Understanding Evolution: Key Concepts, Evidence, Mechanisms, and the Impact on Biodiversity

Introduction to Evolution

Best Definition for Evolution

Evolution is the process of development of complex organisms from simple forms over a long period of time. It is a very slow process and results in the origin of new species. Scientists have long tried to discover the origin of living organisms. Various observations about the varieties of plants and animals, the diversities in their structures and the reproductive patterns, lead to the concept of evolution. However, the concept of evolution contradicts that of divine creation which stipulates that God created all living organisms. The theory of evolution implies that all living organism, no matter how different, arose from one common ancestor or one living cell.

Types of Evolution

Divergent Evolution

Divergent Evolution is a type of evolution that produces different functional structures in organisms that have evolved from a common ancestor, due to adaptation to environmental changes. In order words, divergent evolution occurs when two or more closely related species develops into a new species, by developing different structures to meet the environmental demands. Divergent evolution could be responsible for the creation of the diversity of life on earth from the first living cells.

Homologous structures are structures or organs that have the same evolutionary origin but perform different functions. Homologous organs show divergent evolution. Example; the wing of a bat and the arm of a man.

Convergent Evolution

Convergent Evolution is type of evolution that produces similar adaptive functional structures in unrelated groups of organisms. In convergent evolution, unrelated species become more and more similar in appearance as they adapt to the same kind of environment. For example, the wings of birds, bats and insects, have different embryological origins but are all designed for flight.

Analogous structures are structures that perform similar functions but evolved separately. Analogous organs show convergent evolution. Example, the wings of insect, bird and bat.

Evidence of Evolution

Fossil Records (Paleontology)

Fossils are remains or traces of once-living organisms that have been buried and preserved in sedimentary rock, or trapped in natural asphalt, amber and ice. The remains of a dead organism may include the entire organism, molds and castes, hard skeletal structures, petrification, impression, imprints and fecal pellets. The fossil record contain evidence of how life has changed and evolved throughout the earth’s history. The fossils in successive strata of rocks show a gradual change from simple forms to complex forms of life. The geological time scale explains that the oldest rocks formed show the fossils of simple animals only. The rocks formed later show more complex forms of living organisms.

Comparative Embryology

Embryology is a specialized branch of biology, which deals with the formation and development of the embryo. Embryos of many different kinds of animals: mammals, birds, reptiles, fish, etc. look very similar. At a certain stage of development, they are fish-like; possess gill slits or cleft in the pharynx and a tail. This shows that vertebrates descended from aquatic ancestors and therefore passes through some embryonic stages of its evolutionary ancestors.

Evidences of Evolution in Embryo Development

Comparative Anatomy

Comparative anatomy is the scientific study of similarities and differences in the structure of living things. Comparing the forelimbs of the human, the bat, the bird, and the alligator all have the same pentadactyl limb plan. The humerus, radius, ulna, and carpals in each forelimb. Though the limbs look different on the outside, they are very similar in skeletal structure. More significantly, they are derived from the same structures in the embryo. This suggests that these animals evolved from a common ancestor.

Comparative Biochemistry

Biochemistry is the study of the basic chemical structures and processes that occur in cells. The biochemistry of all living things shows that all organisms share a common ancestry. Carbon, Hydrogen, Oxygen and Nitrogen form the three main organic compounds, Carbohydrates, fats and proteins. These three organic compounds combine together to form a complex substance called protoplasm. The protoplasm of all living things, from amoeba to man, has several similar physical and chemical properties. This protoplasm is built into structural units of living organisms called cells. The cells of plants and animals exhibit fundamental similarity in all living things.

The study of molecules in organisms also reveals that almost all living organisms have DNA and use the same genetic code (A, T, G and C). The genetic code for the synthesis of protein is universal. E.g., the codon UUU in RNA is used to synthesis the amino acid phenylalanine in all living things, whether Amoeba, Tilapia or human. This is because they descended from a common ancestor.

