Darwin’s Rathtars

In honor of Star Wars week at the Athens Science Observer, I wrote a guest post on Rathtars and all they can teach you about evolution. Enjoy!

A rathtar roams free aboard Han Solo’s ship the Eravana. Image: Wookieepedia

When Kanjiklub and the Guavian Death Gang boarded the Eravana, the three most beloved characters in The Force Awakens suddenly found themselves in a tight spot. Thanks to a con that was risky even by Han Solo’s standards, our trio was left stranded while the film’s more charismatic heroes made a narrow escape on the Millennium Falcon. Yes, after eating a large number of the galaxy’s most dangerous gangsters and scaring off the rest, those poor, adorable rathtars were left to fend for themselves.

Thanks to the ship’s presumably heavy infestation with Corellian scavenge rats combined with a rathtar’s ability to eat literally anything, the marooned rathtars would have been able to feed and reproduce without a problem. But how would their newfound isolation affect them? Would they continue to be a colony of rathtars just like the ones on their home planet?

When a new population is founded by a few individuals from a larger group — like, for example, when three rathtars are stranded on a Baleen-class heavy freighter — a phenomenon called the “founder effect” is observed. The founder effect is a loss in genetic diversity in this new colony resulting from a random sampling of the individuals from the original population that isn’t necessarily representative of that original population. What does that mean in Galactic Basic?

Say, for example, that most rathtars have tentacles ranging in length from eight to 11 horrifying feet long and an appalling number of blood-red eyes. However, by sheer chance, or maybe because they are easier to catch, the rathtars Han Solo happened to capture had tentacles that were a merely terrifying eight and a half feet long and puce-colored eyes.

The growing rathtar colony on the Eravana was derived from those select few individuals Han Solo captured. Therefore, even though rathtars throughout the galaxy have a much wider variety of tentacle lengths and eye colors, it can be expected that after several generations, all of the Eravana rathtars will have eight and a half foot long tentacles and puce-colored eyes. There was a loss in genetic diversity in the new group, meaning that fewer versions of the genes that determine tentacle length and eye color are available to choose from when a new rathtar is produced.


Galapagos finches sketched by Darwin during his 1845 journey on the H.M.S. Beagle. Finches have very little in common with rathtars, as rathtars are horrifying. Image: Wikimedia Commons

This founder effect was famously first described by Darwin in the context of finches living on the Galapagos Islands. He noted that finches living on different Galapagos Islands appeared to have a common ancestry, but had grown different characteristics once isolated on their separate islands. Like with the Eravana rathtars, the finch populations on the different islands were established by a small number of individuals from the larger, mainland finch populations.

Over time, the differences in genetic diversity between the finch populations weren’t the only reason why they no longer resembled each other. Darwin noted that the finches’ beaks were different sizes and shapes, based on whichever type of beak was best suited to eating the specific seeds and nuts available on their islands. Something very similar would have happened to the Eravana rathtars.

Not much is known about the rathtars’ home world, but it is likely quite different from the metallic confines of a freighter. As a result, the Eravana rathtars would have also gone through the same process as Darwin’s finches, known as adaptive radiation, in order to fit into their new environment.

With successive generations, rathtar traits would naturally be selected to help them thrive on the Eravana, like smaller body size to fit through the narrow corridors and more nimble tentacles to better snack on unsuspecting Corellian scavenge rats. Given enough time, the Eravana rathtars might even become so distinct from rathtars in general that they would form a completely new species!

So if you, like me, are concerned about the marooned rathtars, worry no more! Thanks to natural selection and a presumed rat infestation, they aren’t lost and lonely, drifting aimlessly in space; the Eravana rathtars are the proud founding fathers of a new species in a galaxy far, far away.

Is This a Kissing Blog?

wide the-princess-bride-kiss

Buttercup and Westley’s final kiss in Rob Reiner’s 1987 adaptation of William Goldman’s classic, The Princess Bride

“Since the invention of the kiss, there have only been five kisses that were rated the most passionate, the most pure. This one left them all behind.” –The Princess Bride

Ah, wuv. Twue wuv. With that record-shattering kiss, Buttercup and Westley traded vows of everlasting love, the promise of a lifetime’s “As you wish”es, and approximately 80 million bacteria.


Yes, a research group at TMO in the Netherlands investigated how kissing affects a couple’s oral bacteria and found that Valentines swap more than just spit. Just like in your intestines, stomach and skin, your mouth and airways are home to a whole host of bacteria that help keep you healthy, known as your microflora.

