Mammal body hair is a complex structure that involves several basic parts, including a shaft, a root, and a follicle. The most common theory currently in vogue is that hair evolved from reptile scales. Although both scales and hair preserve well in the fossil record, especially in amber, no evidence of hair evolution has been found after more than a century of searching. Another problem is that all primates have thick, coarse hair called fur, and explanations as to how this fur was lost in human evolution are deficient and contradictory.