Humans Caused 322 Animal Extinctions in Past 500 Years

Our species caused 322 animal extinctions over the past 500 years, with two-thirds of those occurring in the last two centuries, according to a paper published in a special issue of the journal Science this week.

Many animals are threatened with human-caused extinction now, with researchers expressing particular concern over amphibian and invertebrate (creatures without a backbone) losses. Numbers of the latter group have nearly halved as our population doubled in size over the past 35 years.

Ecologists, zoologists and other scientists believe that, without urgent steps to stem the losses, we are facing global scale tipping points from which we may never look back or recover.

"Indeed, if current rates (of human population growth) were to continue unchecked, population size would be, by 2100, about 27 billion persons -- clearly an unthinkable and unsustainable option," co-author Rodolfo Dirzo, professor of environmental sciences at Stanford University, told Discovery News.

Dirzo and his colleagues call for "decreasing the per capita human footprint," by developing and implementing carbon-neutral technologies, producing food and goods more efficiently, consuming less and wasting less.

They also say it is essential that we ensure lower human population growth projections are the "ones that prevail."

Haldre Rogers and Josh Tewksbury, authors of another paper in the same issue, believe that, "animals do matter to people, but on balance, they matter less than food, jobs, energy, money, and development."

They continued, "As long as we continue to view animals in ecosystems as irrelevant to these basic demands, animals will lose."

Keeping animals alive and ecosystems healthy translate to big bucks on a global scale. Tewksbury, director of the Luc Hoffmann Institute of the World Wide Fund for Nature, pointed out that Southeast Asia's Mekong River Basin, through its fisheries, supports 60 million people. Rogers, a researcher in Rice University's Department of Ecology & Evolutionary Biology, added that 73 percent of visitors to Namibia are nature-based tourists, with their money accounting for 14.2 percent of that nation's economic growth.

"Whale watching in Latin America alone generates over 275 million dollars a year," Tewksbury said. "Multiple studies have demonstrated how turtles are worth more alive than dead."

In the United States, he added, shark-watching results in $314 million per year, directly supporting 10,000 jobs.

He and the other researchers point out that human health, pollination, pest control, water quality, food availability and other critical factors are also dependent on ecosystem stability.

In the United States, he added, shark-watching results in $314 million per year, directly supporting 10,000 jobs.

He and the other researchers say that human health, pollination, pest control, water quality, food availability and other critical factors are also dependent upon ecosystem stability.

Yet another paper in the latest issue of Science outlines controversial measures, beyond basic conservation efforts, to improve the current situation. These include re-wilding, meaning placement of underrepresented species back into the wild; human removal of invasive species; and, perhaps most controversial of all, de-extinction: bringing already extinct species back to life.

"People are currently grappling with the implications of de-extinction, including how to select the best candidate species," co-author Philip Seddon, a zoologist at the University of Otago, told Discovery News.

Rogers said that restoration and re-introduction have shown progress.

"The return of the bald eagle and the California condor to the skies and the wild turkey to the lands of the U.S. are great success stories," she said.

She and Tewksbury are also working on the island of Guam, where the invasive brown tree snake has rid the island of birds, causing the forests there to be without seed dispersers for 30 years. This, in turn, has contributed to financial challenges for locals.

It's a mistake, though, to limit the value of non-human animals to their economic value, the researchers believe.

"From the cave paintings that represent the dawn of art to the icons of culture and sport around the world today, wild animals are a part of our fabric, and in a very real, evolutionary sense, these animals have made us who we are," said Tewksbury.

"The loss of these animals from landscapes around the world is thus a loss for all of humanity."

Large mammals, such as the tapir, are the first to disappear in human-modified ecosystems.

New technologies could make it possible to bring extinct species back to life, concludes a paper published on April 4 in the journal Science. These advances include back-breeding (assembling or reassembling an extinct species' genes), cloning and genetic engineering.

Woolly Mammoth

A leading candidate for de-extinction is the woolly mammoth. Russian scientist Semyon Grigoriev, of the Sakha Republic's mammoth museum, plans to replace the nuclei of an elephant egg with nuclei extracted from woolly mammoth bone marrow. The elephant would theoretically become a surrogate mother to a baby mammoth.

Tasmanian Tiger

Tasmanian tigers died out in 1936, in part because they had little genetic diversity which translates to "bad news for a species," said Katherine Belov, professor of comparative genomics at the University of Sydney. "Species are less able to adapt to change." Even if Tasmanian tigers -- or other animals -- are resurrected, it will take some time to build up diversity again.

Passenger Pigeon


Experts believe billions of these birds populated the Americas when Europeans arrived. Loss of habitat and commercial exploitation of the birds for their meat are thought to have killed them all off.

Efforts are now underway to revive the species by extracting DNA fragments from preserved specimens, and later, using band-tailed pigeons as surrogate parents.

Pyrenean Ibex


The Pyrenean ibex, a horned mammal once common in Europe, was one of the first subspecies targeted for de-extinction. Scientists began the attempts in late 1990s, when the last female Pyrenean ibex was still alive. Even if researchers could successfully clone that individual, there would be no males for her to breed with. Instead, genetic engineering might be required.

Saber-toothed Cat


Since saber-toothed cat bodies are sometimes found frozen, it might be possible to extract preserved DNA and clone the animal. About 5 years ago, scientists did just that with a mouse that was dead and frozen for 16 years. Woolly mammoth remains are also sometimes found in a well-preserved, frozen state.

Dodo Bird


The dodo, a flightless bird, proved to be a tasty meal for humans and other predators. In 2007, scientists found a remarkably well-preserved dodo in a cave. Dodo DNA could be used to resurrect this avian species.


Ground Sloth


Ground sloths, relatively slow, lumbering animals, were easy targets for prehistoric big-game hunters. Scientists have found remains that still bear soft tissue. As with woolly mammoths, there's a chance extracted DNA could be used to back-breed or clone the large sloths.

Irish Elk


The Irish elk has been extinct for 11,000 years. Like the woolly mammoth, it inhabited colder regions. As a result, bodies are sometimes found frozen and in relatively good condition, making them candidates for DNA extraction.

Neanderthal

Earlier this year, Harvard geneticist George Church -- with tongue in cheek -- said that he was seeing an "adventurous female human" to be a surrogate mother to a cloned Neanderthal. While Church was really just theorizing about what it would take to bring a Neanderthal back to life, the possibility could be a reality, should any scientist undertake such a controversial project.

Dinosaur

Paleontologist Jack Horner is leading a project to create a dinosaur out of a chicken -- a "dinochicken." He told Discovery News that birds "are dinosaurs, so technically we're making a dinosaur out of a dinosaur." He and his colleagues have been genetically engineering chickens to reactivate ancestral traits, such as long tails, which are more associated with non-avian dinosaurs.