What were the three key observations made by darwin that allowed him to deduce that natural selection is a primary driver of evolution? a. the number of adults tends to remain the same over time, individuals vary very little over time, and natural selection works on only the best of those adults in each generation. b. species change and adapt based on environmental pressure, individuals change within their lifetime, and offspring inherit the changes. c. genetic drift, gene flow, and mutations provide the change necessary in populations that affect future generations. d. organisms produce more offspring than survive, variation exists among members of populations, and advantageous variations increase in relative frequency over time?