When did the human population reach 500 million people?

____ refers to positive or negative responses to social interactions

a. Attachment b. Temperament c. Sociability d. Social smile

The two types of glial cells are called ________ and ________

a) occipital; lobitical b) oligodendrocytes; Schwann cells c) occipital; Schwann d) oligodendrocytes; lobitical