Wild Things
Slate’s animal blog.

Oct. 9 2015 8:45 AM

The Strangest, Most Amazing Lactation Methods Ever Seen in Mammals

My wife has amazing breasts.

I should explain that I’m talking about her mammary glands, in particular. (All mammals have mammary glands, though not all mammals have breasts. Some of them don’t even have nipples. But we’ll get to that.)


A few weeks ago, my wife and I welcomed our second child into the world—a wee little squeaker named June. After nearly nine months of sipping her meals through a straw in her belly, this bitty baby popped out, threw some shade at the doctor, and immediately began to suckle from my wife’s breast.

And I guess that’s when it struck me—not only did my wife’s body just funnel all of its resources into the creation of this animal, rearranging organs and increasing its blood supply by 50 percent in the process, but once it had expelled her, my wife’s body shifted modes like a Transformer to further accommodate its mewling creation.

In the hours and days to come, my daughter’s near-constant stimulation would trigger hormones to wash over my wife’s body, initiating lactation. Her mammary glands would produce colostrum, a concentrated proto-milk full of immune cells, antibodies, and protein that kick-starts the infant’s digestion and growth. The colostrum would give way to a more regular supply of milk composed of thousands of bioactive molecules that ward off infection, prevent inflammation, promote immunity, spur organ development, and cultivate a healthy microbiome.

My wife’s body would produce just as much milk as my daughter could drink, replenishing the supply in between feedings, and tweaking the recipe as the baby grew. Human milk is made to order depending on the time of day, the length of the feed, and the diet of the mother.

Like I said: absolutely sucking amazing.

So in honor of my daughter, my wife, and amazing mammary glands, I did some digging into the wonder that is mammalian lactation.

More than 200 million years before the “Got Milk?” campaign, the first mammals crawled onto the scene. Mammary glands are the main unifier of all us mammals—from moles, dogs, and koalas to tigers, lemurs, and platypuses.

“There are over 5,600 species of mammal, probably closer to 6,000 once they all get described, and they all start life on a diet of milk,” says George Feldhamer, professor emeritus at Southern Illinois University and author of the widely used textbook Mammalogy. But as Feldhamer points out, lactation can differ greatly among those of us in the milk-maker tribe.

Human milk, for instance, is a watery brew with just 3.8 percent fat and 1.2 percent protein. Compare that with the milk of a blue whale, which is 38.1 percent fat and 12.8 percent protein. Blue whale milk has the consistency of “loose, runny cheese” and smells like it was made in a Bass-O-Matic.

As the largest creatures to ever live, blue whales also hold the record for the biggest bazookas—each mammary gland is nearly 5 feet long and weighs almost 250 pounds. Like humans, blue whales have two such glands, which means each adult female is carrying around a quarter of a ton of milk-producing machinery. Of course, all this milk-making power is what helps the blue whale calf pack on 37,500 pounds during its suckling period.

But the leviathans aren’t even the fattiest milk producers in the animal kingdom. That prize goes to hooded seals. Their milk can reach 61 percent fat, a richness even Paula Deen would find excessive.

But decadence in nature is never needless—hooded seal mothers nurse their pups for just four days on pack ice before returning to the sea to find food. This is the shortest lactation period of any mammal. That means the pups must pack on as much weight as possible, as quickly as possible, or die alone on the ice. Drinking nearly 45,000 calories of liquid butter each day is the only way such an arrangement can work.

While we’re talking about marine mammals, I should probably clarify that neither seals nor whales are swimming around with anything resembling cleavage. All marine mammals lack breasts as we know them and keep their working parts inside the body proper.

The pinnipeds (seals, sea lions, and walruses) have retractable nipples, which sounds like a burn straight out of the junior-high locker room but in truth just means the nipples tuck inside when they’re not in use. This likely cuts down on drag in the water and protects the tidbits from the cold.

The cetaceans (whales, dolphins, porpoises, narwhals, and the like) take this trick a step further by burying their nursing parts below a fold of skin called the “mammary slit.” These nipple-housing envelopes are found on either side of another, longer slit, which contains the genitals.

Because dolphins and whales don’t really have lips like most mammals, it’s been posited that the mother’s abdominal muscles actually squeeze the mammary glands and eject milk into the calf’s mouth. There’s some evidence that the babies can assist the process by curling their tongues into troughs, the better to create suction and gulp down their liquid lunches.

