Here's why:

* Species Definition: A species is defined as a group of organisms that can reproduce with each other and produce fertile offspring.

* Reproductive Isolation: Different species are reproductively isolated, meaning they cannot produce fertile offspring with members of other species.

* Larger Groups: While there are larger groups of organisms (like genera, families, orders, etc.), these groups are based on broader similarities and do not necessarily imply the ability to interbreed.

Let me know if you have any other questions!