Bio 160 Unit 5-1

1. Bio 160Unit 5-1 Week Five – Lecture One

2. The beginnings of the theory of evolution • Darwinism • Darwin put forth the idea that species change over time and that living species have arisen from earlier life forms • These were NOT new ideas, proposed many times over many centuries • The idea that species were fixed was put out by Aristotle and later picked up and set forward by Judeo-Christian, western culture and has been propagated by the western church • Even within the dogma of the church, questions were still asked

3. Darwin believed the early theories of plate geology as set forth by the fossil record and used it to explain the similarity of his fossil findings during his voyage on H.M.S. Beagle • The book On the Origin of Species by Means of Natural Selection put forth the fossil evidence of his findings, his theories on evolution and an explanation of evolution via natural selection • Darwin never denied the existence of a Divine Creator – argued how things changed, not who changed them, and never put forth that humans came from monkeys – only noted common structural features

4. Fossil record records evolutionary adaptations • 2 categories of adaptations: evolutionary and ecological • Evolutionary adaptations are inherited by a species over time to enhance that organism’s ability to survive and reproduce in a particular environment • Ecological adaptations occur to individuals in a short period of time to enhance survivorship

5. Evolutionary adaptations are recorded in fossil records • Fossils are laid down in layers of sedimentary rock • As layers pile up, sediment is compressed into rock, trapping the hard tissue remains of organisms in it • The rock can be dated, or given a place in the chronological order of time, so fossils can also be dated

6. Evidence to support theory of evolution • Word evolution = change over time – once again, it is how, not who! • Biogeography – the geographical distribution of species around the planet • Must look at how the world was, not as it is now • Comparative anatomy – comparison of the anatomical structures of different species • The order of nature is to be conservatory therefore every structure, at one time, had a function • Since many of the structures are very similar, they once had a function and came from a common genetic ancestor • These structures are homologous structures, having different functions now but a common ancestor • Remember the homeotic genes!

7. Comparative embryology – comparing different structures that appear during the development of different organisms • common development indicates common ancestry • Molecular biology – looking at common genes and gene sequences • Homeotic genes • Evolutionary relationships

8. Natural selection proposed as basic mechanism driving evolution • Natural selection states that reproduction is not equal. Some have better strategies than others. • Individuals that best meet specific environmental demands have the greatest reproductive success, allowing the favorable traits to be represented more and the unfavorable ones less and less • Artificial selection done through human’s using selective breeding mechanisms in other organisms lends proof

9. Natural selection tends to be regional and timely, adapting organisms to their local environment • Evolutionary changes can happen in a fairly short amount of time

10. Population genetics and evolution • Modern synthesis theory suggests that populations are the units used in evolution and changes are made in populations through genetics • A population is a group of individuals living in the same place at the same time • A population is the smallest unit that can evolve • Evolution is a change in the frequency of certain heritable traits over successive generations and can be measured

11. Sexual species – a group of populations whose individuals have the potential to interbreed and produce fertile offspring • Looking at the evolutions in a population focuses on the gene pool, the total collection of genes in a population at any time • The gene frequencies over generations can be mapped and measured • In an idealistic population, Hardy-Weinberg equilibrium can be expected • Hardy-Weinberg equilibrium says that the shuffling of genes that occurs during sexual reproduction can not, by itself, change the overall genetic make-up of a population

12. Assumptions are made that the population is an idealized, non-evolving population that remains constant over the generations • Such populations do not occur in real life. However, the H-W, equation does allow for tracking the allele frequencies in real populations to map evolutionary trends • Population must be very large • Population is totally isolated • Mutations do not alter gene pool • Mating is random

13. 5 potential causes of population evolution • Genetic drift – change in gene pool of a small population due to chance • A population must be infinitely large to eliminate genetic drift as an evolutionary agent • Will be more noticeable in a smaller population • Bottleneck effect – genetic drift resulting from an event that drastically reduces pop. size • Founder effect – random changes that occur in a small colony of a larger population

14. Gene flow – the gain of loss of alleles in a population by the movement of individuals or gametes • Fertile individuals move in or out of a population, or when pollen or other gametes are transferred from one population to another • Tends to reduce genetic differences between populations • Mutations – a random change in an organism’s DNA that creates a new allele • Does not have much of an effect in a large population • Over long-term, highly vital to evolution because it is the only force that can produce new alleles