Of all the sucklers though, opossums are the most committed. Following a gestation period of just 12 days, baby opossums emerge from their mother’s vaginas blind, deaf, naked, and with brains that are only 9 percent developed, which isn’t much of a brain even for an opossum. About the only thing these marsupials have going for them is a massive set of claws, which they use to climb up the mother’s body and into her pouch. Once inside, those who find a teat latch on and don’t let go for two straight months.

The nipples swell inside the babies’ mouths, creating a lock so tight that scientists have found that trying to forcefully separate a baby from its mother can result in torn lips and nips. (I think I just heard my wife shudder from the next room.)

Over the course of 60 days, the opossum’s nipple will stretch and grow up to 35 times its original length. This creates a tether between mother and child not unlike an umbilical cord and every bit as vital. A baby opossum that does not find a nipple after birth will be dead in minutes. And the same goes for any offspring that become detached before they’re ready to wean.

Nipples—what strange little bio-valves they are. For all the time we spend talking about nip slips and Instagram’s nipple censorship policies, we pay scarcely little attention to the wild nipples all around us.

According to the 2015 edition of Guinness World Records, the animal with the most nipples is the female shrewish short-tailed opossum, which can boast a 27-gun salute. When scientists dart and collar female polar bears, they can determine an approximate age by nipple size, since the teats get longer and wider as the animals become teenagers. Kangaroos nurse two different generations of joeys at a time, which means one nipple is devoted to carbohydrate-rich milk for the neonate in its pouch and another nipple delivers fat-rich milk for the yearling living outside. (Kangaroos are baby-making machines.)

In porcupines, bleached fur around the nipples is proof that the female has reared young in the past. Uldis Roze, porcupine expert and author of The North American Porcupine tells me that porcupettes (really, that’s what they’re called) have also been documented to play a little game of Simon with their mother’s nipples. They first tug at one nipple, then another, then another, suckling milk from each gland in an order that they will repeat throughout their nursing months.

Anyone who has owned a cat or dog knows that nipple placement also varies throughout Mammalia. Ours are near our armpits, as are elephants’. But many other animals—cows, squirrels, giraffes—keep theirs toward the hindquarters.

And then there are bats. Bats are already pretty special when it comes to mammals, because they’re the only ones that said, “Eff it, we’re conquering the sky!” Bats also have fascinating sex lives. So perhaps it’s not so surprising that they have awesome nipples.  

Like us, bats nurse from teats on the upper body. But reports kept coming in over the years from scientists seeing another set of nipples located down on the pelvis of some species. In many cases, the “pubic teats” did not seem to be attached to functioning mammary glands. So what possible purpose could these extra nipples serve? Oh, an awesome one.

Pubic teats “are used as devices for the young to hold onto when the mother is flying,” says Nancy Simmons, curator-in-charge of mammals at the American Museum of Natural History.

The pup simply latches onto the mom’s pubic teat, wraps its legs around her neck like it’s doing a reverse-hurricanrana, and then the two fly off into the night.  

All of this is described in Simmons’ 1993 paper in which she examined the nipples on 1,723 bat specimens representing 206 species. Her work remains the definitive word on bat nipples—which one can only hope affords her plenty of free drinks in every bar on Earth.

While we’re talking about lactating Chiropterans, I should at least mention that the only male mammal that has been shown to produce milk in the wild is also a bat.

Dayak fruit bats captured in Malaysia have been shown to express a relatively small amount of what appears to be milk. However, before you start lauding these guys for being some sort of male milk nurses, I should also say that there’s no evidence that they help nurse the pups. And their drippy nips may be more of an effect of their diet than some sort of evolutionary advance.

“It is likely that Dayak fruit bats ate leaves or fruits containing plant estrogens, which stimulated their mammary tissue, which then produced some secretion,” says Paul Racey, professor emeritus at the University of Aberdeen and author of a dissenting opinion on whether male bats truly lactate.

Whatever the case, there’s a yet more impressive feat than males making use of their nipples—and that’s nursing young without any nipples at all.

I refer of course to the monotremes, the only mammals left alive that lay eggs.

Who needs nipples? Not this echidna, on display in Sydney, Australia.

Photo by ROMEO GACAD/AFP/Getty Images

“The platypus and echidnas don’t actually have nipples,” says Feldhamer. “They have mammary glands, they secrete milk, but it just drips out onto tufts of fur.”

Still, there’s a lot to be said in support of nipples. In addition to guiding the milk directly into the baby’s yawning maw, nipples minimize the milk’s exposure to microbes. Perhaps this is why scientists have found the presence of an antibacterial agent that occurs exclusively in monotreme milk.

