While a real-life Jurassic Park may not be opening any time soon, bringing back more recently-extinct species, like the woolly mammoth or the dodo, is a distinct possibility. But while scientists in the movie "were so preoccupied with whether or not they could, they didn't stop to think if they should," real-world scientists are now considering the latter. With various "de-extinction" projects in the works right now, researchers at University of California, Santa Barbara (UCSB) have published a paper analyzing the ecological benefits, risks and responsibilities of reintroducing once-extinct species into modern ecosystems.

Bringing back a creature as huge as the woolly mammoth – which hasn't walked the Earth in over 4,000 years – is, well, a mammoth undertaking. Well-preserved remains are relatively common in the Siberian permafrost, but the cells are usually too degraded to be very useful – a stumbling block that's tripped up previous attempts.

But what if scientists do find a way to revive mammoths? What then? The world has changed drastically in the past four millennia, and there simply might not be a place for them in the ecosystem anymore.

"The idea of de-extinction raises a fundamental and philosophical question: Are we doing it to create a zoo or recreate nature?" says Benjamin Halpern, co-author of the study. "Both are reasonable answers, but restoring species to a natural state will be a much, much harder endeavor. We offer guidelines for how to make ecological de-extinction more successful and how to avoid creating 'eco-zombies.' "

Eco-zombies are described as resurrected creatures that no longer have any ecological function in today's world, making them at best, useless, and at worst, disastrous. To prevent the wasted resources and potential negative effects of eco-zombies, the researchers suggest three criteria for selecting species for de-extinction, in order to best restore ecological function. And unfortunately, the woolly mammoth performs poorly on all three counts.

First, species that went extinct more recently should be prioritized over those, like the mammoth, that disappeared thousands of years ago. Not only would these animals have a better chance of adapting to the current climate and ecosystems, there might still be time for their reintroduction to counteract the cascading impact of their extinction. A few thousand years on, the world has adapted to a lack of mammoths, and their reappearance may just cause more problems than it solves.

Secondly, animals make better candidates for de-extinction if their ecological functions are truly valuable, and nature hasn't yet found a way to replace or replicate. The Christmas Island pipistrelle bat, for example, was the only bat in its environment that ate insects, so bringing it back could help restore the balance to that ecosystem. Given it might have died out as recently as 2009 means it fits the bill for the first point, too.

And finally, the researchers suggest concentrating on species that can be "returned to functionally meaningful abundance levels." If we can only clone and release one or two individual animals, there's not really any point.

"You need to have enough individuals to perform their function well enough to affect the ecosystem," says co-author Molly Hardesty-Moore. "One wolf hunting and killing has minimal impact, but hundreds of wolves performing that function will change the ecosystem."

While there are ethics debates around de-extinction as a concept, the researchers maintain that the process could be useful, as long as considerations like these are made.

"What some are proposing to do with de-extinction will be like manufacturing a part from the engine of a Model T and trying to shove it into a Tesla," said lead author Douglas McCauley. "You just can't take a part and put it into a brand new system and expect it to work without considering how its ecological context has changed."

The research was published in the journal, Functional Ecology.