Organ comes in an does this progression once, then guitar comes in, just strum 8th 
notes the whole time:

C Em Am G

C (x32010@1)                   Em (022000@1)          Am (x02210@1)       G (320003@1) It's been a million years since I last saw a caveman.
C (x32010@1)                 Em (022000@1)   Am (x02210@1)               G (320003@1)  
  I like the way he walks, I like the fire he builds.
C (x32010@1)                      Em (022000@1)                 Am (x02210@1)              G (320003@1) We hunt the beasts and make the bird calls, we go to sleep at night.
C (x32010@1)                 Em (022000@1)             Am (x02210@1)   G (320003@1) We go to sleep at night, under the starry sky.

C Em Am G (x2)

C (x32010@1)                     Em (022000@1)          Am (x02210@1)       G (320003@1) It's been two million years since I last saw a caveman.
C (x32010@1)                 Em (022000@1)   Am (x02210@1)               G (320003@1)  
  I like the way he walks, I like the fire he builds.
C (x32010@1)                      Em (022000@1)                 Am (x02210@1)              G (320003@1) We hunt the beasts and make the bird calls, we go to sleep at night.
C (x32010@1)                 Em (022000@1)             Am (x02210@1)   G (320003@1) We go to sleep at night, under the starry sky.

C Em Am G (x6)

C