This is far from an exhaustive list of everything interesting about mammalian lactation. The Stejneger’s beaked whale, for instance, has milk that’s blue-green in color. Rodents and many other mammals (including humans) tend to have half as many offspring per brood as they do nipples. The dwarf mongooses of Tanzania are one of the only wild mammals in which females that have never been pregnant will spontaneously lactate to cooperatively care for other young in the pack.

Every way you look at it, lactation is biological alchemy. That jug of cow’s milk in your fridge or breast milk in the freezer? It’s evolution in a bottle.

But now if you’ll excuse me, I have a baby to burp.

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Oct. 8 2015 11:03 AM

Why Elephants Don’t Get Cancer

Being an elephant is risky business. I'm not talking about poaching, habitat loss, or fighting with males in musth—I'm talking about the simple fact of living. Every time an elephant cell divides, it runs the risk of going haywire and developing into an out-of-control tumor. Since elephants have 100 times the number of cells that human beings do, they should have 100 times the risk of getting cancer. That's a lot of mistakes waiting to happen.

In reality, given their size and prodigious lifespans, elephants have one of the lowest cancer mortality rates in the animal kingdom: 4.8 percent, compared to a range of 11 to 25 percent for humans. How can this be?


Scientists at the Huntsman Cancer Institute, University of Utah School of Medicine, and Primary Children’s Hospital helped figure out the answer, published Thursday in the Journal of the American Medical Association. Another team, made up of University of Chicago researchers and their colleagues, posted a related paper this week. As it turns out, elephants have developed some ingenious safeguards against developing cancer. Understanding their cellular protections might help us learn more about how to suppress cancer in humans.

There are countless ways that cell division can go wrong. That’s why—as we learned from the winners of this week’s Chemistry Nobel Prize—your cells come equipped with a host of repair enzymes whose sole purpose is to prevent or repair genetic mistakes. These cellular copy editors proofread each strand of newly divided DNA, identifying errors and repairing the faulty bits to ensure that your DNA stays fresh and clean and functional. In humans, just one of those enzymes can fix a thousand different kinds of errors. Not too shabby!  

But elephants have one-upped us. For the JAMA study, researchers first compared cancer rates across the animal kingdom to find out that elephants were remarkably cancer-free given their size. (Other animals fared well, too. For comparison, rock hyraxes have a 1 percent cancer mortality rate, African wild dogs have an 8 percent rate, and lions have a 2 percent rate.) Then, they scoured the elephant genome to find out why.

The answer resided in a key tumor-suppressing protein called p53, known as the "guardian of the genome." Compared to humans, elephants had far more genes for this protein: 38 versions versus just two. The result was a superior genetic safety net for correcting errors and ensuring that damaged, tumor-prone cells get nipped in the bud. "The enormous mass, extended life-span, and reproductive advantage of older elephants would have selected for an efficient and fail-safe method for cancer suppression," the authors write.

To see how the genes suppressed tumors, researchers teamed up with Utah’s Hogle Zoo and Ringling Bros. Center for Elephant Conservation to isolate elephant cells and subject them to cancer triggers. (No elephants were harmed; this was all during routine wellness checks.) When they compared elephant cells to human cells, they found something amazing: The damaged cells in elephants were far more likely to resort to cell suicide—known as apoptosis—to avoid propagating errors in their descendants. It was a brutally efficient, even ruthless, system for protecting the organism at all costs.

To behold an elephant in the wild is to be humbled before majesty. Yet perhaps it isn't just their tremendous size that contributes to this sense of smallness. It's also all the things we can't see: from their advanced memories, to their long lifespans, to their individual cells, so altruistic that they are willing to die for the benefit of the many. From these cancer-resistant Methuselahs, we humans have much to learn.

Oct. 2 2015 2:00 PM

There Aren’t Enough Male Squirrels to Mate With All the Females

Do you ever look in the mirror and think there’s something wrong with you? That maybe your tail isn’t bushy enough, your pelt’s lost its luster, or you’ve eaten a few too many acorns lately? Well, cut it out! I’m here to tell you that it isn’t you—it’s them. No, it’s not your imagination, single women: There literally aren't enough men out there!

That last sentence is the actual headline of a Vice article that presumably exists to make single women feel better about themselves and their supposed predicament. But it’s also scientifically true—at least if you’re a yellow ground squirrel. In the past, zoologists had thought that female squirrels’ lack of romantic encounters stemmed from their body condition, age, or competition from other female squirrels. Now, we know that the main reason some females aren’t having babies is that there aren’t enough males around—and the ones that are around are having a hard time finding them.


