The once-isolated islands of the Galápagos gave Charles Darwin insights into the dynamics of evolution that changed forever the way we think about the world. A century and a half later, scientists are still pursuing the ideas that drove him, but are carrying these studies into a wide range of new locations — some exotic, some close to home.
“The evidence is overwhelming that evolution happened largely as Darwin proposed,” says Jerry Coyne, an evolutionary biologist at the University of Chicago and author of “Why Evolution Is True.” “Working through the engine of evolutionary change — natural selection — we can see evidence of animals and plants adapting to their environment before our eyes.”
Such research took on cosmic importance recently when one of NASA’s Mars rovers found deposits of silica similar to those at the hot springs of Yellowstone Park. On Earth, such deposits typically contain remains of microscopic life.
Described below are some other places where modern followers of Darwin go for fresh inspiration about how life has adapted to nearly every environment on the globe.
25,000 feet under the sea
At the bottom of one of the world’s deepest ocean trenches, scientists have discovered a thriving colony of highly sociable fish — something they never expected to find there. Researchers had assumed that fish in such a harsh environment would be fragile, solitary and motionless, conserving their energy due to a meager food supply. But high-definition submersible cameras captured images of abundant life nearly 5 miles beneath the surface of the Pacific. One camera spotted a cluster of 19 snailfish darting around bait like goldfish in a pond despite near-freezing cold, total darkness, and water pressure of 5 tons per square inch.
“We expected maybe one or two fish, but to see such a big group was amazing,” says Monty Priede, director of the University of Aberdeen’s Oceanlab, which specializes in robotic exploration of the deep sea. “And this is just the snailfish. There are also a lot of crustaceans, including prawns, living down there. We suspect there are half a million fish at these depths in each of the ocean trenches in the Pacific. Somehow they’ve adapted to the extreme cold and intense pressure.”
Oceanlab researchers made these discoveries last fall during a two-week expedition to the Japan Trench off the northeast coast of Japan, using submersible camera platforms engineered to withstand the extreme conditions. It was part of Oceanlab’s Hadeep project, a collaborative venture with the University of Tokyo investigating life in the so-called hadal region of the ocean (anything more than four miles below sea level). The newfound population of snailfish, which feed on tiny shrimp that scavenge detritus on the ocean floor, are believed to be the deepest living fish ever recorded.
Snailfish are thought to have colonized deep ocean trenches relatively recently, in evolutionary terms. Fish are dependent on oxygen that dissolves in the surface water and then sinks downward, but it is only within the past 70 million years that the deep seas have been oxygenated. “Snailfish are the most advanced of the fish. They produce relatively large eggs, and all of them have various kinds of parental care,” Priede says. “These explorations will help answer some tantalizing evolutionary questions. What are the limits of life? Is it possible to have living systems at even greater pressures? We’re just beginning to find out.”
An abandoned copper mine
Land contaminated by runoff from industrial waste may soon be reclaimed by an unusual army of eco-warriors: metal-eating earthworms. Each deposit of metal at sites where these worms are found creates a unique evolutionary event, yielding organisms that thrive in highly polluted environments.
Discovered in abandoned mines in England and Wales, these highly evolved superworms devour toxic heavy metals like lead, arsenic, and copper. “They seem to be able to tolerate high concentrations of metals, and exposure to the metal drives the worms’ evolution,” says Mark Hodson, a soil scientist at the University of Reading in England who unraveled the mechanisms that enable these worms to stomach normally lethal poisons.
DNA analysis of lead-tolerant worms unearthed in Cwmystwyth, Wales, revealed subtle changes in the worms’ genetic makeup that were induced by the metal. Researchers used sensitive X-ray technology to track how the worms metabolized metal particles one-thousandth the size of a grain of salt. “These earthworms have developed adaptive mechanisms for dealing with the soil pollution,” Hodson says. “When they ingest the soil, the metal accumulates in their tissues. But they have modified calcium pathways and secrete an enzyme that converts the metal into a less toxic form.”
When the worms process the polluted soil, they excrete a slightly different version of the metal that is easier for plants to absorb. Eventually, Hodson says, “we might be able to recruit these earthworms to accelerate the remediation process: Just pop them in the soil and use them to clean up contaminated sites.”
The wilds of New Guinea
Even though it is only about one-tenth the size of the United States, New Guinea has 7 percent of the world’s biodiversity, making the island a living laboratory for evolutionary biologists like Christopher Austin, who observes firsthand the adaptive mechanisms that spark the creation of novel species. In the past 20 years, Austin, a herpetologist at Louisiana State University’s Museum of Natural Science, has discovered nearly a dozen new species of lizards on the tropical island.
New Guinea’s unusually varied topography and climate have spawned a diverse array of habitats. They range from steamy lowland jungles, swamps and floodplains to cloud forests, alpine grasslands and glaciers capping mountains more than 16,000 feet high. The island harbors some of the world’s most unusual organisms, including kangaroos that live in trees and lizards that have green blood.
But New Guinea does not divulge its secrets readily. “There’s a very limited road system, and most of our travels are either by foot or by small airplane,” says Austin, who often spends weeks camped on the banks of the Sepik River in the north-central rainforest where he collects lizards, snakes, and frogs. Back in his lab at Louisiana State, he analyzes their genetic material to better understand how New Guinea’s many unique species diverged from their relatives and took on their distinctive forms.
