http://www.huffingtonpost.com/2014/03/27/autism-rate-1-in-68_n_5041858.html Diagnosis effect - The amount of people who have autism now is proportional to the amount of people who had autism in the past. There isn't an actual increase or decrease in people who have autism, the only thing that is changing are the amount of diagnoses due to the advancing medical industry. Human nurture - With the rapidly evolving medical industry, there are more and more treatments and procedures that babies are going through that may be affecting neural developmental health. The deteriorating air quality is also a factor that has been proven to be harmful for babies in and outside the womb. These, including many other environmental reasons, are increasing the amount of people who develop autism. It's important to keep in mind that the increase in autism rates vary greatly on location, with the United States having both the highest rates of autism, and the fasting rising rates of autism.