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.)

Despite living in the carotid artery of Northeast traffic, I still share my property with a particularly prehistoric kind of wildlife. Each spring, monstrous snapping turtles emerge from the salt marshes and rip up our garden to lay eggs. Then in late summer the baby turtles hatch and crawl out of the mulch to head for the water again.

This was the scene outside our front door (I highly recommend setting the movie to full-screen). The baby snapping turtles, each the size of a jumbo chicken egg, crawled to the light one by one and clambered onto our stone steps. As this video demonstrates, baby snapping turtles deal with these unexpected situations without much hesitation. They climb to the edge of their world and keep going.

Luciano-tattoo-crop

Luciano Valenzuela writes,

I got this tattoo after finishing my PhD at the University of Utah working on the ecology of southern right whales that visit the coast of Peninsula Valdes (northern Patagonia), Argentina. The tattoo depicts a Surface Active Group (SAG). SAGs are usually thought as mating groups or whales in apparent courtship behavior. At Peninsula Valdes the SAGs that we normally see are much smaller with only a handful of whales, but the energy displayed by these animals is just as impressive as the large groups seen in other populations or species. The tattoo is actually a modification of Figure 1 in Kraus and Hatch (2001) showing a SAG of North Atlantic right whales. I think once you see them from close proximity you can appreciate how powerful and gentle at the same time these huge animals can be.

Kraus-and-Hatch-cropHere’s the original figure.

You can see the rest of the Science Tattoo Emporium here or in my book, Science Ink: Tattoos of the Science Obsessed.

Here are a few numbers about DNA–some big ones, and then some very small ones.

The human genome contains about 3.2 billion base pairs. Last year, scientists at the University of Leceister printed the sequence out in 130 massive reference-book-sized volumes for a museum exhibit. From start to finish, they would take nearly a century to read.

A typical gene is made up of a few thousand bases. The human genome contains about 21,000 genes that encode proteins. There are other genes in the human genome that encode molecules known as RNA, but how many of those RNA molecules actually do anything useful in the cell is a matter of intense debate. A lot of the human genome is made of neither protein- or RNA-coding genes. Much (maybe most) of it is made up of dead genes and parasite-like stretches of DNA that do little more than making copies of themselves.

As I wrote recently in the New York Times, 3.2 billion base pairs and 21,000 genes are not essential requirements for something to stay alive. E. coli is doing very well, thank you, with a genome about 4.6 million base pairs. That’s .14% the size of our genome. Depending on the strain, the microbe has around 4100 protein-genes. That’s about a fifth the number of protein-coding genes that we carry. The high ratio of genes to genome size in E. coli is the result of its stripped-down, efficient genetics. Mutations that chop out non-functional DNA spread a lot faster in microbes than in animals.

E. coli, in turn, has proven to be positively gargantuan, genetically speaking, compared to some other species. As scientists explore more of the microbial world, they find species with smaller genomes. In my column for the Times, I wrote about the record-holding tiny genome, belonging to a microbe called Tremblaya. Its genome is a mere 139,000 base pairs. That’s .004% the size of our genome. You could print the entire sequence in a single slim paperback you could slip in your pocket. And in that sleek genome are just 120 protein-coding genes–.6% of our own collection of protein-coding genes.

Whenever I report on such record-breakers, I try to stress that they are only breaking records at that moment. Tremblaya has the smallest genome known. Or, I should now say, it had the smallest genome known last month.

This month in the journal Genome Biology and Evolution, Gordon Bennett and Nancy Moran describe a new record holder, called Nasuia deltocephalinicola. It has a genome of just 112,000 base pairs. Imagine taking that slim novella and ripping off the last chapter. Ironically, Nasuia packs in more genes into its DNA than Tremblaya–137 protein-coding genes, Bennett and Moran estimate.

What’s really striking about all these current and former record-holders for small genomes is that they all live in a single exotic ecological niche. Without exception, they can be found inside plant-feeding insects. Tremblaya lives in mealy bugs, for example, while Nasuia lives in a leafhopper (Macrosteles quadrilineatus).

Inside those hosts, these microbes carry out chemical reactions on the food that the insects eat. The insects feed on sap and other fluids from plants, which contains few nutrients. But the bacteria can use the compounds floating in the fluid to build amino acids, which the insects can then assemble into proteins.

Leafhoppers, cicadas, sharpshooters, and other related insect species carry related versions of the same stripped-down bacteria. By drawing their evolutionary trees, Bennett and Moran have found that the insects got into a symbiotic relationship with the microbes over 260 million years ago. I’ve reproduced their tree below for those who want some gory details. The blue lines show Nasuia and related lineages of microbes. The insects also acquired another species of bacteria, known as Sulcia. Together, these two microbes split the work for millions of years. (In some insects, fungi also jumped into the mix.)

The ancestors of Nasuia started out as free-living microbes that had genomes on par with E. coli. But once they got inside a host, they were able to lose DNA without paying a price. The insects gave them a stable home, building special organs to shelter them, and they even pass down the bacteria to their offspring. The bacteria cast aside many genes that might otherwise seem essential, such as a number of genes involved in generating energy. All they needed to do was continue to provide a service, by synthesizing some amino acids.

Nasuia holds the record now, but probably not for long. There are many other species of insects left to investigate. Moran had John McCutcheon of the University of Montana have done some back-of-the-envelope calculations to figure out how much smaller the genomes of those symbionts can get. All known insect symbionts share 82 genes in common. It’s possible those genes are absolutely required to survive as a symbiont. But a symbiont also needs to provide a benefit to its host, or its host will likely get rid of it. It takes at least 11 genes to synthesize a single amino acid. Those 93 genes, McCutcheon and Moran estimate, could fit in a genome as small as 70,000 base pairs.

It’s funny that these bacteria allow us to probe one of the most basic questions about life: how simple life can get and yet still qualify as being alive? While those who make fun of science for a living may consider such research a waste of time, studying these stripped-down organisms is also about as practical as science can get. The leafhoppers that house Nasuia, for example, are a nightmare for farmers, causing damage to a wide range of vegetables by spreading fungi and bacteria. Yet they would be helpless if not for their exquisitely simple lodgers. If we can understand how they survive with such tiny genomes, we may be able to stop them from enabling their hosts.

From Bennett and Moran 2013
From Bennett and Moran 2013