4. Which of the following must exist in a population before natural selection ca

Question

4. Which of the following must exist in a population before natural selection can act upon that population? A) genetic variation among individuals B) variation among individuals caused by environmental factors C) sexual reproduction D) Three of the responses are correct. E) Two of the responses are correct. 5. If two modern organisms are distantly related in an evolutionary sense, then one expects that A) they live in very different habitats. B) they should share fewer homologous structures than two more closely related organisms. C) their chromosomes should be very similar. D) they shared a common ancestor relatively recently. E) they should be members of the same genus. Over evolutionary time, many cave-dwelling organisms have lost their eyes. Tapeworms have lost their digestive systems. Whales have lost their hind limbs. How can natural selection account for these losses? A) Natural selection cannot account for losses, only for innovations. B) Natural selection accounts for these losses by the principle of use and disuse. C) Under particular circumstances that persisted for long periods, each of these structures presented greater costs than benefits. D) The ancestors of these organisms experienced harmful mutations that forced them to find new habitats that these species had not previously used. 6.

Explanation / Answer

Ans 4: ( A ) genetic variation among indivisuals.

In the struggle for existence , only those indivisuals survive which posses the most useful variations. This has been called natural selection by Darwin and survival of the fittest by Spencer.

Useful variations present in the surviving indivisuals are passed on to the next generation. Next generation repeats the process of development of variations and natural selection. Organisms , therefore undergo continuous selection.

Favourable variations accumulate over the generations to ultimately form a completely new species.

Ans 5 : ( B ) they should share fewer homologous structures than two more closely related organisms.

Ans 6 : ( C ) Under particular circumstances that persisted for long periods, each of these structures presented greater costs than benefits.

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