Question

The ultimate source of organic variation is
a. Natural Selection
b. Sexual Reproduction
c. Hormonal activity
d. Mutations

Answer 1

The variations between individuals within a species are natural or organic variation. This may be attributed to genetic causes and environmental factors.

Complete answer:

Option A is incorrect. Natural selection is the mechanism whereby organisms adapt to their surroundings. It's the motor that drives evolution.

Option B is incorrect. The process of sexual reproduction introduces variability into the population as the offspring blend together with the alleles that the mother and the father bear. One drawback is that it takes longer than asexual reproduction to reproduce.

Option C is incorrect. Hormones are chemical messengers that are secreted from one cell into the blood or extracellular fluid, influencing the functioning of other cells. A specific cell for a hormone is a target cell because it has functional receptors for that hormone and cells that do not have such a receptor cannot be directly affected by that hormone.

Option D is correct. The cause of the variability is mutations. The rate of gene frequency shift from the mutation stage is very small because of the low levels of spontaneous mutation.

So, the correct answer is Option D.

Additional information:
The previous species were much simpler. Gradually they evolved into complex creatures. Owing to common roots, they are interrelated. They have shelter and a common climate. Generally speaking, evolution is gradual, constant, irreversible, and democratic. Variation is the principal prerequisite for evolution. This mutation is the primary cause of organic evolution. Typically, a mutation in a single inheritable trait (gene) is less probable than one in a million, but once it has happened, it can be passed on to the next generation along the same lines as other inherited properties.

Note: Several other sources of organic variations can be environmental factors (namely, heat cold, rain, drought, food, etc), Endocrine glands, chromosomal aberrations, Aneuploidy, Polyploidy, and Hybridization, etc.