CLASS :SS 3
TERM :FIRST TERM
WEEK :WEEK 10
Theories of Evolution.
- The theories of evolution according to Charles Darwin, Jean Baptist de Lamark
- Evidence of evolution.
- Forces responsible for evolution: mutation, gene flow, genetic drift.
Adaptation is the process by which organisms change their structure, physiology and behaviour in order to survive. This has led to diversity in form, in structure and function among organisms.
The theory of evolution is an attempt to explain how this diversity has taken place. Many scholars made some discoveries on evolution, some of them are;
- George Louis Buffon (1707-1777)
- Carl Linnaeues (1707-1778)
- Jean Lamarck (1744-1829)
- Thomas Malthus (1766-1834)
- Charles Darwin (1809-1882)
- Alfred R. Wallace (19th century)
SUB-TOPIC 1: THEORIES OF EVOLUTION
- LAMARCK’S THEORY (1744-1829)
In the early 19th century, French biologist Jean Baptist Lamarck embraced the idea of progressive change in living world based in part on his study of marine invertebrate fossils.
He was the first biologist to suggest that organisms undergo evolution. He propounded his systematically organized theory of evolution in 1801. This theory is based on the following ideas.
i. The use and disuse of organs
ii. The inheritance of acquired characteristics.
Lamarck believed that species do change over time (through use and disuse of the body parts) and that animals evolve because of unfavourable conditions that the animals try to adapt to.
In his explanation, Lamarck cited example of giraffe and said their ancestors had short neck but kept stretching their necks to reach leaves in high trees during the period of food scarcity. Lamarck posited that this voluntary, constant stretch of their neck slightly changed the hereditary characteristics controlling neck growth and that giraffe transmitted these acquired characteristics to its offspring.
Lamarck was right when he posited that we could acquire traits through voluntary use of body parts but was wrong when he concluded that these acquired characteristics are inheritable.
The following are the main points of the theory;
- The environment forces an organism to have some needs.
- To satisfy these needs, the organism may use an organ.
- The organ that is frequently used develops.
- Characteristics developed by an organism while satisfying the environmental needs are transferred to the offspring.
- The organ that is not used degenerates.
Although the inheritance of acquired characteristics seems to be logical, no evidence has been found to support this view. Genetic materials are contained in the chromosomes. Except for rare mutations, genetical information is passed on unchanged from generation to generation. If acquired characteristics could be inherited, then children of a great sport person would be born with the knowledge of sports. Acquired skills are usually developed anew in each generation. They are certainly not inherited.
DAWIN’S THEORY OF NATURAL SELECTION
About 50 years after Lamarck proposed his theory of evolution, the British naturalist Charles Darwin, revolutionalized the thinking of most Biologists. In 1859, Darwin published a book called origin of species by means of natural selection. Like Lamarck, Darwin stated that living organisms gradually evolved adaptations to the environment. However, Darwin recognized the variations among members of a species. It is these variations rather than the acquired characteristics that aid natural selection.
Darwin’s theory of natural selection can be summarized as follows:
- Species have the ability to produce a large number of offspring.
- The resources of the natural world are limited. Therefore, there must be competition for survival among the offspring in each generation.
- There is great variability within the population of organism.
- No two individuals are the same.
- Much of these varieties are inherited.
- The organisms that survive and produce offspring are those that have inherited the most beneficial traits for surviving in a particular environment.
- As this process continues through many generations, the population gradually becomes better adapted to the environment.
Modern genetic research supports Darwin’s theory. Both Lamarck and Darwin recognized the importance of the environment in evolution. Many biologists generally accept that it is by natural selection of the better adapted organisms by chance and the elimination of the much less adapted ones that evolution or chance occurs. However, some scientists still argue that acquired characteristics can be inherited. While the debate continues, it is generally believed that Darwin’s theory of natural selection is the most valid explanation of how evolution works. Although natural selection explains many of the changes in organisms, it does not explain why variations occur within a population. This is where the field of genetics comes in and supports the theory of natural selection
However, while Darwin recognized that organisms vary, he had no idea of why they vary. This became better understood through the works of Gregor Mendel, and modern discovery in genetics resulting in the modern theories of evolution.
- Name four scientists that contributed to the discovery of evolution.
- Explain the contribution of Lamarck to evolution theory.
