Excerpt
It is interesting to speculate on why the hermaphroditic condition evolved in manysimple animals but not in mammals or birds. Some parasites like tapeworms spend theirentire life inside other organisms, living a bachelor existence while making theirhosts miserable. Coming in contact with a tapeworm of the opposite sex would beproblematic if only single worms can infect hosts; evolution would therefore favorthe worm that was self-sufficient. Being a hermaphrodite also means that you canexplore new frontiers and colonize new habitats all by yourself. However, this isn'ttrue of all hermaphrodites. Many if not most animals that are hermaphrodites can'ttango alone and therefore need another member of their species for procreation. Ofcourse, they don't need to be too selective. Being both male and female, any othermember of their species will do.
The inability to fertilize their own eggs also helps hermaphrodites avoid inbreeding.One has only to look at the Peacock clan in the X-Files episode "Home" tounderstand the dangers, both mental and physical, associated with being related atseveral different levels. Sometimes during a single mating, hermaphrodites take turnsbeing the male or the female, which must be an interesting experience. It was oncethought that hermaphrodites lived longer than males, which would give hermaphroditesa natural selective advantage for evolutionary purposes. More recent studies,however, indicate that the males were engaging in normal macho behavior, which tendedto shorten the lives of males living with other males during the experiment.
Scully's discovery that two worms will kill each other provides the answer to savingthe member of the team that is infected. When an additional worm is added to theinfected person, the two worms finish each other off. What then to do about the oneremaining living worm? This dilemma leads to an unusual reversal of roles for our FBIheroes. Mulder wants to keep the worm alive, arguing that research is needed on itsgenetic structure. Scully, the scientist, wants it destroyed, feeling that the wormis too dangerous to live. The rights of species to survive often conflict with theneeds of humans whose lives or livelihood demand their destruction. The eradicationof poisonous snakes in the Northeastern United States, the elimination of wolves frommany parts of the country, and the destruction of the habitat of the spotted owl inthe Northwestern United States are all due to conflicts between nature and man. Inthe end, Scully wins the argument and the worms are a threat no more.
Mighty Mites in Trees
Cutting down trees in Washington National Forest is not a job for the fainthearted.Chain saws missing their targets...trees crashing about...logs with a mind of theirown...and if that weren't enough, loggers in the X-Files episode "DarknessFalls" deserve an additional measure of hazard pay for the unexpected surprise theyreceive after giving the final death blows to a massive old-growth tree.Unfortunately, none of them live to collect. Tiny wood mites that have made this treetheir home for hundreds of years are not pleased when forced to vacate the premisesafter the tree tumbles to the forest floor. These little mites are not your typicalwood mites. Repulsed by light and glowing a bright iridescent green, the mites soonrealize that the perfect menu for those long summer days isn't dried-up tree, butrather desiccated human, conveniently wrapped in family-sized cocoons.
Radio messages to the dried-up loggers go unanswered, causing the FBI and parkrangers to investigate. Mulder and Scully are shocked to discover that swarms ofmites are responsible for killing the defenseless loggers. With no visible signs ofUFOs or meteor impact craters, Mulder doesn't believe that the mites are the vanguardof an alien invasion. Rather, he theorizes that the mites represent a species thatwas probably extinct except for the inhabitants of the now dead tree. Mulder baseshis views on the fact that modern-day mites aren't repulsed by light and don't glowin the dark or desiccate and cocoon hapless humans. Mulder suggests that preservedeggs of the extinct mites lay dormant beneath the ground for an untold number ofyears until unearthed by the eruption by a nearby volcano. Waking from their longsleep, the eggs hatched into larvae, which then crept into the tree through itsroots. The mites proceeded to feast contentedly on tree innards for hundreds of yearsuntil their home was rudely toppled by the loggers.
For Mulder's theory to be within the bounds of extreme possibility, reviving otherancient eggs that are dormant and snoozing needs to be possible. The oldest eggs thathave been revived are crustacean eggs laid around 1630 in a pond in Newport, RhodeIsland. Sediment caused by Europeans settling in the area covered the eggs and keptthem from hatching. The eggs would still be buried had not Roger Segelken of CornellUniversity unearthed them, which caused many of the eggs to finally hatch.
A considerable gap exists, of course, between reviving four-hundred-year-old eggs andeggs that are millions of years old. However, creatures have been brought back tolife that are far older.
As a high school student, I spent many hours at the Los Angeles Museum of NaturalHistory trying to piece together the skull of a 7-million-year-old horse (before youget too excited, it's not the horse that comes back to life). I vividly remember allthose bones lying in front of me week after week like pieces from a giantthree-dimensional jigsaw puzzle. It was exhausting work. Intense concentration andmuch trial and error led to only a few tiny fragments reuniting with neighboring bonefragments each hour. Before I began working on the horse, I thought that being apaleontologist would be exciting and fulfilling work. But after a few years ofimmersion in one stack of ancient bone fragments after another, I realized that beinga paleontologist trainee left me with a sense of frustration. That horse was nevergoing to trot away when completed. Nor would the ancient bones reveal many cluesabout the true nature of the extinct horse.
