Is Old Age Memory Decline Reversible?

Is Old Age Memory Decline Reversible?

New research suggests that triggering new nerve cell production in adult brains could stave off short-term forgetfulness

Scientists have found that a lessened supply of new nerve cells in the adult brain apparently triggers short-term memory loss typically associated with aging, setting the stage for one day developing therapies designed to maintain a steady supply of fresh neurons to keep the mind sharp.

"Neurogenesis (nerve-cell production) goes down with age … it's known that with old age there's a decrease in short- term memory," says Ronald Evans, a genetics professor at the Salk Institute for Biological Studies in La Jolla, Calif. "We know that if we can increase the process, we know what the consequence could be in the brain, which would be to increase short-term learning and memory."

"New experiences, new memories [and] new learning [are] greatly facilitated by neurogenesis," he adds. "Neurogenesis is in fact a fundamental feature of learning and memory. … Neurogenesis goes down with age; and, it's known that with old age there's a decrease in short-term memory."

Evans is co-author of a study published in Nature that shows impaired short-term memory and learning in adult mice, in which scientists blocked the process of neurogenesis. They did this by engineering mice that lacked one copy of the gene responsible for the production of Tlx, a protein that the team had previously determined was crucial to maintaining and renewing the arsenal of neural stem cells.

"The other allele (gene copy) is normal, but it is susceptible to knockout upon ingestion of [the] orally active estrogen antagonist" tamoxifen, Evans says. "It's a very effective knockdown." After being given tamoxifen (perhaps best known as a breast cancer drug) for eight days, an otherwise normally developing mouse had more than 80 percent fewer new neural stem cells in its hippocampus (a structure in the brain's frontal region linked to short-term memory).

The genetically altered mice performed as well as normal peers did in experiments based on learning out of fear, such as associating a sound or light flash with a shock to a paw. They failed, however, to perform up to speed on a spatial memory task: It took days for the mice lacking new nerve cells to lessen the time it took for them to find a platform floating in a pool of opaque liquid on which they could stand.

Normal mice took about three days to make the connection, but Evans says the knockout mice were still on "a learning curve" six days into the experiment." They eventually learn," he says, "but it takes them much longer."

Martin Wojtowicz, a physiologist at the University of Toronto, downplayed the finding, noting that it contradicts his own research on rats, which found a link between neurogenesis and fear, but not memory. "They see a very subtle effect in the water maze," he says, "but other than that, nothing."

Evans, however, sticks by the team's conclusions, pointing out that Nature required several additional tests be conducted to verify the data. He also notes that in previous studies, researchers irradiated parts of the animals' brains or injected them with cancer drugs that destroyed more than targeted nerve cells, making it difficult to determine whether it was the suspect cells or other damaged areas that were to blame for certain behaviors. In contrast, he says, his team explicitly links neurogenesis to short-term memory, which in the future could lead to a drug designed to stimulate nerve cell production and potentially counter memory loss in older adults.

Affairs of the Lips: Why We Kiss

Affairs of the Lips: Why We Kiss

Researchers are revealing hidden complexities behind the simple act of kissing, which relays powerful messages to your brain, body and partner

 

When passion takes a grip, a kiss locks two humans together in an exchange of scents, tastes, textures, secrets and emotions. We kiss furtively, lasciviously, gently, shyly, hungrily and exuberantly. We kiss in broad daylight and in the dead of night. We give ceremonial kisses, affectionate kisses, Hollywood air kisses, kisses of death and, at least in fairytales, pecks that revive princesses.

Lips may have evolved first for food and later applied themselves to speech, but in kissing they satisfy different kinds of hungers. In the body, a kiss triggers a cascade of neural messages and chemicals that transmit tactile sensations, sexual excitement, feelings of closeness, motivation and even euphoria.

Not all the messages are internal. After all, kissing is a communal affair. The fusion of two bodies dispatches communiqués to your partner as powerful as the data you stream to yourself. Kisses can convey important information about the status and future of a relationship. So much, in fact, that, according to recent research, if a first kiss goes bad, it can stop an otherwise promising relationship dead in its tracks.

