Piece by piece, Jeremy DeSilva of Boston University meticulously pulled foot fossils and casts out of small baggies and placed them on tables in his lab. In an interview with AAAS’ Carla Schaffer, he explained that their remarkable diversity shows that bipedalism evolved in a variety of different ways. There has been no single mode of upright walking among our ancestors. 

As critical as they are for moving around, human feet are far from perfect. For one thing, they are prone to flat-footedness, ankle sprains and other painful conditions, DeSilva said at the AAAS Annual Meeting. And, their design is inefficient. Each human foot is made up of 26 individual bones, a complicated structure compared to the single blades in the prosthetic legs of some paralympic runners.

"If you were going to start from scratch and have a structure that was going to push off the ground in the way that we require our foot to do, you wouldn't have 52 moving objects in that structure," said DeSilva. "The reason that the human foot is structured the way it is, is because we evolved from a foot that was a mobile grasping appendage." 

Feet aren’t the only human body part that the evolution of bipedalism has rendered imperfect. Joining DeSilva in a symposium about “the scars of evolution,” Bruce Latimer of Case Western Reserve University described the problematic evolution of the human spine.

Many common, modern-day back problems are rooted in the fact that we have evolved from an animal whose back was horizontal. Turn that structure upright, and “now you’re asking for trouble,” Latimer said.

Further complicating matters, the spine also developed into an S-shaped structure as humans shifted from quadrupedal to bipedal walking.

Latimer asked his audience to imagine trying to stack 24 cups and saucers and place a book on the top, to build a structure akin to the human spine and skull. While this might be hypothetically doable, adding curves to the structure would be impossible. 

“I could give you all the duct tape in the world and you couldn’t possibly do it,” Latimer joked.

Upright posture had myriad benefits for our ancestors and was a fundamental milestone in human evolution. These changes had tradeoffs, though. Common ailments such as spontaneously fracturing vertebrae and herniated disks are distinctly human ailments that other species generally don’t suffer from, Latimer said.