Geologists have suggested that we live in a new geological time period, characterised by the influence of people on planetary processes – the Anthropocene. Plastic has been incorporated into rock, the atmosphere has been changed and the radioactive signature of nuclear bombs can be detected in sediments. These are lasting marks of the deep and fundamental changes we are making to the Earth.
In the biological realm, humans are having equally profound effects on the evolutionary tree of life, particularly through extinctions. The dodo, a one-metre tall flightless relative of pigeons, was only to be found on the island of Mauritius. Within 70 years of Dutch sailors arriving there, however, it was extinct.
As the dodo and its close relative, the Rodrigues solitaire (now also extinct), were the only living representatives of the subfamily of pigeons, Raphinae, this branch of the evolutionary tree of life was quickly pruned away.
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Closer to home, the great auk swam and fed in the ocean but bred on rocky North Atlantic islands; this large bird foraged in the seas around Ireland. It was last seen in the mid-1800s after being hunted to extinction for down to stuff into pillows.
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You could argue that the great auk, dodo and Rodrigues solitaire were rather clumsy flightless birds that were confined to fairly limited island habitats or breeding grounds, and therefore did not stand a chance in the modern world.
It is estimated that 1 million species are likely to be threatened with extinction in the coming decades
However, even being mind-blowingly common does not protect a species from extinction. The passenger pigeon, native to North America, was notable for the enormous migratory flocks that blackened the skies as they passed over in their multitudes. By 1900, they too were extinct, due to being hunted for meat by European settlers and the deforestation of their habitat to turn it into agricultural land.
These cautionary examples are just the tip of the iceberg. It is estimated that 1 million species are likely to be threatened with extinction in the coming decades. The tree of life could be severely thinned out, with negative consequences for people as the contributions that nature makes to our wellbeing and survival are also degraded. Extinction is the end point of a process that reduces the population sizes, distribution and genetic diversity of a species, but a particular species’ contribution to ecosystem function may disappear long before the last individual dies.
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While the dodo and great auk exist as specimens in museums and have yielded DNA which can be analysed, this DNA is much degraded and it is exceedingly difficult to reconstruct the full genome of these species. The idea of de-extinction – bringing these species back via genetic engineering, cloning and hybridisation with closely related living species – has been mooted. However, there are significant challenges to working with old, degraded DNA, and the resources needed may be better spent on preventing future extinctions.
Habitat protection and restoration are the most important conservation measures we need to prevent extinction in the wild
“Frozen zoos” house living cell collections which contain high-quality genetic material which can be reintroduced to living populations to boost genetic diversity in a scenario where 19 per cent of animal species are considered threatened with extinction and tissue sample collection for them is considered an urgent priority.
Other categories of risk include species which are vulnerable to climate change, the last remaining representatives of an evolutionary branch, species restricted to a single remaining location, and those at risk of overexploitation through trade. We recently identified three species that occur in every risk category and which should be urgently prioritised for living tissue collection: the whooping crane, crested ibis and Siberian crane. More than 90 per cent of species listed as “extinct in the wild” could be secured in living tissue banks by collection of small samples from animals in zoos and aquaria during routine veterinary procedures.
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Habitat protection and restoration are the most important conservation measures we need to prevent extinction in the wild. Zoos, aquaria, tissue and seed banks are needed to maintain and preserve genetic diversity for acutely threatened species, and museums demonstrate what we have already lost. Just 78 great auk and circa 1,500 passenger pigeon specimens are kept in museums worldwide, and both of these species are in the Trinity College Dublin Zoological Museum.
Yvonne Buckley is an ecologist at the Irish Research Council and laureate and professor of zoology at Trinity College Dublin