- State three facts presented by Darwin in his theory.
- Outline the key points of Darwin’s theory of natural selection.
- Evaluating the contributions of various scientists to the discovery of evolution,
1. What are the key elements of Darwin’s theory, and how do they contribute to our understanding of evolution?
2. What are some of the evidence supporting Darwin’s theory, and how do they help to explain the mechanisms of evolution?
3. How did Darwin’s work on natural selection differ from that of other scientists such as Lamarck and Mendel, and what were the key differences in their theories?
4. How has modern genetics helped to refine and improve our understanding of natural selection, and what are some of the key insights that have emerged from this research?
5. What are some of the remaining challenges and unanswered questions in our understanding of natural selection, and how are these being explored by biologists today?
Darwin’s theory of natural selection.
1. Darwin’s theory of natural selection is based on the idea that organisms evolve and adapt to their environment over time through a process of variation, selection, and inheritance.
2. This theory was developed in the mid-19th century by Charles Darwin, who observed that organisms within a population exhibit a wide range of variations in traits such as size, color, and shape.
3. These variations can be due to environmental factors such as climate or food availability, or they may be due to random chance and genetic mutations.
4. According to Darwin’s theory, the organisms that are best able to survive and reproduce in their environment will pass on those traits to their offspring, leading to the gradual emergence of new species over time.
5. While Darwin’s theory has been continually refined and expanded upon through modern research in genetics and evolutionary biology, it remains a powerful explanation for how evolution works at both a micro and macro level.
6. Despite its significance in the field of biology, however, Darwin’s theory continues to be a subject of debate and controversy among scientists, with some arguing that other mechanisms like Lamarckian evolution may also play a role in determining how species evolve.
EVIDENCE OF EVOLUTION
Since evolution is an extremely slow process, occurring over a long period of time, it is very difficult to observe evolution visibly or to obtain direct evidence of evolution in action. However, scientists from many fields have gathered at great deal of indirect evidence that supports the theory of evolution.
The following are the sources of such evidences.
- Evidence from Fossil Records.
- Evidence from Embryology;
- Evidence from comparative Anatomy
- Evidence from vestigial organs
- Evidence from Biochemisty and Genetics.
i. Evidence from Fossil Records.
Fossils are remains of organisms preserved mainly in sedimentary rocks. It is believed that the history of life on earth is recorded in fossils. The age of rocks in which fossils are found are determined by using radioisotope or carbon dating. The history of a particular evolutionary change can be traced through a series of fossils when carefully arranged according to their age from the oldest fossils the most recent ones. An example is the evolution of the most modern horse (Equus) from the dawn horse; Eohippus, 60 million years ago.
ii. Evidence from Embryology;
When comparing the development of closely related organisms, it is often difficult to tell the early stages of one species from the early stages of another. The similarity of organisms often used as evidence of evolution. If two organisms descended from a common ancestor, they may still have developmental stages that are very similar.
iii. Evidence from comparative Anatomy
All vertebrates show a basic plan which points to a common ancestry. These are features showing progressive complexity in the structure of vertebrates from fishes to mammals. For instance, there are progressive evolutionary changes in the anatomy of the heart among the classes of vertebrates.
Fishes have a simple heart with one auricle and one ventricle; reptiles have two auricles and a partially divided ventricle. In the course of these changes, the circulation of blood also changed from a single to a double circulation.
iv. Evidence from vestigial organs
Vestigial organs are small or incomplete organs that have no apparent function. They have
become reduced and useless. The presence of vestigial organs helps to explain evolution. According to the evolutionary theory, vestigial organs are the remaining parts of previous functioning organs. For examples, the muscles of the ear in man is a vestigial organ while in horse it plays important role in twisting back the ear to catch sound. The appendix in man is vestigial while it functions as caecum in herbivores.
v. Evidence from Biochemisty and Genetics.
Modern genetics also provides evidence of evolution. All organisms use the same genetic code to synthesis proteins. A universal genetic code is consistence with the idea that all organisms evolved from a single organism that used the code.
Biochemists have compared the amino acid sequence of proteins found in different organisms. Organisms that are closely related often have proteins with similar amino acid. In dissimilar organisms, the amino acid sequences of protein show many more differences.
State the evidence of evolution and discuss any one of them.
