Environmental Engineering Reference
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much biodiversity the planet as a whole is losing may be rather ill-founded. Local biodiversity matters
much more. Species act locally; we should think locally about them.
On the second question, Thomas points out that all five earlier great extinctions led to a burst of
evolutionary renewal. Yes, there was a short-term loss of species, but even as it happened nature was
gearing up to make good the loss. The Darwinian engine of evolution raised its game. Thus, the demise
of dinosaurs created space for mammals to evolve. So, he argues, why not look forward to the new di-
versity of the Anthropocene?
Already new hybrids and species are forming as native and alien species both adapt to changing con-
ditions and as their genes mingle. The new science of molecular genetics is revealing these evolutionary
stirrings. “There is an extraordinary amount of hybridization going,” Thomas tells me. “Genes are jump-
ing around. Darwin talked about a tree of life, with species branching out and separating. But we are
discovering it is more like a network, with genes moving between close branches of the evolutionary
tree, as related species interbreed. This hybridization quickly opens up new evolutionary opportunities.”
The argument is that the homogenization of global biodiversity will be counteracted by new evolution.
Alien species are a big part of Thomas's evolution revolution, turning up in unexpected places and
churning the genetic soup. “In Britain, hybridization involving introduced plant species seems to be hap-
pening at least as fast as native species are going extinct,” he says. Thomas is not alone in his thinking.
“Evolution can be very rapid under the right conditions. Climate change is going to be one of those
things where the conditions are met,” said Arthur Weis of the University of Toronto. 7
As Thomas and I looked out of his lab window on the bleak winter campus of York University, none
of this seemed likely. Nature looked somnolent. But his computer screen was soon flashing with papers
from across the world describing the unexpected extent of promiscuous genetic exchange. Tim Benton
of Leeds University, who took over from Thomas when the latter moved to York, found major genet-
ically transmitted changes in wild soil mites within fifteen generations of them changing their environ-
ment. The genetic changes doubled the age at which the mites reached adulthood. 8
That was in the lab. But there are plenty of stories from the field. Oxford ragwort ( Senecio squalidus )
originally lived on the slopes of Mount Etna in Sicily. It was brought to Britain in about 1700 by botanist
William Sherard and was tended in the Oxford Botanic Garden. Eventually it escaped, first working its
way along the walls of Oxford colleges where, by the late eighteenth century, it was reportedly “very
plentiful.” 9 Later, as Britain developed a network of railway lines, it adopted the stone beds of the tracks
as a new habitat comfortingly similar to the lava beds back home. It made its way along the railway to
London and elsewhere. At some point on this journey, it mixed its genes with Senecio cousins such as
the sticky groundsel ( Senecio viscosus ), creating a number of hybrids that eventually turned into fully
fledged new species. Among them are Senecio cambrensis and the most recent addition, Senecio ebor-
acensis , which was recently named York groundsel, after the city it was found in. 10 Thus a species in-
troduced to Britain under circumstances that would horrify people defending native biodiversity has be-
come a dramatic example of evolution in action. The alien ragwort is not destroying biodiversity; it is
creating it.
The Oxford ragwort is far from alone. A new fertile hybrid primrose, Primula kewensis , arose
when Primula verticillata from Africa met Primula floribunda from the Himalayas at Kew Gardens in
London. And whenever the southern European Rhododendron ponticum meets its Appalachian cousin,
Rhododendron catawbiense , the result seems to be a new hybrid. One now widely found in North East
Scotland is both fertile and frost-resistant.
Often, migrants evolve in the course of adapting to their new surroundings. That has happened to
the thistle-like plants called Centaurea melitensis that missionaries took from Spain to California in the
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