The extinction of species is a natural part of evolution. Since life began on Earth approximately 3.5 billion years ago, there have been at least five major extinction events that led to the loss of over 75% of species. However, in most cases, life found a way to bounce back from these mass extinctions through the process of evolution.
Evolution is driven by natural selection, the process by which traits that aid survival and reproduction are passed on to future generations. When the environment changes, individuals with advantageous traits tend to survive and reproduce more successfully than those without the traits. Over many generations, a species evolves to become better adapted to its environment.
Could extinct species re-evolve?
In theory, it is possible for an extinct species to re-evolve if the right conditions are met. First, there would need to be living descendant species that still carry some of the key genes of the extinct species. For example, the dodo bird went extinct in the late 1600s, but other pigeon species with dodo ancestors are still living.
Second, the environment would need to change in a way that makes the extinct species’ traits advantageous again. If an ecological niche emerges that happens to be perfectly suited for the extinct species’ particular traits, those traits would become beneficial once more.
Third, there would need to be enough time for evolution to occur. The accumulation of advantageous traits takes place incrementally over many, many generations. Re-evolving a species as distinct as the dodo could take millions of years.
Challenges to re-evolution
There are several major barriers that make the re-evolution of extinct species unlikely:
- Genetic limitations – Species that have been extinct for tens of thousands to millions of years are unlikely to have living descendants that still carry their unique genes.
- Lack of evolutionary pressure – The ecological niches of most extinct species no longer exist, so there is no selective pressure to favor their traits.
- Low probability – The specific circumstances required for re-evolution to occur are highly improbable once a species has gone extinct.
While not impossible, the planets would have to align perfectly for an extinct species to naturally evolve back into existence. The odds are stacked heavily against such an event occurring.
De-extinction
If an extinct species were to return, the most likely route would be through cloning or genetic engineering rather than re-evolution. Technologies for bringing extinct species back to life are known collectively as “de-extinction.”
Cloning from preserved DNA
For species that went extinct recently enough to have well-preserved DNA samples, direct cloning is a possibility. The DNA could be inserted into a closely related surrogate mother to produce an offspring. This technique was used to clone the extinct Pyrenean ibex in 2009, although the cloned ibex died soon after birth.
Gene editing living species
For species with no intact DNA but living relatives, scientists may be able to use gene editing to insert lost genes back into the genome of the living relative. This approach, currently being attempted with the woolly mammoth, could catalyze evolution toward a more mammoth-like animal.
Challenges of de-extinction
While de-extinction holds promise, there are still substantial technical barriers:
- Limited DNA samples – High quality preserved DNA is rare.
- Incomplete genetic data – Entire genomes are needed to account for all traits.
- Lack of genetic diversity – Small founder populations from cloning or editing would lack diversity.
- Missing ecological niches – Most extinct species’ environments no longer exist.
There would also be significant ethical concerns over whether we should revive extinct species, and how to ensure their welfare if we did.
Case studies: Candidates for de-extinction?
Woolly mammoth
Woolly mammoths are a top candidate for “resurrection” via gene editing of Asian elephants to be cold-adapted like their extinct cousins. Researchers have sequenced much of the mammoth genome.
Challenges:
- Asian elephants are a distant relative.
- Only partial mammoth genome is available.
Benefits:
- Could restore lost ecosystem roles in the Arctic.
- Aid conservation of endangered Asian elephants.
Dodo
The dodo is an iconic extinct species. Living pigeons may retain some dodo genes, enabling partial de-extinction.
Challenges:
- No intact dodo DNA exists.
- Related pigeons are genetically distant.
- Dodo’s tropical habitat is gone.
Benefits:
- Could attract public interest to conservation.
- Highlight risks of extinction.
Passenger pigeon
Passenger pigeons were once the most abundant bird in North America before being driven to extinction in the early 1900s. Preserved specimens may provide sufficient DNA.
Challenges:
- No living closely related species exists.
- Forest habitat has been fragmented.
Benefits:
- Could restore ecosystem functions.
- Cautionary tale of overexploitation.
Conclusion
While de-extinction may be technically possible for a handful of recently extinct species, there are steep barriers when it comes to re-evolving species that disappeared long ago. The complex genetic and ecological requirements make it exceedingly unlikely for extinct species to naturally evolve back into existence once lost. Investments in conserving extant biodiversity are likely to pay greater dividends than attempts to revive what is already gone.