SUB-TOPIC 3: FORCES RESPONSIBLE FOR EVOLUTION
The modern theories of evolution are referred to as Neo-Darwinism. This makes use of present day knowledge of genes and chromosomes to explain the sources of genetic variation upon which natural selection works. It also postulates that other forces play a part in evolution although natural selection is more regular. Scientists have identified mutation theory, gene flow and genetic drift as other natural forces responsible for evolutionary changes.
In 1901, Hugo de Vries, a Dutch botanist, presented his mutation theory of evolution. He based his theory on many years of work with primrose plants. Of the 50,000 plants, about 800 showed spectacular new trait not present in the parent plant. Yet, these new trait were passed on to the offspring of the plants in which mutation had occurred. De Vries concluded that, mutation must occur often in other organisms too, and that the change by mutation was the basis of evolution. It has also been confirmed that chromosomal mutations though occurring less often than gene mutation, result in larger and better adapted plants. Today, many biologists believe that mutations contribute significantly to evolution.
Evolution is believed to occur when new species of organisms are formed. Other ways besides mutations, in which evolution is believed to occur in modern times include isolation and the migration of a population to different environments.
II. GENE FLOW
A phenomenon whereby individuals more from one population to another introducing a new gene to the populations is referred to as gene flow. Gene flow moves alleles among populations through the process of interbreeding and migration of breeding individuals.
Gene flows increases variation within a population by introducing new alleles produced in another population. For example, chance dispersal can occur between two populations of related wildflowers, one red and the other white wildflower population. Due to the chance dispersal by strong wind, the gene for the red flowers may be introduced to the white population gene pool.
Persistent gene flow tend to decrease diversity among populations, causing gene pools to become similar. Restriction of gene flow between populations is important for the development of new species.
III. GENETIC DRIFT
Genetic drift is changes in allele frequencies of a gene pool due to chance or random events. It can cause the loss of an allele in a population even if the allele results in greater evolutionary fitness. It can also cause a situation where the allele can be found in every member of the
population i.e. fixed even if the allele decreases fitness. Genetic drift is believed to be more widespread in small population where a chance or random event can wipe out the carriers of the allele completely from the population or drastically reduce their numbers.
- List three forces or factors that are responsible for evolutionary changes.
- Define mutation
- How does mutation contribute to evolutionary changes?
- Which of the following biologists proposed the theory of acquired characteristics? (a) Lamark
(b) Darwin (c) Wallace (d) De Vries
- Which of the following evidences is not used to support the theory of evolution? (a)Analysis of fossil records (b) Mutation (c) Embryology (d) Vestigial organs
- The origin of species by natural selection is a contribution by ……….
(a) Lamarck (b) Button (c) Linnaeus (d) Darwin
4. Remains of organism preserved in rocks are called
(a) Fossils (b) Evolution (c) organic evolution (d) embryology
ANSWERS TO QUESTIONS
1. a, 2. b, 3. d, 4. a
Mutation is a process in which genetic materials change, allowing for new traits to be formed. It is one of the major forces responsible for evolutionary changes, as it introduces new genetic variation into populations. Mutations can occur through a variety of mechanisms, such as exposure to environmental toxins or radiation, and are an important driver of genetic diversity. Other factors that contribute to evolutionary changes include migration, gene flow, and genetic drift. These processes can introduce new alleles into populations, changing the gene pool and driving evolutionary change. Overall, mutations are an important force behind the development of new species and adaptation to environmental conditions over time.
- Discuss how three named animals are adapted for feeding procreation and securing mates for reproduction
- Discuss the contributions of Lamarck or Darwin to evolution
- (a) Outline any four evidences you could use to convince your friend that evolution is a continuous process
- Explain two of the factors that are responsible for evolution
- Draw the progressive evolutionary changes in the anatomy of the vertebrate’s heart.
- Discuss briefly the relationship between classification and evolution.
- Treat several past questions on evolution (SSCE)
- Do the assigned readings on evolution and use it to explain the process of formation of new species.
- Evaluate two resources (books, articles, websites) that discuss evolutionary concepts. What is their bias? How do they compare to other resources you have studied? Can you identify any gaps or weaknesses in their arguments? How would you improve upon the information they present? Support your insights with evidence from the readings.