A shortage of males has been shown to be a factor in female reproductive failure in some insects, fish, and spiders. But in most mammals, it’s the reverse: Females tend to be the limiting factor. After all, one male can impregnate plenty of females. Plus, raising the young takes time and resources—just ask your mom!—and most of that burden falls to the females. Sadly, male squirrels aren’t really into parenting: “They mate, and they eat,” as zoologist and study author Nina Vasilieva puts it.

"When you touch them they seem nearly liquid," says study author Nina Vasilieva of Russian male yellow ground squirrels, which are larger than their American counterparts.

Olga Batova

But when Vasilieva studied the sex lives of wild squirrels near the Russian village of Dyakovka over four years, she found some unusual traits that made females the scarcer resource. First, female yellow ground squirrels live alone in single-squirrel burrows, where they spend nine months out of the year quietly sleeping. Second, when they finally do emerge, they have a very limited span of time—as short as a single day—in which they are receptive to mating. If they fail to mate within that time, they have to wait until the following year. And, given that their lives last a brief two to three years, that's cutting it close. "I actually saw with my own eyes some sad females which were not visited by any males," Vasilieva says forlornly. 

Before you feel too sorry for the females, though, consider that it's no walk in the park to be a male squirrel either. After all, he's stuck chasing an elusive, silent target that pops up once a year. Where’s squirrel Tinder when you need it?

Make no mistake: These females want to mate. In squirrels, “it’s reasonable for females to invest in reproduction as much as possible, even if she is in bad physical condition,” says Vasilieva. “Female ground squirrels have a very low reproductive cost. Actually, reproduction does not affect female survival and future reproduction in yellow ground squirrels at all.” But they aren’t exactly making it easy for the male squirrels. As a result, researchers found that 30 to 40 percent of sexually mature females failed to reproduce, they reported Friday in the journal Science Advances.

This finding goes well beyond squirrels: The dearth of males at the right time and place could also apply to lemurs or to other hibernating rodents, Vasilieva says. But perhaps there’s a larger message here for us all. Ladies, stop blaming yourself for the fact that there don't seem to be enough eligible men around. You’re perfect just the way you are. But also, best not to spend the majority of your time in an underground hole.

Sept. 25 2015 2:53 PM

Watch a Majestic Siberian Tiger Get Released Back Into the Wild

It’s Friday. Fall (and football) is here. Weather’s supposed to be decent. All that being the case, at about 4 p.m. this afternoon, you’ll likely be pacing around your office like a tiger in a cage, ready to be released into the wild of the weekend. And for an idea of what that will look like, watch the video above.

The video in question—which comes to us from the good people at GoPro—shows Zolushka, a Siberian tiger, being returned to the wild. Rescued from poachers by the International Fund for Animal Welfare as a cub, her re-entry is just one example of the organization’s larger attempts at restoring the global tiger population. While there were once more than 100,000 wild tigers in Asia, that number is now believed to be somewhere between 3,700 and 4,200.


So not only is the incredible footage a thrill to see, it also affords us the opportunity to watch good, meaningful work in action—and, of course, provides a little Friday afternoon inspiration as well.

But be warned: Should you try to mimic Zolushka’s sprint for freedom after clocking out today, be prepared to be significantly less majestic in doing so. 

Sept. 24 2015 4:49 PM

Ridiculously Gorgeous Rare Bird Finally Photographed

It's hard to believe the mustached kingfisher is a real bird. First of all, it looks more like a Baltimore Orioles–themed stuffed toy than a bird. Second, it's only found on the remotest of mist-caressed islands, similar to the legendary Pokemon bird Articuno. Finally, it has long eluded human capture, with only three specimens ever before collected, all females. “Beautiful but very cryptic,” is how birdlife.org describes it. “Very few sightings, and male plumage remains undescribed.”

Until now.


Last week, a team led by Chris Filardi, director of Pacific Programs at the American Museum of Natural History’s Center for Biodiversity and Conservation, identified and photographed the first-ever male mustached kingfisher. It happened one fateful morning while the team was surveying biodiversity in the mountainous forests of the "sky island" of Guadalcanal in the Solomon Islands.* Suddenly, Filardi heard the unmistakable call: “ko-ko-ko-kokokokokokokoko-kiew!” A dark shape criss-crossed his path. And then, silhouetted against the dappled sunlight, he saw it: the mustached kingfisher in its full, mustachioed glory.

A kingfisher bird.
A kingfisher bird.

Photo courtesy American Museum of Natural History/Sammy Qalokale

He put down his binoculars. He didn't need them anymore.

