GORONGOSA NATIONAL PARK, Mozambique
We
are flying in a Bat Hawk aircraft — which may be named for a raptor
that preys on bats but looks more like a giant, lime-green dragonfly —
and my hair, thanks to the open cockpit, has gone full Phyllis Diller.
Scudding
above flood plains the colour of worn pool table felt and mud flats
split like jigsaw puzzles, we dip toward the treetops and see herds of
waterbuck scatter with an impatient flash of their bull’s-eye rumps.
We are searching for the elusive tuskless elephants of
Gorongosa, elephants that naturally lack the magnificent ivory staffs
all too tragically coveted by wealthy collectors worldwide.
Tuskless
elephants can be found in small numbers throughout Africa, but
Gorongosa is known to harbour a sizable population of them, the legacy
of a violent 15-year civil war. Tusked elephants were slaughtered for
their ivory at a harrowing rate, and the park’s rare tusk-free residents
thus gained a sudden Darwinian advantage.
Today, about
a quarter of the park’s 700 or so elephants are tuskless, all of them
female, and I am determined to catch a glimpse of at least one. Yet a
week of ground searches has proved fruitless, and now we are circling in
a plane and still nothing and, holy mother of Horton, how can such
massive creatures go missing?
“There!” Alfredo
Matavele, the pilot, cries triumphantly, pointing toward a cluster of
trees. “And there!” pointing toward a watering hole. And there and
there. “Do you see them?” he demands.
Oh yes, I see
them. Dozens, scores, cliques and claques of elephants, ears flapping
like flags, trunks slowly swinging, and many of their faces decidedly
free of ivory eruptions. I have found them at last, my sisters in dental
deprivation.
Other people may admire elephants for their brains or their
complex social lives; I feel a bond with this mutant crew. After all,
I’ve learned that we share a basic developmental anomaly, which may well
be traceable to the same underlying glitches in our DNA.
Elephant
tusks happen to be overgrown versions of the upper lateral incisors —
the teeth right next to the front teeth, before you get to the canines.
Simply put, tuskless elephants lack lateral incisors.
I,
too, lack lateral incisors; moreover, the trait runs in families.
Tuskless elephants often have tuskless kin. Both my daughter and my
younger brother are missing their lateral incisors. No wonder we’ve
always had trouble ripping the bark off trees.
Scientists
do not yet know the precise cause of tusklessness, but they’ve made
great progress in deciphering the genetic program behind mammalian tooth
development generally. It turns out to be an old and widely shared
code.
“Tooth development has been very conserved during
evolution,” said Irma Thesleff, a developmental biologist at the
University of Helsinki in Finland. She has found that mutations
associated with tooth abnormalities in mice also show up in genetic
studies of people with missing or malformed teeth.
“Elephants
are no more different from humans than mice are,” Thesleff said, “so
it’s quite possible that the same gene or genes are involved” in
elephant tusklessness and human toothlessness.
For
example, it could be a typographical error in the genetic code for a
signalling molecule called wnt10a. “This is one of the most commonly
mutated genes in humans with missing teeth,” Thesleff said.
And
oh, we gap-mouths are everywhere. An estimated 8 percent of the
population is missing one or more of the 32 teeth found in the standard
adult set, and that figure rises to about 30 per cent if you include a
natural absence of the four extra wisdom teeth that many people get
yanked out anyway.
Missing
lateral incisors is thought to be the second most common form of tooth
agenesis. One archaeological study of a 9,000-year-old farming community
in Basta, Jordan, found that 36 per cent of the inhabitants lacked
lateral incisors. Researchers viewed the elevated rate as evidence of
inbreeding.
The normal background rate of the condition
is more like 2 to 4 percent, which, coincidentally or otherwise, is
close to the background rate of tusklessness among African elephants.
Even
more common in humans than a lack of lateral incisors, said Ariadne
Letra, an associate professor at the University of Texas School of
Dentistry at Houston, is the absence of the lower second premolars, the
teeth with two cusps located in the bottom jaw just before the
four-cusped molars.
(I discovered in the course of
reporting this story that my husband was born without his second
premolars, so I guess I’m grateful my daughter has any teeth at all.)
Through
animal studies, scientists have learned that teeth can grow in macabre
isolation from other body systems, as if they yearned for a career as
novelty dentures at a Halloween party. Isaac Salazar-Ciudad, a
theoretical biologist who studies tooth development at the University of
Helsinki, explained that if you remove part of the primordial mouth of a
mouse embryo and culture it in a dish, it will develop an array of
normal-looking mouse teeth.
Although the basic genetic program is widely shared, tooth building is also flexible, susceptible to evolutionary influences.
Teeth
develop through the interaction of two types of embryonic tissue,
epithelial and mesenchymal, which early in gestation — by about Day 28
in humans — start folding up into each other origami-style to form a
series of large and small buds. Those buds can then be sharpened into
canines or incisors for slicing into flesh, or flattened and sculpted
into molars with any number of cusps for processing fibre plants.
