I would like to add that the development of a brain is another huge milestone. Somehow Hawking forgets to mention that.
And the development of the computer and Internet is a big milestone in the external transmission period in my opinion.
If you like this kind of reading, I recommend the book:
Bill Bryson's A Short History of Nearly Everything
It's by far the most entertaining, enjoyable, and well written science text I've ever read/listened to. You can download it on iTunes -- go with the unabridged. I listened to the abridged one first and liked it so much I downloaded and listened to the unabridged one... twice. And then proceeded to listen to four of his other non-science books.
Get on the Bill Bryson train. You won't be disappointed.
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