As part of our Autism Now series, below is an extended transcript excerpt, edited for length, relevance and clarity, with Dr. Craig Newschaffer, professor of epidemiology and biostatistics at Drexel University, on the causes of autism.

The rise in the number of reported autism cases has caused a surge in research to find the causes. For the latest thinking, Robert MacNeil speaks with four leading researchers about the issue. It's part three of the Autism Now…