Humans Have Become The Biggest Force In Evolution.
The Zoque people
of Mexico hold a ceremony every year during which they grind up a poisonous
plant and pour the mixture into a river running through a cave.
Any of the river's molly fish that float to the surface are seen as a gift from the gods.
The gods seem to be on the side of the fish, though - the fish in the poisoned parts of the river are becoming
to the plant's active ingredient,
If fish can evolve in response to a small religious ceremony, can you imagine the effects of all the other changes we are making to the planet.
We are turning grassland and forests into fields and cities, while polluting the air and water. We are hunting species to the brink of extinction, as
well as introducing new pests and diseases to just about every part of the world.
Species living today are likely to be wiped out over the next century or two as a result of this multiple onslaught,and what is now becoming clear is
that few of the species that survive will live on unchanged.
Far from being a slow process,evolution can occur very rapidly when the environment changes,so,as we alter the planet faster and more drastically,we
are becoming the main force driving evolution.
of Stanford University in California,says
"The intensity of the ecological effects of man,is pretty obvious
Some of the fastest rates of evolution ever measured in the wild are in plants and animals harvested by humans,the few populations for credible data,
are on a average evolving 3 times as fast, as populations subjected only to natural pressures.
Most predators target the young or the weak,Humans are different, we target the biggest and the best, or those with characteristics we desire,now
combine this with our ability to kill in large numbers and the result is extremely rapid evolution of our prey.
Many examples have emerged of how hunting can transform the hunted.
The targeting of large animals has resulted in a fall in the average size of Caribou
in some areas,
for instance, while trophy hunting has led to Bighorn Sheep
in Canada and mouflon in France
evolving smaller horns.
But the most dramatic example is the shrinking of tusks in Elephants
, and in some even their complete
In eastern Zambia, the proportion of Tuskless female
shot up from 10 per cent in 1969 to nearly 40% in 1989 as a
result of poaching
More dramatic rises in tusklessness have been reported in many parts of Africa, with some
losing tusks too.
in Germany suggest that female elephants preference for tuskers has partly counteracted the effect of hunting,and goes on to say
"even if all poaching stopped,it would still take a very long time for the percentage of tuskers to rise again
in countries like Zimbabwe now have a policy,were they charge hunters a
smaller Trophy Fee
for shooting tuskless elephants,anywere
from $3000 instead of the basic $12500 for a tusker.
The use of synthetic pesticides like DDT
took off in the
in 1946., and by 1948 resistance had been reported in 12 insect species, and then in 1966,
James_F._Crow of the University of Wisconsin Madison
reported that the count had exceeded 165
He was noted at the time for saying.
“No more convincing examples of Darwinian evolution could be found than those provided by the development of resistance in one species after
Rats and mice around the world have become resistant to the Poison Warfarin
, and in Europe some have
even become resistant to warfarin’s replacement, SuperWarfarin
In Australia, meanwhile, rabbits are becoming resistant to the poison used to control their numbers, called
Pesticide resistance has been studied far more closely than other kinds of ongoing evolution,and in many cases we know which mutations are involved,
how they make organisms resistant
and sometimes even how the mutations spread through
Resistance arises due to mutations that alter the shape of proteins and prevent insecticides binding to their targets, were as DDT and pyrethroid
compounds kill insects by opening sodium ion channels in nerve cells, but in the malaria-carrying mosquito
, variants of the channels that cannot be opened this way have evolved on
at least four separate occasions.
Other main mechanism of resistance involves enzymes that inactivate pesticides before they can kill,and some resistant strains of gambiae,produce
large quantities of an enzyme called CYP6Z1
that can inactivate DDT.
Pesticide resistance is becoming such a serious problem that strategies for preventing it evolving in the first place are taken increasingly
seriously,and one approach is to alternate the type of pesticide applied, to try to avoid applying sustained selective pressure in one direction.
The pests seem to be evolving faster than we can develop new pesticides, and in one region of Burkina
, gambiae has become resistant to all four classes of insecticides used for malaria control.
Between 1947 and 1976, two factories released half a billion
kilograms of polychlorinated biphenyls
) into the
in the north-east US. The effects on wildlife weren't studied at the time, but
today some species seem to be thriving despite levels of PCBs, many of which are toxic, remaining high.
At least one species, the Atlantic tomcod
- an ordinary-looking fish about 10 centimetres
long - has Evolved resistance
"We could blast them with PCBs and dioxins with no effect
," says Isaac Wirgin
of New York Uninversity Scholl of Medicine.
Many of the ill effects of PCBs and dioxins are caused by them binding to a protein called the
The Hudson tomcod all have a mutation in the receptor that stops PCBs binding to it,
Wirgin and colleagues reported earlier this year.
