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What Do Snails Think About When Having Sex?

It starts with a light, soft touch, one tentacle gently reaching out, hesitant, hopeful, hanging lightly in the air. There’s a pause. Skin touches skin. One softly strokes the other and slides closer, and then, carefully, they wrap themselves together, stroking, probing, entwining. They glisten as they move, and because they are snails, everything happens very slowly. The rubbing, the rapture, the intensity of it all—snail sex is extraordinarily lovely to look at. (If you aren’t at your office desk or on a train where people can see your screen, I’ve got one about a garden snail named Chip who’s trying to lose his virginity, or take a quick peek—30 seconds will do—of this coupling in a garden.)

Lovely but So Dangerous

Garden snails make love in the open—on garden patios, in clearings on the forest floor—and they do it luxuriantly for one, two, three hours at a time, under the sky, where they can be seen by jays, orioles, frogs, snakes, shrews, mice, beetles, and other animals that might want to eat them. Snails can’t make quick getaways, so exposing themselves like this is dangerous, crazily dangerous. What’s going on? What’s making them so impervious, so deeply preoccupied with each other? Here’s one answer: Snail sex is very complicated. Snails have a lot to think about when they make love—because they’re hermaphrodites.

Unlike you, garden snails can produce sperm like males and carry eggs like females at the same time.

Drawing of a proud snail, with its hands on its shell hips
Drawing by Robert Krulwich
Drawing by Robert Krulwich

Which is both an advantage and a problem. Professor David George Haskell, a Tennessee biologist, once squatted down on a patch of forest floor and watched what you just saw in that video—a snail couple going at it—except with a magnifying glass and only a few feet from the action. What he noticed was their mood. Hot as it was, he writes in his book The Forest Unseen, “Their extended courtship and copulation is choreographed like cautious diplomacy.” Snails don’t pounce, they circle. They “slowly edge into position, always ready to pull back or realign.” Their sex is tense, charged, on, off, then on again, “a prenuptial conference over the terms of the union.” What are they negotiating about?

In most animals, snails included, sperm is plentiful, cheap to produce, and fun to unload. So one presumes that both copulating snails are eager to get that part done.

A drawing of two snails, both looking at each other with thought bubble exclamation points above their heads
Drawing by Robert Krulwich
Drawing by Robert Krulwich

Eggs, on the other hand, are limited and hard to produce—and therefore precious. You don’t let just anybody fertilize your egg sack. So, in Haskell’s imagination, if one of these snails picks up “a whiff of disease” on the other, it may be happy to poke but is not at all interested in being poked. No one wants its precious eggs fertilized by a sick dad, so the receiving snail might lock its partner out of its opening while also trying to penetrate it. This could produce feelings of frustration, confusion, and even unfairness in the other.

A drawing of two snails looking at each other, one with an exclamation mark thought bubble and one with an X through an exclamation mark thought bubble
Drawing by Robert Krulwich
Drawing by Robert Krulwich

“In hermaphrodites,” writes Haskell, “mating becomes fraught, with each individual being cautious about receiving sperm while simultaneously trying to inseminate its partner.” Sexually speaking, two snails with four minds—a foursome in a twosome—makes for complex fornication. That’s why snails are always on tiptoe, Haskell thought as he watched them on the forest floor: They have so much to figure out.

Picture of a brown snail peering its head around to the side
Photograph by © Tetra Images / Alamy
Photograph by © Tetra Images / Alamy

Hermaphrodite Abundance

So why be a hermaphrodite? Are there a lot of them? Well, here’s a surprise: They’re everywhere.

Eighty percent of the plant kingdom produces both seeds (pollen) and eggs (ovules) and can give or receive, making them hermaphroditic. They’ve learned that when the weather gets wet or cold, bees can’t be depended upon to buzz by and pollinate, so they have a we-can-do-this-ourselves backup plan.

Animals, generally speaking, are sexual, divided into male and female. But, writes Stanford biology professor Joan Roughgarden in her book The Genial Gene, if you subtract insects, which make up more than 75 percent of the animal kingdom and are not hermaphrodites, we are left, she calculates, “ … with a figure of 1/3 hermaphrodite species among all animal species.” That’s a hunk of hermaphrodites.

