The starship and the canoe

From jacket: Freeman Dyson is an astrophysicist, one of America's most renowned and most imaginatively creative. His son George, with no degree to his name, lives by himself in a tree house in British Columbia. The elder Dyson looks to the stars for man's salvation; he wants to go there himself, in the vanguard of a great migration...The younger Dyson - as "earthbound" as his father is "star-crossed" - looks to the wilderness regions of our own planet and sees human destiny in the renewal of man's pretechnological resources.