Oral bacteria were almost certainly the first to be viewed by humans when back in 1683, Antonie van Leeuwenhoek (the father of microbiology) scraped some tarter off his own teeth and stuck it under a microscope. As many as 600 different species of bacteria can be found in the human mouth, some of which are responsible for common problems like gum disease and tooth decay. However, keeping the bacteria living in your mouth happy and balanced helps keep out disease-causing bacteria, stops bad breath, and may even help prevent more serious diseases elsewhere in your body, including stroke, cardiovascular disease, and diabetes.

While the makeup of a person’s microflora is important, it isn’t static. The mouth is an open system, meaning that the composition of the bacteria living there can be changed by things like your genes, age, diet and who you…interact with.

princess bride grandson

INTIMATE kissing? Are you trying to kill me?


The Dutch research group that performed this study swabbed the mouths of random visitors at the Artis Royal Zoo in Amsterdam. Then, the researchers had them make out for ten seconds before re-sampling. You can’t make this stuff up.

The researchers found that among their amorous zoo-goers, romantic partners had more similar oral microflora composition pre-kiss than two people not in a relationship. In particular, partners showed the most striking similarities in the microflora associated with their tongue. The long-term couples’ microflora didn’t change much post-kiss, but this is most likely because they are in like with each other and already swap bacteria fairly regularly.


The scientists conducting the study then wanted to know precisely how many bacteria are passed around per make-out sesh. To answer that question, they gave one partner of each couple probiotic yogurt containing what they referred to as “marker bacteria” and, again, had them snog away.

They then resampled everyone’s mouths to see how much bacteria had transferred from the person who ate the yogurt to the person who did not. It turns out that on average, 80 million bacteria were swapped from one mouth to the other per 10-second make-out.

aaaaaas youuuuu wiiiiiiiiiish

Aaaaaaaaassss youuuuuuuuu wiiiiiiiiiish!


True love is not as easy as one simple kiss, however; it requires effort and real commitment. In fact, the researchers found that in order for a couples’ microfloras to really change to resemble each other, they need to kiss — intimate kissing, they specified — nine times per day.

So, friends, to have the sort of love that cannot be tracked, even with a thousand bloodhounds, that cannot be broken, even with a thousand swords, that is second only to a good MLT — remember to say those three little words every time your Valentine wants a smooch: As you wish.

Finding Vibrio

anglerfish scene gif

“…Good feeling’s gone.” Image: Disney Enterprises, Inc./Pixar Animation Studios

“Come on back here! I’m gonna getcha! I’m gonna swim with you…I’m gonna be your best friend!”

Little did Marlin and Dory know that the light — and the hungry anglerfish attached to it — already had millions of best friends without whom it couldn’t glow. Thanks to bioluminescent bacteria like Vibrio fischeri and Photobacterium phosphoreum, many species have found a way to shine in the most unlikely of habitats.


Bioluminescence is the production and emission of light by a living thing. This light has a wide variety of uses, from confusing prey, to startling predators, to attracting a mate. Bioluminescent organisms can be found on most of the branches of the tree of life, from bacteria all the way up to fish.

Bioluminescence probably originated in the ocean, and is more commonly found in marine species than in ones on land. Bioluminescent marine species live across all of the ocean depths; the greatest number of bioluminescent species can be found in the ocean’s dimly lit twilight zone, but of the organisms that have adapted to life in the ocean’s deep, dark midnight zone, about 90% are bioluminescent!


A bioluminescent jelly. Image: Joshua Lambus, Flickr

Unlike the light generated by an incandescent light bulb, bioluminescent light comes not from heat, but from energy released by a chemical reaction in the organism. All bioluminescent reactions involve a “luciferin” compound and a “luciferase” protein, both from the Latin word “lucis,” meaning “of light.” When a luciferin and a luciferase come together with oxygen and ATP (a cell’s fuel source) the reaction releases energy that we see as colored light.

Luciferins and luciferases come in many different flavors — over a dozen chemical luminescence systems are known — suggesting that bioluminescence has evolved many different times under different conditions. The luciferins and luciferases usually seen in marine bioluminescent species react to produce green or blue light, as these wavelengths of light travel well through seawater without getting absorbed or scattered.


Many bioluminescent species are able to produce light on their own, but others, like our toothy anglerfish friend, have had to get more creative. A large number of bioluminescent species are not bioluminescent in their own right, but have evolved a symbiotic relationship with bioluminescent bacteria.

