The Sixth Extinction: The Holocene Extinction, Conservation Paleontology & The Possibility of De-Extinction
What Good is a Fossil Record?
That is to say, what benefit does society receive from the existence of fossils of the ancient world? There are many of them that are scientific, or even aesthetic:
But are there any pragmatic benefits? YES!
Compared to the earlier Pleistocene Epoch, the Holocene has been an epoch of climate stability. It was rare in the Pleistocene to have a 12 kyr warm pulse with only a degree or two of average change; instead, we see fluctuations of up to 7-9 C°:
And all our agricultural, freshwater, coastline, etc., needs were developed in the context of this period of stability.
Agriculture has allowed human populations to soar:
Agriculture allowed humans to capture more and more of the land's biomass. Also, as agricultural lands expanded, wildlife tended to be displaced, bringing their population down. Furthermore, wild species of animals were domesticated into new forms (aurochs into cattle; boars into pigs; mouflon into sheep; wild goats into goats; wild horses into horses; wild asses into donkeys; etc.): the wild species tended to decline from habitat loss and hunting while the domestic forms flourished under human husbandry.
The colonization of the Brave New Worlds (Sahul and the Americas) was not the end of the expansion of Homo sapiens. During the Holocene humans spread to many oceanic islands in the Pacific, Indian Ocean, and elsewhere. In the wake of new arrivals, many species became extinct. For example, the total number of bird species at 1 CE was probably 3000 more than today, largely do to losses of island avian species.
Let's take a look at some of the patterns of extinction.
Historic Cases Recognized at the Time:
But there are many other larger-scale or more dramatic extinctions during the Holocene:
Madagascar: Humans (settlers from Borneo, rather than nearby southeastern Africa) reached the island of Madagascar between 350 and 550 CE. They arrived with an agricultural system based on slash-and-burn. Through a combination of habitat destruction and direct hunting, they wiped out such as:
New Zealand: These islands remained uninhabited until 1280 CE, when Polynesians first arrived. By 1400 (possibly before) they had wiped out many taxa, including:
In the case of the moa there is direct evidence of hunting and feeding by humans, and this seems likely in the case of the adzebills, too. The Haast's eagles were probably victims of trophic collapse: with the moa gone, there was no targets left (other than men) large enough to serve as prey.
Tasmania: Part of Sahul, it was isolated from mainland Australia as the sea rose in the last deglaciation. Its inhabitants lost a substantial part of earlier technology, such as bone tools, boomerangs, hooks, sewing, and the ability to start fires. In many ways, they had reverted to Homo erectus-grade technologies. In Tasmania some of the larger animals that were wiped out on mainland Australia survived, most famously the thylacine or Tasmanian tiger or Tasmanian wolf (Thylacinus cynocephalus. This animal was a marsupial predator strongly convergent on placental wolves. With the settlement by Europeans in 1803, a systematic campaign of extermination of both the Tasmanian people and Tasmanian tiger began. Sadly, both were successful. The native population of Tasmania was hunted down to the last individual and their language and culture lost for all time: the last full-blooded Tasmanians were the women Truganini who died on 8 May 1876 and Fanny Cochrane Smith who died in 1905. The thylacines actually survived longer, with the last specimen "Benjamin" dying in captivity on 7 September 1933. Below is a compilation of all surviving film footage of this species (all of it in zoos, rather than in the wild):
The mainland Old World: But these are all small, isolated lands. Surely extinction hasn't happened in recent times on the continents? Sadly, here to. For example, the quagga (Equus quagga quagga, an extinct southern African subspecies of plains zebra: 12 August 1883), the aurochs of Eurasia (Bos primigenius, although technically a pseudoextinction as the domestic cow Bos taurus is a descendant: 1637), the tarpan of Eurasia (Equus ferus ferus, the ancestor of the domestic horse Equus caballus: 1879 for the last scientifically verifiable non-hybrid), and others. And the extinctions in North America were particularly striking.
