1. What is a Species?
A group of potentially or actually interbreeding populations, with a common gene pool, which are reproductively isolated from other groups

2. The problem with the species definition
The species concept is a human construct used to make sense of the natural world. While extraordinarily helpful in understanding life, it fails to capture the full complex reality of continually evolving populations of organisms.

3. Sibling Species
Species that can’t interbreed, but have no significant differences in appearance.

4. Very different appearance that can interbreed?!

6. Two tigons (male to the left, female to the right)

7. A Liger-Lion/Tiger

8. A "boblynx" -- a hybrid of bobcat and lynx;

9. A "zonkey" -- a hybrid of zebra and donkey;