"It was like finding a unicorn," he told me over the phone. "It’s unimaginable. You dream about it. You can almost taste it. And all of a sudden, there it is.”  

This was “a bird I have sought for nearly 20 years,” he said in a beautifully written blog post. “One of the most poorly known birds in the world was there, in front of me, like a creature of myth come to life.” 

Thanks to Filardi and his team, we can now describe the male’s plumage: His head is a burnt orange, his beak is a split-open carrot, and his “mustache” takes the form of two violet bands, one around his chin and the other extending from his eyes, lending him both decoration and dignity. He juts forth the pale roundness of his fluffy breast, indignant. 

Firaldi holding a puppet, I mean mustached kingfisher.
Filardi holding a puppet—I mean, mustached kingfisher.

Photo courtesy American Museum of Natural History/Rob Moyle

The remote "sky island" of Guadalcanal, Papua New Guinea.
The remote "sky island" of Guadalcanal.

Photo courtesy American Museum of Natural History/Patrick Pikacha

The Uluna-Sutahuri people of Guadalcanal have long lived in the midst of this legendary bird, which is known to them as Mbarikuku. But this is the first time it has been photographed and recorded. Due to habitat degradation (logging) and deadly predators (pesky invasive cats), the kingfisher is exceedingly rare, with numbers estimated at between 250 and 1,000 and dwindling. 

Previously, taxonomists had lumped together this bird and a very similar one, the larger Bougainville mustached kingfisher. The new observations made by Filardi's team reveal that this is almost certainly its own species, based on its distinctive call, reproductive isolation and history, and “striking difference in plumage." The next step is to run genetic tests on the captured specimen, to see how different the two species truly are.

As Filardi puts it: “The question is: Is it a Siberian tiger and a Bengal tiger, or is it a Bengal tiger and a lion?”

*Correction, Sept. 24, 2015: This post originally misstated that Guadalcanal is in Papua New Guinea. It is in the Solomon Islands.

Sept. 4 2015 2:21 PM

Between a Hawk and a Hard Place

Finding the perfect place to raise your precious little ‘uns is no easy feat. It's a lot harder if you happen to be a hummingbird. Now, instead of school districts and playgrounds, you’ve got to worry about pesky jays snatching your young straight from the nest. Fortunately, nature has the solution: Just add hawks!

That’s what researchers from the University of Arizona found out after following the fates of more than 300 black-chinned hummingbird nests in the Chiricahua Mountains over three years. These hummers, along with Cooper’s hawks and Mexican jays, coexisted in what ecologists call a “trophic cascade,” a food web in which the behavior of top-level predators directly impacts the survival of those below it. They published their findings today in the journal Science Advances.


Researchers knew that hummingbirds tended to cluster their nests close to hawks. But at first, they couldn’t figure out why. It turned out that, while hawks didn’t pose much of a danger to tiny, agile hummingbirds—“They’d burn more calories chasing them than they would get from catching them,” says Harold Greeney, who led the study—they sure made the jays nervous. So whenever there were hawks roosting nearby, the jays set up shop in the trees far above them, out of the way of hummer territory.

When the researchers plotted the success of hummingbird nests and compared it to the vicinity of hawks, they found a “cone of protection”: an oasis in which hummingbirds could raise their families in peace, enjoying a better chance of survival. Hawks, it turned out, were hummingbirds’ winged protectors.

A stroke of luck aided researchers in discovering the profound impact that these taloned angels had on hummingbirds’s livelihoods. The summer after their first year of observations, a host of raccoonlike mammals called coati climbed up into the trees in the research site and ate as many hawk nests as they could lay their claws on. Within two weeks, researchers saw the cone of protection effect disappear—revealing how much the hummers relied on hawks for their protection. “It was so fortuitous,” Greeney says, adding, “Well, for us. Not for the hawks.”

Once the hawks were gone, the jays moved in, targeting both eggs and hummingbird babies. “Every single hummingbird got eaten,” says Greeney, whose extensive hummingbird expertise has been featured in PBS documentaries.

These new findings provide conservationists with a clear example of how ecosystems can be interconnected on a deep level. The hummingbird-hawk system is not unique: A similar system exists in the Arctic, where snow geese prosper when they cluster around snowy owls who viciously attack their enemy, the arctic fox. In freshwater lakes, algae blooms best in places where predatory crayfish keep away smaller fish and snails that feed on algae.

When humans mess with these kinds of systems, or even try to preserve them by protecting one species, they risk disrupting a delicate balance in which each animal species affects the others. As Greeney puts it: “For conservation, no animal is an island unto itself.” 