Every new species that Austin discovers is another piece of the puzzle. And because of the looming threats created by global climate change, what he is uncovering in these remote rain forests could have far-reaching consequences.
“We are in the midst of one of the most remarkable patterns of extinction that has ever happened,” he says. The current temperature spikes are destroying delicate ecosystems and threatening the survival of millions of species of plants and animals around the globe. “We need to understand the balance between extinction and speciation [the creation of new species] if we have any hope of salvaging this planet.”
The Canadian Arctic
In 2004, on a remote island in the Arctic wilderness, American scientists uncovered the remains of a fossil fish, Tiktaalik roseae, that first crawled on land about 375 million years ago. The find has deepened our understanding of this crucial evolutionary milestone and has illuminated the complex bodily changes that occurred when our distant ancestors moved out of the water.
Tiktaalik is a strange creature, a combination of the limbs, skull, neck, and ribs of four-limbed animals and the more primitive jaw, fins, and scales of fish. It seems to be an intermediate step between fish and land-living animals, a key link in the evolutionary chain that led to amphibians, reptiles, and dinosaurs.
Researchers had conducted five annual fossil-hunting expeditions to Canada’s Ellesmere Island, 830 miles south of the North Pole, before they finally hit pay dirt five years ago. The conditions were harsh. Even in July, when the sun never sets, there were freezing temperatures, high winds, and nearly constant rain. One afternoon a member of the team spotted what looked like the snout of a flatheaded fish sticking out of a cliff.
The newly discovered fossil fish was a predator that could reach 9 feet in length. It lived in shallow freshwater but was able, researchers believe, to pull itself out of the water and move around on land. (The name Tiktaalik means “large freshwater fish” in Inuktitut.) In the late Devonian period, nearly 400 million years ago, the area where the fossils were found was near the equator and had the temperate climate of the Amazonian rain forest. As the earth’s continental plates shifted, the land drifted north to the Canadian Arctic.
An analysis of Tiktaalik’s anatomy, completed this past October, indicates that the evolution of fins into sturdy limbs was accompanied by other anatomical innovations, including the rudiments of an articulated neck.
“What allowed this lineage of animals to start to exploit the land was not just a matter of changing the fins to limbs but also the ability to move their head so they could navigate in shallow water,” says Ted Daeschler, a team co-leader and a paleontologist at the Academy of Natural Sciences in Philadelphia. “The fossil record has shed light on these major evolutionary shifts.”
The Chihuahuan desert
Cuatro Cienegas, nestled in a valley surrounded by towering mountains, is an oasis in northern Mexico’s Chihuahuan desert, with more than 400 ponds and outlet streams fed by underground springs. Scattered over 200 acres, these pools of sparkling blue water are home to 70 species of plants and animals that are found nowhere else on earth. The area has become a mecca for scientists, in part due to the presence of stromatolites — reeflike structures created by blue-green algae that were abundant before the rise of multicellular animals.
The unique ecosystems of Cuatro Cienegas may yield insights into what sparked the Cambrian transition, a pivotal time about 540 million years ago when simple, single-celled life developed into a wide variety of multicellular forms.
“There was a sudden and explosive diversification of animal life from some trigger that we haven’t as yet identified,” says Jack Farmer, a paleontologist at Arizona State University in Tempe. “Cuatro Cienegas may provide clues because the mechanisms that control the region’s biodiversity may have operated during the Cambrian period.”
Scientists have found that about half of the organisms at Cuatro Cienegas are most closely related to marine life, even though the oases here have not been in contact with the ocean for tens of millions of years.
“How do you get marine organisms so far from the ocean?” wonders James Elser, a biologist at Arizona State who makes regular trips to the site. “One theory is that they were deposited as the geological system formed and were trapped inside limestone until they were liberated eons later to form their own ecosystems. There’s a vestigial community — an experimental time machine — and studying them in the present might tell us something about the past.”
The intensive care unit
In a perfect world, hospitals would strictly be places where the sick go to get well. Unfortunately, the hothouse environment of the hospital provides a window into an insidious side of evolution. All too often an epic battle for the survival of the fittest is taking place on almost every ward, transforming what should be sterile surfaces into incubators for antibiotic-resistant bacteria.
Because infectious microbes reproduce quickly and have enormous populations, changes in their genetic makeup over several generations can show up in just a few days. Moreover, they are up against overwhelming natural selection pressures: powerful antibiotics that kill off all but the hardiest microbial mutants. This ratchets up the normally leisurely pace of evolution by many orders of magnitude. “It’s Darwinism at its finest,” says Carl Bergstrom, an evolutionary biologist at the University of Washington in Seattle who studies drug-resistant bacteria.
Hospital-acquired infections kill 90,000 people a year — more than HIV, breast cancer and influenza combined. The magnitude of the problem has scientists like Bergstrom in a race against time as they attempt to harness what they know about evolutionary theory to slow the rate at which bacteria become resistant. Bergstrom’s tools are computers and mathematics, and the testing grounds for his ideas are the hospital intensive care units that provide him data.
“We keep inventing new antibiotics, but bacteria evolve resistance almost immediately, so we’re constantly playing catch-up,” he says. “How can we make the best use of the antibiotics we’ve got now? We’re using mathematical models to generate hypotheses about how we can shape and alter prescription practice to minimize or delay the evolution of resistance.”
Click hereto see Discover's special package on Darwin in honor of his 200th birthday and the 150th anniversary of "The Origin of Species."
© 2009 Discover Magazine