Some scientists believe that the fusing of lips evolved because it facilitates mate selection. “Kissing,” said evolutionary psychologist Gordon G. Gallup of the University at Albany, State University of New York, last September in an interview with the BBC, “involves a very complicated exchange of information—olfactory information, tactile information and postural types of adjustments that may tap into underlying evolved and unconscious mechanisms that enable people to make determinations … about the degree to which they are genetically incompatible.” Kissing may even reveal the extent to which a partner is willing to commit to raising children, a central issue in long-term relationships and crucial to the survival of our species.

Satisfying Hunger
Whatever else is going on when we kiss, our evolutionary history is embedded within this tender, tempestuous act. In the 1960s British zoologist and author Desmond Morris first proposed that kissing might have evolved from the practice in which primate mothers chewed food for their young and then fed them mouth-to-mouth, lips puckered. Chimpanzees feed in this manner, so our hominid ancestors probably did, too. Pressing outturned lips against lips may have then later developed as a way to comfort hungry children when food was scarce and, in time, to express love and affection in general. The human species might eventually have taken these proto-parental kisses down other roads until we came up with the more passionate varieties we have today.

Silent chemical messengers called pheromones could have sped the evolution of the intimate kiss. Many animals and plants use pheromones to communicate with other members of the same species. Insects, in particular, are known to emit pheromones to signal alarm, for example, the presence of a food trail, or sexual attraction.

Whether humans sense pheromones is controversial. Unlike rats and pigs, people are not known to have a specialized pheromone de­tector, or vomeronasal organ, between their nose and mouth [see “Sex and the Secret Nerve,” by R. Douglas Fields; Scientific American Mind, February/March 2007]. Nevertheless, biologist Sarah Woodley of Duquesne University suggests that we might be able to sense pheromones with our nose. And chemical communication could explain such curious findings as a tendency of the menstrual cycles of female dormitory mates to synchronize or the attraction of women to the scents of T-shirts worn by men whose immune systems are genetically compatible with theirs. Human pheromones could include an­drostenol, a chemical component of male sweat that may boost sexual arousal in women, and female vaginal hormones called copulins that some researchers have found raise testosterone levels and increase sexual appetite in men.

If pheromones do play a role in human courtship and procreation, then kissing would be an extremely effective way to pass them from one person to another. The behavior may have evolved because it helps humans find a suitable mate—making love, or at least attraction, quite literally blind.

We might also have inherited the intimate kiss from our primate ancestors. Bonobos, which are genetically very similar to us (although we are not their direct descendants), are a particularly passionate bunch, for example. Emory University primatologist Frans B. M. de Waal recalls a zookeeper who accepted what he thought would be a friendly kiss from one of the bonobos, until he felt the ape’s tongue in his mouth!

Good Chemistry
Since kissing evolved, the act seems to have become addictive. Human lips enjoy the slimmest layer of skin on the human body, and the lips are among the most densely populated with sensory neurons of any body region. When we kiss, these neurons, along with those in the tongue and mouth, rocket messages to the brain and body, setting off delightful sensations, intense emotions and physical reactions.

Of the 12 or 13 cranial nerves that affect cerebral function, five are at work when we kiss, shuttling messages from our lips, tongue, cheeks and nose to a brain that snatches information about the temperature, taste, smell and movements of the entire affair. Some of that information arrives in the somatosensory cortex, a swath of tissue on the surface of the brain that represents tactile information in a map of the body. In that map, the lips loom large because the size of each represented body region is proportional to the density of its nerve endings.

Kissing unleashes a cocktail of chemicals that govern human stress, motivation, social bonding and sexual stimulation. In a new study, psychologist Wendy L. Hill and her student Carey A. Wilson of Lafayette College compared the levels of two key hormones in 15 college male-female couples before and after they kissed and before and after they talked to each other while holding hands. One hormone, oxytocin, is involved in social bonding, and the other, cortisol, plays a role in stress. Hill and Wilson predicted that kissing would boost levels of oxytocin, which also influences social recognition, male and female orgasm, and childbirth. They expected this effect to be particularly pronounced in the study’s females, who reported higher levels of intimacy in their relationships. They also forecast a dip in cortisol, because kissing is presumably a stress reliever.

