Do environmental or genetic factors affect growth of organisms most?

Examples of local environmental conditions could include availability of food, light, space, and water. Examples of genetic factors could include large breed cattle and species of grass affecting growth of organisms. The environment in which an organism lives plays an important role in modifying the rate and extent of growth. Environmental factors may be either physical (e.g., temperature, radiant energy, and atmospheric pressure) or chemical. Organisms and the cells of which they are composed are extremely sensitive to temperature changes; as the temperature decreases, the biochemical reactions necessary for life occur more slowly. A lowering of the temperature by 10° C (18° F) slows metabolism at least twofold and often more.

I copied this stuff from a bunch of different biology websites. It doesn't answer your exact question but I would have to say based on what I typed here it would be the environment that affects the growth of an organism more.

they deliver oxygen to the blood