See, it all has to do with brain maturation. The most common age for dying of SIDS is 2 to 3 months. I saw you had a graph of that here. Yeah, the left and right hemispheres. Alex Well, humans do have that, but here they are talking about two different kinds of brains, the reptilian brain and the mamamlian brains.
Humans have both.
And all the automatic aspects, such as breathing. But when mammals evolved, they grew a new layer, called the cortex, on top of the reptilian brain. This came to control the lower brain centers by inhibiting them. So, instead of just reacting to the environment automatically, the cortex would allow thinking and reasoning to control behavior. It says in this book that the subcortex is born already functioning, but the cortex is immature, non-functioning.