But the researchers were surprised to find that oxytocin levels rose only in the males, whereas it decreased in the females, after either kissing or talking while holding hands. They concluded that females must require more than a kiss to feel emotionally connected or sexually excited during physical contact. Females might, for example, need a more romantic atmosphere than the experimental setting provided, the authors speculate. The study, which Hill and Wilson reported in November 2007 at the annual meeting of the Society for Neuroscience, revealed that cortisol levels dropped for both sexes no matter the form of intimacy, a hint that kissing does in fact reduce stress.

To the extent that kissing is linked to love, the act may similarly boost brain chemicals associated with pleasure, euphoria and a motivation to connect with a certain someone. In 2005 anthropologist Helen Fisher of Rutgers University and her colleagues reported scanning the brains of 17 individuals as they gazed at pictures of people with whom they were deeply in love. The researchers found an unusual flurry of activity in two brain regions that govern pleasure, motivation and reward: the right ventral tegmental area and the right caudate nucleus. Addictive drugs such as cocaine similarly stimulate these reward centers, through the release of the neurotransmitter dopamine. Love, it seems, is a kind of drug for us humans.

Kissing has other primal effects on us as well. Visceral marching orders boost pulse and blood pressure. The pupils dilate, breathing deepens and rational thought retreats, as desire suppresses both prudence and self-consciousness. For their part, the participants are probably too enthralled to care. As poet e. e. cummings once observed: “Kisses are a better fate / than wisdom.”

Litmus Test
Although a kiss may not be wise, it can be pivotal to a relationship. “One dance,” Alex “Hitch” Hitchens says to his client and friend in the 2005 movie Hitch, “one look, one kiss, that’s all we get ... one shot, to make the difference between ‘happily ever after’ and, ‘Oh? He’s just some guy I went to some thing with once.’ ”

Can a kiss be that powerful? Some research indicates it can be. In a recent survey Gallup and his colleagues found that 59 percent of 58 men and 66 percent of 122 women admitted there had been times when they were attracted to some­one only to find that their interest evaporated after their first kiss. The “bad” kisses had no particular flaws; they simply did not feel right—and they ended the romantic relationship then and there—a kiss of death for that coupling.

The reason a kiss carries such weight, Gallup theorizes, is that it conveys subconscious information about the genetic compatibility of a prospective mate. His hypothesis is consistent with the idea that kissing evolved as a courtship strategy because it helps us rate potential partners.

From a Darwinian perspective, sexual selection is the key to passing on your genes. For us humans, mate choice often involves falling in love. Fisher wrote in her 2005 paper that this “attraction mech­anism” in humans “evolved to enable in­di­vi­duals to focus their mating energy on speci­fic others, thereby conserving energy and facilitating mate choice—a primary aspect of reproduction.”

According to Gallup’s new findings, kissing may play a crucial role in the progression of a partnership but one that differs between men and women. In a study published in September 2007 Gallup and his colleagues surveyed 1,041 college undergraduates of both sexes about kissing. For most of the men, a deep kiss was largely a way of advancing to the next level sexually. But women were generally looking to take the relationship to the next stage emotionally, assessing not simply whether the other person would make a first- rate source of DNA but also whether he would be a good long-term partner.

“Females use [kissing] … to provide information about the level of commitment if they happen to be in a continuing relationship,” Gallup told the BBC in September. The locking of lips is thus a kind of emotional barometer: the more enthusiastic it is, the healthier the relationship.

Because women need to invest more energy in producing children and have a shorter biological window in which to reproduce, they need to be pickier about whom they choose for a partner—and they cannot afford to get it wrong. So, at least for women, a passionate kiss may help them choose a mate who is not only good at fathering children but also committed enough to stick around and raise them.

That said, kissing is probably not strictly necessary from an evolutionary point of view. Most other animals do not neck and still manage to produce plenty of offspring. Not even all humans kiss. At the turn of the 20th century Danish scientist Kristoffer Nyrop described Finnish tribes whose members bathed together but considered kissing indecent. In 1897 French anthropologist Paul d’Enjoy reported that the Chinese regard mouth-to-mouth kissing to be as horrifying as many people deem cannibalism to be. In Mongolia some fathers do not kiss their sons. (They smell their heads instead.)

