Since the mid-1900s, medical researchers have dreamed of fixing genetic disorders by supplying people with working versions of genes. By the late 1990s, that dream–known as gene therapy–seemed very, very close. Scientists were developing engineered viruses that would infect patients with DNA that would allow their bodies to make the proteins they needed to survive.

But then, in 1999, a young man who had volunteered for a trial died. The whole field of gene therapy went into a tailspin. Only in recent years has it recovered.

I’ve written a story for Wired about that turnaround, focusing on the career of the scientist who oversaw that fateful 1999 trial, James Wilson. For the past fourteen years Wilson been hunting for better viruses for gene therapy, and his viruses are now involved in some of the most promising research for treating diseases ranging from hemophilia to blindness. To find out more about Wilson and gene therapy, check out “The Fall and Rise of Gene Therapy.”

Let me just say at the outset that this post is about the baculum. Some of you may not want to read about the bone found in the penises of many mammal species. I want to give you a chance to head off for tamer blogs. But you might want to stick around. There’s some real science below–and some evolution in action.

Last week in the New York Times I wrote about the evolution of monogamy (here and here). The occasion for the articles were two new studies in which scientists analyzed hundreds or thousands of species of mammals, tracing the evolution of monogamy and other social arrangements. This big-picture approach to evolution can yield some important insights, but the finer details are hard to make out.

If you look at us humans (monogamy, polygamy, and assorted other stuff) versus chimpanzees (monogamy is for losers!), you’re only looking at the tips of two deep branches. Chimpanzees may be our closest living relatives, but our common ancestor with them lived about seven million years ago. After the two lineages split from that ancestor, they’ve been evolving in different directions ever since. We can make some inferences about what that evolution was like based on ourselves, chimpanzees, and other living mammal species. But this kind of research doesn’t give us a visceral sense of how the sexual habits of mammals evolve from generation to generation.

That’s why it was so interesting to come across a new study from Leigh W. Simmons and Renée Firman at the University of Western Australia. They’ve been able to observe sexual evolution of mammals unfold in their laboratory. Last week’s studies were like a satellite view of the continents. Here, we’re down on the ground.

How males and females live with one another depends on the conditions in which their species lives. If a single male can mate with lots of females, for example, he will end up with a lot of offspring. But if the females are spread out too far, he may not be able to guard them all from other males who want to mate with them too. In such cases, natural selection may favor males that prefer to stick with just one female.

In species where males compete with each other a lot for females, evolution may produce new pieces of anatomy. Some males evolve extravagant horns to fight off rivals. Even their genital anatomy can change. This is likely to happen when females mate with many males. The males fight against each other even during sex. Some male insects, for example, using spiny genitals to scrub out their competitors’ sperm.

Evolutionary biologists hypothesized that these extravagant sexual organs were the result of an evolutionary race between males. They found support for this idea when they compared individual males to each other. It turned out that the males that had the most offspring tended to have the spiniest penises.

More recently, researchers have started to watch these organs evolve. In 2011, for example, Swiss scientists reported a study they carried out on seed beetles, which have spines on their genitals for scrubbing away rival sperm.

The Swiss scientists isolated each male with just one female. In that arrangement, the males had no competition for mates. The researchers then let the beetles mate for 21 generations. The spines on the male’s genitals got measurably smaller. That’s just what scientists had predicted based on evolutionary theory. Without any competition from other males, there was no advantage to spiny penises.

Simmons has documented a lot of the evidence for this evolution of male genitals in insects, and now he and Firman have turned their attention to mammals. To be more precise, they’ve turned their attention to the baculum–a bone that they call “one of the most puzzling enigmas of mammal morphology.”

The baculum is long in some species and stubby in others; it can be straight or hooked, barbed or shaped like Neptune’s trident. In a few species, like our own, it’s just missing altogether.

Scientists have developed several possible explanations for its existence. Some have suggested that by making the penis rigid, the baculum lets a male deliver more sperm into a female. Those extra sperm may outnumber those of rival males. Others have suggested that the baculum helps the sperm travel further towards an egg. Still others have proposed that it stimulates the female, triggering ovulation.