The
core of a tooth, the pulp, holds the blood vessels and nerve fibres,
while the bulk consists of a bonelike material called dentin. The outer
coating of calcium phosphate enamel is the hardest substance in the
body, which is why animal teeth account for a disproportionate share of
the fossil record.
And when lengthened into structures
that breach the boundary of the mouth and grow throughout life, teeth
become tusks — for digging, fighting, hauling, piercing, threat display.
The
diversity of shapes that teeth can assume, combined with their
mineralized hardness, said Salazar-Ciudad, “could be why they have been
repurposed as tusks and used for so many tasks.”
In
most cases, tusks are recast canines, curving to the side and upward in
wild boars and warthogs, or drooping down in walruses like Yosemite
Sam’s moustache. In narwhals, the unicorns of the Arctic, the tusk is
built of a single overgrown canine that penetrates through the narwhal’s
left upper lip in a permanent open wound, which ends up hosting tiny
shrimplike creatures with an appetite for shed whale skin.
The
narwhal tusk “is the only straight tusk in nature, and the only spiral
tusk, too,” said Martin Thomas Nweeia, a narwhal expert who lectures at
the Harvard School of Dental Medicine.
Tusks, as a
rule, are multipurpose devices. Boars and warthogs apply theirs
offensively and defensively, to battle one another during mating season
and to gore predators many times their size.
Walruses
use their tusks like grappling hooks, to haul themselves out of the
water and onto the ice, and as weapons against polar bears and in sexual
contests — but not, as commonly believed, to forage for food or pry
open oysters.
The purpose of the narwhal’s tusk remains
a subject of contention. Some researchers suggest the whales use it to
stun their fish prey. Nweeia and his co-workers propose that it is a
kind of sensory organ, for detecting changes in water salinity and
temperature.
Elephants are the true masters of the
Swiss army tusk. They use their mighty incisors to dig for salts and
minerals, to break off branches and get at the foliage, to pry into
trees and peel off the bark — “They really love to eat bark,” said Joyce
Poole, scientific director of Elephant Voices, a research and advocacy
group working at Gorongosa — to scoop an errant calf out of a mudhole or
lift a sleeping one to its feet.
They coordinate
tusks, trunks and feet to de-thorn acacia trees and soften tough
grasses, and they stash leafy branches across their ivory shelves for
later consumption.
Just
as people are left- or right-handed, so elephants have a favoured tusk.
“If they’re going to break a branch over a tusk, they use the same tusk
repeatedly,” Poole said. A groove forms in the preferred tusk over
time.
But it can take two tusks to tangle. From my
perch in the Bat Hawk, I watched a pair of large bull elephants spar by
locking together their massive tusks, which can weigh well over 100
pounds each — seven times the weight of an average female tusk.
Yet
the biophysical properties that make tusks such splendid tools to own
have all too often proved...
their owners’ undoing. People have long coveted ivory for its beauty, ductility and presumed magical properties.
their owners’ undoing. People have long coveted ivory for its beauty, ductility and presumed magical properties.
The
first appearance of narwhal tusks in medieval Europe is thought to have
given rise to the myth of the unicorn, and to a mad surge in demand for
the 9-foot spiralling spears. Elizabeth I is said to have paid 10,000
pounds for a narwhal tusk, then the price of an average castle.
The
drive to harvest walrus ivory may well have contributed to the
settlement of Greenland in the 10th century, and led to the near
extinction of walrus populations around Norway, Iceland and other parts
of the North Atlantic.
Elephant ivory, however, is
considered the finest in the world, and elephants have long been
slaughtered to supply it. Despite international efforts to ban the ivory
trade, demand still drives a business worth at least $1 billion a year.
The
persistence of elephant poaching has prompted researchers to wonder
whether elephants really needed their tusks, and whether they might not
be better off if the tuskless trait were to spread more widely through
the African population.
Shane Campbell-Staton, an
assistant professor of ecology and evolutionary biology at the
University of California, Los Angeles, and his colleagues have begun
systematically comparing tusked and tuskless elephants in Gorongosa,
seeking not only to identify the genes involved in tusklessness but also
to solve perplexing patterns of inheritance.
Why, for
example, are nearly all the tuskless elephants of Africa female? Among
Asian elephants, a related species, many males are tuskless, and recent
studies suggest they fare surprisingly well on the sexual battlefield
when pitted against tusked rivals.
Campbell-Staton is also looking at downstream effects of tusklessness.
“We
know tusks play an important role in obtaining food,” he said, “so if
individuals don’t have that tool, are they using the environment
differently, and could those changes have consequences for other animals
dependent on elephants as ecosystem engineers?”
Maybe,
but from the look of it, the tuskless elephants of Gorongosa are
thriving. “They’re in fantastic condition, this is a very good habitat
for them, and there’s no indication they’re suffering nutritionally,”
Poole said.
Lateral incisors: Who needs them? Better by far to keep the poachers at bay.
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