Biogeography (Geographic Distribution of Living Organisms)

The geographical distribution of various animals is also seen as evidence of evolution. The differences in various regions on earth cannot be explained by climate alone, but are evidently the result of a continental drift.

It is thought that at one time the Americas, Africa, Antarctica and Australia all formed one large continent called Pangaea. When it split up into the continent we known today, the various animals evolve independently according to their geographical and climatic surrounding. Marsupial animals are thought to have developed first in North America and that they spread from there to Australia and New Zealand through Antarctica before the continents broken apart. The mammals in South America are quite similar to those in Africa and it is believed they had common ancestors before the separation of the two continents.

Vestigial Organs

Some organisms have structures or organs that seem to serve no useful function. For example, humans have a tailbone at the end of the spine that is of no apparent use. Some cave-dwelling salamanders have eyes even though members of the species are completely blind. Such functionless parts are called vestigial organs or structures. Vestigial organs are often homologous to organs that are useful in other species. The vestigial tailbone in humans is homologous to the functional tail of other primates. Thus, vestigial structures can be viewed as evidence for evolution: organisms having vestigial structures probably share a common ancestry with organisms in with organisms in which the homologous structure is functional.

Theories of Evolution

The following scientist were involved in the theory of organic evolution.

□ Jean Baptiste Lamarck’s

□ Charles Darwin

Lamarck’s Theory of Evolution

Lamarck’s theory involves the inheritance of acquired characters. Theory is resolved into three components:

□ Influence of the environment

□ Use and disuse of body parts

□ Inheritance of acquired characters

According to this theory, individuals of the same species growing and developing under different environmental conditions differ from each other. This means that organism react to external environmental changes which might give rise to new species. Example, short necked ancestors of the modern giraffe voluntarily stretched their necks to reach leaves high in trees during times when food was scare. Also, animals living in cold environment develops thick fur to survive.

In animals for example the use, or exercise of certain parts of the body results in the development of those parts. This means that new characters are acquired in life and can be passed on to the offspring giving rise to new species. E.g., the development of the long neck in giraffe. Also, parts of the body which are not used or exercise might degenerate and disappear or persist as vestiges e.g., the appendix and coccyx (tail) in human.

This theory made people to start thinking but it was not generally accepted because acquired characteristics are not inherited.

Father of Evolution

Charles Darwin and Alfred R. Wallace

Darwin’s Theory

Charles Darwin published a book “The origin of species’’ in the year 1859. He proposed that the new species came about by a process called ‘natural selection.’

The theory is resolved into three components:

□ Over-production of offspring and subsequent struggle for existent among the offspring.

□ Variation of natural population

□ Elimination of unfavorable variations which results in the survival of the fittest.

According to this theory, if all the offspring of organisms survive, there will be a geometric increase in the number of organisms. This will lead to shortage of food supply, water and space. This would in turn results in struggle for existence due to competition for the limited resources. There exists variation within species. Some variations are better suited to the environment while others are not. Therefore, in the struggle for existence individual with favorable variations survive. These survivors pass on their character to their offspring. Individuals with less favorable variations perish. The survivors are better adapted to their environment. A gradual change of this type may eventually lead to formation of new species.

Darwin described that nature selects such organisms, i.e., there is natural selection. Herbert Spencer referred to this as ‘survival of the fittest.’ Darwin explained that favorable variations are passed on to the offspring down the generations. After a certain period of time the organisms appear so different from the original species that ultimately a new species is evolved.

Alfred Russell Wallace's theory

In 1858, when Wallace was on a collecting trip in Indonesia, he wrote a 20-page essay outlining his theory of natural selection and sent it to Charles Darwin. Darwin almost yielded to Wallace the honor of being the first man to announce the hypothesis. Darwin and Wallace presented their papers to the Linnaean Society in London on July 1st 1858. For this reason, many biologists regard both Charles Darwin and Alfred R. Wallace as joint founders of 'The Theory of Evolution by Natural Selection'.

