De-extinction, the process of bringing saber-toothed tigers, woolly mammoths and other extinct animals back into the world, has become increasingly plausible with recent advancements in modern genomics research. What was once discussed only in the context of science-fiction plots has now become a conceivable reality.

But as this reality approaches closer, researchers and policymakers face difficult ethical questions regarding the numerous foreseen and unforeseen implications of reintroducing life into the world.

Ross MacPhee, a mammalogy researcher and curator at the American Museum of Natural History in New York City, offered a public lecture last week (Oct. 2) outlining what he considers to be the most pressing ethical and logistical questions facing de-extinction efforts, with special focus on the woolly mammoth. [6 Extinct Animals that Could be Brought Back to Life]

"I think it's important that there be regulation," MacPhee said during his talk. "I think it's important that there be safeguards, but I don't think there's any way of stemming the flow. This is the world that we live in, and I don't expect that to change very seriously in the future."

Still, de-extinction doesn't have to be harmful to the animals or the ecosystem, MacPhee said. "It also won't necessarily be good, but it probably will be."

Here are some of the major ethical and logistical questions MacPhee believes should be considered before scientists go through with de-extinction:

1. Where would the woolly mammoths live?

MacPhee joked that it was easy enough for him to convince New Yorkers in the audience that the mammoths could be placed in the Great Plains — where the behemoths once roamed before becoming extinct about 10,000 years ago — because New Yorkers have no concept of what the Great Plains actually look like today.

While few scientists expect massive herds of mammoths to take over the Great Plains with de-extinction, the question of where they would live and if they would live comfortable and safe lives are important and responsible questions to consider before going through with the task, MacPhee said. Needless to say, the plains are not what they were when the mammoths roamed North America: People live there now. Croplands, grazing lands, highways and interstates have all been established without taking woolly mammoths into account. [Steps to Bring Woolly Mammoths Back to Life (Infographic)]

2. What would the mammoths eat?

Researchers suspect mammoths ate a diet similar to that of modern elephants, which includes grasses, shrubs, roots and other small plants.

But with much of the Great Plains now cleared for croplands, what would stop mammoths from raiding these fields? And would humans have the right to force the mammoths off of their land?

If humanity, or a well-equipped group of scientists, chooses to bring the animals back into the world, they must consider how to treat the animals if the beasts behave in ways that complicate humans' daily life, and whether that treatment is ethically acceptable given the decision to bring those animals back.

3. If they proliferate, would we treat them as pests?

To put this question into perspective, MacPhee presented the story of the wild North American horse, which evolved roughly one million years ago and roamed the continent thereafter until going extinct about 10,000 years ago, around the same time that the woolly mammoth went extinct.

Thousands of years later, roughly 500 years ago, Europeans reintroduced horses that they had domesticated back onto the continent. Many of those horses became feral and are now known as wild horses or mustangs.

Wild horse populations have since blossomed, and now tens of thousands of the animals roam the western United States. As the population continues to bloom, the Bureau of Land Management has begun to treat the horses as an invasive species, taking measures to try to control the population by culling and euthanizing many of the horses every year.

"This species evolved in North America, and some regard them now as an invader," MacPhee said. "Would the same thing happen with mammoths?"

4. Would de-extinction detract from modern conservation efforts?

Some argue that de-extinction could potentially divert resources away from efforts to protect modern threatened animals. This is an ethical consideration that researchers and funding agencies would need to consider in allocating their resources, MacPhee suggested.

5. Would the 21st-century microbial world suit the woolly mammoth digestive tract?

All animals rely on bacteria and other microscopic organisms, called microbes, to break down food and aid in digestion. Some animals have similar microbiomes — or ecosystems of microbes within their bodies — but others develop their own distinct microbial ecosystems.

If the original woolly mammoth microbiome went extinct with the mammoth, which researchers say it could have, would the woolly mammoth struggle to digest food in the 21st century?

"In many cases, the overall phenotypes [physical appearance] of organisms and their ability to digest food is directly tied to the microorganisms in them," Susan Perkins, a member of the audience and a curator at the American Museum of Natural History, told LiveScience after the talk.

The question is more of a thought experiment than a serious concern, Perkins said. The Asian elephant — the woolly mammoth's closest relative — likely has a microbiome similar enough to the woolly mammoth's gut bacteria that it would probably not have serious digestive problems. Still, in bringing the woolly mammoth back into a world in which they have not adapted to live, humanity must consider these types of questions for the sake of the animal and the sake of humans' own ethical obligations.

MacPhee did not claim to have answers to the ethical questions he presented, but emphasized the importance of continuing the conversation as de-extinction draws closer.

"It's morally complex," MacPhee said toward the end of his talk. "It's not black and white. It's many shades of gray. Maybe even 50."

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