Wednesday, February 3, 2010

Natural Selection: Elephants in Sri Lanka

Dancer is studying genetics in science. We were discussing how more and more Asian Elephants in Sri Lanka are becoming "tuskless". In a typical population of this species about 1/2 of the male elephants have tusks (females are without tusks). It is thought that lack of tusks is caused by a single recessive gene.
In the "wild" scenario tusks are an advantage for the males. Tusks are useful when foraging for food as well as for fighting other males for mates. The tusk gene makes a more successful individual.

In Sri Lanka, political unrest and instability make poaching elephant tusks for the illegal ivory trade a lucrative business. In this environment, tuskless males and females are ignored by the poachers. This makes the tuskless gene an advantage. In Sri Lanka today around 90% of male elephants are "tuskless" instead of the 50-50 mix that occurs normally.

To illustrate how this happened we did this experiment with jelly beans. Red jelly beans represent "tuskless" elephants an the white ones are "tusked" elephants. More red than white jelly beans are needed for experiment.

Twenty beans of each color are placed in a paper bag. The kids took turns being a poacher and pulling a bean out of the bag without looking.
If a white jelly bean is pulled out it is eaten by the poacher. Red jelly beans are replaced along with two more red jelly beans to represent the offspring that would eventually result.

We did this for three seasons of six poachings each. Below see the change in percentages after each season.

---------- - Start --- Season 1 --- Season 2 --- Season 3

Tusked ---- 50% -- --- 39% ----- 31% ----- -- 23%

Tuskless --- 50% -- --- 61% -- --- 69% -- ---- 77%

The "elephant" herd after poaching. Many more red tuskless elephants than white tusked elephants.

In 1900 there were about 20,000 elephants in Sri Lanka, today there are less than 3500.

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