Evolution
Theory of Evolution Theory a well supported testable explanation of phenomenon occurring in the natural world. Evolution the process by which modern organisms changed over time from ancient common ancestors. Microevolution change in allele frequency in populations over generations. Macroevolution large scale change, such as the formation of new species.
Summary: Theory of Evolution Species are different due to variation in their genes (variation results from random mutation). Some individuals are better suited for survival, and will leave more offspring (natural selection or survival of the fittest ). Over time, change within species leads to the replacement of old species by new species as less successful species becomes extinct. There is clear evidence from fossils, anatomy, physiology, DNA, and embryology that the species now on Earth have evolved from ancestors that are now extinct.
3 Patterns of Biological Diversity Species group of similar organisms that can breed and produce fertile offspring. 1. Species vary globally different yet ecologically similar animals are found in different yet similar environments. 2. Species vary locally different yet related species occupy different habitats in one area. 3. Species vary over time fossils of extinct species are similar to current species.
Artificial Selection Artificial Selection nature provides variation (variety) in organisms traits, but humans choose to breed those organisms that have the most useful traits. Example: humans breed cows that produce the most milk. Example: humans breed trees that create the most fruit.
Natural Selection Darwin proposed a mechanism for evolution that he called natural selection. Individuals whose characteristics are well-suited to their environment survive and reproduce. By surviving, these attributes can be passed onto their children, causing an increase of these traits in the species population, thus causing a gradual change in the characteristics of the population. Individuals whose characteristics are not well-suited to their environment die, or leave few offspring. Because natural selection favors a certain trait over others, more individuals in the population carry the genes for that trait. AKA: survival of the fittest
Parameters of Evolution by NS 1. Struggle for existence more organisms are produced than can survive. Competition individuals or groups of organisms compete for similar resources (territory, mates, food, water, etc.) in the same environment. 2. Variation and adaptation some variations are better suited. Adaptation heritable characteristic that increases an organism s ability to survive and reproduce. 3. Survival of the fittest individuals with adaptations that are well suited to their environment survive and reproduce. Fitness measure of how well an organism survives/reproduces.
Common Descent Common descent all species (living and extinct) descended from a common ancestor. Over many generations, adaptations caused a successful species to evolve into a new species. The fossil record provides evidence for this descent with modification.
Patterns of Evolution Divergent evolution single species or group of species evolve over a short period of time into different forms living in different ways due to a change in environment that makes new resources available. Aka adaptive radiations Ex. Dinosaurs, Darwin s finches. Convergent evolution similar structures are produced in distantly related organisms. Ex. Mammals that feed on ants/termites evolved independently 5 times. Coevolution 2 species respond to changes in each other over time. Neither can survive without the other.
Evidence for Evolution includes: 1. Geographic distribution of species 2. Fossils 3. Anatomy (homologous structures) 4. Physiology (analogous structures) 5. Embryology 6. Universal genetic code 7. Biochemical homology
1. Geographic Distribution of Species Species of animals on different continents had similar structures and behaviors. Darwin theorized that animals on each continent were living under similar ecological conditions and were exposed to natural selection in a similar way. Similar selection pressures caused animals to evolve common features.
2. Fossils A fossil is the preserved or mineralized remains (bone, tooth, shell) or trace of an organism that lived long ago. Fossils show evidence that support the ancestry between species. Fossils trace the evolution of modern species from extinct ancestors. Example: Fossils have shown that whales evolved from four legged land mammals; 1990 s transitional forms of whales found.
3. Anatomy Evolutionary relationships can be viewed by studying and comparing anatomy. Scientists view the anatomy of limbs and see common similarities. Over course of evolution, vertebrates moved into environments causing different survival needs. Homologous structures parts of different organisms (that are often quite dissimilar) that developed from the same ancestral body parts. Forelimbs of whales, bats, crocodiles, and chickens have similar anatomy but are modified for different functions common ancestry. Are similar in structure but differ in function!
Homologous structures -differ in function, similar in structure
4. Physiology Analogous structures -- structures that are similar in appearance and function but have different origins and usually different internal structures. Examples: a bat s wing and a insect s wing--both are wings and both are used for flight, but a bat has bones and an insect does not. Analagous Structures -differ in structure, similar in function
Vestigial structures any body structure that has reduced or no body function. Examples: A human s appendix; a whale s pelvis. As species adapt to environments the change in form and behavior and continue to inherit these structures as part of the body even though they have no function.
5. Embryology Embryology shows links between different species. Embryos of different species in early development are indistinguishable from each other. Common cells and tissues develop in similar patterns in all vertebrates. Illustrates descent from a common ancestor.
6. Universal Genetic Code Genetic code mrna codons specify particular amino acids. The genetic code of all organisms on Earth (bacteria, yeast, fruit flies, humans) is the same! Example: the AUG codon always codes for the amino acid methionine.
7. Biochemical Homology Similar DNA, RNA, and amino acid sequences amongst species in same taxonomic group. Remember comparing your insulin gene DNA and amino acid sequences to that of a cow? Allele Frequencies Population mating group of organisms of the same species. Gene pool all genes (and their alleles) present in a population. Allele frequency - # of times allele occurs in a population. Changes as population evolves over time. Natural selection operates on individuals, but causes a change in the allele frequency.
Mutations: -Sources of Genetic Variation The main source of genetic variations in populations is mutations!!!! These mutations occur randomly. Not all mutations affect an organism s fitness. Only heritable mutations matter for evolution. Neutral mutations don t change phenotypes. Other sources of variation include: 1.Genetic recombination during crossing over and independent assortment in meiosis.
NS and Phenotype An organism s genotype and environmental conditions makes up its phenotype. Natural selection operates on variation in organisms phenotypes. Higher fitness = phenotypes better suited for the environment.
Types of Selection in Populations When NS on polygenic traits affects the fitness of phenotypes, it leads to selection: Directional Selection organisms at one end of the curve have a higher fitness than those in the middle or at the other end. Stabilizing Selection organisms in the center have highest fitness. Disruptive Selection organisms at the ends of curve have highest fitness.
Other Source of Changes in Allele Frequencies Genetic drift change in allele frequency that occurs in small populations due to random chance. Genetic bottleneck change in allele frequency following a dramatic reduction in population size. Founder effect change in allele frequency following migration of a small subgroup out of the population to start a new population.
Macroevolution and Speciation Species population of organisms that can interbreed. Speciation evolution/formation of a new species. When environments change, the process of evolution enables some species to adapt to new conditions and thrive while some species fail to adapt and become extinct. Niche - combination of an organism s profession and place where it lives. No 2 species can occupy the same niche in the same location for a long period of time! The more efficient species will survive and reproduce driving the other to extinction.
Isolating Mechanisms of Speciation Reproductive isolation occurs when 2 populations can t interbreed - causes speciation! Once reproductive isolation occurs, natural selection increases the differences between the separated populations. 1. Behavioral isolation different courtship. 2. Ecological/habitat isolation can only mate in specific or preferred habitats. 3. Mechanical isolation no sperm is transferred. 4. Gametic isolation no fertilization of egg occurs. 5. Temporal isolation reproduce at different times. Geographic isolation population becomes divided (isolated) by a physical barrier.
Rates of Speciation Gradualism slow, steady change leading to new species. Punctuated equilibrium brief periods of rapid change leads to the formation of new species. Rapid change occurs when a small population is isolated from the rest of the population or migrates.