John Bowlby (1907-1990) was a British psychologist most known for the development of attachment theory. Bowlby defined attachment as a “lasting psychological connectedness between human beings." Along with Mary Ainsworth, Bowlby developed attachment theory which is an evolutionary based theory that suggests that infants are biologically predisposed to form attachments with primary caregivers in early life as a means to increase their likelihood of survival. This theory proposes that caregivers are used as a secure base by infants and this sense of security allows the child to explore and increase their knowledge about their environment. Evidence for this theory includes species-specific learning biases like the tendency for infants to identify and prefer their primary caregiver's face.