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Wild Species Threatened by Hybridisation

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17 10 08 - 04:03
Humans are wreaking havoc on evolution in ways that are only recently becoming clear. Hybridisation is threatening several iconic species in America.

Some iconic American animals - wolves, bears and bison - are not the creatures that they used to be. The problem is hybridisation, the "contamination" of one species' DNA with that of another.

More likely is that climate change is increasing the likelihood of polar-grizzly hybridisation. Tracking experiments show female polar bears are increasingly giving birth on land rather than on pack ice, which brings them into "hybrid range" with grizzlies. A bear shot by a sport hunter in 2006 was confirmed in lab tests to have had a grizzly father and a polar bear mother.

Geneticist Jennifer Leonard of Uppsala University, Sweden, has been studying the population in the Great Lakes. Her results show that the wolves in these states are now genetically distinct from the grey wolves which populated the area before humans cleared the forests.


Wolves have been hybridising with coyotes - which are able to back breed with parental stock, thus spreading the mixed genetics through the population. And human breeders’ attempts to cross wild bison with cattle have resulted in six of the 15 North American bison populations containing cattle genes.

When a species goes extinct due to its interbreeding being caused entirely by environmental changes caused by humans it is just as tragic as the straight-forward die-off of a species for which humans are to blame. The natural species, evolved over millennia, will still have been eradicated. What remains of it may yet contain the genetic resources to once again evolve the pure strain, but the set-back is likely to be permanent as long as humans continue interference.

The rapid climate change, unlike natural changes that spur evolution/speciation, is too fast to allow adaptation through natural selection, and that is why we now face an age of mass extinctions, a biodiversity crisis and global species loss.

According to the latest research, species around the world are going extinct faster that previously thought, at a rate not seen since the extinction of the dinosaurs. The Living Planet index which was released today shows that due to destructive human activity, the diversity of all life on earth has decreased by over 30%, nearly a third in fact in the past thirty-five years.

The Zoological Society of London and the Global Footprint Network also gave the following statistics: land species have declined by 25%, marine life by 28% and freshwater species by 29%. The reports editor Jonathan Loh stated that to see such a sharp fall off in the species of the planet was "completely unprecedented in terms of human history". "You'd have to go back to the extinction of the dinosaurs to see a decline as rapid as this... In terms of human lifespan we may be seeing things change relatively slowly, but in terms of the world's history this is very rapid."


Because humans embrace pluralism and see mixing as a way to enjoy diversity, rather than destroy it, many readers' comments on the New Scientist article on species loss through hybridisation show passive-aggressive scepticism of its significance. Repeatedly, people say that such interbreeding can only increase diversity and fail to consider that evolution is a process of emergence of ever more specialized branches and certainly not a story of blending and merging of branches! Cognitive dissonance over how humans in the modern world fit into Nature’s order can explain this confusion.

Hybridisation can result in the whole type of animal being eliminated over time by natural selection - although more likely it simply would evolve back to something specialized for its niche. Humans ourselves are risking our own mass extinction.

We live in the Anthropocene epoch, a time where humans have impacted geographically on the planet in much the same way as a large asteroid creating similar mass extinction in the distant past. Just as an asteroid impact is thought to have left an iridium layer at the “K-T boundary” in the Earth, we humans will have created our own distinctive layer within the Earth’s crust, showing when we lived: a layer of trash and pollution, evidence of another mass extinction, and other clues as to the idiocy humans practiced.

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"To-morrow, and to-morrow, and to-morrow,
Creeps in this petty pace from day to day,
To the last syllable of recorded time;
And all our yesterdays have lighted fools
The way to dusty death. Out, out, brief candle!
Life's but a walking shadow; a poor player,
That struts and frets his hour upon the stage,
And then is heard no more: it is a tale
Told by an idiot, full of sound and fury,
Signifying nothing.

From William Shakespeare's "Macbeth"