Why are pears pear-shaped and not spherical like apples?

In the wild the shapes of pears and apples can seem almost interchangeable. Fruit farmers prefer the distinct shapes so that the consumer can easily tell the difference between the two.

http://www.ars.usda.gov/SP2UserFiles/person/24438/appleshape.jpg

Buddha-shaped pears

https://theextremehorticulturist.wordpress.com/2015/07/19/buddha-shaped-pear/

The original wild fruits of the apple and pear would have been something like the crab-apple https://en.wikipedia.org/wiki/Crab_apple and the rose hip (all being fairly closely related). Most apples are apple shaped but some of the older varieties can be a bit odd; on the other hand, pears vary from pear-shaped to virtually spherical. One way of telling them apart (but not verified...) is that apples float but pears sink. I must say I've never heard of bobbing for pears. (Found at https://en.wikipedia.org/wiki/Pear )

How come star is answering star's question?

Because its not against the Posting Rules.