How old is autism? That's a very good question. I know of one individual many years ago that could have possibly been seen as having some autistic traits. For a while he lived alone, and he really had no childhood. He had no friends. Because of his lack of socializing, he was quite lonely. He had some great accomplishments. He was said to be the first zoologist in history. He also became the first landscaper and horticulturalist. He was very able to take care of gardening and the raising of plants. But on the other hand, he had weaknesses. In his awkwardness, he hid. I don't know if you consider these to be autistic traits, but they are kind of interesting to look at. The man I have been talking about is Adam. He lived in the Garden of Eden.
Well, I was having fun with that. Even though I am a Christian, I realize not all of you are. But regardless, it might be interesting to search the Bible (Or your Bible of your faith) to see the profiles of ancient people. And if you say, "that's myth," you can still research it because these texts are ancient---and the authors were profiling traits they must have been aware of.
So how old is autism? I think it has always been with us.
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"My journey has just begun."