Santrock (2009) in Life-Span Development suggests that the infant is dependent upon not only the biological aspects that continually develop in the infant, but also the importance of the concept of “nurture”. For example, being more positive emotionally towards the infant, induces a more reflexive response of smiling and laughter. 

“Nature vs. Nurture”. “We have to be like kids again”. These phrases I keep hearing over and over again for some reason. “We have to go back to being kids and having fun again”. “We have to be like infants who are continuously curious about their surroundings, and being “cute” along the way”. 

But really the point to realize is the importance of the environment as it provides a space to bring out the “best” characteristics of what we often love so much when we see a baby smiling.