For the past 2k to 4k years maybe. Before, it was very easy to spend time alone. Walk 10 minutes away from your tribe and bam - you're all alone.
Think back to high school. Sure, you could go off and study by yourself if you want. But the ambient social situations around you can't be banished for long.
I spent a lot of spare periods buried in mid-20th century Canadian and American literature and would often isolate myself in the cafeteria to read since a lot of classes would occupy the library during regular periods.
The school's resident radio DJ-hopeful (and a swell guy) would hop up on the table in a reclined pose, head-on-hand, and ask me why I was sad.
Not sad, just reading. It was surprisingly hard to communicate that to some people. And I was one of the AV/creative guys producing the in-school TV show!