In fact, up to 10 percent of humanity does not touch lips, according to human ethology pioneer Irenäus Eibl-Eibesfeldt, now head of the Max-Planck-Society Film Archive of Human Ethology in Andechs, Germany, writing in his 1970 book, Love and Hate: The Natural History of Behavior Patterns. Fisher published a similar figure in 1992. Their findings suggest that some 650 million members of the human species have not mastered the art of osculation, the scientific term for kissing; that is more than the population of any nation on earth except for China and India.

Lopsided Love
For those cultures that do kiss, however, osculation conveys additional hidden messages. Psychologist Onur Güntürkün of the Ruhr-University of Bochum in Germany recently surveyed 124 couples kissing in public places in the U.S., Germany and Turkey and found that they tilted their heads to the right twice as often as to the left before their lips touched. Right-handedness cannot explain this tendency, because being right handed is four times more common than is the act of kissing on the right. Instead Güntürkün suspects that right-tilted kissing results from a general preference that develops at the end of gestation and in infancy. This “behavioral asymmetry” is related to the lateralization of brain functions such as speech and spatial awareness.

Nurture may also influence our tendency to tilt to the right. Studies show that as many as 80 percent of mothers, whether right-handed or left-handed, cradle their infants on their left side. Infants cradled, face up, on the left must turn to the right to nurse or nuzzle. As a result, most of us may have learned to associate warmth and security with turning to the right.

Some scientists have proposed that those who tilt their heads to the left when they kiss may be showing less warmth and love than those who tilt to the right. In one theory, tilting right exposes the left cheek, which is controlled by the right, more emotional half of the brain. But a 2006 study by naturalist Julian Greenwood and his colleagues at Stranmillis University College in Belfast, Northern Ireland, counters this notion. The researchers found that 77 percent of 240 undergraduate students leaned right when kissing a doll on the cheek or lips. Tilting to the right with the doll, an impassive act, was nearly as prevalent among subjects as it was among 125 couples observed osculating in Belfast; they tilted right 80 percent of the time. The conclusion: right-kissing probably results from a motor preference, as Güntürkün hypothesized, rather than an emotional one.

Despite all these observations, a kiss continues to resist complete scientific dissection. Close scrutiny of couples has illuminated new complexities woven throughout this simplest and most natural of acts—and the quest to unmask the secrets of passion and love is not likely to end soon. But romance gives up its mysteries grudgingly. And in some ways, we like it like that.

A Visionary Approach Using Stem Cells to Repair Eye Damage

A Visionary Approach Using Stem Cells to Repair Eye Damage

New eye research center in India aims to fix visual impairments with the help of stem cells

 

 
STEM CELL RESEARCH at the LV Prasad Eye Institute in Hyderabad, India, involves the generation of reparative tissue in the laboratory, which is used to replace damaged or diseased tissue.

 
REHAB: At the LV Prasad Eye Institute, a child learning how to read uses a handheld magnifier in one of the two near-vision examination rooms.

A new vision research center opening in India today becomes the latest in a handful of facilities dedicated to exploring the potential of adult eye stem cells to repair vision damage. The Champalimaud Center for Translation Eye Research (C-TRACER), part of the LV Prasad Eye Institute in Hyderabad, India, will continue research begun by LV Prasad scientists, who use eye stem cells from living adults to grow new cells that are then implanted into damaged

The center's goal is to restore vision to some portion of the 65 million people worldwide—about 1 percent of the world population—considered to be legally blind, which the National Federation of the Blind defines as a central visual acuity of 20 / 200 or less in the stronger eye, even when aided by a corrective lens. Especially in developing countries in Africa and Asia, "most of these people are needlessly blind," says D. Balasubramanian, research director for both LV Prasad and the new facility.

Some of these people have vision problems caused by currently untreatable diseases, he notes, but others simply because they cannot afford or do not have access to relatively simple fixes such as surgery to remove cataracts (clouding of eye lenses).

Balasubramanian says the research center, which is being funded by the philanthropic Champalimaud Foundation in Lisbon, will be critical to improving eye care in his country where an estimated 15 million people suffer from eyesight woes, many of them genetic. "Hundreds of millions of Indians marry within their community," says Balasubramanian, a former director of the Center for Cellular and Molecular Biology and dean of the University of Hyderabad. "So there is a lot of inherited blindness that is gene-derived. Almost one in every 4,000 live births in India [for example] seems to produce congenital glaucoma."