So Who’s a Hermaphrodite?

They’re not animals we pay much attention to (flukes, flatworms, killifish, parrot fish, moray eels, barnacles, slugs, earthworms, and tapeworms, among many others), but they are switch-hitters: They can either give or receive or switch sides during their lifetime. “All in all,” writes Roughgarden, “across all the plants and animals combined, the number of species that are hermaphroditic is more-or-less tied with the number who has separate males and females, and neither arrangement of sexual packaging can be viewed as the ‘norm.’”

Anyone who thinks that male/female is nature’s preference isn’t looking at nature, says Roughgarden. And she goes further.

Adam and Eve or AdamEve?

She wonders, Which came first, the hermaphrodite or the male/female? We have lived so long with the Adam and Eve story—Adam first, Adam alone, Adam seeking a mate, God providing Eve—that the question seems almost silly: Of course complex animals started with males and females.

Painting of Adam and Eve in the Garden of Eden, Eve is offering Adam an apple
Adam and Eve, 1537 (panel), Cranach, Lucas, the Elder (1472-1553) / Kunsthistorisches Museum, Vienna, Austria / Bridgeman Images
Adam and Eve, 1537 (panel), Cranach, Lucas, the Elder (1472-1553) / Kunsthistorisches Museum, Vienna, Austria / Bridgeman Images

But Roughgarden wonders if animals started as hermaphrodites …

Composite of Adam and Eve painting, creating one person
Composite image of Adam and Eve created by Becky Harlan from original paintings by Lucas Cranach © [Royal Museums of Fine Arts of Belgium, Brussels / photo : Guy Cussac, Brussels]
Composite image of Adam and Eve created by Becky Harlan from original paintings by Lucas Cranach © [Royal Museums of Fine Arts of Belgium, Brussels / photo : Guy Cussac, Brussels]

… and then “hermaphrodite bodies disarticulate[d] into separate male and female bodies?” How would that have happened? Roughgarden cites a paper she did with her colleague Priya Iyer.

They propose that maybe the earliest animals started out as both sperm and egg carriers, and a subgroup got especially good at inserting their penises into enclosures, aiming, and directing the sperm to its target (the authors call it “home delivery”). They did this so effectively that they needed fewer and fewer eggs and essentially became sperm sharpshooters or, as we call them now, “males.”

That development gave others a chance to give up sperm altogether to concentrate on chambering their eggs in nurturing nooks, thereby becoming “females,” and so more and more animals found it advantageous to be gendered.

Ayer and Roughgarden aren’t sure this happened. They say that, on available evidence, the story can go “in either direction.”

The alternate view is almost the story you know. It’s Adam and Eve, with a twist: In the beginning, early animals were gendered—except when it was inconvenient.

If, for example, you imagine a group of, well, let’s make them snails …

Drawing of a group of snails standing in front of a volcano erupting
Drawing by Robert Krulwich
Drawing by Robert Krulwich

… and something awful happens—there’s a terrible disease, an ice age, a new ferocious predator, or maybe a volcanic eruption…..

Drawing of a snail all alone after the fallout of a volcanic eruption, standing in front of a volcano puffing smoke
Drawing by Robert Krulwich
Drawing by Robert Krulwich

… so that we’re left looking at a lone individual, all by itself, looking around for a reproductive opportunity, crawling across the landscape, hoping to bump into somebody, anybody, to reproduce with, and after a long, long, anxious period, it finally sees what it’s been looking for. It crawls closer, closer, the excitement building.

Drawing of a snail in a vast and sunny landscape seeing another tiny snail in the distance
Drawing by Robert Krulwich
Drawing by Robert Krulwich

But as it gets within wooing range, it suddenly sees that—oh, no—it’s the same gender!

