Question

Match the type of natural selection with the correct example.

a) tall giraffes and short giraffes are prominent but average height giraffes are rare

b) tall giraffes and short giraffes are rare but average height giraffes are common

c) only giraffes with very long necks survive

1.   disruptive selection

2.   stabilizing selection

3.   directional selection

Which of the following is an example of convergent evolution?

a) two populations of birds that evolved from a single species

b) two plant populations that evolved from a single plant species

c) two small animal populations that developed in different continents but share long floppy ears in common

d) two individuals that built their musculature at the same gym so they could compete against each other

Which of the following is NOT a key principle of natural selection?

a) Characteristics of organisms are inherited

b) More offspring are produced than are able to survive

c) Offspring vary among each other in regard to their characteristics

d) All offspring will survive if they help each other out during rough times

With natural selection, generally, the longer an organism lives, the more reproductive opportunities it will have. TRUE OR FALSE

With natural selection, generally, more organisms will exist with the same favorable trait than the previous generation. TRUE OR FALSE

All bacteria are harmful because they cause disease. TRUE OR FALSE

All protists are harmful because they pollute rivers and lakes. TRUE OR FALSE

Which of the following is an example of a dimorphic organism?

a) Mold growing on the surface of a food and yeast growing inside an infected person--both from the same organism.

b) Bipolar disorder in humans expressing two personality traits

c) Two appearances of a microscopic organism depending on whether you are looking a the top of the cell or the bottom

d) An organism like the butterfly that has a wormlike, larvae stage and a winged, insect stage.

Answer 1

Natural selection is the driving force of evolution. Alleles that provide a selective advantage to the prevailing environmental conditions are selected and non-adaptive/deleterious alleles are subsequently eliminated from the population. There are three types of natural selection.

1. Stabilizing selection: It is also known as centripetal selection. It operates in a stable environment and eliminates individuals at the two ends of the phenotypic distribution. It preserves individuals with the average phenotypic distribution. It is not a driving force of speciation. However, it eliminates deleterious genotypes from the population. Ex: A greater mortality rate is observed in babies when the birth weight is higher or lesser than the average weight.  

2. Directional selection: It is also known as phyletic evolution or anagenesis. It operates in a gradually changing environment. It eliminates individuals with one end of the phenotypic distribution and preserves individuals with the other/opposite end of the phenotypic distribution. The average value of the phenotype is gradually shifted to either of the ends. It is a good driving force of speciation. Ex: Mosquitoes with high DDT resistance are selected over less resistant strains.

3. Disruptive selection: It is also known as centrifugal selection or adaptive radiation. It operates in heterogeneous environmental conditions. It eliminates individuals with the average phenotypic value and selects individuals with either end of the phenotypic distribution. The phenotypes are moved away from the starting average value. It is a major driving force of speciation. Ex: Evolution of different species of finches on the Galapagos islands.

a) Tall giraffes and short giraffes are prominent but average height giraffes are rare = Disruptive selection

b) Tall giraffes and short giraffes are rare but average height giraffes are common = Stabilizing selection

c) Only giraffes with very long necks survive = Directional selection

Option C is correct.

Convergent evolution = Appearance of the same trait in two unrelated species.

Option D is correct.

Natural selection does not refer to the survival of the entire species/population due to helping each other.