Evolution and Speciation

Evolution and Speciation

• Evolution refers to the cumulative changes in heritable characteristics within a population over generations.
• Cumulative change involves the accumulation of small changes over time.
• Heritable characteristics refer to gene-controlled traits passed from parents to offspring.
• A population is a group of organisms, not individual organisms.
• Evolutionary change differs from Lamarckian ideas, as acquired traits are not heritable.

Theories of Evolution

• Lamarckism suggests organisms acquire traits during their lifetime and pass them on, has been disproven.
• Darwinism, supported by genetics, posits that variation exists in populations due to genetic differences (alleles).
• Natural selection ensures individuals with advantageous traits survive, reproduce, and pass on those traits.

Evidence for Evolution

• A universal genetic code across organisms signifies a common ancestor.
• Similar DNA and protein sequences among species suggest closer evolutionary relationships, humans share ~98–99% of DNA with chimpanzees.
• Homologous structures, or similar structures with different functions, indicate a common ancestor.
• The pentadactyl limb in vertebrates has evolved for varied purposes like swimming in whales and flying in birds.
• Through selective breeding, humans have bred plants and animals for desirable traits, resulting in rapid evolutionary changes, dogs were domesticated from wolves around 15,000 years ago.
• Homologous structures share similar structures but have different functions and comes from divergent evolution.
• Analogous structures perform similar functions but arise from different evolutionary paths resulting from convergent evolution.
• Wings of birds, bats, and insects are and example of analogous structures

Speciation

• Speciation happens when populations of a species diverge into two or more species.
• Speciation requires reproductive isolation through geographical, behavioral, or temporal barriers.
• Bonobos and chimpanzees evolved separately due to the Congo River.
• Speciation increases biodiversity as species adapt to different environments, extinction reduces it.

Geographical Isolation and Reproductive Isolation

• Geographical isolation occurs through physical barriers like rivers and mountains that prevent populations from interbreeding.
• Behavioral reproductive isolation emerges from differences in mating behaviors like songs in meadowlarks.
• Temporal reproductive isolation comes from species reproducing at different times, like cicadas with 13- and 17-year life cycles.

Adaptive Radition

• Adaptive radiation occurs when a single ancestral species evolves into multiple species to inhabit different ecological niches.
• Adaptive radiation increases biodiversity and demonstrates divergent evolution.
• Darwin's finches on the Galápagos Islands evolved into 18 species due to varied environmental pressures.

Barriers to Hybridization

• Hybrids are offspring of two different species, often sterile.
• Prezygotic barriers prevent fertilization through behavioral, temporal, or ecological isolation, or through mechanical isolation due to incompatible reproductive anatomy.
• Postzygotic barriers occur after fertilization, resulting in hybrid inviability, infertility, or breakdown.

Polyploidy and Abrupt Speciation in Plants

• Polyploidy involves organisms with more than two sets of chromosomes, often from errors during meiosis.
• Polyploidy is common in plants, such as knotweed species, and can lead to immediate speciation.
• Plants with even chromosome sets can reproduce sexually where as plants with odd sets, often sterile, reproduce asexually.

Types of Speciation

• Allopatric speciation occurs when new species form due to physical separation of populations by mountains, rivers, or oceans.
• Sympatric Speciation new species form within the same geographical area due to reproductive barriers.
• Examples of sympatric speciation include temporal isolation like cicadas with different life cycles, and behavioral isolation, like different courtship behaviors in Western and Eastern meadowlarks.

Natural Selection

• Natural selection facilitates evolution as better-adapted organisms are more likely to survive and reproduce.
• Variations are differences seen among individuals within a species and favorable variations lead to better adaptation.

Components of Darwin's Natural Selection Theory

• Variations are seen among organisms in a population and is passed down to offspring.
• Overproduction leads to competition for limited resources and a struggle for existence.
• In the struggle for existence, organisms with traits that are better suited to the environment survive and reproduce.
• Organisms that survive pass on these variations to offspring.

Mechanism of Natural Selection

• Natural selection enables evolutionary change and biodiversity.
• Isolation prevents interbreeding due to geographical or other barriers.
• Darwin's finches(Galapagos) and Anole Lizards (Caribbean islands) demonstrate isolation and environmental differences which led to evolution into distinct food sources and specific ecological niches.

Paradigms

• A paradigm is a distinct set of concepts and understandings, including theories.
• Natural selection is an example of a paradigm shift from Lamarck's theory.
• Prior to Darwin, creationism suggested species were immutable and divinely created.
• Darwin proposed natural selection as the main mechanism of evolution, driven by environmental pressures and variation within populations.

Mutations and Sexual Reproduction

• Biodiversity stems from genetic, species, and ecosystem variation.
• Mutations are errors in copying genetic information they can be neutral, harmful, or beneficial, and sexual reproduction introduces genetic variation through crossing over, independent assortment, and random fertilization.

Overproduction and Competition

• Economist Thomas Malthus influenced Darwin's concept of natural selection.
• Natural selection drives species to reproduce far more offspring than can survive.
• Competition for limited resources, like food, water, shelter, space, and mates, determines the environment's carrying capacity.

