Well it maybe obvious but the science is now showing there is a genetic link. From Science:

Marathon running might be in some people’s genes, according to a new study, which shows that a genetic mutation that boosts muscle endurance has spread widely in some human populations.

There are two types of skeletal muscle fibers. Fast fibers, which use sugars for fuel and do not require oxygen, kick in for tasks that require maximum force and quick action, such as sprinting. Slow fibers, which employ oxygen-using (or aerobic) pathways, power activities that require endurance, such as long-distance running. A protein called alpha-actinin-3 is made mostly by fast fibers and is implicated in their capacity for rapid force generation. About 18% of people of European descent do not produce the protein at all due to mutations in both their copies of the gene ACTN3, which codes for alpha-actinin-3. Previous studies have shown that endurance athletes such as long-distance runners have higher frequencies of this mutation, whereas sprinters and athletes in other sports that require quick muscle strength have lower frequencies.

Link.