Among the disorders that Balasubramanian has targeted is retinitis pigmentosa, a group of inherited diseases that cause degeneration of the retina (in the back of the eye where millions of photoreceptors capture light rays that the brain turns into images). "There is no cure for this and it is certainly a genetic disease," he says. People with retinitis pigmentosa experience a gradual decline in their vision because the eye's photoreceptor cells slowly die off.

C-TRACER researchers are trained to think in terms of the full cycle of developing treatments—from laboratory to operating room to clinical rehabilitation, or, as Balasubramanian says, "from bench to bedside." One example of this research is the practice of using stem cells taken from a healthy eye's limbus, the area around the cornea where stem cells are stored, to create a layer of healthy cells to replace damaged ones in the cornea, the transparent, dome-shaped layer of cells covering the front of the eye. Ophthalmologists do this by creating a patch of cells from a surgically removed slice of the limbus and stitching it to the damaged cornea. Similar limbal stem cell transplant work has been done by physicians at the University of Melbourne's Center for Eye Research Australia and the Bernard O'Brien Institute of Microsurgery in Fitzroy, Australia.

Although the stem cell approach was not invented at LV Prasad, the institute has treated about 500 patients with a success rate of nearly 75 percent, Balasubramanian says. C-TRACER and LV Prasad has also tuned its work to pay particular attention to the genetic conditions that lead to visual impairment. C-TRACER will open with a staff of five scientists, 22 graduate students and six clinical researchers. The facility occupies 16,000 square feet (1,485 square meters) on the LV Prasad institute's fifth floor, but plans are to expand to 25,000 square feet (2,320 square meters) by 2009.

Champalimaud-funded C-TRACER in an effort to prevent and treat vision-related disease and illness in Portugal, Portuguese-speaking countries and throughout the developing world. The four-year-old foundation also offers a $1.48 million (1 million euro) Champalimaud Vision Award annually to researchers who have provided "major breakthroughs in the understanding of vision or in the alleviation of visual impairment and blindness," says foundation executive committee member João Botelho.

This year, the foundation will further its philanthropic medical research support by breaking ground on the Champalimaud Center for the Unknown, a Lisbon research center slated to open in October 2010 and serve as the foundation's international headquarters.

In addition to the funds that LV Prasad received from Champalimaud to create C-TRACER, the institute will also receive $1 million in funding over the next five years from the Indian Ministry of Science & Technology's Department of Biotechnology.

Smog Can Make People Sick, Even Indoors

Smog Can Make People Sick, Even Indoors

When the air is thick with pollution, "sick building" complaints become more common

 
SICK BUILDING: When ground-level ozone known as smog increases outside, so do the number of sick workers inside office buildings.

Smog caused by ground-level ozone isn't just an outdoor air problem. A new study shows that when the irritant's level rises outside, the number of people inside suffering from so-called "sick building syndrome" also increases. (Ozone, an air-polluting oxygen molecule (O₃), forms when sunlight strikes motor vehicle tailpipe emissions.) 

"We found that outdoor air pollution, ozone, is associated with symptoms of lower-respiratory and upper-respiratory stress that occur in buildings to workers," says environmental health scientist Michael Apte of Lawrence Berkeley National Laboratory in California, who analyzed U.S. Environmental Protection Agency (EPA) data gathered on office air quality across the country. "These symptoms are prevalent at fairly high levels throughout the U.S. and are similar in other parts of the world."

Sick building syndrome is a term used to describe a broad range of ailments, including dry eye, congestion, difficulty breathing, fatigue and headaches that strike workers inside office buildings but disappear when they leave the premises. Previous studies have shown that individuals may exhibit such symptoms when irritating chemicals and particles are found in the air and that ventilation with clean air can help alleviate or prevent the problem.