A symbiotic relationship is one in which two living organisms live in or on each other in a close, physical way (from the Greek sym, “together,” and bio, “life”). Such relationships aren’t always good ones; the luminous bacteria that live symbiotically with the Tanner crab, for example, are parasitic and damage the crab’s legs. In the case of the deep-sea anglerfish and its photobacteria, however, the relationship is a mutualistic one, meaning both the fish and its glowy roommates benefit from their partnership.

Luminous bacteria living in the seawater, like Vibrio fischeri or Photobacterium phosphorum, float through pores in the bulbous sac, or esca, on the end of an anglerfish’s lure and colonize it. This lure is a completely mobile appendage whose luminescence helps female anglerfish lure charming, anthropomorphized prey to their mouths and attract their unfortunate potential mates.


Bioluminescent bacteria and algae can cause glowing red tides, as seen here in Black Point, Anglesey. Image: Kris Williams, Flickr


While photobacteria can glow on their own, they just…don’t. Before they’ll start to glow, photobacteria like V. fischeri need a little help from their friends.

Bacteria are surprisingly social organisms; instead of communicating using words or howls, bacteria send signals to each other by releasing chemicals into their environment. The more bacteria there are in an area, the more signaling molecules will be floating around them. Many bacteria regulate the production of some proteins — like those that make them glow — in response to changes in levels of these signaling molecules in their surrounding environment.

Vibrio Fischeri

Vibrio fischeri, seen plated here, are quorum-sensing bacteria that regulate their bioluminescence in response to changes in population density.

Photobacteria use this kind of communication, known as quorum sensing, as a sort of light switch. Once the number of other photobacteria reaches a certain level, the bacteria detect the resulting elevated levels of signaling molecules around them. In response, the genes that encode the luciferin and luciferase proteins get turned on and the bacteria begin to glow. If the numbers of bacteria drop, however, those genes get switched off again and the glowing stops.

Quorum sensing was first observed in V. fischeri — the glowing made it easy to see the correlation between bacterial density and regulation of the genes responsible for light production. Eventually, it became clear that the process wasn’t specific to V. fischeri and its bioluminescent abilities, but was common to the regulation of many different types of proteins across the bacterial family tree.


Whether glowing bacteria or luminescent fish, the ocean’s bioluminescent organisms are stunning, sometimes literally. The next time you’re on a deep sea adventure and see a pretty light, perhaps don’t stand in awe too long—you might just go from ardent admirer to snack in a flash.

Jurassic Pests

Drs. Sattler and Grant treat the sick triceratops in the film adaptation of Jurassic Park (1993).   Image: imdb.com

Drs. Sattler and Grant treat the sick triceratops in the film adaptation of Jurassic Park (1993).
Image: imdb.com

When considering the practical issues surrounding opening Jurassic Park, several obvious areas of concern immediately come to mind: finding an isolated chain of tropical islands, building immense electric fences, hunting versus feeding regimens, and kitchen-oriented velociraptor escape plans. Equally as important as containment of the island’s inhabitants, however, is the prevention of dino diseases that could quickly put the park out of business.

Fortunately for Jurassic Park’s veterinarians, we already have a pretty good sense of some of the major diseases that could afflict the park’s main attractions. Through careful analysis of the fossilized clues dinosaurs left behind the last time they roamed the earth, paleobiologists have discovered that the Land Before Time was crawling with the microbial ancestors of many bugs that plague tropical regions today.

A sauropod coprolite, with external surface above and cut and polished surface below.  Source: Graham Young, The Manitoba Museum

The prettiest poo you’ll ever see: a sauropod coprolite, with external surface above and cut and polished surface below. 
Image: Graham Young, The Manitoba Museum


Dinosaurs were kind enough to leave ample clues as to what plagued them in the form of coprolites – Latin for “dung stones” and English for fossilized dinosaur poo. Left behind in the coprolites are indicators that ancient forms of the very same worms and protozoa that infect humans and other modern vertebrates were also a problem for dinosaurs.

Though remains of adult parasitic worms did not survive the intervening years, fossilized eggs from trematodes, commonly known as “flatworms” or “flukes,” and three types of nematodes, or roundworms, were found in coprolites. Preserved cysts of the protozoan Entamoeba antiquus, a cousin of the modern-day gastrointestinal parasite Entamoeba histolytica, have also been seen entrapped in coprolites.

Though their eggs and cysts were shed in the dinosaur’s feces, the mature forms of all four parasites would have resided in the dinosaurs’ intestines, just like their modern-day descendants. The forms of the parasites found fossilized in the dinosaur dung are the toughest stages of these parasites’ life cycles, and help them endure the harsh environment outside their cozy host long enough to infect another individual.


