IB BIO - 5.4 Evolution

• 5.4.1 

  • Define evolution.

• 5.4.1 

  • Define evolution.

Evolution is the process of gradual change in the heritable traits of populations of organisms over successive generations. It occurs through mechanisms such as natural selection, genetic drift, mutation, and gene flow, leading to the emergence of new species and the diversity of life on Earth. Evolutionary processes result in the adaptation of organisms to their environments, the formation of new species through speciation events, and the extinction of others. Evolutionary theory, as proposed by Charles Darwin and Alfred Russel Wallace in the 19th century, is the foundational principle of modern biology and provides a framework for understanding the origin, diversification, and interconnectedness of all living organisms.

• 5.4.2 

  • Outline the evidence for evolution provided by the fossil record, selective breeding of domesticated animals and homologous structures.

• 1. Fossil Record:

  •    - The fossil record provides evidence of evolutionary change over time by preserving the remains or traces of ancient organisms in sedimentary rocks.

  •    - Fossils of extinct species show transitions between different forms of life, revealing intermediate stages of evolutionary development.

  •    - Paleontologists have discovered fossils of organisms that exhibit anatomical features intermediate between ancestral and descendant species, providing evidence of evolutionary relationships.

  •    - Transitional fossils, such as Archaeopteryx (a transitional form between dinosaurs and birds) and Tiktaalik (a transitional form between fish and tetrapods), offer compelling evidence for evolutionary transitions.

• 2. Selective Breeding of Domesticated Animals:

  •    - Selective breeding, also known as artificial selection, involves humans intentionally breeding organisms with desirable traits to produce offspring with those traits.

  •    - The process of selective breeding has been applied for thousands of years in the domestication of plants and animals for agriculture, companionship, and other purposes.

  •    - Selective breeding has led to the development of diverse breeds of domesticated animals with distinct characteristics, such as size, color, coat pattern, behavior, and productivity.

  •    - The observed changes in domesticated species through selective breeding demonstrate how genetic variation within populations can be manipulated to produce rapid evolutionary change, supporting the principles of natural selection proposed by Charles Darwin.

• 3. Homologous Structures:

  •    - Homologous structures are anatomical features in different species that have a common evolutionary origin, indicating shared ancestry despite their diverse functions.

  •    - These structures may have similar basic anatomical arrangements, but they have been modified over time to perform different functions in different species.

  •    - Examples of homologous structures include the pentadactyl limb (the limb with five digits) found in vertebrates, such as humans, bats, whales, and birds, despite variations in their functions (e.g., grasping, flying, swimming).

  •    - The presence of homologous structures supports the concept of descent with modification, suggesting that organisms with shared ancestry have inherited similar structural features from their common ancestors but have adapted them to suit their respective environments and lifestyles.

• Overall, the fossil record, selective breeding of domesticated animals, and homologous structures provide compelling evidence for the occurrence of evolution and the interconnectedness of all living organisms through common ancestry. These lines of evidence support the fundamental principles of evolutionary theory and our understanding of the history of life on Earth.

• 5.4.3 

  • State that populations tend to produce more offspring than the environment can support. 

• Populations tend to produce more offspring than the environment can support due to a phenomenon known as "overproduction of offspring." This concept is a fundamental principle of population ecology and evolutionary biology and is influenced by several factors:

  • 1. Reproductive Capacity:

    •    - Organisms within a population typically have high reproductive capacities, meaning they can produce large numbers of offspring during their reproductive lifespan. This reproductive potential varies among species but is often influenced by factors such as age at maturity, frequency of reproduction, and fecundity (the number of offspring produced per reproductive event).

  • 2. Limited Resources:

    •    - Environments have finite resources such as food, water, shelter, and space that are essential for the survival and reproduction of organisms. These resources are often limited relative to the number of individuals within a population.

    •    - The availability of resources can fluctuate over time due to factors such as seasonal changes, environmental disturbances, competition with other species, and human activities (e.g., habitat destruction, pollution).

  • 3. Competition:

    •    - Within populations, individuals compete for access to limited resources necessary for survival and reproduction. This competition can be intraspecific (between individuals of the same species) or interspecific (between individuals of different species).

    •    - Intraspecific competition for resources such as food, mates, and territory can be intense, particularly when population densities are high. This competition can lead to reduced access to resources for some individuals, affecting their survival and reproductive success.

  • 4. Environmental Constraints:

    •    - Environmental factors such as predation, disease, climate, and abiotic conditions (e.g., temperature, precipitation) can impose constraints on population growth and limit the number of individuals that can survive and reproduce successfully.

    •    - Predation, for example, can regulate population size by controlling the abundance of prey species. Similarly, disease outbreaks can reduce population densities by causing mortality or reducing reproductive output.

