Biological Evolution Review Important figures Natural Selection: Natural selection is a mechanism of evolution. Organisms that are more adapted to their environment are more likely to survive and pass on the genes that aided their success. This process causes species to change and diverge over time. Charles Darwin: Made of the theory of evolution by natural selection. Thomas Malthus: The theory that animals of a tendency to produce more offspring then they can feed. Jean Lamarck: According to Lamarck, organisms altered their behavior in response to environmental change immediately. Evidence for Evolution Anatomy Homologous Structures: Similar structures that are derived from a common ancestor but no longer have the same function. For example the same types of bones are found in Humans, Cats, Horses, and Whales, yet they are arranged differently. Analogous Structures: structures that may have the same function, but they do not necessarily have the same structure & they are not derived from a common ancestor. (bird & insect wings) Vestigial Structure: Structures present in modern animals that are no longer in use (no current function). They give hints to the evolution of an organism. Pelvic bone in whales but they dont use it. Embryology Similar stages of embryological development are seen in different species. All vertebrates have tails and gills in early stages of embryonic development. Geographical Distribution Geographically close environments are more likely to have related species than distant places. Isolated regions such as Australia have unique species that are not found anywhere else (marsupials). Islands have species that are similar to nearby continents or other islands, but show slight differences (finches of Galapagos). Fossils Fossils form when organisms are buried in sediment that turns into rock. They show that past organisms were different from today's. The depth of fossils helps determine their age, and techniques like radioactive and carbon dating can give accurate ages. Newer fossils are more similar to living organisms, while older ones look less like them. Fossils are found in a chronological order, starting with invertebrates (older) and followed by vertebrates (like fish, amphibians, reptiles, birds, and mammals). Molecular Biology All living organisms use the same genetic code (DNA/RNA) to create amino acids and proteins. By comparing DNA sequences, scientists can see how closely related different species are. For example, humans and chimpanzees have a 2.5% difference in their DNA, while humans and lemurs have a 42% difference. Many organisms also share common proteins, such as hemoglobin, which is important for basic functions like respiration. Sexual Selection Sexual selection is a mechanism of evolution in which members of one biological sex choose mates of the other sex to mate with, and compete with members of the same sex for access to members of the opposite sex. For female birds may find male birds with brighter colour more attractive. Biological Fitness Biological fitness, also called Darwinian fitness, means the ability to survive to reproductive age, find a mate, and produce offspring. Antibiotic Resistance Antibiotic resistance is when bacteria change to resist antibiotics that are used to effectively treat them. This makes certain bacterial infections difficult to treat. Overuse and misuse of antibiotics cause antibiotic resistance. Peppered Moth Industrialization caused trees to become black so peppered moths who were black survived more. Natural Selection. Microevolution Mutation: A mutation is a permanent change in the DNA. Mutation may lead to a new allele that allows an organism to have a survival advantage when environmental conditions change. Good example of this is Antibiotic Resistance. Genetic Drift: Changes in allele frequency in a population that happen by chance ❑ Seen in small populations Bottleneck Effect: A drastic reduction in population (as a result of natural disaster, hunting, etc.) will cause certain alleles to become over- or under-represented in future offspring (allele frequencies change Founder Effect: A change in allele frequencies that result from a small number of organisms that inhabit a new area Gene Flow: Movement of alleles from one population to another (due to migration) E.g. in plants, pollinators or wind may move pollen from one group of flowers to another, possibly introducing new alleles for colour etc. Assortive Mating: Individuals with similar phenotypes mate with one another more frequently than would be expected (e.g. size, age, coloration) Natural Selection: Directional selection favors individuals at one end of the phenotypic range. Most common during times of environmental change or when moving to new habitats. (e.g. peppered moths Diversifying/disruptive selection favors extreme over intermediate phenotypes. Occurs when environmental change favors an extreme phenotype. Stabilizing selection favors intermediate over extreme phenotypes. Reduces variation and maintains the current average. Artificial Selection The deliberate selection (by people) of organisms with desired traits. Traits can be useful: cows producing more milk, crops with larger fruits. Traits can be ornamental: roses, cats/dog Species Sympatric Speciation – Populations become reproductively isolated even when living in the same geographic area – Happens when chromosomes suddenly change Allopatric Speciation Population splits into 2 isolated groups due to a geographical barrier Gene pools become so different they can no longer successfully interbreed, even if brought back together Rates of Macro-Evolution Gradualism (evolution by creeps) large evolutionary changes in a species occur slowly and steadily due to the accumulation many small changes rate is constant and many transitional forms seen Punctuated Equilibrium (evolution by jerks) evolutionary history shows long periods of no change punctuated by periods of rapid change fossil record shows periods with sudden appearance of many new species. Major environmental events can cause rapid spurts of change/speciation followed by periods of little or no change Reproductive Isolating Mechanisms Pre-zygotic barriers (barriers that prevent fertilization) Post-zygotic barriers (barriers that exist after fertilization that prevent future successful mating) Prezygotic Mechanisms Behavioural: bird songs, mating rituals, pheromones (only attract similar species) Habitat: terrestrial/aquatic, altitude Temporal: different mating seasons Mechanical: anatomically incompatible Gametic Isolation: egg and sperm must recognize each other (e.g. via chemical signals Postzygotic Hybrid Inviability: zygote dies before birth due to genetic incompatibility e.g. sheep & goats – Hybrid Sterility: offspring survives but is sterile (unable to reproduce) e.g. horse + donkey = mule (sterile)