Sept. 3 2015 2:20 PM

The Dog (and Meerkat and Polar Bear) Days of Summer

Sept. 2 2015 4:19 PM

What Makes an Animal “Cute,” Anyway?

Scientists on social media are redefining “cute.” Prompted by two researchers at Virginia Tech, Anne Hillborn and Marcella Kelly, scientists have been posting photos of their most adorable research organisms to Twitter with the hashtag #CuteOff. Whether or not these critters qualify may be in the eye—or the research study—of the beholder.

It’s hard to argue against the appeal of some of these cute and cuddlies, like a cheetah cub:


Though sleeping monkeys will give that cub a run for its money.

Then again, who doesn’t love a teeny tiny frog?

But you might find it a bit harder to find these specimens particularly adorable.

You may have mixed feelings about sea pigs, but come on, it’s called a sea pig.

Someone described this tenrec as a “cute little monster.” Maybe cute, but certainly not cuddly.

The Field Museum wants you to appreciate the squeee-worthiness of this bat. No? Come on, just a little squeee. Look at it!

What we’re learning from #CuteOff is that one person’s “squeee!” may be another person’s “squ ... ewww.”

So what’s going on here? Do researchers really think their own study organisms are the cutest in the land, or are they biased? What makes a creature cute?

It could be big eyes. Asked about this by a reporter, Kelly responded, “I think that’s probably part of it, especially with baby animals, but there were plenty of animals that did not have big eyes …” (“Or any eyes,” the reporter interjected) “that scientists tweeted that I thought were surprisingly cute.”

Researchers who study humans’ preferences for physical attributes of other species or inanimate objects have found that infant-like features, such as large, wide-set eyes and an enlarged head, as well as human-like traits, are considered most appealing. Since the middle of the 20th century, researchers (and pet product marketers, certainly) have been investigating this phenomenon and its implications.

Recent research by Julie Hecht and Alexandra Horowitz showed that most of the undergraduate students participating in their study who were shown digitally-manipulated photos of adult mixed-breed dogs preferred the photos of dogs with bigger eyes, more space between their eyes, and smaller jowls. Hecht and Horowitz’s findings support those of other researchers who showed that dogs exhibiting paedomorphic, or juvenile, facial expressions are preferentially selected by humans, giving them a competitive advantage in their modern environment. This suggests that the domestication of wolf populations involved not only selection for tameness, but perhaps trended toward irresistible “puppy-dog eyes,” as well. Humanlike personality cues are also important when it comes to our animal friends’ faces. In Hecht and Horowitz’s study, participants were likely to prefer photos of dogs with colored irises and a distinct “smile,” characteristically human-like traits.

The appearance of wide-set eyes and a smile certainly make this nudibranch a contender for the #CuteOff.

In humans, symmetry and averageness are typically perceived as attractive traits. A more average face is one that is more similar to a computer-averaged composite of multiple faces. In 2003, Jamin Halberstadt and Gillian Rhodes tested whether this principle applies to humans’ perceptions of birds, fish, and an inanimate object—an automobile. Using computer-generated line drawings, the researchers found that a sense of familiarity was associated with study participants’ preference for the more average drawings of all three items. Halberstadt and Rhodes also discovered a general preference for “averageness,” independent of a sense of familiarity, for birds and fish; multiple research studies have suggested this is tied to our perception that a more average face is an indication of genetic or physical quality.

These studies may help us understand why wide-eyed furry mammals tend to be easy, go-to entries in the #CuteOff, or why one cheetah is considered cuter than another, but they still don’t really explain why some researchers consider the “ticks of the sea” legit contenders for the #CuteOff and the rest of us, well ...

Perhaps this is related to the fact that we think our dog, cat, rabbit, hamster, fish, snake, or child, is the cutest of all the dogs, cats, rabbits, hamsters, fishes, snakes, or children, for reasons certainly related to our personal bond or connection with them. In the same vein, maybe each researcher is going to think her study critter is the cutest of all the study critters, even if it is prickly, slimy, blood-sucking, creepy-crawly, or just plain devilish.

But, really, I do have the cutest dog of all the dogs.

Does cute matter?

Physical preference can affect decision-making, and when it comes to scientific research, conservation, and pet adoption, it turns out cute does matter. As Hecht and Horowitz point out, the endangered species that tend to get the most attention are those more closely related to humans or with “decidedly human-like” characteristics. Additionally, studies have reported that appearance and personality are two of the key factors affecting people’s choice of pet when adopting from a shelter. Shelter staff and volunteers should help potential adopters find the pet that is the best fit for their family and home to discourage picking an animal based on appearance alone.

