The brain is the meeting point of our genes and our surroundings—where nature and nurture meet. Our social environment has an impact on our brain circuitry and biochemistry, both of which are regulated by hereditary factors. These neurobiological mechanisms, in turn, can have an impact on behaviors. The study of the biological mechanisms by which neural systems mediate behavior is known as neurobiology. Much of neurobiology has focused on nervous system cells over the last half-century. The structure and physiology of nerve cells (neurons) and supporting glial cells, as well as the functional contacts (synapses) produced between neurons, have all been thoroughly studied.