However, reasonable evidence exists that historical extinctions and extirpations—local extinctions in which a species ceases to exist in the specific geographic area of study—are at least partly attributable to infectious disease. Avian malaria and bird pox are believed to have decimated certain bird populations in Hawaii in the late 19th century. In the mammal kingdom, the abrupt disappearance of native rats on Christmas Island in the Indian Ocean at the turn of the 20th century is believed to have been caused by disease-carrying, flea-ridden black rats that arrived there on a merchant ship.
In recent years, numerous extant species have come under attack by invading infectious disease. In Australia, koalas are besieged by two major pathogens, one of which can cause sterility or blindness. The World Wildlife Fund claims that infections of these types could lead to the extinction of koalas within 50 years. Whether these or other species disappear remains to be seen, but research indicates that disease caused by pathogens and parasites is not likely to be the primary factor in the extinction-threatening process. (Loss of habitat, human overhunting, and competition with new species are possible and/or contributing causes.)
Emerging diseases such as Ebola, HIV/AIDS, SARS, and H1N1 influenza have wreaked worldwide societal havoc and resulted in tens of millions of deaths. Reemerging infectious diseases, which appear in new places or in drug-resistant strains, also pose a significant threat to human life. Among these diseases are dengue virus, West Nile virus, and even cholera, which affects 3 to 5 million people each year and causes more than 100,000 deaths annually—despite the existence of a safe and effective vaccine.
The songs of humpback whales have been instrumental in bringing awareness of their dwindling numbers and the fight for bans on deep-sea whaling.
What Do Whales Sing About?
Humpback whales sing some of the most beautiful songs in the animal world. It’s not just “woo, woo, woo”—their songs last 10 to 15 minutes and have a definite form, usually consisting of five or six unique phrases. Only the males sing, which has led many scientists to theorize that they croon to attract females. The hole in this argument, though, is that no one has ever actually seen a female whale show any interest at all in a male’s song.
Male songbirds change their tunes to impress potential mates, but a group of male humpbacks all sing the same song. If the song changes midseason, they all adopt the same change. We don’t really know why they sing together. They might be trying to create a sense of peace before they mate, or they could be staking out their territory. Either way, it makes the competitive-mating theory seem less believable.
We’re also not quite sure why they change their songs in the first place. It could be that one whale tweaks part of the song, and if it’s catchy, the rest pick it up quickly. David Rothenberg, professor of philosophy and music at the New Jersey Institute of Technology, whose book analyzes whale songs, tested this by playing the clarinet to a whale swimming under his boat, and the whale seemed to change his song in response.
Another theory is that whales’ brains are programmed to change the tunes no matter where they are in relation to other whales. For example, scientists have made recordings of humpbacks in Hawaii and the Gulf of Mexico altering their songs in similar ways at the same point in the mating season, even though there’s no way the groups could be hearing each other’s songs.
Most of the research money goes to studying whale songs for conservation efforts (each whale has a unique voice, so it’s a good way of estimating how many are out there), not translating their meaning. That hasn’t kept the public from enjoying the soulful sounds, however, as several record companies have released albums featuring whale songs. One particular recording by biologist Roger Payne, released in 1970, is the best-selling natural sounds album of all time.
Can We Clone Extinct Animals?
It’s looking more and more likely that scientists will be able to resurrect some lost members of the animal kingdom through cloning. Disappointingly, dinosaurs would not be first on the list—more recently vanished species would offer the most viable DNA samples for reconstruction.
A Japanese team led by Akira Iritani, professor emeritus of Kyoto University, is hoping to deliver a real, live woolly mammoth within five or six years. Mammoths are unusually good candidates for resurrection: Although they’ve been extinct for thousands of years, their northerly habitat means that numerous mammoth bodies have been found entombed in ice. Although freezing damages DNA, Teruhiko Wakayama of the Riken Center for Developmental Biology has developed a technique for salvaging viable DNA from long-frozen mice. The mammoth team has adapted this method to extract undamaged nuclei from mammoth egg cells.
There’s a lot of work still to do, however. The mammoth egg nuclei will need to be implanted in elephant egg cells, and the (hopefully) viable embryo that results would then need to be carried to term by an elephant mother—a process that may well present new problems, despite the strong genetic similarity between mammoths and elephants. But with a little luck and a lot of scientist-hours, we may have our very own baby mammoth to study. And from there, who knows? Pet dinosaurs could be closer than we think.
Could Cockroaches Survive a Nuclear Holocaust?
First of all, nothing would live through the intense heat at ground zero. For instance, the 15-kiloton bomb that exploded over Hiroshima ignited a 1,800-degree Fahrenheit (982-degree Celsius) firestorm that incinerated everything within a radius of 1¼ miles (2 km). Outside that radius, however, roaches, and other insects and smaller organisms, stand a pretty good chance of surviving the subsequent fallout.
The average cockroach can withstand a dose of about 6,400 rads (the standard measurement for radiation exposure). In comparison, the lethal dose for humans is only 500 rads—roughly the equivalent of 42 simultaneous full-body CT scans.