Evidence of other prehistoric parasites has been found coprolites’ more popular fossil cousins, dinosaur skeletons.

For years, paleobiologists have hypothesized that lesions seen on the jawbones of Tyrannosaurus rex and its cousins were bite wounds due to fighting. However, recent investigations have shown that the lesions were actually caused by an ancestor of the protozoan Trichomonas gallinae, which is best known for causing similar disease in the beaks of modern birds.

A Tyrannosaurus rex mandible with multiple trichomonosis-type lesions (indicated by white arrows).  Image: Wolff et al., PLoS One September 2009

A Tyrannosaurus rex mandible with multiple trichomonosis-type lesions (indicated by white arrows).
Image: Wolff et al., PLoS One September 2009

In case you needed another reason to play nice with your neighbors, it turns out that the paleobiologists’ first guess actually wasn’t too far off. Though these particular bone lesions are due to disease rather than bite wounds, scientists now hypothesize that fighting and even cannibalism within tyrannosaurs were instrumental in spreading the disease.


Especially considering the park’s tropical location, of particular concern to Jurassic Park’s vets are vector-borne diseases, which are transmitted from host to host by another living organism. During the Cretaceous period (around 120 million years ago), many insects that would be familiar to us today made an appearance, bringing with them diseases that evolved to be carried by these new species.

The most prevalent vector-borne diseases are spread by blood-feeding arthropods like mosquitoes and ticks. Dinosaurs had very tough, thick hides composed of tuberculate scales, which sit next to each other but don’t overlap. Like biting insects feed off of large reptiles today, paleobiologists believed their ancestors likely fed from dinosaurs by biting the bits of skin exposed between scales.

This mosquito trapped in amber still contains the blood from its last meal in its stomach.  Source: Didier Desouens

This mosquito trapped in amber still contains the blood from its last meal in its stomach.
Image: Didier Desouens

If any bugs playing taxi to a pathogen found themselves stuck in tree sap, the fossilized sap – called amber – would freeze the bug and the contents of its gut, providing modern-day scientists with a snapshot of what that bug ate. Looking at amber-imprisoned mosquitos and sand flies under a microscope has revealed that (fortunately for Jurassic Park’s geneticists), not only did these insects feed on dinosaurs, they carried with them several familiar diseases.

Leishmania and malaria are two vector-borne protozoan parasites found in amber-preserved sand flies and mosquitoes, respectively. Today, there are a whopping 198 million cases of malaria worldwide every year, most occurring in sub-Saharan Africa; leishmania comes in behind it with 1.3 million cases annually.

Though it’s not completely clear how the disease progressed in dinosaurs, in humans, leishmania takes several different forms, from a painful, disfiguring skin disease to an often-fatal enlargement of the spleen and the liver. Malaria infects and destroys red blood cells, causing severe anemia, and, in severe cases, neurological problems and pregnancy loss. It’s likely these diseases manifested in similar ways in ancient reptiles.


With many of the diseases that burdened dinosaurs in their heyday still around today, Jurassic Park’s chief veterinarian has a lot to look out for. Fortunately for him, his charges gave him plenty of advance notice of what to expect – about 200 million years’ worth.

The Andromeda Strain

Spain's Rio Tinto is famous for its bright red hue and very acidic waters (pH 2.2). The acidity is thought result from the extremophilic bacteria living in the water. Image: Montuno, Flickr

Spain’s Rio Tinto is famous for its bright red hue and very acidic waters (pH 2.2). The acidity is thought result from the extremophilic bacteria living in the water.
Image: Montuno, Flickr

In Michael Crichton’s sci-fi thriller The Andromeda Strain, a military satellite crash-lands outside a sleepy Arizona town. After the towns’ citizens die suddenly of a mysterious illness, it becomes clear that the satellite was knocked out of orbit by a meteoroid contaminated with a deadly extraterrestrial microbe.

While this premise makes for a great story, how plausible is it? Can microbes survive a trip through space?


In order to survive space travel, a microbe would need to be very hardy.

Some microbes have the ability to go into a dormant state and shield themselves with a tough endospore. As spores, microbes can survive extreme conditions until they end up in a place where they are better suited to grow and reproduce.

