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Imagine a world where once-extinct species roam the Earth again. That sounds a lot like something from Jurassic Park, right?

Thanks to a in Texas, the woolly mammoth—extinct for thousands of years—may be on the verge of being brought back to life.

The breakthrough has come as biologists have engineered mice with traits from the woolly mammoth, most notably sharing the long, wavy hair that made the mammoth so distinct. While the woolly mouse won’t directly lead to the mammoth, the breakthrough demonstrates the feasibility of gene editing that the scientists hope will lead to the resurrection of the mammoth by 2028.

“To bring woolly mammoth back in 2028 is maybe over-optimistic,” Illinois Tech Department of Biology Chair Lei Li says. “To get the whole woolly mammoth back, specific sets of genes or gene pathways that are required for the development of bones, muscle mass, blood, etc., must also be worked out. This may involve tens of thousands or maybe millions of genes.”

How did these scientists accomplish this feat? They started by identifying specific genes that gave the mammoth its distinctive traits. Using a gene-editing tool called CRISPR, they were able to re-write the mouse’s stem cell to give it those traits. Over five rounds of experimentation, 38 mouse pups were born, all possessing the same distinctive woolly hair.

While a full-sized, eight-ton mammoth would require many more genetic modifications from an Asian elephant—the team’s starting point, as it is closely related to the mammoth—the scientists’ success in creating woolly mice serves as a proof of concept.

As interesting a development that this breakthrough is, there are significant concerns surrounding de-extinction, including about introducing new ecological stresses on an already stressed environment.

“They may interrupt the entire ecosystems,” says Li. “The survival of a species not only depends on availability of food and water, but also adequate niches and habitats. They must have a perfect spot on Earth for survival. Introducing a new species to the world may create some problems for existing species.”