Behaviors like sucking and grasping are considered reflexes. Those reflexes are present in all mammals and are relatively primative, the more modern parts of o

Behaviors like sucking and grasping are considered reflexes. Those reflexes are present in all mammals and are relatively primative, the more modern parts of our brain eventually learn to suppress them and they typically disappear in most humans after around 1 year old. Interestingly, patients with brain lesions in certain places or with diseases like parkinsons sometimes lose the ability to suppress these reflexes. More info: https://www.ncbi.nlm.nih.gov/books/NBK395/ https://www.ncbi.nlm.nih.gov/books/NBK395/