A drawing of two snails with moustaches
Drawing by Robert Krulwich
Drawing by Robert Krulwich

No possibility of babymaking here. And this happens half of the time. (Statistically, that’s the likelihood.) Now instead of being your friend, male/femaleness is your enemy. What wouldn’t you give for a hermaphrodite, a he/she snail that could, in a pinch, be whatever sex you need it to be. With a hermaphrodite, you can (again statistically) always make a baby. What a relief. So maybe that’s what happened. Gender difference disappears when gender no longer helps produce more babies (and when you don’t have to stick around and be a parent).

Which is the true story? We don’t know. Maybe the only story is that nature is flexible. When gender is useful, you get genders. When not, you don’t. What we forget, being humans, is that there are so many ways to flirt, to combine, to make babies—and the world is full of wildly different ways to woo. Tony Hoagland knows this. He’s not a scientist but a poet who lives in New Mexico, and in his poem entitled “Romantic Moment,” he imagines a boy on a date who sits next to his girl imagining … How shall I put this? … how the Other Guys do it.

Romantic Moment by Tony Hoagland

After the nature documentary we walk down,
into the plaza of art galleries and high end clothing stores

where the mock orange is fragrant in the summer night
and the smooth adobe walls glow fleshlike in the dark.

It is just our second date, and we sit down on a rock,
holding hands, not looking at each other,

and if I were a bull penguin right now I would lean over
and vomit softly into the mouth of my beloved

and if I were a peacock I’d flex my gluteal muscles to
erect and spread the quills of my cinemax tail.

If she were a female walkingstick bug she might
insert her hypodermic proboscis delicately into my neck

and inject me with a rich hormonal sedative
before attaching her egg sac to my thoracic undercarriage,

and if I were a young chimpanzee I would break off a nearby tree limb
and smash all the windows in the plaza jewelry stores.

And if she was a Brazilian leopard frog she would wrap her impressive
tongue three times around my right thigh and

pummel me lightly against the surface of our pond
and I would know her feelings were sincere.

Instead we sit awhile in silence, until
she remarks that in the relative context of tortoises and iguanas,

human males seem to be actually rather expressive.
And I say that female crocodiles really don’t receive

enough credit for their gentleness.
Then she suggests that it is time for us to go

to get some ice cream cones and eat them.

Thanks to the poet Thomas Dooley for suggesting Tony Hoagland’s poem, and to Mr. Hoagland for giving us permission to print it here in full. Reading “Romantic Moment” I giggled a little to think of eating ice cream on a sugar cone as a homo sapien mating ritual—but thinking back, I think he’s onto something. The poem can be found in Tony Hoagland’s collection Hard Rain.

Book in Brief: Sex on Earth

Panda sex may have no greater defender than Jules Howard. I mean, presumably the pandas themselves would be more invested in this topic, but as far as I’m aware the bears aren’t usually invited to contribute commentary to the Guardian. They have to rely on Howard, and thankfully he’s been an able defender of the Ailuropoda melanoleuca love life.

More often than not, pandas are cast as cuddly evolutionary mistakes. They seem so backward. On the brink of extinction, some of the captive members of their species haven’t had the good graces to appreciate that we are trying to save them and therefore breed out of gratitude. What a blinkered view of life. Yes, male and female giant pandas have to find each other on just the right day to start the biological process of making an adorable little fuzzball. Yet, Howard points out, pandas were managing to do this for over two million years before our species started destroying their habitat and pushing them to oblivion. We’re the problem, not them, and this goes for zoos, too.

sex-on-earth-howardFor a long time, Howard points out, zookeepers took a very human-centric view of what would turn on a panda. (Panda porn? Seriously?) Given that we’ve all but abandoned our sense of smell to glean information about the world and each other, it took a while for specialists to realize that scent plays an important role in getting pandas ready to mate. The panda baby boom started once researchers finally realized this simple secret. Pandas aren’t evolutionary mishaps. We failed by not only cutting into their numbers, but in thinking that what titillates us would work for a species we last shared a common ancestor with over 66 million years ago. So begins Howard’s new book, Sex on Earth.

I must admit that upon receiving my review copy, my first thought was “Another book about animal sex?” We seem to be awash in literature on the subject, with Dr. Tatiana’s Sex Advice to All Creation still the pinnacle of procreation-focused popsci. Not to mention Isabella Rossellini’s Green Porno film series and live show.  But, as I quickly discovered, the crowded field is exactly what let Howard to write a book that stands out.

