A mirror neuron is a neuron that fires both when an animal acts and when the animal observes the same action performed by another. Thus, the neuron "mirrors" the behavior of the other, as though the observer were itself acting. Such neurons have been directly observed in human and primate species, and in birds. There are scientists who express skepticism about the theories being advanced to explain the function of mirror neurons. In a 2013 article for Wired, Christian Jarrett cautioned that: