EVOLUTION OF MAN
Define the term evolution
Describe the origin of life
Describe the evidence of organic evolution
Describe theories of Organic evolution that is Lamarck’s theory and Darwin’s theory.
Explain the development of resistance by pests, insects, etc.
Evolution is the gradual change of organisms from simple life forms to more complex life forms over a long period. The scientific view of development is that the present-day plants evolved from the other pre-existing ones. Also, another scientific view of the origin of life explains that lightning and thunderstorm combined the elements to form compounds of life; this is called chemical evolution.
An example of organic evolution is the gradual change from early man (Dryopithecus) to the present man (Homo sapiens sapiens). In summary, several theories explain the origin of life, and they include;
Biblical creation theory
The scientific theory. There are two categories.
a) Organic Evolution-The present-day organisms emerged from the pre-existing ones.
b) Chemical Evolution-Life began after the elements were combined to form compounds of life due to lightning and thunderstorm. For instance, Ammonia is a combination of hydrogen and nitrogen.
Evidence of organic Evolution
Evidence of evolution is scientific indications the present organisms emerged from simple life forms.
Significant evidence of organic evolution include;
Before we start explaining this evidence, it is essential to state that the organisms initially shared a common ancestry origin. Due to some factors, as we are going to tell, these organisms started to evolve in different lines leading to present diversity in living organisms. I have given definitions, a short description, and an example in each evidence of organic evolution.
Explanation of evidence of Organic Evolution
1. Cell biology
Cell biology is the study of structures and functions of cells of living organisms.
The study of cells shows that plants and animals share a common ancestry because Plant and animal cells share some cell organelles. For instance, both animal and plant cells have a nucleus, plasma membrane, lysosomes, endoplasmic reticulum, mitochondria, etc. However, from common ancestry, plants and animals started to evolve in different development lines, leading to the present-day differences between their cells. For instance, Plant cells have a cellulose cell wall, chloroplast, and large central vacuole, while animal cells lack these organelles.
Also, animal cells have centrioles, while pant cells lack centrioles. The study of the mammal cells shows that living organisms share some biological compounds. Examples of the compounds are Adenosine triphosphate (ATP), DNA (Deoxyribonucleic acid).
Mammals share some blood pigments like hemoglobin, which shows that they are from the same origin.
2. Geographical Distribution
Initially, there was one landmass with living organisms. Due to continental drift, the single landmass broke apart to give rise to present-day continents. The species were therefore isolated from the same ancestry of the same lineage. Organisms of the same species evolved to give rise to a variety of species in the separate regions. It was due to the need to adapt to similar climatic conditions in different areas. Example. The emergence of (Monkeys with varying lengths of tails) different monkeys species in Africa forest and forest in South America.
3. Comparative Embryology
Embryology is the study of how embryo formed and its development. A comparison of the early fetal stages of different animals reveals similar morphological features at some stages of their development. This close resemblance of the embryos at the early stages of development shows that the organisms share a common ancestry. The closer the similarity of the two or more embryos of different species, the closer the phylogeny relationship between the two species. For example, at some stage of embryonic development o of both man and fish possesses a tail.
4. Fossil records
Fossil is the remains of ancestral forms deposited in the sedimentary rocks. Fossil is an excellent source of organic evolution because they show they act as direct evidence of biological evolution. Fossil can determine the time of existence of an organism through carbon-dating—the remains of species that lived a long time ago deposits on the deeper strata of sedimentary rocks. In contrast, fossils of organisms that lived a few years ago, deposits on the sedimentary rocks’ upper part. Therefore, the fossil-remains vary in complexity, depending on the time the organism existed. For first lived organisms, their fossils are less complicated, and for the recently lived ones have very complex.
Fossils can show the phylogeny relationship of two or more organisms, depending on the closeness of the resemblance of the fossil-remains.
Use of fossils as evidence of organic evolution has the following limitations;
a) Destruction by physical phenomena like faulting and earthquakes
c) Missing links due to total decomposition of the fossil by saprophytic
5. Comparative Anatomy
Anatomy is the study of structures of living organisms. A comparison of the anatomy of different species reveals a common ancestry of living organisms and their evolution. There are three types of structures of development.
a) Homologous structures.
Homologous structures are structures of the same embryonic origin that are modified to perform different functions in different organisms, such as pent dactyl limb and beaks of birds.
The pent dactyl limb have a standard basic structure, but modified to do different functions in different organisms as follows;
-Man use it for grasping,
-Zebra use it for running
-Bat use it for flying
The beak of birds have the same basic structure but are modified to perform different functions in birds making the birds feed in various types of food as follows
– Flesh eaters
This phenomenon where the structure of a common embryonic origin is modified to perform various functions in different organisms is called Divergent of evolution.
b) Analogous structures
Analogous structures are structures from a different embryonic origin that perform the same function in different organisms. Examples include wings of birds and wings of insects which used for flight by the animals. Wings of insects and wings of birds and wings are structurally different but perform the same function. The phenomenon where the structures of different embryonic origin are modified to achieve a similar role is called convergent evolution
These are structures that have significantly decreased in size and have no function in an organism.
