From the color of your hair to the shape of your toes, you are distinctly human. Humans look very different from one another, yet we are all members of the same species, Homo sapiens. A species is often defined as a group of organisms that can reproduce naturally with one another and create fertile offspring. While that definition seems straightforward, the classification of a species can be difficult and at times riddled with controversy.

Some organisms easily fit into this definition of a species, but many do not. Asexual organisms have only one parent, so they do not reproduce with each other. Some organisms commonly reproduce with similar species in the wild, forming genetic hybrids. In 2006, the first wild polar bear–grizzly bear hybrid was confirmed in Canada. Called “pizzly” or “grolar” bears, these hybrid bears can produce fertile offspring. However, polar bears and grizzly bears are still classified as different species due to their habitat needs.

These naturally occurring, wild rule breakers make it difficult for scientists to clearly define species. Genetics may provide the answer. Through genetic analysis, scientists can now classify species through patterns in DNA. This technology has uncovered new relationships between species—and a few unexpected surprises. A recent genetic analysis revealed that giraffes—long thought to be one species—are actually four distinct species. Discoveries such as this could lead to conservation concerns, should scientists discover a new endangered species “hiding” in a larger population of similar organisms.