Hey, if we don't mutate, how will we ever get to the point (as a species) where we don't like hotdogs? Sounds like this isn't that much of a problem.
I'll take my mutation the good old fashioned way thanks - radiation works best!
What's blooming from China's budding space program? Bigger flowers and supersize veggies: For more than a decade, the Asian nation has made use of Earth's upper atmosphere (thick layer of surrounding gas)--up to 402 kilometers (250 miles) high--for seed-breeding research. A variety of seeds, including corn and water-melon, have traveled in space for up to two weeks in recoverable satellites and high-altitude balloons.
How did space affect the seeds? Evidently, the high radiation (strong invisible energy waves) of space mutated, or genetically modified, the seeds' DNA--hereditary material stored in their cells, reports China's Xinhua News Agency.
These mutations may explain why peony flowers grown from "space seeds" are larger and more colorful than normal; the mutations may also explain jumbo, half-pound bell peppers and a new breed of fast-growing rice...
http://findarticles.com/p/articles/mi_m1590/is_11_59/ai_98541295
So, I gather, it's the atmosphere that's stopping us from becoming a race of giants hmmm?