Some microbes don’t just survive in harsh conditions such as very high or low temperatures, pHs, and pressures, but thrive in them. These microbes are called extremophiles, meaning “lover of extremes.” Extremophiles are found on Earth near deep-sea vents, in an asphalt lake, and in every other unlikely, inhospitable environment imaginable. Deinococcus radiodurans, for example, has no problem being pounded with gamma radiation. To each his own.

Considering the extreme conditions of outer space, extremophiles and spore-forming microbes are the most likely to survive space travel.


For an extraterrestrial pathogen to wipe out humanity, it must first find a way to leave its home planet without being killed in the process. Meteoroids from planets are released into space by an impact event, in which a very large object hits a planet with such force that it catapults pieces of that planet out of orbit.

An impact event, like this artists's depiction of a comet crashing into a planet, would cause the release of meteroids into outer space. Image: NASA

An impact event, like this artists’s depiction of a comet crashing into a planet, would cause the release of meteroids into outer space.
Image: NASA

There are three main forces associated with this kind of launch that a microbe would have to survive: acceleration, compression shock, and heating. In order to release from Mars, for example, a piece of rock would be accelerated at a rate of about 390,000 times the acceleration due to earth’s gravity, experience shock of up to 385,000 psi, and be heated to anywhere from 100 to 660 °F.

Needless to say, most of the organisms tested were killed during simulations of launch conditions. However, experimental evidence suggests that anywhere from 5 to 5 million spores of some organisms could still survive per kilogram of rock.

As this kind of impact can launch up to 1 billion kilograms of rock into space, this could still leave a very large number of living microbes to go off and wipe out intelligent life on an unsuspecting planet.


The earth is protected from cosmic rays by its magnetic field. Outside the earth's magnetosphere, however, ionizing radiation can do permanent damage to an organism's DNA. Image: NASA

The earth is protected from cosmic rays by its magnetic field. Outside the earth’s magnetosphere, cosmic radiation will not turn you into the Human Torch; it will give you cancer.
Image: NASA

The journey through outer space would prove the most arduous of the challenges facing a microbe hoping to colonize a new planet.

Outside of the protective magnetic fields that surround a planet, objects traveling through outer space are bombarded by high-energy ionizing radiation from galactic sources and the sun.

Despite comic books’ assertions to the contrary, getting hit by cosmic rays will not turn the bugs into superbugs. These stray X-rays, gamma rays, and other harmful particles damage an organism’s DNA. Though there are limits to these abilities, many extremophiles have developed ways to prevent or even repair DNA damage due to radiation.

For microbes below the surface of the meteoroid, radiation, microgravity, and extreme temperatures are not nearly as alarming as desiccation, or the lack of water caused by extreme vacuum. Without water, even the hardiest of organisms can’t perform basic processes required for it to function, leading to its slow but inexorable degradation.

Because of the dangers of desiccation, a microbe would have to take a relatively short journey if it was to survive outer space.

Austrian astronomer Edmund Weiss's 1888 depiction of the 1833 Leonid Meteor Shower.

Austrian astronomer Edmund Weiss’s 1888 depiction of the 1833 Leonid Meteor Shower.


Compared to the merciless battering it takes during launch and the bleak, unforgiving landscape of space, the forces involved in landing are relatively easy for a microbe to survive.

When a meteoroid comes close enough to Earth’s gravitational pull, it enters the upper atmosphere at speed of 10-20 km/s. Though friction heats and melts the surface of the now-meteor, as it takes less than a minute to fall to the surface of the earth, the heat doesn’t penetrate beyond the outer few millimeters of rock.

Assuming the meteor is big enough, this means the heat of re-entry would only kill microbes near the surface, which probably did not survive the journey up to this point, anyway.

The meteor is broken into fragments in the lower atmosphere and scattered over a wide area. This actually is a good thing for any microbes hoping to make Earth their new home, since it increases the chance they will land someplace nice to grow.


In order for a worldwide outbreak of the disease – a pandemic – to occur, even more chance is involved.

The extraterrestrial microbe would have to happen to land somewhere where it can both grow happily and be found by people. A contaminated meteorite that lands at the South Pole is unlikely to spark the zombie apocalypse unless the zombies in question are also penguins.

The microbe would also have to be both infectious and harmful to people. Though a microbe humans haven’t evolved to deal with is more likely to cause disease, it is far from certain that an extraterrestrial microbe would be pathogenic.


While it’s not impossible for an extraterrestrial microbe to land on Earth and begin obliterating entire towns, the sheer number of unlikely events involved makes the chances of its happening vanishingly small. An alien pandemic-Armageddon actually happening would be akin to the Universe declaring, “I hate you, Planet Earth!”