all men, and women, are NOT created equal other than in their humanity. you heard it here, first.
by this i mean, we are equally human but do not have equal traits: smarts, looks, strengths, weaknesses, etc. as such, some of us will be "blessed" as measured by our cultural biases, socioeconomic needs, and other aspects that may be particular to our respective circumstances. thus, if you have to pick a coconut off the top of a tree, and you are a lousy climber, or are scared of heights, you may just have to get along without coconut in your diet. if it means some beautiful woman will not accept your amorous entreaties, so be it.
by the same token, one man's blessings are another's curses. so, the ability to climb a tree is cool if you live on a remote tropical island; but get transported to NYC and you're kind of screwed when it comes to high paying job opportunities.
so it is with fitness. some of us, when we train with various forms of exercise, get bigger, stronger, faster, leaner, looser, or more durable. but, some, doing the same exercises, will not see the same or comparable results. this is not a bad thing....unless you're in competition. as this article points out -http://well.blogs.nytimes.com/2011/03/16/is-fitness-all-in-the-genes/?ref=health -
exercise has its own merits even if you are genetically inclined to NOT increase aerobic capacity. granted, you may not see as dramatic a result in terms of blood pressure or blood sugar levels; you may not get fast enough to win the race; you may not even get lean enough to get on the cover of a magazine. but you will get faster than you'd be had you not exercised; leaner than you'd be had you just read the mag; and your blood values will surely not improve blaming your family history for your condition.
in other words, academically this is a very interesting line of inquiry. psychologically it may even work to mollify one's distress at lack of results. but physically/medically, genetics are always a ceiling and floor. you have the capacity to reach higher or stay lower. exercise is one way you can reach high, and stay off the floor, even if you're not able to reach the same heights as your co-exercisers.