Elephants without tusks? The mammal evolves due to brutal poaching

In a strange development, an increasing proportion of female elephants in Mozambique's Gorongosa National Park have been born without tusks. As per scientists, this is an evolutionary response to the brutal killing of elephants for their ivory tusks during the country's 15-year civil war. 

Experts working in the park started noticing the phenomenon after the war ended in 1992. 

Field data and analysis of old video footage found that the proportion of tuskless female elephants increased more than threefold between 1972 and the year 2000. 

Ryan Long, an associate professor of wildlife sciences at the University of Idaho said that this was the period during which the elephant population tumbled from roughly 2,000 to about 250 individuals. 

According to a study published in the journal Science, scientists have now developed a better understanding of the genetic basis for the tusklessness and why it only appears to affect female elephants.

As per the analysis, the tuskless females were five times more likely to survive during the 28-year period than their tusked female counterparts. 

In Gorongosa, in the 1970s, 18.5 per cent of the female elephants did not have tusks, while three decades later 5 per cent did.

Also read | Polar bears return to Pacific Arctic for first time in 20 years

Long, an author of the study was quoted by CNN as saying, "Evolution is simply a change in heritable characteristics within a population over successive generations, and based on the results of our study, the shift toward tusklessness among female elephants at Gorongosa fits this definition perfectly."

"The fact that it occurred so rapidly is rare indeed, and is a direct function of the strength of selection," he said via email. "In other words, it happened so quickly because tuskless females had a MUCH higher probability of surviving the war, and thus a MUCH greater potential for passing their genes on to the next generation."

As a part of the study, the researchers took blood samples of 18 female elephants, with and without tusks. They also sequenced their genomes. It was then revealed that the females with no tusks had a genetic variation in a very specific region of the X-chromosome. This plays a role in tusk development.

The exact genetic and developmental mechanism that leads to tusklessness in females has not yet been understood.