Isaac Wirgin also said,
"The mutation is present in other tomcod populations too,but the levels are a lot lower then those in the Hudson
Pollution resistance in one species can have unexpected consequences for others.
The tomcod’s tolerance allows it to accumulate extraordinarily high levels of PCBs in its body,is a threat to animals higher up the food chain –
IE: humans with a taste for fish.
The most famous example of evolution in action was a response to pollution, as the Industrial
got under way, Cream coloured peppered moths in northern Britain
to stay hidden on trees stained by soot.
Most evolutionary changes in response to pollution seem to be invisible.
The spoil heaps of many old mines, are covered in plants that appear normal, but are in fact growing in soil with high levels of metals such as
copper, zinc, lead even arsenic that would be toxic to most of these and other species.
The evolution of tolerance has occurred extremely rapidly in some cases, sometimes within just a few years of the soil being contaminated.
Crusts of radiotrophic fungi fractalizing across the walls of
Chernobyl’s blown out reactor core, cancer eating microbes drifting through the hyper-toxic waters of a lake full of mine tailings in Montana, the
charred trunk of a ginkgo tree re-sprouting delicate leaves after the atomic blast at Hiroshima, Detroit’s feral houses and its ghetto pheasants –
all these things indicate that despite the current ecological apocalypse, despite catastrophic climate change and the mass extinction of biota –
nature itself isn’t going to go away any time soon.
No matter how much destruction we wreak, there are processes of regeneration lying in wait that are quietly evolving around us, or biding their
time until we turn our backs. It’s as if the earth has a sentient biological field that sucks up our poisons and smothers the detritus of our
civilization so that life itself can go on.
Though it’s quite likely that we will precipitate the extinction of our own species along with the countless others we have already wiped out, the
bio-field will survive, as it must. It is the immune system of the planet and the signs of it are everywhere if you know where to look. Regular
readers will know I’ve long been interested in ruderal ecologies, which evolve when we stop maintaining architectural landscapes and they gradually
transform into habitat for a range of pioneering organisms such as ragweed, coyotes and Ailanthus trees.
Lately though, I’ve been tracking the absorption of various mass produced objects into the bio-field, some long discarded, others still in daily
The shiny, manufactured surfaces we so fetishize are little match for the relentless progression of slimes, films and crusts that soon moves in to
obscure them. Yet there is something magnificent in these ancient, incremental processes. Life on earth has a future. And it’s far beyond
In 1935, the South American cane toad
was introduced to Australia to
feeding on sugar cane, but the cane fields were not to the toad’s
liking, but the rest of the countryside was.
The toad has spread aggressively at the expense of many native species.
The highly poisonous animals are having a big effect on predators, such as the Australian black snake, who are developing resistance to cane toad
toxins, also the red-bellied black snake and green tree snake, are changing in a surprising way – their mouths are getting smaller, and the only
reason must be snakes with big mouths can eat large toads that would contain enough toxin to kill them.
The toads themselves are also changing, they are now colonising regions that were too hot for the founder population, suggesting that they are
evolving tolerance to more extreme conditions.
The toads leading the invasion
are becoming better colonisers as
they have bigger front legs and stronger back legs than toads living in the areas already colonised.
Radio tagging has confirmed that these “Super Invader
toads can travel faster, as you might expect.
They are probably evolving because the first toads to reach new areas benefit from more food and less competition, and have more offspring as a direct
result of this, and the changes are likely to be transient, once the toads stop spreading, the “super-invader” traits will gradually be lost i
In areas of the US that have been invaded by fire ants, native fence lizards have evolved longer legs, which can only suggest its to make it faster,
as a dozen fire ants can kill a lizard in minutes.
Michael Kinnison of the University of Maine in Orono
has been actively
experimenting,and in one of his experiments, he moved juvenile chinook salmon from one river in New Zealand to another, and salmon were introduced to
the country around a century ago, and Kinnison wanted to assess the extent to which they had adapted to conditions in individual rivers.
He found drastic differences in survival, even though the fish appear identical
“When a population was locally adapted, it performed twice as well”
Kinnison suspects that lots of small changes can add up to make a huge difference to a population’s success.
“Contemporary evolution may be relatively modest on a trait-by-trait basis, but its overall contribution to the performance of populations may
These findings explain why there is often a lag between the introduction of new species and their rapid spread,when a newly arrived species is likely
to find itself in an environment that is not ideal, and its population is very small, meaning there is little genetic diversity, and in these
circumstances, a species will spread only slowly, if at all.
As the population begins to adapt to local conditions, maybe via invisible changes such as mutations in immune genes it is likely to start to grow and
Because more mutations occur in larger populations, it will then evolve faster, enabling it to spread quicker and further, but if this turns out to be
common place in nature, it could only mean bad news, as it suggests that many introduced species that seem to be behaving themselves could yet start
spreading explosively and cause serious problems.