Exploring Natural Selection and Key Evolutionary Adaptations

This essay discusses natural selection and evolutionary trends, highlighting disruptive and directional selection with examples like the pepper moth evolution. It explains how natural selection contributes to antibiotic resistance in bacteria and details the evolutionary adaptations required for the transition from aquatic to terrestrial life, including skeletal and reproductive changes. Furthermore, the essay explores the evolution of plants from primitive forms to seed plants, emphasizing the reduced dependence on water for sexual reproduction through pollen dispersal and seed development. Desklib offers similar essays and study resources for students.

Running head: ESSAY QUESTION
ESSAY QUESTION
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1ESSAY QUESTION
Answer 1.
The two types of selection that occurs within an environment to ensure the selection
in organisms is disruptive and directional selection. Due to directional selection the
phenotypes of the organism will undergo variation with the change of the environment. An
example is the evolution of pepper moth that occurred in England during the industrial
revolution. Before industrial revolution, the moths were mostly light coloured which enabled
them to blend with the surroundings, in the trees and lichens. After the revolution with the
increasing soot in the environment, the light coloured moths were easily spotted by its
predators. Therefore the melanic form of the moth increased to provide better camouflage.
Disruptive selection eliminates the organisms that do not lie on the extreme values of a
relevant trait (Biology Stack Exchange 2018). An example of this is seen in lobsters where
alpha males get mates by force which the small males cannot. Therefore these small males
who cannot overtake the alpha males are eliminated by selection.
Answer 2.
According to Darwin’s theory of survival of the fittest, natural selection eliminates
the weak organisms in the nature and enhances the survival of the strong ones. Similarly in
pathogenic bacteria it has been seen that natural selection has helped in obtaining resistance
against antibiotic drugs (Corbett-Detig, Hartl and Sackton 2015). When the drug is used for
the first time it eliminates the organisms, but some of them may survive. Those that survive
adapt themselves to deal with the particular drug effects. If these organisms reproduce in the
body of the host then the next generation produced will be able to adapt better to the effects
of the antibiotics. If the drug is used again then these organisms will be resistant to its effects
and again on reproduction will continue to make the host ill.

2ESSAY QUESTION
Answer 3.
The evolutionary trends that were required for the transition from aquatic to
terrestrial life consisted to several modifications in the body systems. This helped them to
solve the problems of support and locomotion, gas exchange, desiccation, reproduction,
feeding, and the function of some sensory systems. For the transition the organisms had to
adapt to the differences between land and water, mainly to the dehydration on land
ecosystem. The changes in the skeletal support took place by changes in the pelvic and
pectoral fins and strengthening of the vertebral column. The pelvic girdle became attached to
the vertebral column to provide support to the lower limbs, thereby changing ways of
locomotion (Galmes et al. 2014). Ways of reproduction was also changed because earlier the
organisms depended on water for fertilization and development. New ways of excretion was
also adapted as they depended on water to wash away the excess amount of ammonia from
the excretory product.
Answer 4.
The evolution of primitive plants to seed plants has allowed sexual reproduction to
depend less on water. The seed plants produce pollen which helps in dispersal of the
gametes to great distances through air or other means, where water is not required. Unlike the
haploid cells present in fern spores and others that needed moisture for gamete development,
seeds contain diploid embryo (Biswas and Johri 2013). The seed coats inhibit desiccation
hence there is no need of constant water supply. The pollen grains are male gametophytes
which can reach the female organs, carried away by wind, without the need of water.

3ESSAY QUESTION
References
Corbett-Detig, R.B., Hartl, D.L. and Sackton, T.B., 2015. Natural selection constrains neutral
diversity across a wide range of species. PLoS biology, 13(4), p.e1002112.
Galmes, J., Kapralov, M.V., Andralojc, P.J., Conesa, M.A., Keys, A.J., Parry, M.A. and
Flexas, J., 2014. Expanding knowledge of the R ubisco kinetics variability in plant species:
Biswas, C. and Johri, B.M., 2013. The gymnosperms. Springer Science & Business
Media.nvironmental and evolutionary trends. Plant, Cell & Environment, 37(9), pp.1989-
2001.
What is the difference between disruptive, d. (2018). What is the difference between
disruptive, divergent and diversifying selection?. [online] Biology Stack Exchange. Available
at: https://biology.stackexchange.com/questions/58998/what-is-the-difference-between-
disruptive-divergent-and-diversifying-selection [Accessed 18 Jun. 2018].