Philip Reno (
29 Sep 1995 20:38:07 GMT

Alex Duncan ( wrote:
: In article <> H. M. Hubey,
: writes:

: In most quadripeds the the bend at the knees is in the opposite direction
: from humans; and the primates seem to be already close to human. What
: could have caused this change? If we look at slowly changing from one
: angle (most animals) to primates, somewhere in the middle of evolution
: the whole leg would have to rotate 180 degrees and have the legs face
: outwards or inwards, practically making the animals lame. Is this
: explained by any theory, other than one that begs for catastrophic
: changes (i.e. punctuated equilibrium) without really explaining anything.
: Maybe they didn't need their legs at all during this time.

This really isn't a problem, because the "backwards" knee in most
quadrepeds, such as dogs and cats, and other bipeds, such as birds, is
really the ankle joint. These animals all walk with only their toes
touching the ground, with their metatarsals extending up to the ankle
or "backwards" knee. If one looks at animals that walk with their
whole hind foot touching the ground, such as monkies and bears, it
will be noticed that the knees bend in the same direction as humans.