How do scientists explain why some herds of elephants have started producing only calves with very short tusks is a example of natural selection?

Pretty simple really.

These elephants were being hunted purely for their long tusks. 

The ones born - by chance - with shorter tusks were considered not worth the risk so were not killed by the hunters. 

Over time the long tuskers were hunted to extinction but the shorter tusked elephants continued to breed and to pass on the “short tusk” gene to their offspring. 

Soon only short tusked elephants were left and the herd began to grow again - left alone by the hunters who went elsewhere in search of longer tusks.  

Hopefully elephant hunters will soon become extinct. 

In business the companies who failed to see the digital revolution coming and who failed to learn how to operate on the internet were like the long tusked elephants. Gone.

Now the same can be said for individuals who fail to see that their jobs may well become extinct or that they really need to learn new skills and create multiple income streams. 

The moral of the story? 

Get the short tusks 

Here they are 

Cheers