Darwin and Natural Selection Was from England. Beagle Expedition: found unique species that looked similar to species from other parts of the world. Found that many of the plants and animals on Galapagos resembled those in nearby South America Voyage of the HMS Beagle The Origin of the Species On The Origin of Species by Means of Natural Selection Nov. 1859 Charles Darwin Darwin suggested that humans are related to apes Other scientist Lamarck believed that over the lifetime of an individual, physical features increase in size because of use and decrease from nonuse Malthus suggested that human pops. do not grow unchecked because death caused by disease, war, and famine slows growth Natural Selection Natural selection: organisms with favorable traits for a particular environment survive, reproduce, and pass these traits on to the next generation (those with less favorable traits are less likely to survive). Adaptation- inherited trait that has become common in a population because the trait provides a selective advantage Evolution of Humans The Descent of Man, and Selection in Relation to Sex Charles Darwin 1871 Darwin outlined sexual selection to explain the evolution of humans 4 Tenets of Natural Selection All populations have genetic variation. The environment presents challenges to successful reproduction. Individuals tend to produce more offspring than the environment can support. Individuals that are better fit their environment tend to live longer, reproduce more, and spread their genes throughout the population. Darwin’s 4 Facts Exponential Growth of Populations Factors will prevent Exponential Growth(Steady State) Variability among species Traits are inheritable Darwin’s 2 Inferences Competition for resources Individuals most fit for their environment will survive. Sources of Genetic Variation Mutation/ Translocation- Mutation slowly introduces new alleles which natural selection helps distribute (can be harmful, beneficial or have no significance) Crossing Over- exchange of homologous chromosome segments Independent Assortment- assortment of chromosomes Sexual Reproduction- combination of allelles of two individuals Immigration- incoming allelles to a gene pool Mechanisms for Evolutionary Change Natural Selection Population Genetics and Evolution Populations evolve when natural selection causes changes in their allele distribution. Natural selection causes the greatest changes to populations’ gene pools, but is not the only cause of change Gene Pool- all the alleles of a population of a species In a population’s gene pool, each allele has a certain frequency which governs the frequency of phenotypes If a population’s allele frequencies do not change, it is not evolving and is said to be in genetic equilibrium Individuals don’t evolve, populations of species do! Other Influences on the Gene Pool In small populations, change events (crossing over, translation errors) can cause shifts in a gene pool = genetic drift Individuals may move into or out of a population, bringing or taking alleles with them = migration Population Evolution Gene flow-the movement of genes into or out of a population due to interbreeding. Immigration- the flow of alleles into a population. Emigration-the flow of alleles out of a population. Genetic drift- the random change of allele frequency in a population, not due to natural selection. Population Evolution Artificial selection- a process in which humans consciously select for or against particular features in organisms. Genetic bottleneck-an event in which the populations’ size is greatly reduced; reduces genetic variability Founder effect-changes in gene frequency from starting a new population from a small number of individuals; reduces genetic variability. Adaptations Structural: Can change the size and/or shape of a body part For example: thorns, wings, mimicry (copy the appearance of another species), camouflage (blend in with environment) Change within a population over time (anywhere from 100 years to millions of years) depending on type of adaptation, rate of reproduction and environmental factors Physiological Help populations overcome chemicals they encounter (antibiotics, pesticides, herbicides, etc) Develop rapidly (example: bacterial resistance to penicillin) Evidence for Evolution Fossils Anatomical relationships Embryological development Genetic comparisons Fossils Fossils can help provide a record for life However, the fossil record is incomplete there are large gaps - therefore each and every step of evolution can not be followed Scientists need to find intermediate species - and once they do, they can provide us with a step by step sequence of evolution Anatomical Comparisons Homologous Same form, different use Indication of common evolutionary ancestor Vestigial structures structures Evolutionary remnants of structures that were important in a past ancestor Embryological Development There are noted similarities between the embryological development of all vertebrates (fish, chicken, rabbit, human, etc) Presence of gills and tails in all supports evidence that gill-breathing vertebrates preceded air-breathing, terrestrial species Genetic Comparisons All living things use DNA. All living things use the same genetic code. Can show relationships between species (human and chimpanzee DNA are 99% identical and are closer than chimpanzees are to apes) Can help reveal when species diverged from their ancestral types Types of Natural Selection Stabilizing Selection - favors average traits (average sized spiders fair better than both large and small) Directional Selection - favors one extreme of a trait (the longer the beak the better) Disruptive Selection - favors both extremes of a trait (intermediate at disadvantage - often eliminated) Evolution of a Species = Speciation Species = group of organisms that look alike and have the ability to interbreed and produce fertile offspring in nature Speciation occurs when Interbreeding is prevented Production of fertile offspring is prevented Causes of Speciation Isolation of populations - Two populations of the same species do not mate because of some form of separation If populations can’t interbreed due to isolation, their allele frequencies can become more and more different from each other Each population will adapt to its environment, eventually preventing breeding with members of other populations (reproductive isolation) Changes in chromosome number causes instantaneous speciation Most speciation happens gradually Types of Isolation Geographic- geographic barriers form that separate two populations. Ecological- different environmental factors may cause isolation (wet vs. dry, soil conditions, etc.) Reproductive- mating structures and behaviors may isolate two populations Temporal- two populations may reproduce at different times Types of Evolution Divergence (ex: adaptive radiation); Single populations splits to adapt to different environments Convergence Unrelated species become similar as they adapt to a similar environment. Analogous structures • Same use, different form • Not evidence of a common evolutionary ancestor Rate of Speciation Fossil record suggests the rate is variable Gradualism: slow, steady process of change Punctuated equilibrium: long periods of genetic stability punctuated by rapid changes to new environmental conditions Pace of Evolution Gradualism- the pace of natural selection is gradual change. Punctuated Equilibrium- model of evolutions that states there are differing periods of rapid change and periods of little to no change. Why? What could cause this?