by Rebecca Shoer
Tusks are one of the most dignified and awe-inspiring
natural ornaments in the animal kingdom.
No matter how cute or cuddly an elephant can look when goofing around,
there is nothing as entrancing as an individual calmly sporting a full grown
pair of bone-white tusks. (An individual
with tusks is called a "tusker" by the elephant community). Of course, in Asian elephants, only the males
bear tusks; in African elephants, both males and females have tusks. Male elephants use their tusks for a wide
range of activities, from combat and defense against other males to scraping
nutritious bark off of trees. Females
are able to use their small tushes, which are essentially miniature tusks, to
perform some of these tasks as well.
Since the females get along fine without toting around such unwieldy ,
albeit impressive, burdens, why bother evolving tusks at all? Most likely, males developed longer and
longer tusks over many generations due to a process called sexual selection. This means
that, for some reason or another, female Asian elephants prefer to mate with
males that have long tusks. Possessing
long tusks may signal how healthy an elephant is or how good his genes are, as
they take a lot of extra energy to grow and maintain. Tusks are oversized, living teeth, and grow
at a rate of about 15 centimeters per year.
If a male can survive in the wild while also carrying an impressive set
of tusks, he is most likely very healthy as well as socially dominant.
Picture by Lisa Barrett
This sort of sexual selection is happening constantly in the
natural world, as mating preference subtly changed over millennia. However, outside forces can affect the
evolution of species. Sudden
environmental changes can make a once-advantageous physical trait burdensome,
or a flashy physical trait that indicates health may become attractive to
predators. For elephants, such an
outside force has appeared: the ivory trade.
Ivory has long been prized for its decorative and aesthetic
value. It is easily carved, and has been
used for statues, jewelry, and decoration for centuries. However, the demand for ivory has recently
been increasing at a dramatic and unsustainable level, and modern technology
has made it far too easy to kill and extract ivory from elephants. Automatic weapons and abject poverty make for
a dangerous combination, and anti-poaching efforts have made barely a dent in
the poaching rate. If nothing is done to
reduce the demand for ivory trinkets, elephants will swiftly become extinct in
the wild.
Picture by Rebecca Shoer
However, in addition to human-led efforts to combat the
poaching trade, evolution has begun playing a role in this battle. The process through which animals with
advantageous adaptations survive is called natural
selection. Those individuals that
survive better and for longer are most likely to pass their genetic material
down to their offspring. The poaching
trade, however, is an example of artificial
selection. It is not the elephants'
natural environment, but the unnatural ivory trade, that is deciding which
elephants pass down their genetic material to the next generations. Put simply, if an elephant with spectacular
tusks is killed before he has a chance to mate and have offspring, the genes
for his tusks are lost. Even if elephant
females would prefer to mate with such a male, he is no longer available, and
females must mate with the males that are still present.
Thus, humans have created an artificial advantage for males
to not possess tusks. As the number of tuskers decreases, poachers
are "forced" to kill elephants that have relatively small tusks. Thus, those males that simply never develop
tusks, and do not possess the genes necessary to grow tusks, are suddenly at a
mating advantage. The number of their
tusk-ed brethren is swiftly disappearing, and tuskless males are being provided
with mating opportunities they would never get in a natural, non-poaching
environment.
Just how prevalent are these tuskless males? Professor Zhang Li of Beijing Normal
University reports that, of the few hundred elephants left in China, the
incidence of tuskless males has increased from 2 - 5 percent of the population
to 5 - 10 percent. A study done by Oxford
University also reports that the size of tusks has reduced significantly since
the advent of the modern ivory trade in the 19th century. Although these numbers may not appear
particularly large, such a percent change (perhaps from 5 to 10%) is unnaturally
rapid when compared to an evolutionary timescale. Elephants are adapting to the new
environmental threats that humans have created.
Photo via Centre for Ecological Sciences, Indian Indian Institute of Science
However, evolution is a notoriously slow process, and when
combined with the long generations of elephants, such an adaptation is most
likely too little, too late to save elephants from the threat of poaching. Elephants can live up to their mid sixties in
the wild, and at the current rate of population decrease, elephants could be
extinct in a single generation. Though
the rise of tuskless males is an interesting example of a species adapting to a
new threat, it will not be enough to save wild elephants alone. It is human behavior that must change, if
this species is to exist for generations to come.
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