From an article entitled, “Mirror, Mirror: Our Brains are Hardwired for Empathy“, this passage talks about how mirror neurons, and the possible biological basis for empathy was accidentally discovered during unrelated research on monkeys:

In 1996, an Italian neuroscience research team led by Giacomo Rizzolatti and Vittorio Gallese was studying grasping behaviors in monkeys. They attached electrodes to the monkeys’ brains in order to observe precisely which neurons fired when a monkey grabbed a raisin with its hand. The research was routine: monkey grasped, specific neurons fired.

Then, during a break, one of the researchers hungrily reached out for a raisin. His fellow researchers coincidently noticed something extraordinary on the monitor: Neurons in the monkey’s brain fired—the exact same neurons that had fired earlier when the monkey grasped a raisin itself!

The team was astonished: Nothing like this had ever been seen before. Their serendipitous finding was the first clue to the existence of what scientists now call “mirror neurons,” so-called because they appear to actually reflect the activity of another’s brain cells. The monkey’s response was not just simple recognition, as in “I know what the researcher is doing.” That kind of observation is activated elsewhere in the brain. What happened between monkey and researcher required a brand new concept, an altogether new theory of behavioral interdependence. The monkey’s neurons fired as if it had made the same movement itself. This was a genuine brain-to-brain connection. In an instant, the definition of interconnectedness, the notion of empathy, changed forever.

[Fore more info on this, refer to my earlier post: Monkey See, Monkey Do]