will contain mitochondrial DNA from that host species. This
mitochondrial DNA will end up being present in every cell of the
new organism, and it’s still up for debate how important that type
of DNA is in speciation. So, the new creature might look a bit
(or even a lot) like its extinct predecessor, but it is not a genetic
facsimile, and it may not behave in the same way.
For extinct mammals, cloning methods require embryos to be
grown in the womb of a closely related species. For a thylacine,
for example, this could be a Tasmanian devil, but it introduces
environmental differences even before birth that could have
important epigenetic consequences, changing the way genes are
expressed. Fostering by a closely related species will likely result
in an absence of at least some behaviours that would have been
natural prior to extinction. So, we could make a mammoth-like
elephant but not a mammoth. We can’t resurrect species, but
we can probably create proxies similar to the extinct species.
Extinction really is forever, but these proxies could still play an
important role in restoring ecosystems.
The case for de-extinction
Understandably, de-extinction comes with ethical concerns. Many
worry about the animal rights issues for the resurrected species
and their surrogate mothers, and scientists ‘playing God’. Some
also suggest we will care less about conserving species if we
believe extinction is not forever and we can simply ‘de-extinct’
species later on. Others raise the issue of a handful of resurrected
individuals in zoos or labs, marvelled at as curiosities but with no
hope of a return to the wild: essentially, scientific circus freaks.
Conversely, many de-extinction fans feel we have a moral
obligation to restore species that humans drove to extinction.
They argue that resurrected proxies could play an important
conservation role. When a species goes extinct, it leaves a hole in
an ecosystem. If another species does not move into the vacant
niche, then that job no longer gets done. The loss of moa from
New Zealand likely altered the composition of forests because
moa were such important browsers. Could bringing back moa
help restore New Zealand’s forests? An overriding motivation for
many de-extinction fans is, understandably, excitement around
the possibilities and the technological advances; it’s very sexy
science. But to move from cool to conservation, de-extinction
needs to overcome numerous hurdles.
Ecosystem re-integration
The ecosystems for many de-extinction candidates have
experienced numerous changes in the time since extinction. If
the habitat the species used to live in no longer exists, should we
even consider bringing that species back? New Zealand now plays
host to over 2400 naturalised exotic plant species – it’s impossible
to predict how a moa proxy would interact with them and
whether the outcomes would be positive or negative. A species’
contribution to its ecosystem also doesn’t stop with what it eats.
Every individual animal carries its own communities of
microbiota – bacteria, fungi, and microbes – as well as parasites,
all of which are important players in the health of the individual
and the ecosystem it inhabits. Many of these tiny organisms
disappeared with their extinct hosts. If we bring back proxies,
should we also bring back proxies of their internal fauna? It’s a
tough ask given that we often don’t know the exact composition
of these internal ecosystems. Resurrected proxies might
resemble their extinct counterparts biologically, but resurrecting
their ecology is perhaps even more challenging.
Importantly, we don’t necessarily need to bring back extinct
species to fill functional gaps in ecosystems. If a species has
been lost in one area but still exists in another, once the
reasons for extinction have been removed, the species could
be reintroduced. Tasmanian devils don’t have to be confined
to Tasmania – they could rip apart carcasses all across their
historical Australian range, given half a chance. Alternatively, if a
species with an important ecosystem function is totally extinct,
but another species could fulfil the role, that species could be
introduced. This has already been trialled, introducing a tortoise
from the Seychelles to resume the grazing and seed dispersal
functions of the extinct giant tortoise of Mauritius, and is planned
for more tortoise species in Madagascar and the Galapagos.Avoiding a genetic bottleneck
Small initial starting populations could also quickly turn
de-extinction into re-extinction. In conservation management, we
generally try to avoid populations becoming too small, as that
leads to reduced genetic diversity, inhibiting a species’ ability
to adapt to changing circumstances. The chance of inbreeding
also increases, which can cause issues with reproduction and
survival, keeping the population small and leading to an almost
inescapable extinction vortex. If the resurrected proxies are to
become functional, self-sustaining populations, they will need to
overcome this issue.
It’s also highly unlikely that we would know how much
genetic diversity originally existed in the population before it
went extinct. We might have genetic material from museum
collections and/or fossils, which will give us some idea what
variants of each gene previously existed in the species, but it is
unlikely to be the whole story. So we might be able to genetically
engineer some of the historical genetic diversity back into the
resurrected proxy, but not all of it. Our resurrected proxy will
potentially be more vulnerable to disease events and climate
change than its extinct predecessor – not the strongest start.The first extinct species
to be ‘resurrected’, and
the only one at the
time of writing, was the
Pyrenean Ibex, although
the kid died shortly after
birth. Image: Joseph WolfConsideration must be given to how restoring
species affects their former ecosystem. If moa
were brought back, would we have to restore
Haast’s eagle, which preyed on moa but is now
also extinct? Image: John Megahan [CC]Wildlife Australia | 41