Sometimes, cute can be overrated.

Sept. 1 2015 12:13 PM

Animals That Scientists Thought Never, Ever Have Sex Actually Do Have Sex

This article originally appeared in Sick Papes, a blog about exciting new science papers.

As all you puddle-suckers know, there are entire universes of microscopic organisms living in every drop of puddle water, moss moisture, and sidewalk juice. Indeed, it was within a drop of filthy gutter scum that Antony van Leeuwenhoek (1632–1723) observed single-celled and other microscopic organisms for the first time. He also provided the first microscopic drawings of human sperm, which lead to some great drawings of little tiny men scrunched up inside the head of a sperm. [Editor’s note: this man-in-sperm theory is no crazier than the truth of how humans develop.] The revolutionary nature of Leeuwenhoek’s observations are even more impressive considering how shitty the microscope that he used was: Made of a single hemisphere of glass fixed to a metal plate, these scopes had a fixed focal distance of about 0.5 millimeters but magnified up to 275 times, and apparently had a resolution approaching one micron.


Today’s Sick Pape focuses on one of the types of animals that Leeuwenhoek saw when he magnified a drop of water: rotifers. Rotifers are microscopic animals (not bacteria, not amoebas—multicellular animals) measuring between about 100–500 microns yet possessing a complex anatomy including a nervous system and a digestive system. And for the past two decades, rotifers in the genus Bdelloidea have been the subject of intense research for one reason: They never, ever have sex.

Sexual reproduction is thought to be essential for the long-term survival of a species. There are a handful of animals that will occasionally pop out a virgin birth, but this is typically done just for a ratings bump at Animal Planet during the holiday season. In general, there are no species that exclusively reproduce asexually and manage to last more than a few million years. While there may be short-term Darwinian benefits to cloning yourself, only sexual reproduction can provide the cosmic intermingling and chromosomal diversity that organisms need to survive the long evolutionary grind.

Bdelloid rotifers thus pose a major question: How has this species survived for hundreds of millions of years without ever having sex? Male bdelloid rotifers have never been observed, nor has anyone ever witnessed meiosis or mating. Instead, the females just happily clone themselves forever like a goddamn metaphor I can’t think of right now. The big question has always been: How come these ladies haven’t gone extinct? What’s their secret?

Over the past few decades, bdelloid rotifers have been whispering their secrets into the quivering ears of Matt Meselson’s lab. Meselson is one of the best scientists who has ever lived, responsible for “the most beautiful experiment in biology” as well as helping to discover mRNA and many other Old Testament breakthroughs (as well as crusading for years against biological weapons). Which is just to say, he knows what the funk he’s talking about. And his lab has shown that bdelloid rotifers have a variety of alien mechanisms for increasing their genetic diversity without having sex. Namely, these rotifers suck up random DNA from their surroundings and shove it into their own genomes, and they also shatter their entire genome and then rebuild it with errors.

And now, Meselson (who is currently in his 80s) and his lab have done something that is so rarely done these days: They have provided strong evidence that their entire premise was wrong and that bdelloid rotifers actually do reproduce sexually. I want to emphasize that none of their past research was wrong; each of their past experiments still hold up, all the crazy DNA-sucking-and-shattering is still real, it’s just that these strategies exist in addition to sex (albeit, very infrequent sex).

Meselson and his squad begin their Sick Pape with an ominous threat that would terrify the Edward Snowdens and Chelsea Mannings among us: “Certain methods … offer definitive means for detecting infrequent or atypical sex.” [Editor’s note: What you or I do in private is not the business of the Meselson lab or the state.] However, instead of using the CIA interrogation methods implied by this terrifying abstract, they stick to modest and routine population genetics strategies. Specifically, these folks test for patterns of genetic similarity between different rotifers that imply they are the product of sexual reproduction in the not-too-distant past, and they find it.

For those who want to come into the methodological weeds with me, the “certain methods” to detect infrequent sex is this: You sequence a few genes from each of several rotifers and then look for a pattern where Gene X from rotifer 1 is very similar to its homolog in rotifer 2, whereas Gene Y is similar to its homolog in rotifer 3. This implies that there has been recent sex that has jumbled up different chromosomes between individuals in the population. To be sure that this wasn’t the result of direct DNA transfer between rotifers 1 and 3, these auteurs do the same test at several genes and show that the same pattern holds for all these genes, making it very, very unlikely to have been direct horizontal transfer of DNA.

