In 1999, a new disease came to light–a brutal fever that sometimes led to fatal encephalitis. After the first outbreak in Malaysia, scientists traced the cause of the disease to a virus called Nipah. Although it was new to medicine, Nipah virus didn’t come out of thin air. It had replicated for generations inside Indian Flying Foxes, a common species of fruit bat in southeast Asia. The virus spilled over into humans, thanks to the fondness both species have for date palms. Now Nipah virus can spread from person to person.

This scenario sounds like it came from the pitch meeting for last year’s creepfest Contagion. Unfortunately, it’s all quite well documented. So is the emergence of many other viral diseases. (Check out David Quammen’s book Spillover for a sweeping view of these new diseases.)

In my Matter column this week in the New York Times, I take a look at a new way to battle these emerging diseases: by figuring out how many viruses there are in mammals that might spill over in the future. Scientists have taken the first step to such a virus catalog with a suitable species: the Indian Flying Fox. And unfortunately, it’s chockful of mammal viruses, most of which are new to science. Here’s the full story. (Also check out fellow Phenom Ed Yong’s report on the study fo The Scientist.)

A decade ago, I traveled to Princeton to spend some time with a young philosopher who had decided to start scanning people’s brains. I was working on a book about the history of neurology, called Soul Made Flesh, and I was fascinated by how the study of the brain had emerged from a scientific attempt to save souls. I wanted to end the book with a look at how scientists study the brain 350 years later, and during my research I discovered the work of Joshua Greene. He was taking the arguments that moral philosophers had developed over many years and testing them out on flesh-and-blood brains, monitoring neural activity as people worked through moral problems.

In addition to putting Greene into my book, I ended up writing a profile of him called “Whose Life Would You Save?” for Discover (which you can also read in a collection of my articles available at Byliner). Here’s how it starts…

Dinner with a philosopher is never just dinner, even when it’s at an obscure Indian restaurant on a quiet side street in Princeton with a 30-year-old postdoctoral researcher. Joshua Greene is a man who spends his days thinking about right and wrong and how we separate the two. He has a particular fondness for moral paradoxes, which he collects the way some people collect snow globes.

“Let’s say you’re walking by a pond and there’s a drowning baby, ” Greene says, over chicken tikka masala. “If you said, ‘I’ve just paid $200 for these shoes and the water would ruin them, so I won’t save the baby,’ you’d be an awful, horrible person. But there are millions of children around the world in the same situation, where just a little money for medicine or food could save their lives. And yet we don’t consider ourselves monsters for having this dinner rather than giving the money to Oxfam. Why is that?”

Philosophers pose this sort of puzzle over dinner every day. What’s unusual here is what Greene does next to sort out the conundrum. He leaves the restaurant, walks down Nassau Street to the building that houses Princeton University’s psychology department, and says hello to graduate student volunteer Nishant Patel. (Greene’s volunteers take part in his study anonymously; Patel is not his real name.) They walk downstairs to the basement, where Patel dumps his keys and wallet and shoes in a basket. Greene waves an airport metal-detector paddle up and down Patel’s legs, then guides him into an adjoining room dominated by a magnetic resonance imaging scanner. The student lies down on a slab, and Greene closes a cagelike device over his head. Pressing a button, Greene maneuvers Patel’s head into a massive doughnut-shaped magnet.

Greene headed off to Harvard a couple years later, where he’s now an associate professor of psychology. Over the years other scientists have also taken up the study of moral neuroscience, but Greene still stands out among them thanks to the philosophical rigor with which he thinks about the nature of morality. Over the years, he’s expanded his research from the basic biology underpinning morality to the different ways that it gets played out in human societies–and how, paradoxically, different forms of moralities bring people into conflict.

So I’m very curious now to check out a book he’s written about his research and ideas, called Moral Tribes, coming out next month. The Edge has a sneak preview of Greene’s ideas in the form of a video talk by Greene and a transcript. Check it out.

I just went back and listened to this interview I did on “Radiolab” with Robert Krulwich a couple years ago. It’s about the life within us. I led Robert on a quick tour through our gut, stopping to describe a few of the many species that lurk inside our bodies.

It all still holds true, I think–except for one thing I say at 3:02.

It’s at that point that I say that in the womb, we’re sterile. Only as we’re being born, I inform Robert, do we start to getting inoculated with microbes.

I thought I was right at the time. Scientist after scientist told me that. I read it in scientific reviews.

But now a number of scientists are having some serious doubts about sterile fetuses. In fact, mothers might be seeding their babies in the womb, bestowing on them the friends that will help them get through pregnancy safely and get off to a good start in life.

If Krulwich ever asks me again about the microbiome, I’ve got something to add.

This fascinating new prospect is the subject of my new “Matter” column today in the New York Times. Check it out. (Here’s an alternate link if the recent NYT hacking woes are still causing grief.)