Interesting that you bring up body rhythms.  The reason I became interested
in our ancient ancestors in the first place was my conversation with a sleep
therapist.  He advised we were not designed to wear sunglasses outdoors or
work in an enclosed environment and suggested my circadian rhythm was out of
whack.  He told me to walk east each morning at sunrise for 40 minutes.
Evidently, while we sleep, the essential amino acid, tryptophan, is emitted
from our brain which allows us to sleep.  We were intended to awake with the
sun (after falling asleep in our caves at sundown) and toil outdoors all day.
 The sunlight entering our eyes would immediately shut off the stream of
tryptophan, allowing it to build up again, for use again that night.  He
explained, if it is not shut off by exposure to sunlight, it continues to
seep from the brain during the day, which causes a shortage when it is needed
at night.

Now, I don't know if any of this is true, but it does sound right.  I've
given this ancestor of mine quite a lot of thought.  In comparison, I get up
at 5:30 every day, (no time to walk into the sunlight) jump into my
push-button, automatic, climate-controlled Lexus, work behind a computer all
day under artificial light and sit on my bum.  When I get home, I'm usually
too tired to exercise, so I sit some more, reading under more artificial
light or watching television until I go to bed under the air conditioner.
That's after I've eaten something my ancestor would have buried.  It's all
beginning to sound pretty disgusting to me.  If my body was designed to be
outside gathering goodies in the sunlight while tromping up and down the
hillside and putting myself to bed at sundown, I think I have degenerated
into something not unlike a robot.  It's no wonder I don't sleep and our
society is plagued with obesity and disease!

Thanks  to all for your helpful comments.

Janet