Under the Knife: A History of Surgery in 28 Remarkable Operations

by Arnold van de Laar

The most conspicuous fault can be seen in the arteries running to the legs. They still make a 90-degree bend characteristic of quadrupeds, deep down at the back of the pelvis. This bend was necessary because the hind legs of an animal are at right angles to the trunk. Since we spent most of the time we were evolving from primitive land animals to humans walking on four legs, natural selection has made the 90-degree bend in our arteries wide, spacious and gradual. That causes the least possible turbulence in this stretch of the circulation system, which is important for our survival, as turbulence in the arteries can cause damage to the artery wall. Because we now walk upright, however, after making the gentle, gradual bend of the quadruped, the leg arteries now have to bend back another 90-degrees in the groin. This is not a smooth curve, but a sharp kink that has not adapted and does cause turbulence. That leads to hardening of the arteries (arteriosclerosis), resulting in narrowing of the blood vessels near the kink. And that is why hardening of the arteries in humans is most common in the groin.