ASSIGNMENT SYSTEMATICS AND PRINCIPLES OF TAXONOMY UNIVERSITY OF SARGODHA TOPIC

ASSIGNMENT
SYSTEMATICS AND PRINCIPLES OF TAXONOMY
UNIVERSITY OF SARGODHA
TOPIC: – NATURAL SELECTION LEADS TO EXTINCTION AND REGRESSION
Submitted to:- Dr. KHALID MUKHTAR
Submitted by:-
NIDA IQBAL
Roll no:-BZOF15M019
Class: – BS ZOOLOGY 7th semester (reg)
Date:- – -2018

CONTENTS:-
Natural selection
Definition
Introduction
Natural selection leads to evolution
NATURAL SELECTION LEADS TO EXTINCTION
Natural selection leads to extinction of dinosaurs
Main causes of extinction
Role of human activities in extinction
NATURAL SELECTION LEADS TO REGRESSION
Conclusion
References

NATURAL SELECTION:-
Organisms which have favorable genes and are able to survive in a specific environment are selected by the nature and this mechanism is called natural selection. We can also say that natural selection means “survival of the fittest organism in an environment”.

NATURAL SELECTION LEADS TO EVOLUTION:-
CHARLE’S DARWIN said that every organism changed itself from lower life forms and new specie was produced by the natural selection in the primary way. According to Darwin theory, “Natural selection leads to evolution”.

Natural selection favors the fittest genes and denies the unfit or unfavorable genes. Any organism only evolves by natural selection when different processes and too many variations occur in the species that it becomes new specie.

NATURAL SELECTION LEADS TO EXTINCTION:-
Natural selection is the mechanism that causes changes in populations in which organisms having favorable genes and suitable to survive in a specific environment are selected by nature. These organisms reproduce and transfer these genes to next generation by natural selection. It is actually a genetic process in which favorable genes from existing gene pools are selected which is able to survive in a specific environment. These genes of similar information reshuffle or genetically recombine in different ways in response to specific environment and causes variation or speciation of that organism.

Natural selection or survival of the fittest actually leads to loss of genetic information. In natural selection most suitable and favorable genes for the specific environment are selected, but if the environment and climate changes, It cause the EXTINCTION of that organism. Natural selection reduces the genetic variations in the populations of species as shown below,

EXAMPLES:-
Human darker skin color has ability to reflect or dissipate UV radiation as heat. Human lighter color has ability to absorb vitamin D when exposed to sunlight. Human having more melanin pigment (darker skin) are able to live in equatorial regions and reduce the risk of skin cancer by reflecting UV light. Human with lighter skin color with less melanin are able to survive more suitably in Polar Regions because their skin has ability to absorb more vitamin D from sunlight. But if climate changes due to drastic conditions and people with darker skin color are exposed to Polar Regions, their skin will dissipate sunlight and deficiency of vitamin D will occur. Similarly if lighter skin colored human are exposed to equatorial region,
their skin has no ability to dissipate UV radiations and soon they would caught by skin cancer. If this situation continues, gradually specie will extinct soon.

In this way animal with “best suitable genes” to specific environment will continue to survive and animals with” least suitable genes” will eventually die. Organism adapted to specific environment will also die soon if drastic changes occur in the climate of that environment.

NATURAL SELECTION LEAD TO EXTINCTION OF DINOSAURS:-
Dinosaurs and other animals extinct because of drastic change in an environment. There was drastic change of environment from Mild Antediluvian environment to world overwhelmed by catastrophic flood due to Great ICE AGE. Genes of dinosaurs selected by natural selection were adapted to Mild Antediluvian environment, and when climate changed due to adverse conditions, Genes could not able to survive in that environment and it caused the extinction of dinosaurs. Due to change in environment reproductive success of an organism can also change.

ENVIRONMENTAL CHANGE BY INVASIVE SPECIE:-
Any invasive species can change the environment. When environment changes, genes adapted according to that environment are unable to survive and extinction occurs. For Example,
Some birds’ genes are adapted to survive in Guam. When an invasive species Brown tree snake was introduced there, it killed the Guamanian birds and gradually these birds become extinct.

A microbe causes a little illness to its host. But if this microbe is transferred to new environment as an invasive species, host in the new environment will not has immunity to that microbe, and then this microbe will have sudden risk of extinction.

MAIN CAUSES OF EXTINCTION:-
Natural selection only allows desirable characters to survive and eliminate those genes that have not desirable characters according to environment. When environmental changes occur due to drastic conditions, that organism becomes unable to survive in that environment. Organisms with best desirable genes selected by natural selection are limited in number and are in minority. When climate changes minority are unable to compete with majority of survival means Moreover, when new species formed or forming, it exerts pressure on already existing species and finally cause extinction of that specie. The introduction of new breed of animals causes extinction of previously existing animals.

ROLE OF HUMAN ACTIVITIES IN EXTINCTION:-
Due to human activities, pollution causes toxicity and changes in climatic conditions. Due to pollution animals which cannot cope with polluted environment are eliminated by natural selection and which remains are unable to reproduce and gradually extinct.

Natural selection favors the well adapted species. These well adapted species are able to kill those species that are not well adapted to increase their survival. So extinction of these animals that are not well adapted to their environment is by natural selection.

So, we can say that “Natural selection causes extinction of species that are not very well adapted for survival”.

NATURAL SELECTION LEADS TO REGRESSION:-
Regression is the process in which partial or complete reduction of organs occurs that have lost their adaptive significance.

Natural selection may cause regression or reduction. Some examples of regression or reduction are given below,
EXAMPLES:-
In human beings tail regressed with the passage of time by natural selection because tail was no more important.

Moreover, notochord reduced and replaced by cartilaginous skeleton and later by bony skeleton as evolution occurred by natural selection.

When vertebrates emerged on dry land, their gills are replaced by lungs and gills regressed in them.

Natural selection favors that characters that can be adapted according to the environment and causes regression of other characters.
CONCLUSION:-
Natural selection leads to extinction when climatic conditions changes, and leads to regression of that body parts which are no more important to adapt in the specific environment.

REFERENCES:-
Gustaffson (1986), relation between heritability and proportion of fitness (graph).

Evolution-facts.org, evolution encyclopedia vol. 2, chapter 13 natural selection.

Creation science today, Biological Scientific Evidence for Creation, Natural Selection and Extinction.

How natural selection leads to extinction,Quora.com
http://Anthropology-world.blogspot.comhttp://www.starsandseas.com/SAS Evolution/SAS