Example of vestigial structures
The nictitating membrane in mammals
Wings of Kiwi (flightless bird)
Vestigial tail in man
Theories of Organic Evolution
These theories explain the mechanism of organic evolution. There are several theories of biological evolution, but here, only two significant approaches are covered. The two major ones are;
John Baptiste De Lamarck’s theory. (Lamarck’s theory)
Charles Darwin’s theory. (Darwin’s theory)
Lamarck’s theory is the theory of use and disuse. It states that when the environment where the organism lives demands a particular structure from an organism, then the organism responds by developing that structure. When the situation does not need the use of a specific structure, then suddenly it reduces in size and ceases to function (that is, it becomes vestigial)
Example to explain Lamarck’s theory
-The emergence of long neck giraffes
-Vestigial tail in man.
-Reduced wings in kiwi
Lamarck described that, after the organism has acquired a particular characteristic, it transmits it to its offspring. For example, short-necked giraffe develops a long neck to reach the leaves of taller plants. The giraffe (which acquired the long neck) then is capable of producing a young one with a long neck.
In summary, Lamarck’s theory has two ideas:
An organism responds to the environment demand by developing a structure needed by the environment. Parents transmit the acquired characteristics to their offspring.
N/B. Lamarck’s theory is biologically unacceptable because of acquired characteristics that do not affect an organism’s genotype cannot be inherited.
ii) Darwin’s theory.
Darwin’s theory states that the environment selects organisms with favorable characteristics, while those with unfavorable traits perish. This phenomenon is called natural selection.
Features of Darwin’s theory of natural selection include;
A variation is observable differences among organisms. E.g., the environment will contain both short neck and long neck giraffes—an example of variation is the length of the neck of a giraffe. The characteristic of offsprings are those inherited from the parents, and it occurs by chance. It means that Parents give rise to the progeny of varying features depending on the parents’ gene that fused to produce the offspring.
For example, a long neck giraffe and a short neck giraffe inherit these characteristics from their parents, respectively.
ii) Struggle for existence
It is the second feature of natural selection. It explains that organisms within a natural environment will compete for scarce environmental resources like food, shelter, oxygen concentration, etc.
For example, in an ecosystem, the long-necked giraffe will compete with a short-necked giraffe for a tall pant’s leaves.
iv) Survival for the fittest.
As the organisms compete for the limited resources in the environment, those with advantageous (favorable) characteristics will survive, while those with disadvantageous (unfavorable) characteristics will perish. The process is called natural selection.
For example: As long-necked giraffes compare with short-necked giraffes, the long neck giraffes are more adapted to the environment (they have favorable characteristics). They will easily reach the leaves of a tall plant. Hence they will survive. On the other hand, the short-necked giraffes are adapted poorly to the environment they have unfavorable characteristics). Therefore, they cannot reach the leaves of a tall plant; hence after sometimes, they will die of hunger.
The environment selects the organisms with favorable characteristics for reproduction. These organisms, therefore, transmit their desirable traits to their offspring)
iv) Mutation and transfer of beneficial characteristics to offsprings
Mutation produces offspring of the unfavorable characteristic. The organism with favorable features that may give rise to progeny with undesirable characteristics after a long period of successive reproductions. The mutation occurs due to change in genetic composition in parental genes which are transmitted to the offspring. The change in genetic structure is called gene mutation.
Microbial Resistance to drugs, pesticides, and insecticides
Resistance is reduced effectiveness of a drug, pesticide, or insecticides. When disease-causing organisms are exposed to drugs, the drug may be useful only for a short time before the microorganism becomes resistant. What happens is that chemicals from a drug cause a mutation in the disease-causing organism. The mutated genes are transmitted to the offspring resulting in a different resistant strain of the same organism.
For example, Malaria parasites have become resistant to many drugs due to the above explanation.
Natural selection in action.
Example; (White and black colored pepper moths)
In Europe, before industrial evolution, white-colored pepper moth could easily camouflage with the back of the trees (had favorable characteristics) and could not be easily seen by their predators. On the other hand, the black colored moth could not camouflage well with the back of the trees; hence it had unfavorable characteristics, and therefore, it was easily seen by the predator. Due to the difference in their color, the white-colored peppered moth population increased while the number of black peppered moth significantly reduced before the industrial revolution.
After the industrial revolution, the smoke from the industries turned the backs of the trees black. Therefore, black peppered moths could now camouflage easily with the end of trees against predators while the white ones could not hide well with the backs of trees and could easily be seen by predators. Therefore, the black peppered moths survived, and there number increased in the towns near industries while the number of white peppered moths significantly reduced in cities after the industrial revolution.
End of topic review questions.
Describe the evidence of organic evolution
Explain why Darwin’s theory is biologically acceptable, while Lamarck’s theory is biologically unacceptable.
State two ideas of Lamackarian theory
Define the term natural selection.
Define the term Divergent evolution.
Differentiate between analogous structures and homologous structures, giving examples in each case.
State three limitations of using fossil records as evidence of organic evolution.
Explain why some pesticides are not active on some pests.
State Darwin’s theory.
Define the term organic evolution