Girls are a minority on the spectrum. But they are there. The "ASD gene" to the best of my knowledge is there is only a small amount of data suggesting it is a gene.
There has been diagnoses of autism for a very long time. But in the old days people were both reluctant to give or receive it. Typically it would involve instutulizing the subject and include treatments similar to schizophrenia. Now that resources are available and with the revision of DSM-5 effectively expanding what is considered Autism.
The list of assignable causes is also ever expanding. Of the studies I have read. A more mature biological age of the father seems to carry more weight than anything else studied.
Even the geographacial differences are becoming less, as recent studies looking into the methodology of countries involved have found flaws that result in much more similar occurrences across borders.
