Another quote from Ted Seth Jacobs:
Geometric and Organic Shapes. There is a radical difference between shapes of things made by nature and those manufactured by man. Although nature is capable of producing some startlingly geometric forms, most living creatures, and especially we humans, are irregularly shaped. Our shapes are adapted to carry out specific functions. Unfortunately, many books about how to paint and draw present the human form as a collection of simplified geometric shapes. For example, the head may be described as an egg shape, or the eyes as spheres, along with many squarish planes and slices, cubes and cylinders. It is important to remember that none of these abstract geometric forms exists on the body. Humans are human-shaped.