  • 5. Natural Selection:

    •    - The overproduction of offspring results in competition among individuals for limited resources, leading to differential survival and reproductive success. Individuals with traits that confer advantages in obtaining resources or avoiding predators are more likely to survive and reproduce, passing on their advantageous traits to future generations.

    •    - This process of natural selection acts as a mechanism for adaptation, shaping the characteristics of populations over time to better suit their environments.

• Overall, the tendency of populations to produce more offspring than the environment can support is a key driver of population dynamics and evolutionary change. It reflects the inherent challenges organisms face in acquiring essential resources for survival and reproduction in environments with finite carrying capacities.

• 5.4.4 

  • Explain that the consequence of the potential overproduction of offspring is a struggle for survival.

• The consequence of the potential overproduction of offspring is a struggle for survival, which arises from the competition for limited resources within a population and the environmental challenges individuals face. Here's how this process unfolds:

  • 1. Limited Resources:

    •    - In any environment, resources such as food, water, shelter, and space are finite and may not be sufficient to support the entire population. This scarcity of resources creates competition among individuals within the population.

  • 2. Competition for Resources:

    •    - With more offspring being produced than the environment can sustain, individuals within the population must compete for access to essential resources. This competition can be intense, particularly when population densities are high or resources are scarce.

    •    - Competition for resources can occur within the same species (intraspecific competition) or between different species (interspecific competition). Intraspecific competition, in particular, can be fierce as individuals with similar resource requirements compete for the same limited resources.

  • 3. Differential Survival and Reproduction:

    •    - As individuals compete for resources, not all individuals will be equally successful in obtaining what they need for survival and reproduction. Some individuals may have advantages over others, such as better access to food, superior competitive abilities, or traits that make them less vulnerable to predation or environmental stressors.

    •    - Individuals with advantageous traits are more likely to survive and reproduce, passing on their genes to the next generation. This process, known as natural selection, leads to the differential success of individuals in the struggle for survival.

  • 4. Struggle for Survival:

    •    - The competition for resources and the differential survival and reproduction of individuals result in a continual struggle for survival within populations. This struggle is driven by the imperative to acquire the necessary resources to meet basic needs and successfully reproduce.

    •    - Organisms must adapt to their environments and develop strategies to maximize their chances of survival and reproductive success. Those that are less well-adapted or less competitive may fail to thrive or may perish, leading to changes in population dynamics and the evolution of populations over time.

• Overall, the consequence of the potential overproduction of offspring is a struggle for survival among individuals within populations. This struggle drives the process of natural selection, shaping the characteristics of populations and influencing their interactions with the environment. It is a fundamental aspect of population ecology and evolutionary biology, driving the dynamics of life on Earth.

• 5.4.5 

  • State that the members of a species show variation. 

• The members of a species show variation. This variation refers to differences in traits, characteristics, and behaviors among individuals within a population of the same species. Variation can arise from genetic differences, environmental influences, or a combination of both. It is a fundamental aspect of biological diversity and is essential for natural selection and evolutionary change. Variation within populations provides the raw material upon which natural selection acts, allowing organisms to adapt to changing environments and contributing to the resilience and survival of species over time.

• 5.4.6 

  • Explain how sexual reproduction promotes variation in a species.

• Sexual reproduction promotes variation in a species through the processes of recombination and genetic diversity. Here's how sexual reproduction contributes to variation:

  • 1. Recombination:

    •    - During sexual reproduction, gametes (sperm and eggs) are produced through a process called meiosis. Meiosis involves the random assortment and recombination of genetic material, leading to the creation of gametes with unique combinations of alleles.

    •    - Each parent contributes a set of alleles to their offspring, and the resulting offspring inherit a combination of genetic material from both parents. When gametes fuse during fertilization, the genetic material from the two parents is combined, resulting in offspring with genetic diversity.

    •    - The process of genetic recombination ensures that each offspring has a unique combination of alleles, leading to variation within the population.

  • 2. Genetic Diversity:

    •    - Sexual reproduction introduces new genetic variation into a population through the combination of alleles from two parents. This genetic diversity arises from differences in the alleles carried by each parent, as well as the random assortment and recombination of genetic material during meiosis.

    •    - Genetic diversity is essential for the survival and adaptation of populations to changing environments. It provides the raw material upon which natural selection acts, allowing individuals with advantageous traits to thrive and reproduce, while less well-adapted individuals may be less successful.

    •    - The presence of genetic diversity within a population increases its resilience to environmental challenges, as it ensures that there is a range of genetic variants that may confer different levels of fitness in response to selective pressures.

• Overall, sexual reproduction promotes variation in a species by generating new combinations of alleles through genetic recombination and introducing genetic diversity into populations. This variation is essential for the adaptation and evolution of species over time, as it provides the raw material upon which natural selection can act, leading to the emergence of traits that enhance survival and reproductive success.

