Hmmm... well I do think people look physically different from generation to generation for a number of reasons beyond style. Improved diet and a different lifestyle has made a difference in body types, and of course what's considered attractive from one generation to the next can change. Marilyn Monroe looks soft compared to the "abs-of-steel" girls of today.
Being fat used to be a sign of prosperity when excess food was a luxury. Now, food is common; there's too much food. Thinness is the status symbol.
A fair complexion used to be the sign of the upper class that didn't have to work in the fields. Nowadays a good tan shows you spend a lot of time out on the tennis courts or the golf course.
But the differences that Rick and Marty sense may not all be strictly anatomical. That's my grandfather on the left, my dad in his fifties in the middle, and me on the right at about the same age. Obvious differences of hairstyle and clothing aside, I think they have more of an air of being real "adults" somehow.
It might have something to do with the way people carry themselves; the way they "project" their experiences in life. My dad was born in 1914 and picked fruit as a teenager to help the family get through the depression. His dad had to flee the Japanese in Korea, and go from being a scholar to a field laborer here. Whereas I grew up never having to worry about where my next meal was coming from. Do their harder lives show in their eyes? It seems like the kind of thing a good actor could convey through subliminal body language thus making themselver look "physically" different.
So does your theory have something to do with factors beyond these that I've mentioned? Some actual physical evolution?
