Nature's Gift and Curse of Tusks to Elephants

"Tooth development has been very conserved during evolution."
"Elephants are no more different from humans than mice are, so it's quite possible that the same gene or genes are involved [in tusklessness in elephants and human toothlessness]."
Irma Thesleff, developmental biologist, University of Helsinki, Finland

"We know tusks play an important role in obtaining food, 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?"
Shane Campbell-Staton, assistant professor of ecology and evolutionary biology, University of California, Los Angeles

"They're [the tuskless elephants of Gorongosa, Mozambique] in fantastic condition, this is a very good habitat [Gorongosa national park] for them, and there's no indication they're suffering nutritionally."
Joyce Poole, scientific director, Elephant Voices research and advocacy group, Gorongosa 

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Science has not yet unravelled the mystery of what causes tusklessness in elephants, but through slow and steady research some progress has been made deciphering the genetic program of mammalian tooth development in general, where scientists have discovered an ancient, widely-shared genetic code. Mutations linked with tooth abnormalities in mice show up as well through genetic studies of humans who have missing or malformed teeth.

Elephant tusks are overgrown upper lateral incisors -- those teeth located right beside the front teeth, before the canines. Tuskless elephants, therefore, don't have lateral incisors. Throughout Africa tuskless elephants are anomalous, found in discrete numbers. Gorongosa is an exception; there a sizeable population of tuskless elephants occur. The tusked elephants were victims of a remorseless civil war which incidentally saw elephants slaughtered for ivory. The tusklessness of those surviving elephants without ivory represented their Darwinian advantage.

The result of that ravaging of the park's tusked elephants is that roughly a quarter of the 700 elephants living in the park are tuskless females. Among humans, missing lateral incisors represent the second most common form of tooth agenesis of which the normal rate of the condition lies between two to four percent, roughly analogous to the rate of tusklessness among African elephants.

Generally speaking, tusks are canines curving to the side and upward in wild boars and warthogs, or they droop downward in walruses, while in narwhals of the Arctic the tusk is a single overgrown canine penetrating through the left upper lip of the animal giving them their iconic 'unicorn' appearance. As multipurpose aids tusks are useful implements. Those incisors are used by elephants to dig for salts and minerals; break off branches to reach foliage; they're used to pry and peel off tree bark; to scoop a calf from a mudhole or lift a resting one to its feet.

Bull elephants contest one another by locking their tusks in combat. Those tusks can each weigh up to and over 45 kilograms, seven times the weight of an average female tusk. Those naturally-endowed implements so useful to the elephants have led to their deaths in enormous numbers by poachers setting out to harvest valuable ivory which has always been in high demand as a beautiful material used to carve detailed pieces of artful objects.

International efforts to have the trade banned have had only partial success, with the ivory so valuable that no amount of protection suffices entirely to acutely limit a billion-dollar illicit and inhumane trade. A situation that has led researchers to consider whether elephants would be better off without those mighty tusks, imagining the loss to the trade should the tuskless trait spread throughout the African population with a little bit of help from scientific human intervention.

This intriguing conundrum has the attention of Dr. Campbell-Staton and his colleagues at University of California who have been comparing tusked and tuskless elephants in Gorongosa, hoping to identify and isolate the genes involved in tusklessness, and to solve the patterns of inheritance. As for example, why it is that almost all the tuskless elephants of Africa are female.

Gorongosa Blog