It may come as a surprise to you, but there's a good chance that hair patterns are determined by our genes. Researchers at the Johns Hopkins School of Medicine did some experiments on mice to test the theory.
Normally, mouse hairs all point in the same direction. The researchers bred mice lacking a gene called Frizzled 6, which they knew is responsible for hair patterns in fruit flies. Sure enough, the gene-less mice developed bad hair.
Instead of having nice, smooth fur they had swirls and tufts and hair going the wrong way on their legs and chest. Without the hair-pattern gene, the mouse's hair didn't have a pre-set plan telling it how to grow, so it just kinda did its own thing.
People have a nearly identical gene, so there's a good chance that Frizzled 6 works in humans the same way it does in mice.