A great deal of writing – and film – on animal reproduction focuses on the superlative and hyperbolic. Who has the biggest penis? Who does the craziest mating dance? Are animals into BDSM? And on and on. But Howard argues that in focusing on the shocking and lewd, or what seems to be so through the humans lens, we’re actually missing what sex is all about. Worse still, we risk misunderstanding the very nature of sex by projecting our own desires and fears upon the staggering diversity of species that do it differently than we do.

Take the stickleback, for example. With bowerbirds and clownfish that change sex, the spiny little fish might seem a bland place to start. But through a visit to stickleback researcher Iain Barber’s lab, Howard explains how critical the fish has been to researchers wishing to parse the science of courtship and mating. For example, in a classic experiment, Niko Tinbergen showed that the red color of ready-to-mate males makes other males get all het up. Unfortunately, Howard points out, some male researchers were so taken with the vigorous, vibrant sticklebacks that they cast the female fish as dull, unimportant, and, as one zoologist wrote, “nothing but a roving gipsy.” It took until about 1990 for behaviorists to finally realize that females play an active role in choosing their mates and are not simply providers of eggs for stickleback seed. This historical perspective is what makes Sex on Earth different. As Howard weaves his tales of glow worms, hedgehogs, penguins, and more, he always keeps one eye on how humans have interpreted – and often misinterpreted – animals as reflections of ourselves.

Howard had hooked me with the sticklebacks and kept me reading on. Not only because of the clarity and humor in his prose, but for his careful consideration of how our species has warped the sex lives of other animals to reinforce our own preferences and taboos. Sex on Earth isn’t yet another catalog of what we might consider bizarre behavior. There are plenty of sticky details for those wishing to brush up their cocktail party chatter, sure, but Howard has done far better than that. Sex on Earth is a refreshingly self-aware exploration of the most intimate moments in nature and how the incredible variety of life has led us to frame our own thoughts about this near-ubiquitous biological drive. Not to mention that anyone who takes the time to set up a camera system by the side of a local pond to watch frogs make the next generation of little hoppers has not only my interest, but my admiration.

[Note: In an early chapter, Howard lists me along Darren Naish and David Hone as part of a gaggle of science writers who see dinosaur sex everywhere. Given that I’m due to give a talk on just that subject at London’s Natural History Museum next month, I can’t deny the charge.]

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Galápagos Redux: When Is It OK to Kill Goats?

Two weeks ago, I wrote about scientists who intentionally killed 80,000 feral goats on one of the islands in the Galápagos archipelago. The effort was in the name of biodiversity and conservation, sure, but was it right? The post spurred some fascinating questions and comments, particularly from Jason G. Goldman, who writes The Thoughtful Animal blog at the Scientific American Blog Network. I put Jason in touch with LWONian Michelle Nijhuis, who just wrote a feature for Scientific American about how conservationists decide which species to save. Below you’ll find their conversation.


Michelle: So what was your first reaction when you read Ginny’s post about the “Judas goat” and the extermination of feral goats in the Galápagos?

Jason: I thought it was actually a fairly clever method of addressing the problems caused by this invasive species. But what was in some ways more interesting to me was the comment made by one of Ginny’s co-travelers: “I really enjoyed the trip, but the one big downer for me was the extermination of the goats and the donkeys and their very anti-Darwin approach…” My assumption was that the phrase “anti-Darwin approach” was meant to suggest that this is a case of humans unfairly intervening in a situation, or “playing God.” But it strikes me as an extremely anthropocentric view of evolution and natural selection. Isn’t human behavior – whatever drives it – itself a selection pressure?

Michelle: That caught my attention, too. We as humans have applied selection pressure to the Galápagos by bringing the goats in, and now we’re applying – or releasing – a different sort of pressure by taking them away. I’m wondering about your perspective as a cognitive neuroscientist – when I read about an effort like this, my logical brain supports the effort to restore ecological processes and biodiversity – but my emotional reaction to the killing of so many goats is different than the reaction I’d have to killing a bunch of invasive cockroaches, or, say, getting rid of a flu virus. Do we feel more concerned about goats and other mammals partly because their brains are more similar to ours?