Mechanisms of Evolution

Evolution is the process by which populations of organisms change over time. Several mechanisms drive these changes in the genetic makeup of populations, each contributing to the diversity of life on Earth. The primary mechanisms of evolution include natural selection, genetic drift, mutations, gene flow, and non-random mating. Here’s a detailed look at each:

1. Natural Selection

Natural selection is the process by which certain traits become more common in a population because they confer a survival or reproductive advantage. It operates on the principle that individuals with traits better suited to their environment are more likely to survive and reproduce, passing those advantageous traits to their offspring.

Example: The peppered moth in England displayed two color variations—light and dark. During the Industrial Revolution, pollution darkened the trees, making the light-colored moths more visible to predators. As a result, the dark-colored moths, which were better camouflaged, had higher survival rates and reproduced more, leading to an increase in the dark-colored population.

Natural selection can lead to three types of selection:

Directional Selection: Favors one extreme of a trait, leading to a shift in the population's trait distribution.
Stabilizing Selection: Favors the intermediate variants, reducing variation and maintaining the status quo.
Disruptive Selection: Favors both extremes over the intermediate traits, potentially leading to speciation.

2. Genetic Drift

Genetic drift refers to random changes in allele frequencies in a population, which can cause significant evolutionary changes, especially in small populations. Unlike natural selection, genetic drift is a random process and does not necessarily favor traits that confer a survival advantage.

Bottleneck Effect: A sudden reduction in population size due to a catastrophic event can lead to a loss of genetic diversity. The surviving population's gene pool may no longer represent the original population's gene pool.
Founder Effect: When a small group of individuals colonizes a new habitat, they may carry only a subset of the genetic diversity of the original population. This can lead to a new population with distinct genetic characteristics.

3. Mutations

Mutations are random changes in the DNA sequence of an organism. They are a source of new genetic variation and can introduce new alleles into a population. While most mutations are neutral or harmful, some can be beneficial and provide the raw material for evolution.

Types of Mutations:
- Point Mutations: A change in a single nucleotide in the DNA sequence.
- Insertions and Deletions: The addition or loss of nucleotide bases in the DNA sequence.
- Gene Duplication: Duplication of entire genes, leading to an increase in the number of copies of a gene.

Mutations can result in new traits that, if advantageous, can spread through the population via natural selection.

4. Gene Flow

Gene flow, also known as gene migration, is the transfer of genetic material between populations. It occurs when individuals from one population migrate to another and breed, introducing new alleles into the gene pool of the receiving population.

Effect on Genetic Variation: Gene flow tends to reduce differences between populations, increasing genetic diversity within a population and making populations more genetically similar.

5. Non-random Mating

Non-random mating occurs when individuals select mates based on specific traits, rather than mating randomly. This can affect the distribution of traits in a population.

Assortative Mating: Individuals preferentially mate with others that are similar to themselves in certain traits. For example, tall individuals may prefer to mate with other tall individuals.
Disassortative Mating: Individuals preferentially mate with those who are different from themselves in certain traits, which can increase genetic diversity.

Non-random mating can lead to changes in allele frequencies and increase the proportion of certain traits in a population.

For further reading and a more in-depth understanding, visit Understanding Evolution by UC Berkeley

Importance of Evolution in Understanding Biodiversity

Evolution is fundamental to understanding the rich diversity of life on Earth. Biodiversity refers to the variety of life forms in different ecosystems, including the variability among species, genetic differences within species, and the ecosystems they form. Evolution provides the framework for understanding how this diversity has arisen and continues to change over time. Here are several key ways in which evolution is important for understanding biodiversity:

1. Origins of Species

Evolutionary theory explains the origins of the vast array of species through the process of speciation. Speciation occurs when populations of a species become isolated and diverge enough to form new species. This process is driven by mechanisms such as natural selection, genetic drift, and mutations. Understanding the evolutionary processes that lead to speciation helps us trace the lineage and relationships between different organisms, illuminating the tree of life.