All three hypotheses have something in common: the baculum evolves thank to its ability to translate mating into fathering. In June, some British researchers published a study that supported that idea. They studied house mice, a species in which females mate with many males each time they’re ovulating. The scientists found that male mice with a wider baculum had more mouse pups than other males.

Simmons and Firman took this research to the next logical step. They reasoned that this difference between male mice should drive the evolution of the baculum. To find out, they ran an experiment similar to the one run by the Swiss scientists. They created two groups of mice: promiscuous maters and monogamous maters.

The promiscuous females got to mate with three males in each cycle. The monogamous ones only got to mate with one. They bred the mice for 27 generations and then took a look at their bacula. As with the seed beetles, the baculum evolved. It became thicker in the promiscuous group and thinner in the monogamous one. For the first time, scientists had observed the baculum evolving.

The experiment still doesn’t solve the mystery of what the baculum for, but Simmons and Firman do have an idea about that–at least for mice. They think that the baculum helps male mice stimulate the female reproductive tract. That stimulation may make it more likely that the male fertilizes the female’s eggs, or raises the odds that a fertilized egg successfully implants itself in her uterus.

If the baculum is indeed driven by sexual selection in mammals, the question naturally arises: where’s ours? “Why human males lack a baculum remains enigmatic,” Paula Stackley, a biologist at the University of Liverpool, wrote last December in Current Biology.

Among primates, monogamous species tend to have much smaller bacula than species where males compete for mating. So it wouldn’t be crazy to assume that the shift towards monogamy in our ancestors made the human baculum disappear altogether (except for a very, very few scary cases).

Things aren’s so simple as all that, however. Chimpanzees, our closest relatives, are far from monogamous. You’d think they had a huge baculum, but it’s only about the size of a grain of rice–about five times smaller than a baboon’s baculum. In fact, all the great apes have tiny bacula. For some mysterious reason, this mysterious bone has been vanishing in our ancestors for some ten million years or more. While the bacula can evolve in a matter of weeks in a scientific experiment, its evolution can stretch out across deep time, as well.

In the New York Times, I report on a pretty remarkable pair of events that have just taken place in the world of genome science–and both having to do with Henrietta Lacks. Cells taken from Lacks’s body in 1951–now known as HeLa cells–have revolutionized cell biology. But neither she nor her family had any say about their use. This woeful situation came to a head recently when it turned out that scientists had sequenced the genome of HeLa cells without any contact with the family. Now the NIH and the Lacks family have worked out an arrangement for controlling access to the genetic data, and today scientists unveiled a high-quality sequence of the genome full of interesting insights into cell biology. But, as I explain in my article, the ethics of genome sequencing are far from settled. Check it out.

In my feature on de-extinction  in the April issue of National Geographic, I tried to capture the debate in the scientific community about whether we should try to bring vanished species back to Earth. It’s been gratifying to see a spirited, sustained conversation going on ever since. The prospect of de-extinction raises important issues that have to be grappled with. Is it better to spend money trying to revive a mammoth or to secure a vast swath of rain forest? Are objections to de-extinction driven by a flawed notion of what’s natural? Would it make more sense to use the emerging tools of biotechnology to prevent endangered species from disappearing, rather than attempting to bring back the extinct ones?

But I’m frustrated by a column by George Monbiot that just appeared in the Guardian, entitled, “Resurrecting woolly mammoths is exciting but it’s a fantasy.” Monbiot singles out National Geographic for scoffing, declaring,

the double-page painting published by National Geographic in April, depicting tourists in safari vehicles photographing a herd of Siberian woolly mammoths roaming the Siberian steppes, is pure fantasy: the animals it shows are mumbo-jumbos.

(We Yanks useÂmumbo-jumbo to refer to gibberish, but after reading Monbiot’s piece, I did some dictionary-ing and discovered that the Brits use it to refer to a meaningless idol.)