• 5.4.7 

  • Explain how natural selection leads to evolution.

• Natural selection is the process by which organisms with traits that are better adapted to their environment tend to survive and reproduce at higher rates than those with less advantageous traits. Over time, natural selection can lead to evolutionary change within populations. Here's how natural selection leads to evolution:

  • 1. Variation:

    •    - Variation exists within populations due to differences in traits, characteristics, and behaviors among individuals. This variation can arise from genetic differences, environmental influences, or a combination of both.

    •    - Individuals within a population may exhibit different traits that confer advantages or disadvantages in their ability to survive and reproduce in their environment.

  • 2. Selective Pressures:

    •    - Environmental factors such as predation, competition for resources, climate, and disease impose selective pressures on populations. These selective pressures influence the survival and reproductive success of individuals with different traits.

    •    - Traits that increase an organism's chances of survival and reproduction in a given environment are considered advantageous, while traits that reduce an organism's fitness are considered disadvantageous.

  • 3. Differential Survival and Reproduction:

    •    - Natural selection results in differential survival and reproduction among individuals with different traits. Individuals with advantageous traits are more likely to survive and reproduce, passing on their genes to the next generation.

    •    - Over successive generations, the frequency of advantageous traits increases in the population, while the frequency of disadvantageous traits decreases. This process is known as adaptation.

  • 4. Changes in Allele Frequencies:

    •    - As advantageous traits become more common in the population due to natural selection, the frequencies of the alleles responsible for those traits also change over time. This leads to shifts in the genetic composition of the population.

    •    - Through mechanisms such as genetic drift, gene flow, mutation, and sexual recombination, new genetic variants may arise and become incorporated into the population, further contributing to evolutionary change.

  • 5. Accumulation of Adaptations:

    •    - Over long periods of time, the cumulative effects of natural selection result in the accumulation of adaptations within populations. Adaptations are traits that enhance an organism's fitness and increase its ability to survive and reproduce in its environment.

    •    - As populations become better adapted to their environments through natural selection, they may diverge from ancestral populations and eventually give rise to new species. This process of speciation is a key outcome of evolutionary change driven by natural selection.

• In summary, natural selection leads to evolution by favoring individuals with advantageous traits, which increases their chances of survival and reproduction, and thereby alters the genetic composition of populations over time. Evolutionary change occurs as populations adapt to their environments through the accumulation of adaptations that enhance their fitness and reproductive success.

• 5.4.8 

  • Explain two examples of evolution in response to environmental change; one must be antibiotic resistance in bacteria.

• 1. Antibiotic Resistance in Bacteria:

  •    - Antibiotic resistance is a classic example of evolution in response to environmental change. Bacteria possess genetic variation that allows some individuals to survive exposure to antibiotics, while others are susceptible.

  •    - When antibiotics are used to treat bacterial infections, they exert selective pressure on bacterial populations by killing susceptible bacteria. However, resistant bacteria survive and reproduce, passing on their resistance genes to offspring.

  •    - Over time, the frequency of antibiotic-resistant bacteria increases within the population, leading to treatment failure and the spread of resistant strains. This process is accelerated by factors such as overuse and misuse of antibiotics, which provide additional selective pressure.

  •    - Antibiotic resistance is a significant public health concern, as it limits the effectiveness of antibiotics and poses challenges for the treatment of infectious diseases. It highlights the rapid adaptive capacity of bacteria in response to environmental changes, emphasizing the importance of responsible antibiotic use and the development of alternative strategies to combat resistant pathogens.

• 2. Industrial Melanism in Peppered Moths:

  •    - Industrial melanism is another well-known example of evolution in response to environmental change. Prior to the industrial revolution, peppered moths (Biston betularia) in Britain exhibited predominantly light-colored wings, which provided camouflage against lichen-covered tree trunks.

  •    - With the onset of industrialization and widespread pollution, the dark forms of peppered moths (melanic morphs) became more prevalent in polluted urban environments. The dark coloration provided better camouflage against soot-covered tree trunks, reducing the moths' visibility to predators.

  •    - As a result, the frequency of the melanic morphs increased in industrial areas, while the frequency of light-colored morphs decreased. This shift in coloration within the population is a classic example of natural selection favoring individuals with traits that enhance their survival in a changing environment.

  •    - Following efforts to reduce pollution and improve air quality in many industrialized regions, the frequency of melanic morphs has declined, illustrating the dynamic nature of evolutionary responses to environmental changes.

• Both examples demonstrate how organisms can evolve in response to environmental pressures, whether through the acquisition of resistance to human interventions like antibiotics or through adaptation to changes in their natural habitat, such as industrial pollution. Evolutionary responses to environmental change highlight the dynamic interplay between organisms and their environments and the ongoing process of adaptation and diversification in natural populations.