1. What is variation? Explain the sources of variation.
Answer: Variation: Variation refers to the differences in characteristics or traits among individuals of the same species. Variation is the raw material for evolution and is essential for natural selection. Without variation, populations cannot adapt to changing environments.
Sources of Variation:
1. Mutation: Mutations are permanent changes in the DNA sequence. They can create new alleles and are the ultimate source of genetic variation. Mutations can be spontaneous or induced by mutagens (e.g., UV radiation, chemicals).
2. Sexual Reproduction: During meiosis, crossing over and independent assortment create new combinations of alleles. During fertilization, the fusion of gametes from two parents further shuffles genetic material, creating unique offspring.
3. Gene Flow: The migration of individuals between populations can introduce new alleles into a population.
4. Genetic Drift: Random changes in allele frequencies due to chance events, especially in small populations.
5. Environmental Factors: Environmental conditions can influence gene expression (phenotypic plasticity), although this is not heritable.
In summary, variation arises from mutations, sexual reproduction, gene flow, and genetic drift. Mutations and sexual reproduction are the primary sources of heritable variation.
2. Assess selection as a possible means of evolution.
Answer: Selection is a key mechanism of evolution. It can be natural or artificial.
Natural Selection:
Mechanism: Individuals with traits better adapted to their environment are more likely to survive and reproduce. They pass these advantageous traits to their offspring. Types: Directional selection (favors one extreme), stabilizing selection (favors intermediate), disruptive selection (favors both extremes). Result: Allele frequencies in the population change over generations, leading to adaptation and potentially speciation. Example: Darwin's finches—beak size adapted to available food sources.
Artificial Selection:
Mechanism: Humans select individuals with desired traits for breeding. Result: Rapid changes in populations, producing new breeds or varieties. Example: Dog breeds, high-yield crops.
Assessment:
Selection is a powerful mechanism of evolution because it is non-random and cumulative. It explains the diversity of life and the adaptation of organisms to their environments. It is supported by extensive evidence from fossils, comparative anatomy, and molecular biology.
In summary, selection (both natural and artificial) is a primary means of evolution, driving adaptive changes in populations over time.
3. Explain the theory of evolution by natural selection with examples.
Answer: Theory of Evolution by Natural Selection: Proposed by Charles Darwin, this theory states that evolution occurs through natural selection. The key points are:
1. Overproduction: Organisms produce more offspring than can survive.
2. Variation: Individuals within a population vary in their traits.
3. Competition: Limited resources lead to a struggle for existence.
4. Survival of the Fittest: Individuals with advantageous traits are more likely to survive and reproduce.
5. Reproduction: Surviving individuals pass their advantageous traits to their offspring.
6. Adaptation: Over generations, the population becomes better adapted to its environment.
Examples:
Darwin's Finches: On the Galapagos Islands, finches with different beak shapes evolved from a common ancestor. Each beak shape was adapted to a specific food source (seeds, insects, cactus).
Peppered Moth: During the Industrial Revolution in England, dark-colored moths became more common because they were better camouflaged on soot-covered trees. After pollution controls, light-colored moths became more common again. Antibiotic Resistance in Bacteria: Bacteria with mutations that confer resistance to antibiotics survive and reproduce, leading to resistant populations.
In summary, natural selection is a mechanism of evolution that leads to adaptation and the diversity of life.
4. Discuss briefly the observations Darwin made during his voyage on HMS Beagle.
Answer: During his five-year voyage (1831-1836) on HMS Beagle, Charles Darwin made several key observations that led to his theory of evolution by natural selection.
1. Diversity of Life:
He observed a vast diversity of organisms in different parts of the world. He noted that organisms in similar environments often had similar adaptations.
2. Fossils:
He found fossils of extinct species that resembled living species. This suggested that species change over time and that extinct species are ancestors of living ones.
3. Galapagos Islands:
He observed that finches on different islands had different beak shapes, each adapted to local food sources. He also observed variations in tortoises and iguanas. This suggested that species could adapt to their specific environments.
4. Geographic Distribution:
He noted that organisms on islands were similar to those on the nearest mainland but had unique adaptations.
These observations led Darwin to propose the theory of natural selection. He realized that variations among individuals, combined with competition for resources, could lead to the survival and reproduction of the fittest.
5. Describe speciation.
Answer: Speciation: Speciation is the evolutionary process by which new and distinct species are formed. It occurs when populations become reproductively isolated from each other and diverge genetically over time.
Steps in Speciation:
1. Isolation: A population is divided by a physical barrier (geographic isolation) or by other mechanisms (reproductive isolation).
2. Genetic Divergence: The isolated populations accumulate different genetic changes (mutations, genetic drift, natural selection) over many generations.
3. Reproductive Isolation: The populations become so genetically different that they can no longer interbreed to produce fertile offspring.
4. New Species: The populations are now distinct species.
Types of Speciation:
Allopatric Speciation: Occurs when populations are separated by a physical barrier (e.g., mountain range, river). Sympatric Speciation: Occurs without physical separation, often due to polyploidy (in plants) or behavioral isolation.
