Patents for drugs, especially lifesaving drugs, are controversial. Patenting incentivizes medical innovation but also keeps medication expensive. Take insulin, a medication first patented in 1923 and still patented, with some revisions, today. It keeps as many as 40 million people alive worldwide, and it's also alarmingly expensive. People have died (or sold all their earthly possessions ... twice) in their struggles to afford it. Its price almost doubled between 2012 and 2016, and it shows no signs of dropping.

In the context of this modern insulin crisis, Salk seems like an early visionary — a scientist who wanted his invention to maximize human welfare, not profit. His famous quote on patenting (or lack thereof) only adds to his image. On April 12, 1955, Edward R. Murrow, a TV journalist, asked Salk who owned the polio vaccine patent.

"Well, the people, I would say," Salk responded. "There is no patent. Could you patent the sun?"

This sound byte has been quoted by everyone from Michael Moore to the Wall Street Journal, often as part of a moral critique of our current patent system. The system certainly merits critique, but Salk may not be the critic people are looking for. Altruism probably wasn't the real reason he never patented his vaccine.

It's not that Salk wasn't altruistic. He seems like a lovely man! The thing is, "his" invention wasn't completely his. He discovered it with funding from the National Foundation for Infantile Paralysis, now the March of Dimes. (Infantile paralysis was an early term for polio.) The non-profit foundation had a stake in Salk's discovery, too, and they looked into patenting it.

They found that it wasn't novel enough to count as a new invention, though. So really, Salk's vaccine was never patented because it was never eligible for a patent, according to Jane S. Smith, who sifted through the March of Dimes' archives for her book "Patenting the Sun."

Even if he had patented the vaccine, though, Salk could have done it for altruistic reasons. Patenting something isn't an inherently money-hungry move. To understand why, let's pause for a second and explain what a patent is, anyway.

Basically, a patent is a way for the government to grant a person property rights to their invention. You own whatever you invented, typically for a term of 20 years, and you can "exclude others from making, using, offering for sale, selling or importing the invention," according to the United States Patent and Trademark Office.

The government won't enforce your patent, though. You have to track down and sue anyone who makes or uses your patented invention, and on your own dime. This means even after you patent an invention, you can selectively prosecute people who make knock-offs. As Slate notes, you could patent something and only prosecute shoddy or dangerous knock-offs that didn't work as promised. Patents don't automatically shut down competition; patent-holders choose to shut down competition.

Salk probably would never have done this, even if he got a patent. As a thought experiment, though, let's imagine he got a polio vaccine patent and enforced it religiously. By one estimate, he would have raked in an epic $7 billion. That's a lot of money to walk away from — and some people still argue that Salk did just that, because he loved humankind so much.

It's unlikely — but hey, it's more possible than patenting the sun.

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Read the whole story in "Patenting the Sun" by Jane S. Smith. We handpick reading recommendations we think you may like. If you choose to make a purchase, Curiosity will get a share of the sale.