For a few scientists who study prehistoric plants and animals, these frustrations arepartially assuaged by finding their tiny subjects encased in amber. Amber depositsare found all over the world, the oldest dating back some 320 million years. Sap,oozing out of wounded trees, trapped and mummified an astonishing variety of insects,crabs, scorpions, leaves, mushrooms, and even lizards. If the sap hardened in anenvironment where there was limited exposure to oxygen, it turned into the colorful,translucent substance known as amber. Amber provides a window into the last actionsof the trapped creatures — a tiny leaf beetle preserved in the act of fighting offthe sap that slowly engulfed it; a jumping spider clutching the millipede it nevergot a chance to eat; little fruit flies reflexively laying eggs; and midges enjoyingone last romantic fling.
Browsing through the beautifully illustrated book on amber by David Grimaldi (AmberWindow to the Past), you can almost envision the centipedes, caterpillars, andlizards quickly scurrying up the nearest tree if released from their amber prisons.However, as lifelike as these trapped creatures look, down to the tiny scales on thewings of moths and the profuse hairs that cover the larvae of owl flies, they are, ofcourse, very dead. These encased animals have about as much chance of coming back tolife as do ancient Egyptian mummies. But what is true of the mummified animals maynot be true of the tiny creatures that inhabited the insides of the dead animals.What if these endosymbionts and endopathogens are still alive, waiting only for acrack in the amber that travels through their mummified animal host to be free atlast?
If these tiny creatures are still alive, then their DNA must be undamaged. The DNA ofan organism is analogous to the hard drive of a computer. The DNA contains all theinformation required for an organism to make or acquire the substances necessary forlife. Imagine how well a computer would operate if its hard drive was shattered intothousands or millions of pieces (trust me, you don't need to conduct your ownexperiment). Intact DNA, which is normally present as a single piece in bacterialcells, forty-six pieces in human cells, or as many as a few hundred pieces in someplant cells, is required for any organism frozen in time to restart its dormantmetabolism and prepare to live again.
Scientists have been very interested in studying the DNA of organisms preserved inamber — and not simply to create living dinosaur amusement parks. By analyzing theDNA from ancestors of modern organisms, insights can be gained into the evolution ofthat species.
The discovery that DNA isolated from animals in amber isn't completely degraded — inother words, it isn't broken into millions of pieces — was established in 1992. Tinyfragments of DNA were sufficiently intact to be analyzed from a 25-million-year-oldtermite and bee. This meant that insect DNA can survive for millions of years, butapparently not in an undamaged form. The next report on ancient DNA was published in1993, on the same day that the movie Jurassic Park was released. Newspaper headlinesproclaimed that DNA from the time of the dinosaurs had been discovered and hintedthat a real Jurassic Park might be just around the corner. The papers didn'tdwell on the minor detail that the ancient DNA came from an organism somewhat lessexotic than Velociraptor — a weevil that inhabited the early Cretaceous period some130 million years ago. Given the likely size of the audience for ancient-weevilamusement parks, the story soon died. However, scientific interest remainsundiminished. Since then, about one third of the attempts to isolate DNA from animalsin amber have been successful.
The survival of even fragmented DNA from creatures trapped in amber is astonishing.Amber, being the sap of trees, is organic material composed mainly of carbon,hydrogen, and oxygen. The high oxygen content implies that the environment inside theamber is oxidizing, which leads to the production of many free radicals that aredamaging to DNA. After millions of years of contact with oxygen, any DNA should belong gone. However, water is also required for DNA to fragment, and amber resin actslike a desiccant to suck water from the cells of the organisms that became trapped.The lack of water must afford some protection to the DNA and allow it to endure themillions of years of exposure to the destructive tendencies of oxygen.
Although the DNA of amber-encased weevils still is highly fragmented, the DNA ofendoparasites or endosymbionts may be much more intact. It is well known that somebacteria and fungi when presented with harsh environmental conditions (such as havingyour host become mummified in sap) are able to form spores. Bacterial spores keeptheir fragile DNA in a watertight container surrounded by a thick, protective proteincoat. Spores are resistant to conditions such as boiling, radiation, pressure, andchemicals that would mean instant death to an unprotected cell. Extrapolations frommodern experiments suggest that spores could survive for several hundred thousandyears if surrounded by organic material that protected their DNA from the sun'sionizing radiation, another producer of free radicals. Spores inside mummifiedinsects should get plenty of protection from radiation due to the organic material ofthe amber and the exoskeleton of the insect. However, it is a far cry from sayingthat spores might survive for one hundred thousand years to showing that they cansurvive for 25 million years.
But this is precisely what Raul Cano from California Polytechnic State Universityshowed in 1995. In an amazing paper published in the eminent journal Science,Cano described extracting bacterial spores from the insides of an extinct species ofstingless bee encased in a piece of amber that was unearthed in the DominicanRepublic. The spores, which Cano revived and successfully grew in the lab, were froma strain of bacteria called Bacillus sphaericus. This was significant, since the samebacteria live inside modern-day Dominican stingless bees.