We honor Ana Signorovitch, the pape’s first author, and her colleagues in the Meselson lab for having the courage to disprove themselves—an uncommon mark of high integrity—and for shining their beautiful light on an invisible little corner of our world. Of course, the timing and mechanisms of sex remain a complete mystery, so please keep up the hard work for many more decades to come!

Signorovitch, A., Hur, J., Gladyshev, E., & Meselson, M. (2015). Allele Sharing and Evidence for Sexuality in a Mitochondrial Clade of Bdelloid Rotifers. Genetics. doi:10.1534/genetics.115.176719

Aug. 27 2015 2:00 PM

Define “Rational”: Is That a Decoy or Your Frog Prince?

“Irrational mate choice” sounds like an accusation my mother might level at me in a terse email subject line, but in this case, it’s the title of a paper on sexual selection in the Panamanian túngara frog (Physalaemus pustulosus) published Thursday in Science magazine. In the paper, behavioral ecologists Amanda M. Lea and Michael J. Ryan report for the first time that female túngara frogs don’t always act rationally when it comes to mating—a finding that could challenge our simple understanding of this kind of mating system.

“This is the first time we’ve found evidence for irrational mating behavior,” says Lea. “If they aren’t making rational decisions, then these models don’t hold up.”


Keep in mind that, in evolutionary biology, rational doesn’t necessarily mean governed by reason (and irrational doesn’t always mean face-palmingly naive). Rather, a rational mating choice is one that conforms to an evolutionary system by which females choose their mate based on his ability to maximize her Darwinian fitness. In the animal kingdom, we expect animals to make these choices as simply, efficiently, and consistently as we choose the best value in off-brand oatmeal.

Yet in the new study, inferior suitors known as decoys—male frogs with a slower call rate*—threw a wrench in the whole “rational system” hypothesis. These decoys snuck into a group of displaying male frogs, thrusting themselves near the better options and throwing off the females’ focus. Weirdly, their presence caused the ladies to switch their initial decisions and instead go for a nearby male with a slower—less appealing—call. Talk about a bad morning after.

One explanation for the switcheroo is that female túngara frogs are easily flustered. (Decoys aren’t the only ones known to have deceived them: “I have to tell you," says Lea, "I’ve attracted many female frogs making these calls.”) You can hardly blame them. Choosing an amphibious amor is already complex enough, what with all the swelling, foaming, ribbitting, and whatnot. Adding another male to the mix, researchers speculate, could overload the female frog’s cognitive resources and cause her to make a mistake. (This confirms my opinion that grocery stores should only stock one of every option.) 

Or the mix-up might be more sinister. Decoys may intentionally create a confusing comparison, taking advantage of the kind of logic used in cognitive tests where people can’t tell that two circles are the same size because of the differently sized circles surrounding them. Similarly, dating is about comparison; the appeal of one prospect changes depending on what’s around him. With the decoy around, the female tends to prefer whatever other male is closest to it—even if he isn’t the most attractive option of the three. Think of him as a particularly ugly wingman: Next to him, the guy sitting next to him suddenly doesn’t look so bad. 

“I used to be a bartender, so this is all very familiar,” says Lea, who likes to compare her study species to human males showing off at a bar. A more modern comparison might be the world of online dating, where individuals casually scroll through prospective mates, comparing each one’s profile picture and vital stats to the one that came before it. “If the past 10 are all really really bad, you might just start to lower your threshold,” Lea says.

“I’m actually surprised no one has looked at that,” she adds. “Someone should do that study.”

The inevitable question: What’s in it for the decoy? It could be that he and the other male are engaging in a mutually beneficial friendship, whereby each takes turns acting like an inferior male to give the other a mating boost (frog bros?). In that case, they would probably be genetically related (actual bros!), so that boosting each other’s mating success would also be helping to support their own gene pool. But Lea thinks there is a likelier—and sadder—reason. 

Perhaps the decoy has no choice. After all, like the peacock, the túngara frog is a species in which the male’s sole purpose is to mate. True, even if he keeps calling, he’s probably not going to get a mate. But if he doesn’t call at all, then he definitely won’t. So no matter how spindly, how unattractive, or how woefully inadequate he may be, the decoy is doomed to just keep calling, and calling, and calling—even when there’s no one there to answer. “I’ve seen these guys die in the field mid-call,” says Lea sadly. “He’s just doing the best he can.”

Correction, Sept. 8, 2015: Rachel E. Gross originally stated that túngara frog decoys have less appealing voices. Actually, their voices are just as appealing.