The EPA from 1994 to 1998 tested indoor air quality and surveyed office workers in 100 buildings in 37 cities—from the smoggiest to the cleanest—across the country. Nearly all of the buildings had mechanical ventilation systems rather than windows or other natural means of circulating air. Officials measured air quality across a broad range of seasonal conditions, from an office in North Dakota on a –18-degree Fahrenheit (–28-degree Celsius) day to a workplace in Arizona on a 108-degree F (42-degree C) day.

The EPA found that, on average, even in buildings with no special history of sickness, nearly 19 percent of workers surveyed complained of dry eye, 21 percent felt congested on the job, 4 percent complained of difficulty breathing, more than 19 percent felt fatigued, and more than 15 percent reported having headaches while at work.

Apte and his colleagues compared the EPA office data with the agency's measures of local atmospheric ozone levels to determine whether they were linked. Their findings, published in the journal Indoor Air: the number of workers suffering symptoms indoors increased with the amount of smog outside—even at levels below the national limit of 80 parts per billion of ozone in air over an eight-hour period set by the EPA.

"Our body is telling us that there is something irritating in the air," Apte says. "People in the work condition are under all kinds of stress, but it does seem to be a real physical response."

The researchers found that the type of air filter used in a building's ventilation system was also tied to the number of ill people. "There is a six times greater likelihood that these symptoms will occur if you have both higher ozone levels and the polyester or synthetic filters," Apte says, "than if you are in lower ozone levels and using a fiberglass filter."

No specific cause for sick building syndrome has been identified, but Apte speculates that the symptoms are due to unstable ozone molecules chemically interacting with the wide range of materials found in an office building, beginning with the polyester air filter. "Glass is really a very inert material," Apte says of the fiberglass filters. "On the other hand, polyester is a polymer and it's got a lot of bonds in there that are capable of being broken up by ozone."

Ozone also reacts with a slew of plastics and other reactive surface molecules, ranging from carpet fibers to the skin's natural oil, to produce toxic chemicals like formaldehyde and other irritants. "Reaction chemistry suggests that the stuff being created is worse than ozone itself," Apte says. "It's like atmospheric chemistry but it's going on in building atmospheres rather than out in the sunlight." In other words, ozone seeping into buildings combines with other chemicals to produce more noxious air.

Researchers estimate that exposure to unhealthy ozone is cumulatively greater from such indoor air pollution than from concentrations that are as much as 10 times higher outside, because people spend the majority of their day indoors. As a result, sick building syndrome costs the U.S. economy as much as $60 billion annually in lost productivity. Installing filters designed to catch ozone before it gets into office air—as well as cutting back on the ozone-forming tailpipe pollution of all those commuters—would help, Apte says. And the problem could be reduced by 75 percent, the study finds, simply by switching from polyester to fiberglass filters in the smoggiest areas.

After all, the ventilation system turned out to be the culprit in the first sick building affliction: Legionnaire's disease, named for a mysterious pneumonia outbreak at an American Legion convention in 1976. The illness was found to come from Legionella bacteria thriving in the hotel's cooling tower and spread through its air conditioning system.

Outdoor ozone air pollution interacting with indoor filters and environments may prove a root cause of at least some of the otherwise unexplained sick building symptoms, Apte says. "I'm hoping that this ozone finding continues to provide an explanation of at least some of the variance in the distribution of symptoms people experience in buildings, though I don't believe this can explain all of them," he notes. "Some day it will no longer be called sick building syndrome."

Can Darwin’s Lab Survive Success?

Can Darwin’s Lab Survive Success?

 

Snorkeling near Pinnacle Rock. Conservationists are concerned about tourist activity in the Galápagos Islands.

FOR anyone touring the Galápagos Islands, it is hard to imagine the globe’s first World Heritage Site is at risk. The marine reserve is populated with sea turtles and humpback whales, and the national park’s trails are inhabited by herons and albatrosses.

Yet last June, Unesco added the archipelago to its “in danger list,” specifically citing the fragile ecosystem and the negative effects of a sizable growth in tourism. The number of visitors to the Galápagos rose more than 250 percent to 145,000 in 2006 from 40,000 in 1990, while the number of commercial flights to the area has increased 193 percent from 2001 to 2006.