Naturally, upon hearing the news of million-year-old bacteria growing in a lab inCalifornia, many scientists were as skeptical as Scully would have been. For thisnews to become truly accepted, the experiment needs to be repeated by otherscientists. Unfortunately, no one except Raul Cano has been able to revive ancientbacteria, although many have tried. The skeptics prefer to believe that the littlebacilli were simply contaminating modern bacteria that just happen to also live inDominican bees and just happened to enter Cano's sterile chamber in California. Thesescientists will have even more reason to be skeptical when they read the most recentpaper from the Cano lab. The latest work describes the isolation from amber of anancient version of a bacterial species called Staphylococcus. Staphylococcidon't form spores, so any revived cells must have survived for millions of years inthe absence of a protective protein shell. If true, then the survival powers of DNAare much greater than previously realized.
If ordinary bacteria can be revived after snoozing for millions of years insideamber, might dormant mite eggs also survive under similar conditions? Mites arearthropods, just like spiders. At first glance, mite eggs resemble considerablysmaller versions of the eggs you eat for breakfast. Crack open the shell and there'sa glob of yolk inside. Mite eggs, however, come in little packets like peas in a pod,and can survive very harsh environmental conditions. If a chicken lays an egg in ahole in late fall and forgets about it, the result will be a dead, frozen chickenegg. But mites, like other land-living arthropods, have eggs that survive the winter.Arthropods make their own brand of antifreeze somewhat similar to the antifreeze usedin radiators to keep car engines from freezing. Also, just like bacterial spores thatmust shut down their metabolism during a long sleep, mite eggs slow down theirmetabolic clocks when in nasty environmental conditions. In another parallel with theancient spores, mite eggs can live in a desiccated environment. They are like cacti,able to suck water in without letting water out.
As sturdy as mite eggs are, surviving for millions of years underground protected bynothing except their waxy cuticle shell is not likely. Mulder uses brevity whenreciting his theory on the origin of the mites — not too surprising given thepresence of desiccated loggers hanging in trees. If he had expanded his explanation,Mulder might have speculated that the eggs survived by virtue of being encased inamber. Some of the one million different species of mites currently sharing ourplanet are internal parasites of insects. If an insect host became entombed in ambermillions of years ago, the mites living inside the insect would suffer the same fate.Any eggs of the trapped mites would be doubly protected from the oxidizingenvironment of the sap and the long-term irradiation of the sun by the body of themother mite and the insect host.
Mulder speculates that the eggs were unearthed by a volcanic eruption. Imagine amassive volcano hurling rocks, trees, and amber into the air. While it is tempting toimagine the heat of the volcano melting the amber prison, thereby releasing thetrapped eggs, any temperature hot enough to melt amber would surely destroy the eggs.It's not, however, beyond the realm of extreme possibility that the amber prison wasflung high into the sky by the force of a volcano and then plummeted back to Earth,slamming into the ground. The force of the impact could cause amber, mummifiedinsect, and mother mite to shatter, releasing the stored eggs. If the eggs were stillalive, they could become stimulated to begin the process of development into anembryo — perhaps they would just need some sunlight and warm temperatures; theancient Rhode Island crustacean eggs required only a bit of fluorescent light and afew degrees above freezing to hatch from their four-hundred-year sleep. Onceawakened, the mite embryos would develop into larvae, which, still groggy after sucha long sleep, might climb into the nearest tree and stay hidden until theirdescendants are rudely disrupted hundreds of years later.
While the light-sensitive mites lie hidden throughout the day, during the night it'sthe humans who need to hide. As Mulder and Scully huddle in the loggers' cabin tryingto will the sputtering generator to keep the single bulb lit, Scully muses on how themites might glow in the dark. While Scully believes that the mites absorb enzymestaken from the bodies that they cocoon, there are better explanations. Fireflies glowin the dark because they can make two items: an enzyme called luciferase and asubstance called luciferin. The firefly enzyme luciferase is able to make light bycombining luciferin with a second substance, ATP, the fuel of cells. Humans don'tmake luciferase, so the mites can't be sucking this enzyme out of humans. However,humans do make and consume about four pounds of ATP every hour. It's possible thatthe mites make both the enzyme luciferase and the substance luciferin but not enoughATP. So maybe the mites were sucking the ATP out of human cells in order tosupplement their own stores of ATP and keep glowing.
Mulder and Scully survive the night in the loggers' cabin but are attacked by themites the following night as they try to escape from the single-minded swarms. Whenthey are recovering in the hospital from their near fatal desiccations, a doctortells Mulder that they found a large concentration of luciferin in their lungs,indicating that the mites probably were producing light using the enzyme luciferase.Although Mulder and Scully recover, the mites are not so fortunate. Teams ofexterminators spray insecticide throughout their mountain site, wiping out theancient swarms and returning the mites to their previous extinct state. It's doubtfulthat anyone, even Mulder, shed any tears over the loss of this particular speciesfrom the planet.
Continues...
Excerpted from The Real Science Behind the X-Filesby Anne Simon Copyright © 2001 by Anne Simon. Excerpted by permission.
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