2. Adaptation to Environments

Evolution by natural selection explains how organisms adapt to their environments. This adaptation can lead to the development of new traits that enhance survival and reproduction in specific environments. By studying these adaptations, scientists can understand the ecological roles of species and how they interact with their surroundings. This is crucial for understanding the resilience of ecosystems and how they might respond to environmental changes.

3. Genetic Diversity

Genetic diversity within species is a critical component of biodiversity. It provides the raw material for evolution, enabling populations to adapt to changing environments and survive new challenges such as diseases or climate change. Evolutionary processes like mutation and gene flow contribute to this genetic diversity. Understanding these processes helps conservationists preserve genetic variation, which is vital for the long-term survival of species.

4. Coevolution and Interactions Among Species

Coevolution occurs when two or more species reciprocally affect each other’s evolution. This can lead to complex interactions, such as predator-prey relationships, mutualism (beneficial interactions), and competition. Understanding these evolutionary dynamics helps explain the complex interdependencies in ecosystems and the evolutionary arms race that can drive the development of specialized traits and behaviors.

5. Evolutionary History and Phylogenetics

Phylogenetics is the study of the evolutionary history and relationships among species. By analyzing genetic and morphological data, scientists can construct phylogenetic trees that illustrate these relationships. This helps in understanding the shared characteristics and evolutionary paths of different groups, as well as the timing of key evolutionary events. Phylogenetic studies are essential for identifying conservation priorities and understanding the evolutionary processes that generate and maintain biodiversity.

6. Response to Environmental Change

Evolution provides insights into how species and ecosystems respond to environmental changes, such as climate change, habitat loss, and pollution. By studying past evolutionary responses, scientists can predict potential future changes and identify species that may be at risk. This information is crucial for developing effective conservation strategies and mitigating the impacts of human activities on biodiversity.

7. Medical and Agricultural Applications

Understanding evolution has practical applications in medicine and agriculture. For example, knowledge of evolutionary principles is used to track the spread of infectious diseases, understand antibiotic resistance, and develop vaccines. In agriculture, evolutionary biology helps in the development of pest-resistant crops and the conservation of genetic resources for future breeding efforts.

For further reading and a more in-depth understanding, visit Evolution and biodiversity University of Manitoba.