One theory on roaches’ resilience credits their weekly larval molt, during which their cells divide half as frequently—and as adults, their cells divide even less often. Because radiation causes the most mutations in DNA that is replicating—which occurs most frequently in dividing cells—this slow replication protects roaches from radiation. So your kitchen’s unpaid tenants may indeed be the ones building the next civilization after we check out.
At the end of the last ice age, some 10,000 years ago, scores of species of large-bodied animals, called megafauna, became extinct throughout the world.
What Caused the Extinction of the Megafauna?
Megafauna—any animal weighing more than 100 pounds (45 kg)—included some of the most bizarre beasts ever to inhabit the Earth: glyptodons, armadillo-like mammals the size of a Volkswagen Beetle; ground sloths weighing 9,000 pounds (4,082 kg) and reaching 20 feet (6 m) in length; megalodons, 50-foot (15-m) sea creatures bigger than the largest great white shark; and beavers that tipped the scales at 200 pounds (90.7 kg). They all thrived for millions of years and then simply vanished.
Some scientists believe that global climate change triggered the mass extinctions, contending that megafauna came into existence in colder, glacial conditions and died out with the commencement of warmer climates. As tundra was replaced with forestlands, species adapted for colder climates, such as mammoths and woolly rhinoceroses, were supplanted by animals better adapted to the new environment, such as deer and pigs.
The megafauna, however, had withstood millions of years of environmental change. Why would they disappear simply because the climate warmed? They wouldn’t, claim supporters of the human intervention theory: By overhunting, humans were directly involved in exterminating scores of megafauna species. The archaeological record indicates that the human exodus from Africa to new locations across the planet and into these animals’ territories was occurring at this time.
Supporters of the climate change theory, however, point to the lack of evidence that human hunters were capable of systematically overkilling megafauna. After all, they reason, one of the world’s most widely hunted large animals, the American bison in North America, managed to s
urvive for nearly 10,000 years after it first became a prey for hunters.
Archaeologist K. Kris Hirst offers a more likely scenario for the extinction of megafauna—that combined forces are responsible. Animals that were not able to adapt to Earth’s changing, colder temperatures died out. Additionally, colder air may have pushed human populations to migrate, upsetting the predator-prey balance. Easy targets were killed off, or the presence of new pathogens led to extinctions.
As it turns out, the disappearance of numerous megafauna species had negative impacts upon Earth’s environment. For example, when gomphotheres, a large elephant-like creature, went extinct in South America about 9,000 years ago, the delicate balance of the region’s food chain was devastated. The animals ate in the forest, and their droppings fertilized other areas. “That no longer happens,” says Yadvinder Malhi, professor of ecosystem science at Oxford University, “and places like the Amazon are today affected by low nutrition as a result.”
Scientists are hopeful that solving the mystery of the megafauna’s extinction will help us better understand how other mass extinctions might happen in the future—including our own.
Why Are Bees Disappearing?
Beekeepers first noticed something strange in 2006—unusually large numbers of bee colonies were dying off. Scientists soon called the phenomenon colony collapse disorder (CCD). It was marked by a hive having a live queen bee but few or no adult honeybees.
The loss of millions of beesin just a few years concerned both scientists and farmers. In the United States each year, bees pollinate agricultural crops worth billions of dollars.
Scientists have suggested several theories for the mysterious disappearance of the valued honeybees. These include natural enemies (such as the Varroa mite or pathogens), deficiencies in the bees’ diet, farming practices, and pesticides. The pesticides that have received the most attention are a class called neonicotinoids. As the name suggests, they are derived from nicotine, and they were introduced during the 1990s. Once applied to a plant’s roots or sprayed on the crop itself, they remain in the plant’s system for at least one growing season.
A 2014 study led by Harvard scientist Chensheng Lu found that honeybees exposed to sub-lethal levels of neonicotinoids were more likely to abandon their hive than bees in a control group. The research, Lu’s team declared, backed up earlier studies that showed “sub-lethal exposure to neonicotinoids is likely the main culprit for the occurrence of CCD.” A U.S. government-funded study, released in 2015, said that the pesticides are probably not the sole source of the disorder, but part of a larger host of causes.
Manufacturers of neonicotinoids argue that the science is unclear about the role their chemicals might play in CCD. After all, unexplained colony losses occurred in the United States before the introduction of the pesticides. And in Great Britain, scientists have found that previous disappearances of wild bees and wasps, also pollinators, occurred at times when farmers changed their practices, such as adding new fertilizers or taking over more wild lands for agriculture.
Whatever the cause, American farmers risk losing some of their crops if colony collapse disorder continues.
Why Do Geese Fly in a V Formation?
In many regions of North America during fall and early winter, you might spot large flocks of geese flying overhead in a large V formation. Typically, one bird maintains the lead position, followed by the others in two lines that fork apart. Why do the geese fly in a V? Why not assume a C or S formation? Recent studies indicate that the V serves two main functions: energy conservation and visual contact.
As a bird flaps its wings in flight, air swirls around its wingtips, creating an upward lift, while air moving off the bottom pushes downward. Flying in a V formation, each goose is generally slightly behind and above the bird ahead of it—a position where the air is getting pushed up. The goose rides the extra lift provided by the bird it is following, thereby conserving the energy required to flap its wings and thus being able to fly farther.
