Which of the following best describes the principle of evolution by natural selection?
a. individuals within a population are genetically identical and natural selection occurs randomly
b. individuals within a population exhibit genetic variation and those that are best adapted to their environment survive
c. individuals within a population exhibit genetic variation and those that are least adapted to their environment survive
d. individuals within a population undergo genetic mutation and natural selection occurs randomly
e. individuals within a population exhibit genetic variation and natural selection occurs randomly

B. Individuals within a population exhibit genetic variation and those that are best adapted to their environment survive.

Explanation:

Nature poses challenges time to time to all the living organisms in the form of harsh climate, scarcity of food, natural disasters such as floods, drought, etc. Such challenges enable some organisms to survive better than the others in the same environment and are said to be selected by the nature.

This capability to survive is also termed as fitness by some scientists.  Darwin however only referred to the reproductive fitness which means those organisms who are better fit in their environment produce more number of offspring than others.

Darwin used the phrase "Natural selection" for this and said it is the natural selection which is responsible for evolution.

answer:   option a) glucagon was secreted by his pancreas before he ate the cookies because blood glucose was low. insulin was secreted after he ate the cookies because his blood glucose was high.

explanation: