Answer:
natural selection operates primarily on characteristics that are tied to reproductive fitness.
Step-by-step explanation:
Based on the information provided within the question it can be said that this is due to the fact that natural selection operates primarily on characteristics that are tied to reproductive fitness. In other words natural selection keeps those traits that allow the species to live long enough in order to reproduce but does not weed out many harmful conditions and non-adaptive characteristics if the species reaches reproductive age.