We take it for granted that human bodies are mostly the same. But two recent news stories show that we don’t always develop in expected ways. In Bangladesh, a woman had a baby; then, 26 days later, she had twins. Turns out, she had two uteruses! And in Portland, Ore., another woman had all her organs backwards, on the opposite side of her body than where they’d be typically.

 

“We have a genetic blueprint for how we form, left to right, front to back, with everything in the right place,” says Michael Tsang. He is a University of Pittsburgh biologist who researches how bodies develop. “All our dimensions are specified very early on in the embryo,” when we are tiny specks in our mothers’ wombs.

 

Usually, a uterus is formed from two tubes that fuse together. But the Bangladeshi woman had a rare hiccup in her DNA (a mutation), so the fusion didn’t happen. That caused the two uteruses. 

 

And usually, our heart fits into a cavity on the left side of the chest. Our other organs pack into our bodies in their particular spots, too. The woman from Oregon had a one-in-a-million condition where left-right patterning is completely reversed. 

 

Luckily, “the complete reversal meant her organs still had space to form and function properly,” says Tsang. So perfectly properly, in fact, that her condition wasn’t discovered until medical students examined her body after she died at the age of 99!