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Galápagos Monday: The People Problem

This is the last installment of my six-week series about the Galápagos Islands. To recap the first five posts: The Galápagos is an archipelago of 14 volcanic islands that scientists since Darwin have gone well out of their way to study. The islands are extremely inhospitable to life, and yet, over long periods of time, life has found a way. Humans are capable of disturbing that ecosystem, but equally capable of restoring it. It’s this last point, the People Problem, that most interests me.

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Galápagos Monday: When Conservation Means Killing

Judas knew what he was doing when he double-crossed his friend Jesus. “What will you give me if I betray him to you?” he asked the conspiring priests in the famous Bible story.

The story of the Judas Goat is more tragic. She had no idea that she was leading her friends to their deaths.

Her captors sterilized her first, then coated her with hormones so she reeked of fertility. Then they collared her with a radio-tracking device and cut her loose. Nearby male goats smelled her and sought her out. As soon as they found her, people swooped in and shot them. The hunters saved Judas, though, so they could repeat the set-up again and again.

It was all part of a six-year, $6 million project in which conservationists killed nearly 80,000 feral goats on Santiago Island in the Galápagos. Similar goat genocides had happened on 128 other islands, including nearby Pinta, but never on any as large as Santiago, which spans 144,470 acres. The goats, introduced by sailers hundreds of years earlier, were decimating all flavors of vegetation there, putting ground birds, giant tortoises and other endemic species in danger. So officials — conservationists from the Galápagos National Park and the Charles Darwin Foundation — decided the goats had to go.

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Galápagos Monday: The Sad Sex Life of Lonesome George

To walk from the Charles Darwin Research Station to the center of the town of Puerto Ayora, on Santa Cruz Island, simply follow the “T-Shirt Mile,” a sleepy stone road lined with dozens of souvenir shops. Mugs, onesies and shot glasses pay tribute the town’s only famous resident, a century-old giant tortoise named Lonesome George. My favorite shirt had a cartoon George in the center, with eyelash-batting lady tortoises on either side of him and one line at the bottom: Not So Lonesome George.

Before his unexpected death on June 24, George had certainly been with his share of females. But for the first 60-odd years of his life, he was the most awkward of virgins.

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Galápagos Monday: World Within Itself

This is the third installment of a six-week series about my recent trip to the Galápagos. You can read the first post, about tortoises and donkeys, here, and the second, about eerie mounds of black coral, here.

If you go to the Galápagos, and even if you go, as I did, in a herd of clumsy American tourists, you will at some point feel like a field biologist. Regulations dictate that you be accompanied by licensed guides, and ours reminded me of my favorite college professors: authoritative and rhetorical most of the time, with sudden bursts of passion when they get a whiff of their pet topic.

Within an hour of my arrival, one of the guides launched into the difference between the islands’ endemic, native and introduced species. Endemic species arrived naturally but struggled to survive in the strange environment. Over many generations, they gradually adapted and are now found, in their modified form, nowhere else on earth. Native species also came naturally, but didn’t struggle as much and didn’t need to change. So they’re found in the Galápagos as well as other places. Introduced species did not “naturally” arrive, but were brought in by people.

My guides seemed to be obsessed with these definitions, mentioning them dozens of times over the course of my eight-day visit. When discussing endemic species — such as the marine iguana or Galápagos tortoise — they beamed like proud parents. But introduced species were the shameful family secret. “What are those trees?” someone asked guide Jason while hiking in the highland swamps of Isabela. “Those are cedars,” he said with a long sigh and a sad shake of his head. “Introduced.”

I rolled my eyes. I understand the concept, professor, really I do, now can we please move on? But, like most of the other times I’ve been annoyed with a good teacher, I was wrong. Several weeks and a lot of reading later, I’m finally beginning to get it. If you understand endemism, you understand the value of the Galápagos.

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Galápagos Monday: Southern Inhospitality

This is the second installment of a six-week series about my recent trip to the Galápagos. You can read my first post, about tortoises and donkeys, here.

