Originally posted by sandyb
Where can this cycle be observed? Please give us some examples.
One of the more interesting examples that shows how a small genetic difference can increase survivability in response to an animals environment and cause a change in the structure of a population in future generations. The tone of the article is a little misleading because the elephants don't "decide to lose their tusks. A random genetic difference caused that. It just becomes a fact that elephants without tusks survive better in an environment that includes poachers.
What makes this particularly interesting is that an elephants "tusks" were most likely the result of a similar genetic difference. The mutation that allows for tusks would have caused the animals that had it to be better fit for survival in an environment that required digging for food and water and fighting for territory and mates. As generations passed, the tusks became larger and larger.
Now that the environment has changed, tusks are a threat to survival and the elephants without tusks are better fit for survival, therefore, more elephants without tusks survive to breed and increase the occurance of the tuskless elephants in the population as they pass the trait on to future generations.
http://news.bbc.co.uk/1/hi/world/africa/180301.stm
World: Africa Elephants 'ditch tusks' to survive
Elephants are beating the ivory poachers, but at a high price
An increasing number of elephants have no tusks, according to a survey.
Research at the Queen Elizabeth National Park, Uganda, showed that 15% of female elephants and 9% of males in the park were born without tusks.
In 1930 the figure for both male and female elephants was only 1%.
Genetic accident
Elephants appear to be losing their tusks
Experts say the reason why some elephants are tuskless is a result of a chance genetic mutation.
They say elephants are losing their tusks as a rapid and effective evolutionary response to escape slaughter by ruthless and resourceful poachers who kill elephants for their ivory trophies.
The BBC's Science Correspondent, John Newell, says the continuing change shows how rapidly evolution can react in response to pressures that threaten the survival of a species.
This allows them to live, breed more freely and produce more offspring without tusks.
Growing trend
Evidence of a trend in tuskless elephants has been reported elsewhere.
Mark and Delia Owens recorded an unusual number of such elephants in 1997 while carrying out research in Zambia's North Luangwa National Park.
Published on the National Wildlife Federation's Website, they write: "Our research indicates that more than 38% of Luangwa elephants carry no tusks.
"Other researchers have reported that in natural, unstressed populations, only 2% of the animals are tuskless."
Crippled creatures
Tuskless elephants are paying a heavy price for survival.
Tusks are used to dig for food and water, to dig up trees and branches and move them around, for self defence and for sexual display.
Conservationists say an elephant without tusks is a crippled elephant.
They say that while being tuskless is better than being dead, they hope that less drastic ways can be found to protect elephants against poachers.