It’s not Monbiot’s position that bothers me. In my article, I wrote about harsh critics of de-extinction as well as advocates. It’s the way he frames his argument at the outset:

There is an obvious, fatal but widely overlooked problem with de-extinction.

Wow! Both obvious and fatal. Not just obvious and fatal, but also widely overlooked! What could this problem be, a problem that conservation biologists and molecular biologists who are exploring de-extinction have somehow failed to notice, a problem that Monbiot is here–at last–to unveil?

This:

The scarcely credible task of resurrection has to be conducted not once but hundreds of times, in each case using material from a different, implausibly well-preserved specimen of the extinct beast. Otherwise the resulting population will not be genetically viable.

Really? That’s it?

I felt a distinct lack of surprise at Monbiot’s big reveal. That’s because I had addressed this very issue in my own article four months ago, noting that reviving a single animal is not the same as bringing back an entire species.

But I didn’t go so far as saying that this was a “fatal” problem, because I discussed the issue with the scientists I interviewed. You’d think from reading Monbiot’s column that these scientists hadn’t the faintest clue of this problem. I picture them sitting in front of their screens, reading Monbiot’s revelations, and smacking their foreheads all at once, roaring, “Of course! How stupid of us!”

You’d have to be a truly stupid scientist to not be aware that the long-term viability of a species depends on a genetically viable population. If a small population is only made up of nearly genetically identical individuals, they run the risk of inbreeding, which can make them unhealthy, vulnerable to diseases, and even infertile.

The scientists exploring de-extinction are aware of this challenge, and they have actually given this matter some thought. They have ideas about how to deal with it. There’s a good debate to be had over whether those ideas could really work in practice, but Monbiot shows no signs of being familiar with them.

Monbiot is arguing that de-extinction cannot work, period, because it would require discovering an intact cell for every individual animal or plant scientists wanted to produce. There are several reasons why this is wrong. For one thing, scientists already have the technology required to engineer diversity into a species.

Museums have hundreds of preserved passenger pigeons, for example, and those birds are not clones of one another. By sequencing the DNA from a number of passenger pigeons, scientists could learn about the genetic diversity of the species. Based on the experiments scientists are already doing on animal cells, it’s conceivable that researchers could synthesize gene variants and plug them into the genome of an extinct animal. By engineering the genomes of the pigeons, scientists would create a flock containing some of the genetic viability that existed before the species became extinct.

If scientists can produce a few dozen genetically diverse passenger pigeons–or gastric brooding frogs, or thylacines, for that matter–it’s an open question whether those creatures could seed a sustainable population. Monbiot seems to be down on the whole idea of restoring small populations. He points to European bison, which have gone from 54 animals to 3,000, but which still have trouble with inbreeding.

But there are more heartening stories, too. Northern elephant seals were hunted down to the same population level, and today their numbers are up to 160,000.

Now we’ve drifted off the original course, though. We are no longer talking about de-extinction, but about the broader question of captive breeding. There’s another good debate to be had about whether to save the black-footed ferret and the California condor. But I guess it’s not as fun as shouting mumbo-jumbo!

Adam Platz writes,

“The equation is called the Friedmann equation and, simply put, governs the expansion of space in a homogenous universe such as our own. In the 1920s Alexander Friedmann, a Russian astrophysicist, sought to unite Einstein’s recently conceived theory of general relativity with a general model for our universe’s behavior. The Freidmann equation resulted. From its basic form, one can derive the density of the universe at a given time, the pressure, the mass, the age of the universe, and finally the rate of expansion of the universe (found in a term known as the Hubble constant). In 2008 during my senior year at Dartmouth, my senior seminar in astrophysics focused in part on this equation. I always found the equation to be elegant and beautiful. My own little god equation. Explaining where we came from and what we are made of. That year I thought up the idea of the tattoo and decided that if in 5 years I was still interested in the ink, I would get it. And so I did in 2013.”

The Wikipedia page for the Friedmann equation is suitably intense. The American Institute of Physics has a more accessible history of Friedmann and other early twentieth-century cosmologists.

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