At dawn on June 6, more than 30 years after Lynn was chasing tortoises at the top of Alcedo, our boat anchored near the volcano’s base in Urbina Bay. By 8 a.m., I was fully breakfasted and eager to begin the scheduled 2-mile hike, on which we were likely to see giant tortoises and land iguanas.

My mood dampened after disembarking on the beach. Even at this early hour, and even doused ear-to-toe with 100-SPF sunscreen, I felt an unrelenting solar assault. (Turns out it’s hard to concentrate on nature’s glories while obsessively imagining your skin cells morphing into irregularly shaped cancerous moles.) The beach was narrow and surrounded by foreboding gray rocks. Maybe this, I thought, is what Darwin meant when describing his first visit to these islands: “Nothing could be less inviting than the first appearance.”

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Galápagos Monday: Lynn’s Tortoises

Every Monday for the next six weeks I’ll be posting about my recent trip to the Galápagos. After a week on a big boat, hopping from one imposing volcanic island to the next, I saw most of the odd creatures that Charles Darwin famously wrote about: century-old tortoises, finches with beaks of all sizes, swimming iguanas. But most of what I learned was new to me — like how the Ecuadorian government hired expert hunters from New Zealand to shoot down thousands of goats by helicopter, or how, in 1954, a massive geological uplift almost instantaneously raised one island’s coast 15 feet, taking with it mounds of coral that have since blackened with dust. Many of the stories converge on what’s, for me, a perplexing theme: that people can be sources of both ecological destruction and impressive restoration. As the climate changes, and population and tourism rates continue to skyrocket, it will be fascinating to see how the economic-political-scientific ecosystem of the Galápagos evolves.

I kick off the series (below, after the jump) with a story about one of my naturalist-guides, Lynn, who has lived on the islands since 1978.


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Dry Spells

In the spring of the year 73, thousands of Roman soldiers raided Masada, a fortress on top of a cliff in the Judean Desert. For seven years, the Jews had tried, unsuccessfully, to split from the Roman empire, and Masada was the last holdout. According to the ancient historian Josephus, when the Romans breached Masada’s walls, they found 960 dead bodies of Jewish extremists, called Sicarii, who had killed themselves to avoid the inevitable enslavement. Because of Masada’s remote location and harsh, dry climate, nothing much happened to the site for the next 2,000 years, until archaeologists started digging it up in 1963. They found attack ramps and siege towers (some of the best examples we have, apparently, of Roman war technologies), palaces, cisterns, swimming pools, 27 human skeletons and, deep under the rubble, a handful of seeds.


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Corridors of the Rainforest

Captain Matty

Captain Matty is a brilliant storyteller. I know because earlier this month I went on his famous tour through the rainforest of Far North Queensland, Australia. As he drove our orange bus up petrifyingly narrow, sinuous roads, Matty told tales, tall and short: about the legendary ‘drop down‘, wicked cousin of the koala, so named because it crashes down from the treetops onto its prey (including, Matty said with a wink, a Swiss-German tourist); about attending poisonous snake bites (it involves a credit card and lots of gauze); and about Aboriginal women who use a sacred waterfall to boost fertility. His most remarkable story was about the rainforest.

The Wet Tropics of Queensland span some 280 miles of coastline on the northeast side of the country, running parallel to the Great Barrier Reef. Thanks to the mash-up of Australian and Asian continental plates 15 million years ago, the area holds a supremely diverse mix of animals and plants (some of which are as much as 415 million years old). It’s difficult to describe without getting carried away, but I’ll try.

The region’s 3,000 plant species include 13 types of rainforest, as well as woody bush, mangroves and swampland. Now fauna: 370 species of birds, 58 frogs, 41 marsupials, 36 bats. Twelve of its mammals — including green ringtail possums, a masked white-tailed rat, and two tree kangaroos — exist nowhere else in the world.

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On Turkey Legs

This story is so kooky that I must lead with the video:

This slow-motion film stars turkeys of different ages, from hatchlings to adults, and yes, they’re furiously climbing a steep wooden ramp. The video comes from a study published earlier this month. But let me start at the beginning.