To all,
http://www.arch.cam.ac.uk/ml12/project/
The basic premise is that the horse did not evolve in nature to carry a
person on its back or to pull wagons and carriages. Therefore, carrying out
these activities causes unnatural physical stresses, at least some of which
we expect to see in the form of bone abnormalities. Furthermore, because the
stresses associated with riding are different from those connected with
traction, we suggest that if horses were used primarily for one or the
other, this could be reflected in their bones
http://www.infoukes.com/history/inventions/
The first horseman rode a horse in Ukraine about 6,000 years ago. James and
Thorpe explain it this way: "...the earliest hard evidence for the
domestication of the horse dates back only to 4000 B.C. -- teeth of horses
from the Copper age site of Dereivka, in southern Ukraine, examined under
the microscope show traces of wear caused by having bits in their mouths.
These were probably made of rope, as the earliest known metal horse bits
date from about 1500 B.C." (p.51).
The second url is an article by Andrew Gregnovich.
Apparently the first horses were not used for riding but for loading and
transport.
Gerry