We know that height in humans is a polygenic trait because it has a lot of variation. The height gene is controlled by at minimum three genes with six different alleles. If all of these alleles are dominant for the tall gene you will be tall if you are dominant for the short gene you will be short if there is no clear dominance between the two genes you will fall somewhere in the middle.
Answer;
-Because of Homeostatic imbalance as we age our body organs become less efficient, and our internal conditions become less and less stable. This event has a risk for illness and produce changes we associate with aging.
Explanation;
-Homeostasis is the body's ability to maintain a relatively stable internal environment even though the outside world is constantly changing. It involves both positive feedback Loops and the negative Feedback loops.
-Aging is a general example of disease as a result of homeostatic imbalance. As an organism ages, weakening of feedback loops gradually results in an unstable internal environment. This lack of homeostasis increases the risk for illness and is responsible for the physical changes associated with aging.
In Nature's rule of law; it is technically both. The only difference between the two would be photosynthesis happens with plants. While cellular respiration happens with living beings.