Overhunting leads to the birth of tuskless elephants in this country
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New studies show that decades of civil war and poaching in Mozambique have led to genetic changes among elephants, with many now being born without tusks.
These findings highlight the dramatic impact that humans can have on animal evolution.
Large tusks usually give elephants an advantage, allowing them to dig for water, cut tree bark for food, and fencing with other elephants.
But during bouts of ivory poaching, these large incisors became a burden to elephants.
Now, researchers have pinpointed how years of civil war and poaching in Mozambique have led to an increase in the proportion of elephants that never grow tusks.
During the conflict that ran from 1977 to 1992, fighters on both sides slaughtered elephants for ivory, to fund the war effort.
In the area now known as Gorongosa National Park, poachers have wiped out about 90% of the elephants.
The surviving elephants were more likely to share a key characteristic: half of the females were inherently toothless - they simply did not have tusks - while before the war, less than a fifth of females lacked tusks.
After the war, these tuskless females transferred their genes to a newer form, with unexpected and surprising results.
About half of their daughters were without fangs.
Even more puzzling, two-thirds of their offspring were female.
The years of upheaval "changed the course of evolution in that population," says Princeton University evolutionary biologist Shane Campbell Stanton, and he and his colleagues set out to understand how the pressure of the ivory trade upended the scale of natural selection.
Their findings were published last Thursday in the journal Science.
Researchers in Mozambique, including biologists Dominic Goncalves and Joyce Ball, monitored nearly 800 elephants in the national park over several years to create a catalog of mothers and sons.
In Gorongosa, the team collected blood samples from seven females with fangs and 11 females without fangs, then analyzed their DNA for differences.
And the elephant survey data gave them an idea of what they were looking for: Since the tuskless elephants were female, they focused on the X chromosome. (Females have two X chromosomes; males have one X chromosome and one Y chromosome.)
They also suspected that the related gene was dominant - meaning that a female only needs one altered gene to be tuskless - and that when passed on to male fetuses, it might limit the development of canines in them.
Their genetic analysis revealed two key parts of the elephant's DNA that are believed to play a role in transmitting the tuskless trait.
The same genes are linked to tooth development in other mammals.
"They provide evidence of genetic changes," says Chris Dremont, a conservation scientist at Victoria University in Canada, who was not involved in the research.
"Their work has helped scientists and the public understand how our society can have a significant impact on the evolution of other life forms."
Most people think evolution is a slow thing, but humans can speed up the process.
"When we think of natural selection, we think of it happening over hundreds or thousands of years, but in fact it's this dramatic selection, which happened over 15 years," says Samuel Wasser, a conservation biologist at the University of Washington, who was not involved in the research. It is one of the most surprising results.”
Scientists are now studying what the tuskless elephants mean to other species and the savannah environment.
Their preliminary analysis of fecal samples indicates that Gorongosa elephants are changing their diet because they are now without long tusks for peeling tree bark.
"Tuskless females eat mostly grass, while canine elephants eat more vegetables and hardy woody plants, and these changes will persist for at least several generations of elephants," said co-author and biologist Robert Pringle at Princeton University.
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