JAMB Biology Note-Evidence of Evolution

Table of Contents

• 1. Fossil Record
• 2. Comparative Anatomy
• 3. Comparative Physiology and Biochemistry
• 4. Comparative Embryology
• 5. Genetic Studies
• 6. Mutation and Role in Evolution
• 7. Tracing Evolutionary Trends in Plants and Animals
• 8. Modern Evolutionary Theories

1. Fossil Record

Overview: Fossils are the preserved remains or impressions of organisms from the past. The fossil record provides a chronological sequence of life forms and offers critical evidence of how organisms have changed over time.

Types of Fossils:

• Body Fossils: Actual parts of organisms, such as bones, teeth, shells, or leaves.
• Trace Fossils: Evidence of an organism’s activity, like footprints, burrows, or nests.

Evidence for Evolution:

• Fossils show the gradual transition of species over time. For example, fossils of early horse species show a transition from small, forest-dwelling animals to larger, grassland-dwelling horses.
• Transitional fossils, such as Archaeopteryx (a link between dinosaurs and birds), illustrate how one species can evolve into another.
• The fossil record also shows the extinction of species and the emergence of new ones, suggesting that evolution is an ongoing process.

2. Comparative Anatomy

Overview: Comparative anatomy is the study of similarities and differences in the anatomy of different species. Similar structures in different organisms suggest a common evolutionary origin.

Types of Comparative Anatomy:

• Homologous Structures: Structures that are similar in different species due to shared ancestry, though they may serve different functions (e.g., the forelimbs of humans, bats, and whales).
• Analogous Structures: Structures that serve similar functions but are not derived from a common ancestor, such as the wings of birds and insects.
• Vestigial Structures: Remnants of organs or structures that were once functional in ancestors but are no longer useful (e.g., the appendix in humans or pelvic bones in whales).

Evidence for Evolution:

• Homologous structures suggest that different species evolved from a common ancestor, as they share similar bone patterns and structures, even though they may perform different functions in each species.
• Vestigial organs, like the human appendix or the pelvic bones in snakes, show evolutionary remnants of structures that were once more useful but have lost their original function over time.

3. Comparative Physiology and Biochemistry

Overview: Comparative physiology and biochemistry involve comparing the biochemical processes and physiological functions of different organisms. Similarities in these processes provide evidence for shared ancestry.

Evidence for Evolution:

• DNA and Protein Similarity: Similarities in DNA sequences between different species suggest common ancestry. For example, humans share around 98% of their DNA with chimpanzees, indicating a close evolutionary relationship.
• Metabolic Pathways: Many organisms share similar metabolic pathways (such as the use of ATP for energy), supporting the idea that these pathways evolved early in the history of life and were passed down through common ancestors.

4. Comparative Embryology

Overview: Comparative embryology is the study of the development of embryos in different species. Similarities in the early stages of development suggest that these species share a common ancestry.

Evidence for Evolution:

• Early embryos of vertebrates (like humans, fish, and birds) look very similar, suggesting that these species evolved from a common ancestor.
• Features such as gill slits and a tail in the embryonic stages of humans, fish, and birds are evidence of common ancestry.
• The presence of similar developmental pathways across different species highlights the shared genetic heritage and evolutionary trends.

5. Genetic Studies

Overview: Genetics provides direct evidence for evolution by showing how genetic variation arises and is inherited over generations.

Evidence for Evolution:

• DNA Sequencing: The comparison of genomes across different species reveals evolutionary relationships. Species that are closely related have similar DNA sequences. For example, humans and chimpanzees share a high percentage of their genetic code, supporting their common ancestry.
• Genetic Drift and Gene Flow: These mechanisms demonstrate how genetic variation can lead to evolutionary changes in populations over time.
• Chromosomal Comparisons: The number and structure of chromosomes vary among species. For example, humans have 46 chromosomes, while chimpanzees have 48. This difference is attributed to a fusion event in human chromosomes during evolution.

6. Mutation and Role in Evolution

Overview: Mutations are random changes in the genetic material that can lead to new traits. While most mutations are neutral or harmful, some provide an advantage and contribute to evolution.

Evidence for Evolution:

• Mutation: Mutations provide the raw material for evolution by introducing genetic variation. These variations are then subject to natural selection, where beneficial mutations increase in frequency over time.
• Antibiotic Resistance in Bacteria: The development of antibiotic resistance in bacteria is a clear example of mutation leading to evolutionary changes. Bacteria that mutate to resist antibiotics are selected for and survive, while others are eliminated.
• Beneficial Mutations: Some mutations confer benefits, such as the sickle-cell trait providing resistance to malaria. This kind of mutation shows how small changes in DNA can affect survival and reproduction, leading to evolutionary shifts in a population.

7. Tracing Evolutionary Trends in Plants and Animals

Overview: Evolutionary trends can be traced by examining changes in plants and animals over long periods of time. By looking at fossil records, anatomical structures, and genetic evidence, we can identify how species have evolved to adapt to their environments.

Evidence for Evolutionary Trends:

• In Plants: The evolution of flowering plants (angiosperms) from non-flowering plants (gymnosperms) is a significant evolutionary trend. The development of various mechanisms like wind or animal pollination helped angiosperms to diversify and dominate terrestrial ecosystems.
• In Animals: The evolution of vertebrates from early chordates, the development of flight in birds from non-flying ancestors, and the adaptation of mammals to different environments (e.g., aquatic mammals like whales) all highlight trends in animal evolution.

8. Modern Evolutionary Theories

Overview: Modern evolutionary theory incorporates knowledge from genetics, mutation, and natural selection to provide a more comprehensive understanding of how species evolve.

Evidence for Modern Evolutionary Theories:

• Genetic Studies: Modern genetics has provided strong evidence for evolutionary theory by showing how genetic variation occurs and how it is inherited. The discovery of DNA and the ability to sequence genes have revolutionized our understanding of evolution.
• Role of Mutation: Mutations in DNA provide the genetic variation necessary for evolution. When mutations are beneficial, they are passed down through generations, leading to evolutionary changes.
• Evolution of Resistance: The evolution of antibiotic resistance in bacteria is a modern example of natural selection and mutation in action.