Continental North America: Here the extinctions included not only rare forms, but some of the most common species to inhabit the continent:
A very, very close call was Bison bison, the plains bison, largest and by far most common large mammal of North America after the megafaunal extinction. Their huge herds made them essentially hunt-proof to the Folsom points--and later bows and arrows--of Native Americans. But arrival of advanced rifle technology, the expansion westward of American farming and railroads, and a tremendous market for bones for fertilizer and hides for many numerous uses led to commercial hunting on a phenomenal scale, bringing species dangerous close to extinction at the end of the 19th Century. Once hundreds of millions formed vast herds, but by 1890 less than 1000 individuals remained. Political and social action from the grassroots on up to Congress and the White House led to protection of this symbol of the American West, and the species was saved and once again roams the West.
20th Century: Beginning of the Sixth Mass Extinction: But all these pale in comparison to the widespread ecological devastation of the 20th and 21st Century. The huge increase in human population, and the requirements to feed this population and supply us with homes and products, means we impact the biosphere on an ever-increasing scale:
It is no longer direct hunting that is the major issue (although still ongoing on land in the form of the pet trade, trade in exotic animal products like ivory, and slaughtering rare species for "traditional Eastern medicine" ingredients). The primary dangers are:
It has been argued that the net result of this is that Earth is in the sixth major mass extinction, as the impact now includes the marine realm, small organisms, etc. (and not just the megafauna). Like all mass extinctions, this stems from the fact that the environmental changes are happening faster than organisms can evolve to adapt to them. Although extinction rates are no where near the level of the Big Five, we have instigated the same type of causes that happened before (extreme eutrophication, like the Ordovician-Silurian and Devonian-Carboniferous; ocean acidification, at least a partial contributor to the Permo-Triassic and Triassic-Jurassic [and PETM]).
Modern conservation ecologists now refer to defaunation: a combination of global extinction, regional extinction (aka "extirpation"), and population decline.
Paleontology to the Rescue? Conservation Paleontology
A big part of the crisis, however, is that even though it is incredibly fast by geologic timescales, this is going on slower than society notices. Additionally, by the time that field ecology really got going, especially in the marine realm (the mid-20th Century), the crisis was well underway. So how do we know what is really "natural"?
That is where conservation paleontology comes in. By looking at the fossil record of the latest Quaternary and early Holocene, we get a description of the biodiversity of the contemporary species prior to any significant influence of humans. Furthermore, more ancient crises (like PETM and mass extinction recoveries) give us evidence of how the biosphere reacts to tremendous rapid changes. This evidence from the fossil record allows conservation biologists to make better plans in dealing with current and near-future changes.
Is Extinction Forever?
But is extinction really the end? A few paleontologists and other scientists have suggested methods to recover ancient ecosystems, or even ancient species.
Re-Wilding: If a species still persists in some region, but has undergone extirpation at another, it is possible to rewild it: that is, to reintroduce the species to a habitat in which it is lost. These efforts are already ongoing at various sites in the world, and generally show promise (so long as introduced invasives can be eliminated, too.) But what about cases where the extinct taxon is globally extinct?
Although the megafauna of the Pleistocene are gone, there are sometimes close relatives from some part of the world that might be used to "fill in" ecologically in regions like North America or boreal Eurasia. The idea is to release ecological equivalents (lions or tigers for Panthera atrox; Indian elephants for mammoths, etc.; and so forth), to allow an approximation of the Pleistocene ecosystem to return.
There are some problems with this approach, however:
De-Extinction: But what if we could REALLY bring back a fossil species. Is it possible to de-extinct (I think the term "re-extant" would be better) fossil species?
Theoretically, there are several approaches, now that fossil genomes have been recovered:
Two projects are ongoing. The so-called Lazarus Project is working to de-extinct the gastric-brooding frog Rheobatrachus silus, which was wiped out in the wild in the mid-1980s. Another team has attempted to clone the extinct-in-2000 Iberian ibex Capra pyrenaica pyrenaica (the clone died minutes after birth).
If restored, the de-extincted species could be restored to the wild as in re-wilding, removing the objection to it being the wrong species. But a whole new set of problems arise:
And, of course, the whole "world has changed--and will change a lot more VERY soon--since the Pleistocene" issue applies.
If you want more information and debates (pro and con) about the de-extinction concept, the TED conference in which the term was introduced is available online. Also, the 2014 Howard Hughes Medical Institute BioInteractive series of talks was about the Sixth Extinction and how we should respond.
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