Example: Darwin's finches on the Galapagos Islands. A common ancestor finch arrived on the islands, and populations on different islands adapted to different food sources, eventually becoming distinct species.
In summary, speciation is the formation of new species through reproductive isolation and genetic divergence.
6. Describe the evidence of evolution according to paleontology.
Answer: Paleontology is the study of fossils, which provide direct evidence for evolution. Fossils are the preserved remains or traces of organisms that lived in the past.
Evidence from Paleontology:
1. Transitional Fossils: Fossils that show intermediate characteristics between two groups. Example: Archaeopteryx—a transitional fossil between reptiles and birds (feathers and wings, but teeth and a long bony tail).
2. Extinct Species: Fossils of extinct species show that life has changed over time. Example: Dinosaurs.
3. Evolutionary Trends: Fossils in rock strata show a sequence of changes over time. Example: The evolution of the horse from a small, multi-toed ancestor to the modern, single-toed horse.
4. Dating: Radiometric dating of rocks and fossils provides a timeline for evolution.
5. Biogeography: Fossil distribution across continents supports the theory of continental drift and evolution.
In summary, paleontology provides direct evidence for evolution by showing the history of life and the changes that have occurred over millions of years.
7. How comparative anatomy proves evolution?
Answer: Comparative anatomy is the study of similarities and differences in the anatomy of different species. It provides strong evidence for evolution through:
1. Homologous Structures:
Structures with the same basic structure and origin but different functions. Example: Forelimbs of humans (arms), bats (wings), whales (flippers), and horses (legs) have the same bone structure. This indicates a common ancestor with divergent evolution.
2. Analogous Structures:
Structures with different origins but similar functions. Example: Wings of birds and insects. This indicates convergent evolution due to similar environmental pressures.
3. Vestigial Structures:
Structures that have lost most or all of their original function. Example: Human appendix, coccyx (tailbone). This indicates descent from ancestors that had functional versions of these structures.
4. Embryology:
Embryos of different vertebrates (fish, amphibians, reptiles, birds, mammals) show similar developmental stages (e.g., gill slits, tails). This indicates a common ancestry.
In summary, comparative anatomy provides evidence for evolution through homologous structures, vestigial organs, and embryological similarities.
8. Describe the evidence of evolution according to selective breeding.
Answer: Selective breeding (artificial selection) is the process by which humans breed organisms for desired traits. It provides evidence for evolution because it demonstrates that populations can change rapidly when selection pressure is applied.
Evidence from Selective Breeding:
1. Rapid Change: Selective breeding shows that significant changes can occur in a few generations.
2. Diversity of Breeds: Humans have created hundreds of breeds of dogs, cats, cattle, and crops, all from a common ancestor. Example: All dog breeds are descended from the gray wolf.
3. Desired Traits: Traits like milk yield, meat quality, disease resistance, and flower color can be enhanced through selective breeding.
4. Analogy to Natural Selection: Selective breeding is analogous to natural selection. In both cases, individuals with desirable traits reproduce more, and the population changes over time.
5. Genetic Basis: Selective breeding works because traits are heritable and controlled by genes.
In summary, selective breeding provides evidence for evolution by demonstrating that populations can change over time through selection, just as natural selection changes populations in nature.
9. A species o snail may have a yellow, pink or brown shell. Each colour shell may have dark bands, or have no bands. The snails are eaten by birds. Following observations were made:
Most snails living on a plain background have no bands. Most snails living on green background are yellow. Most snails living on rough background have bands.
(a) Suggest an explanation or these observations.
Answer: The observations suggest that natural selection is acting on shell color and banding patterns. Snails with colors and patterns that provide better camouflage against their specific background are less likely to be seen and eaten by birds. On a plain background, unbanded snails blend in better. On a green background, yellow snails are better camouflaged. On a rough
background, banded snails are better camouflaged.
(b) Predict the colour of snails living on dead leaves.
Answer: Snails living on dead leaves (brown background) would likely be brown. Brown coloration would provide the best camouflage against dead leaves.
(c) Suggest which colour snails will be in summer and autumn.
Answer: In summer, when vegetation is green, yellow snails would be more common. In autumn, when leaves turn brown, brown snails would be more common.
10. Many small volcanic islands are located near South America; these are called Galapagos Islands. There is only one species of finches on South America continent but there are 14 species of finches on Galapagos Islands. Why there are more species on Galapagos islands as compared to main land?
Answer: The high number of finch species on the Galapagos Islands compared to the mainland is due to adaptive radiation. A single ancestral finch species from the mainland colonized the islands. The islands provided diverse habitats and food sources (seeds, insects, cactus, etc.). The finches adapted to these different niches, developing different beak shapes and sizes. Geographic isolation between islands allowed populations to diverge genetically and become distinct species. On the mainland, there is more competition and gene flow, which limits diversification. Thus, the Galapagos Islands are a classic example of adaptive radiation and speciation.