According to researcher Steven Portugal of the Royal Veterinary College in Hatfield, United Kingdom, birds flying in a V formation display unique mechanisms to conserve energy. In a study conducted with northern bald ibises flying in a V formation, Portugal discovered that each bird controlled its flapping strokes so its own wingtips matched the wingtip path of the bird in front of it. In addition, if a bird got too close to or lagged too far behind the first bird, it modified its flapping speed. The apparent objective of these behaviors is to maximize the amount of lift provided by the first bird. “It’s amazing how quickly they can respond to any changes [by] the bird in front,” says Portugal.
Flying in a V formation also allows geese to maintain visual contact with each other, which helps keep the group intact and flying as a single unit. Military aircraft have patterned their flying formations in the same manner. Researchers study the pros and cons of conserving fuel by reducing drag on the airplane versus the effects of flying directly in another plane’s wake.
CHAPTER 6
Human Triumps and Troubles
What Was the Purpose of Stonehenge?
On Salisbury Plain in Wiltshire, England, the circle of massive stones known as Stonehenge has been a place of mystery for 5,000 years.
Archaeological evidence shows that the monu- ment was constructed in phases between 3000 and 1500 The sheer size of the stones is impressive, with some reaching a height of 30 feet (9 m) and weighing 25 tons (22,680 kg). Stonehenge consists of two circles, an outer circle of sandstone from a nearby quarry and an inner horseshoe made of bluestone, named for its blue sheen when wet or cut. Intense speculation surrounds Stonehenge and its original purpose. Many historians suspected the circle of stones was a healing site or temple of worship. Others theorize that it was an astronomical observatory.
One reason Stonehenge remains mysterious is that the site’s custodian, English Heritage, a commission dedicated to preserving England’s landmarks, does not regularly permit excavations. Most of the data comes from the 1920s, and later the ’50s and ’60s, but the excavations weren’t very well recorded. Some scientists believe that understanding the chronology of when the stones were erected may provide clearer explanations of the significance of Stonehenge.
Recently, two archaeologists gained permission to excavate. Timothy Darvill and Geoff Wainwright think the answer to Stonehenge lies in the bluestones in the center of the circle, whose origins are in the mountains of Wales, more than 150 miles (241 km) away. Wainwright recalls, “The pieces of the puzzle came together when Tim and I looked at each other and said, ‘It’s got to be about healing.’” They believe that prehistoric people brought the stones from a region with natural springs, which they presumed had healing powers. But how humans moved the bluestones over those 150 miles (241 km) is still unknown. There are no markings left by tools on the stones that would suggest they were quarried from their original location. One theory is that glaciers carried the stones most of the way and humans dragged them to their current spot. But evidence for this is lacking.
Inducted in 1986 as a World Heritage Site, Stonehenge is vitally significant to understanding life in the Neolithic and Bronze Ages. It is also the most architecturally sophisticated stone circle in the world, spanning more than 2,000 years of continuous use. Today, Stonehenge has a significant role in religion and culture, inspiring paintings, poems, books, music, and films. While thousands of people visit the monument every year, no day is bigger for Stonehenge than the summer solstice when the Sun rises above the heel stone, a rough stone outside the circle. As the architects of Stonehenge likely intended, this helped ancient civilizations mark the passing of time, and serve as a place of ritual and celebration.
About 37,000 people gathered at Stonehenge on June 21, 2014, to witness the event, admiring the longest day of the year just as prehistoric people did thousands of years ago.
How Were the Easter Island Statues Built?
On Easter Sunday 1722, the crew of a Dutch ship sailing
in the Pacific Ocean roughly 2,000 miles (3,218 km) off the coast of Chile unexpectedly sighted land. Admiral Jacob Roggeveen was astonished to see the island’s coast lined with scores of giant statues. Roggeveen named the island Paasch-Eyland, meaning “Easter Island” in 18th-century Dutch. The current name of the Polynesian island is Rapa Nui.
The builders of the strange stone statues were the descendants of Polynesian voyagers who first settled the island in about 1200. Since their discovery, the 887 mysterious carved figures, ranging in height from 4 to 33 feet (1.2–10 m), have baffled scientists and captivated the public’s imagination. Large heads featuring broad noses, jutting chins, and deep-set slits for eyes rest on standing or squatting torsos. Expressions on the stone faces are solemn, as if the statues are watching over the land or waiting for something.
The statues, called moai, were carved from stone called tuff, an easily workable, compacted volcanic ash. Stone tools were used to create the faces and designs on the statues. Scientists believe that most of the figures were carved in a quarry located in an extinct volcano on the northeastern part of the island. Yet without animals to pull heavy loads or wheels to move stone or wooden platforms, how did the people of Easter Island transport the giant carvings—some of which weigh more than 80 tons—to their resting places, in some cases more than 11 miles (17.7 km) from the quarry?
Some theorists have proposed the statues were dragged across the island, using rope. Others believe the figures were rolled on the trunks of palm trees. Ancient alien proponent Erich von Däniken claims the moai were built and erected by extraterrestrials.
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