15. Nonrandom mating • In most populations mating is selective or localized • Natural selection – only the genetic component of variation can lead to evolution as a result of natural selection

16. Natural selection and variations • Variation is extensive in most populations • Some variation is a product of polygenetic inheritance • Population is polymorphic for a characteristic if 2 or more forms (morphs) of that characteristic are noticeably present • Cline – a gradient of change in an inherited characteristic along a geographical continuum • Random producers of genetic variation • Mutation – usually more harmful than good • Prokaryotes – can evolve rapidly through mutations alone • Sexual recombination – fresh combinations of existing alleles arise in every generation

17. 3 random components of sexual recombination • Independent assortment of homologous chms. during meiosis • Crossing over during meiosis • Random fertilization of egg by sperm • Natural selection sometimes gives a heterozygous advantage • Neutral variation – a variation that provides no apparent selective advantage – very hard to measure • Evolutionary fitness – the contribution an individual makes to the gene pool of the next generation relative to the contribution of other individuals “He who passes on the most wins”

18. Natural selection does not favor genotypes directly, but does allow for selection for phenotypes that selects for specific genotypes • The fitness of any one gene depends on the other genes around it, therefore natural selection selects for whole genomes as it targets whole phenotypes • 3 main modes of natural selection • Stabilizing selection favors intermediate variants • Occurs in relatively stable environments were conditions tend to reduce phenotypic variations

19. Directional selection – shifts overall make-up by acting against one end of phenotypic extremes • Most common during periods of environmental change or new habitat migration • Responsible for producing resistant pests and parasites • Diversifying selection – favors conditions at both ends of phenotypic extremes, not the intermediate • Happens where environmental conditions are widely varied

20. Origin of species • Taxonomy – the classifying and naming of organisms – is based on many different species • Two different ideas try to account for the species gap • Biological species concept – defines a species as populations whose members may interbreed and produce fertile offspring. If 2 interbreed and can not produce fertile offspring, it is failure in sexual reproduction, preventing gene flow and creating the species gap • Does not work in all cases • Can not define extinct species • Does not apply well for asexually reproducing species • Some gene pools are not physically isolated from each other but still do not interbreed, but still may experience some roundabout gene influence • May simply just not have enough info about

21. Evolutionary species concept – defines a species as a cluster of organisms that represent a lineage of decent • Depends on finding unique diagnostic features to separate clusters and their lineage • Main criterion is that a cluster and its unique lineage are clearly recognizable as distinct • Reproductive barriers to keep species separate • Reproductive barriers – biological feature of the organism • Pre-zygotic barriers prevent mating • Temporal isolation – breeding seasons are different • Habitat isolation – species live in same area but not the same exact habitat

22. Behavioral isolation – little or no attraction between different sexes of different species • Mechanical isolation – sex organs are not compatible • Gametic isolation- male and female from different species may copulate, but gametes do not unite to form a zygote • Postzygotic barriers – operate after hybrid zygotes are formed • Hybrid inviability – genes of 2 parent species are not compatible and zygote will not survive • Hybrid sterility – hybrid reaches maturity but can not reproduce itself • Hybrid breakdown – first generation hybrids are fertile and produce offspring, but offspring does not survive

23. Geographical barriers – isolation of gene pools • Allopatric speciation – the formation of a new species as a result of an ancestral population becoming separated and isolated by a geographic barrier • Speciation only occurs when the gene pool undergoes changes that introduce reproductive barriers • Likelihood increases in small and isolated pops • Adaptive radiation – an ancestral population radiates out to new and diverse environments, creating speciation

24. Sympatric speciation does not involve geographical isolation • Speciation happens in a single generation if genetic change produces a reproductive barrier between mutants and parent populations • Important in plant speciation • Models of interpreting the timing of the fossil record • Gradualist model – populations evolve differences gradually as they become adapted to their local environments • Evolutionary changes occur by the steady accumulation of many small ones, evolving gradually from the ancestral populations

25. Punctuated equilibrium – states that speciation occurs in spurts, followed by long periods of little change • Small, isolated populations diverge from the ancestral lineage in a relatively brief period of time. The butterflies look the same at the top their branch as they do at the bottom of the branch • “Abrupt” is a relative term in the expanse of time • Fossil record suggests that a species “last” a few million years on average • Both models are useful in interpreting the fossil record, which indicates both models are valid