Survival of the Fittest

• Favorable variations of better adaptive traits allow species to survive and reproduce.
• Differential Survival and Reproduction promotes natural selection where some individuals survive and reproduce better than others.
• Over time, offspring of survivors constitute a larger proportion of the population which then becomes better adapted to its environment.

Abiotic Factors as Selection Pressures

• Selection pressures drive differential survival or reproduction and alter a population's genetic composition and can include density-dependent and independent factors.
• Density-dependent factors impact the size of the population based on the population's density in a given area.
• Density-independent factors, like availability of oxygen and temperature, affect the size of the population and are not related to population density.

Biological Fitness

• Biological fitness defines an organism's ability to reproduce and pass on its genetic material to offspring.
• Environmental conditions determine biological fitness.
• Survival value refers to traits that assist individuals to survive and reach reproductive age, like mechanisms to avoid predators or resist disease.
• Reproductive potential defines an individuals ability to reproduce and is determined by traits that allows them to attract mates and produce viable offspring.

Intraspecific Competition

• Intraspecific competition is a density dependent factor that drives natural selection, occurs when organisms of the same or different species vie for the same resources.
• Intraspecific competition affects population size, traits passed down, population adaptation can be caused by competition intensification.

Heritable Traits for Evolution

• Heritable traits are traits encoded in genetic material and are beneficial to the organism that can increase survival and reproduction.
• Acquired traits are developed during the duration of the organism's lifetime due to environmental factors.
• Acquired traits only affect phenotype and are not encoded in DNA, thus, they cannot be passed on to offspring.

Sexual Selection for Reproduction

• Sexual Selection specializes in finding a mate for reproduction
• Intrasexual selection is the competition between individuals of the same sex to find a mate
• Intersexual selection Individuals of one sex choose mates based on behavior or physical traits that indicate fitness.

Guppy Experiments

• Spotted males are preferred by guppies without predators.
• Dull-colored males were favored by natural selection with predators present.

Gene Pool

• Gene Pool is the total amount of alleles of all genes within a population.
• Genetic variation is higher when gene pools get larger, and adaptability is higher.
• Decreased adaptation to the environment is the result of decreased gene pool sizes.

Allele Frequency

• A relative frequency of a particular allele within a population is referred to as Allele Frequency.
• Evolutionary changes are shown by how allele frequencies change over generations.
• Geographic Isolation - alleles in the gene pool can change due to natural selection and random chance.

Genetic Drift

• Genetic Drift: Random changes in allele frequency can impact small and isolated populations
• Bottleneck Effect - reduced genetic diversity in surviving population due to disasters
• Founder Effect - limited genetic makeup and variety caused by small group colonizing new area.

Neo-Darwinism

• Darwin’s theory with Mendelian genetics is combined in Neo-Darwinism.
• Evolution is caused by change in the gene pool.
• Natural selection increases beneficial alleles as also reduces harmful ones.
• Mutations are the ultimate source of genetic variation.
• Microevolution: Small changes happen in allele frequency within a population over generations.
• Macroevolution: Large-scale evolution can lead to forming new species.

Types of Natural Selection

• Stabilizing Selection - genetic diversity and average traits are less due to intermediate phenotypes favored
• Directional selection - allele frequency shifts toward extreme traits that are favored.
• Disruptive Selection - individuals with extreme phenotypes are favored for environments that end up leading to speciation.

Hardy-Weinberg Principle

• Hardy-Weinberg Principle - allele frequencies remain identical from generation to generation (genetic equilibrium) if certain criteria are met
• For genetic equilibrium, there must be no mutations, random mating, no natural selection, no gene flow, and large population size.

Artificial Selection

• Artificial Selection - (selective breeding) humans intentionally select individuals with desirable traits to increasing the frequency of those traits in future generations

Classification

• Classification - sorting organisms into groups based on criteria.
• It helps organize interconnections as also to helps to support any further research.

Problems with Traditional Classification

• The fixed ranks do not express the evolutionary change gradually.
• Physical traits that it relays on can be misleading
• Classification can also incorrectly grouped unrelating species.

Scientific Paradigm Shift

• Genetics advances led to shift from genetic classification to morphological classification
• The evolution of scientific theories can be represented by shift.
• Modern classification is based by evolutionary relationships that genetic analysis have determined.

Cladistics

• Cladistics - is a way determining relationships be comparing genetic evidence among species
• Molecular sequences provide the reliant evidence for clads
• (Homo sapiens) are most more similarly than gorillas.

Clade

• Common ancestors and inherited traits share among clades
• Example: The mammal clade include subclasses.
• Genetric mutation accumulates giving molecular clock overy time.

Molecular Clock

• Molecular clock measures evolutionary tine using mutation rates in DNA.
• Factors influencing mutation rates: random genetic changes,selection pressures, Genome size and population size .

Cladogram

• Cladogram: Data of tree like represents species is called cladogram.
• Organize a group of species in a cladogram through the principle of parsimony