SSCE/WASSCE/GCE PASS QUESTIONS AND ANSWERS ON EVOLUTION

OBJECTIVE

1. The theory of natural selection was developed by

A. Lamarck and Darwin

B. Darwin and Wallace

C. Wallace and Mendel

D. Mendel and Larmack

2. Fossil records found in sedimentary rocks offer some explanation for the theory of evolution because

A. the deposite have remains of organisms characteristic of when they were formed

B. different strata have remains of organisms of the same kind

C. only organisms with strong parts are fossilized

D. most animal and plant fossils bear little resemblance to present day living specimens

3. The least evidence in support of the theory of evolution is provided by the study of

A. anatomy

B. ecology

C. geology

D. embryology

4. From which group of animals are the mammals generally believed to have most recently evolved?

A. Reptiles

B. Fish

C. Amphibians

D. Birds

5. Long neck in giraffe is used to illustrate the theory of

A. use and disuse C. origin of life

B. origin of species D. natural selection

6. The natural tendency of organisms as they evolve is to

A. decrease in size

B. increase in number

C. develop specialize structure

D. feed indiscriminately

7. The best explanation for the theories of natural selection is that

A. all organisms have equal capacity for survival in their habitats

B. organisms have varying capacities for survival in their habitats

C. organisms compete for resource and better competitors survive and thrive

D. habitats allow only organisms that will not have to compete for survival

8. From evolutionary standpoint, the older a fossil-bearing rocks is, the more likely it is to contain

A. aves as opposed to amphibians

B. invertebrates as opposed to vertebrates

C. angiosperms as opposed to algae

D. vertebrates as opposed to invertebrates

9. Which of the following is one of Lamarck's theories?

A. Some variations are more favourable to existence in a given environment than others

B. All living organisms are constantly involved in a struggle to existence

C. The size of a given population remains fairly constant

D. New species originates through the inheritance of acquired traits

10. The older fossil-bearing rocks, in contrast to the more recent ones, are more likely to contain

A. animal rather than plant remains

B. invertebrates rather than birds

C. flowering plants rather than mosses

D. reptiles rather than fishes

11. Darwin is considered the first scientist who correctly explained the theory of

A. special creation

B. spontaneous generation

C. use and disuse

D. organic evolution

12. In his theory of evolution, Darwin implied that

A. the struggle for existence among living organisms is sporadic

B. the most successful organisms are those that best adapt to their environment

C. organs of the body which are not regularly used by an organism will disappear

D. any traits acquired by an organism during its lifetime can be passed on its offspring

13. An argument against Lamarck's theory of evolution is that

A. disuse of body part cannot weaken the part

B. disused part is dropped off in the offspring

C. acquired traits cannot be passed on to the offspring

D. trait cannot be acquired through constant use of body parts

14. Which of the following requires the use of carbon dating to prove that evolution has occurred?

A. Comparative anatomy

B. Biochemical similarities

C. molecular records

D. Fossil records

15. An evidence of the relationship between living organisms and their extinct relatives can best be obtained from

A. embryology

B. comparative anatomy

C. comparative physiology

D. palaeontology

16. I. Rattus rattus II. Agama agama III. Bufo regularis IV. tilipia zilli
the order of evolutionary advancement to the above vertebrates is

A. I, II, III, IV

B. I, IV, III, II

C. II, III, IV, I

D. IV, III, II, I

17. An evidence of a common ancestral for fishes, amphibians, reptiles, birds and mammals is the

A. possession of wings by birds and bats

B. cold-bloodedness of fishes, amphibians and reptile

C. presence of gilll clefts in vertebrate embryos

D. possession of scale by fish and reptiles

18. The theory which supports the view that the large muscles developed by an athlete will be passed on to the offspring was proposed by

A. Lamarck

B. Darwin

C. Mendel

D. Pasteur

19. The natural process that produces adaptive evolutionary changes is

A. mutation

B. gene flow

C. genetic drift

D. natural selection

20. According to Darwin, the driving force behind evolutionary change is

A. natural selection

B. genetic drift

C. mutation

D. gene flow

Answers

1. B	6. C	11. B	16. D
2. A	7. C	12. B	17. C
3. B	8. D	13. C	18. A
4. B	9. D	14. B	19. C
5. A	10. A	15. B	20. A

THEORY

1. (SSCE 1993, Q7) Give an account of the theory of each of the following evolutionists

(i) Lamarck (ii) Darwin

Solution

Refer to notes

2. (SSCE 2001, Q7) (a) Explain the term evolution.

(b) Distinguish between convergent and divergent evolution.

(d) What are the views of Lamarck on the theory of evolution?

Solution

(a) Evolution: is the process of development of complex organisms from simple forms over a long period of time. It is a very slow process and results in the origin of new species.

(b) Divergent Evolution: is a type of evolution that produces different functional structures in organisms that have evolved from a common ancestor, due to adaptation to environmental changes. Whilst

Convergent Evolution: is type of evolution that produces similar adaptive functional structures in unrelated groups of organisms.

(c) Embryos of many different kinds of animals: mammals, birds, reptiles, fish, etc. look very similar. At a certain stage of development, they are fish-like; possess gill slits or cleft in the pharynx and a tail. This shows that vertebrates descended from aquatic ancestors and therefore passes through some embryonic stages of its evolutionary ancestors.

(d) Organisms of the same species growing and developing under different environmental conditions differ from each other. This means that organism react to external environmental changes which might give rise to new species. The continuous use of body parts may give rise to new characters or development of those parts and can be passed on to the offspring giving rise to new species.