioning, albeit in a different way. Still, we are beginning to see people born without some body parts commonly understood to be pointless. Studies have shown that around 35 percent of the population are now born without wisdom teeth. (Lucky!) The palmaris longus, a tendon in the forearm present in some but absent in others, once aided in climbing and gripping but is now functionally irrelevant. Research has shown that a small percentage of the population is even born without it—and not having the muscle doesn’t affect grip strength in any significant way. 

[ Related: Why do humans have toenails? Because we’re evolutionary ‘weirdos.’ ]

Since evolution is ongoing, could we be on the verge of shedding more parts as our diets, medical interventions, and technology advance? 

As is often the case with future-oriented scientific questions, the answer is that no one really knows.

“There’s no indication that we have any idea about what the future has in store for us because the pace at which technology is changing and that might be affecting evolution is so great, and it’s a lot less predictable than one would think,” explained Ravosa. 

“We’re learning about vestigial organs largely by looking backward,” he added. “We’ll have to just sit around and see because we can’t predict the future.” 

This story is part of Popular Science’s Ask Us Anything series, where we answer your most outlandish, mind-burning questions, from the ordinary to the off-the-wall. Have something you’ve always wanted to know? Ask us.

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