“Unless we start to make fundamental changes right now, in the next 10 to 15 years we will see the Galápagos suffer from both economic and environmental degradation,” said Dr. Graham Watkins, executive director of the Charles Darwin Foundation, whose mission is to conserve the Galápagos through scientific research. “What we have here is an unsustainable model of development,” he added in a telephone interview from his office in Ecuador.

According to a May report by the Darwin Foundation, “Galápagos at Risk,” of which Dr. Watkins, a zoologist and ecologist, was a co-author, the islands’ crisis does not just stem from an unprecedented rise in tourism, but also from a change in the marketplace.

“Early tourism in the Galápagos was characterized by nature-loving tourists,” the report said, seeking “to learn about Darwin and see the amazing species that helped him to develop his theory of evolution.” It noted that these guests were “easily accommodated by smaller, locally owned tour operators.”

But, the study continued, the market expanded to include “eco-tourists,” who also like to visit places like Machu Picchu, the Ngorongoro Crater in Tanzania, Easter Island and the Great Barrier Reef. These tourists are “often more selective in terms of required comfort and is better served by multinational tour operators,” the report said.

A consequence has been that local owners cannot compete with the foreign-run companies doing business in the Galápagos. Of the $418 million generated by tourism annually, only $63 million is estimated to enter the local economy. And of the 80 tourism boats allowed to operate in the Galápagos, only about 40 percent are locally owned.

“We have to think about the people and not just the plants and animals, or it will all collapse,” Dr. Watkins said.

One of the larger multinational companies in the area was Voyages of Discovery, which until recently was allowed to bring one 500-passenger ship into the islands each month.

“It is ironic that we are no longer permitted to call here, considering we had to operate under stricter environmental guidelines than any of the other boats,” Mark Flager, vice president for sales, marketing and passenger services at Voyages of Discovery, said of Ecuador’s decision last fall to rescind his company’s permit. Though Discovery passengers were transferred to smaller boats to visit the national park trails, which can only be explored with a park department guide and a fixed itinerary, some feel large vessels are incongruous with the spirit of a site Unesco has called a living museum.

“I don’t want to say that only Birkenstock types can come here,” said Johannah Barry, president of the Galapagos Conservancy, which supports preservation and research in the Galápagos, including the Darwin Foundation’s work. “It is just that now it has been Disneyfied, and the high number of people visiting is leading to a different type of experience. It becomes less reflective of the surroundings.”

She added that all the boats waiting to ferry passengers ashore takes away from the natural scenery, Dr. Watkins said: “The big boats are basically hotels that sit in the port. Those passengers are not staying in locally run hotels or eating in the local restaurants.”

But Mr. Flager said Voyages of Discovery’s tour helped local residents even beyond the computers it donated to a school. “Some of our customers even cleaned up one of the beaches in San Cristóbal of litter one day without anyone asking them to do so,” he said, adding that Discovery’s passengers were all “moved by the grandeur of the Galápagos” and returned home as environmental ambassadors for the area.

THE success of the travel business is also drawing Ecuadoreans from outside the islands to move to the Galápagos with the hope of getting a share of the tourist money. Newcomers have flocked to Galápagos Province, putting pressure on its natural resources and introducing invasive species. As a result, the Darwin Foundation report said, the Galápagos now has 748 species of introduced plants compared with 500 species of native plants. Fifty-five of these new species, it added, have the potential to cause “severe impacts to native biodiversity.”

An increase in flight arrivals and the growth of activity sports like sea kayaking and sport fishing are also worrisome, according to Dr. Watkins. “People moving from island to island in boats makes it harder for us to put up barriers to prevent the introduction of new invasive species or infection,” he said, adding that arriving planes are now sprayed to kill insects.

The Ecuadorean government, conservation groups and other organizations are working to develop a new sustainable plan for the Galápagos Islands. “Recognizing the problem was the first step,” Dr. Watkins said.

But neither he nor Ms. Barry wants to dissuade tourists from visiting. They hope travelers will see what Dr. Watkins calls “the Mona Lisa of natural places in the world.” Though he advises visitors to stay longer and spend money at local companies or those that are trying to benefit the local economy. There is one indisputable upside to tourism in this endangered area, though. As Ms. Barry put it, “We have found that when tourists actually visit the Galápagos, they leave caring about it and wanting to support all conservation efforts.”