Evidence for Evolution PDF

Unit 1: Evolution, Bacteria, Archaea, and Eukaryotes Evidence for Evolution  Lecture Outline A. Intro to Evolution a. Diversity of Life b. Evolution explains the diversity of life c. Mechanisms of Evolution d. Microevolution and Macroevolu...

Unit 1: Evolution, Bacteria, Archaea, and Eukaryotes Evidence for Evolution  Lecture Outline A. Intro to Evolution a. Diversity of Life b. Evolution explains the diversity of life c. Mechanisms of Evolution d. Microevolution and Macroevolution e. Darwin and Wallace B. Evidence for evolution a. Fossil record a. Evolution of tetrapods b. Evolution of whales b. Homologous structures c. Convergent evolution d. Developmental homologies e. Molecular Homologies f. Biogeography Evolution explains the diversity of life  Diversity of life All living organisms can be broadly classified into two kinds of organisms, based on cell structure: Prokaryotes: organisms whose cells do not possess a nucleus or (for the most part) other organelles The term “prokaryotes” is only useful when referring to cell structure, not evolutionary relationships Eukaryotes: organisms whose cells posses a nucleus and other organelles 1.24 million species catalogued, but estimated as many as 8.74 million alive today Mind blow: over 99% of the species that ever lived have gone extinct! Prokaryotes Eukaryotes  Evolution explains how the diversity of life arose So how did this vast diversity arise?! Evidence from astronomy, geology, chemistry and biology strongly suggests that living organisms arose ~3.7 billion years ago and have been evolving over billions of years, giving rise to all organisms that have ever existed Evolution is descent with modification Closely related species descend from a common ancestor and change over time Over time, evolution produces groups of organisms whose relationships can be depicted on a kind of family tree called a phylogenetic tree On the right is a phylogenetic tree of all the major groups of organisms All organisms share a common ancestor ~3.7 billion years ago  Mechanisms of evolution What is causing or driving evolution? Natural selection, genetic drift, gene flow, sexual selection (more on these later) Referred to as mechanisms, drivers, or forces of evolution If evolution were a bus: drivers: natural selection, sexual selection, genetic drift, and gene flow fuel: mutations tracks left behind: the branches on a phylogenetic tree Great ape phylogenetic tree  Microevolution and Macroevolution At its simplest, evolution is a change in a population over time Population: a group of organisms of the same species in a specific area Change in the genotype (genetic level) which affects phenotype (physical level) Microevolution is the change in the trait and allele frequencies in a population The result of natural selection and other mechanisms of evolution Macroevolution is the evolution of new species, new traits, and new kinds of organisms The result of microevolution + new mutations + lots and lots of time https://www.evogeneao.com/explore/tree-of-life-explorer Darwin and Wallace: Fathers of Modern Evolutionary Thought Charles Darwin and Alfred Wallace (1840’s) – influenced by Thomas Malthus’ and Charles Lyell’s work, simultaneously proprosed two ideas natural selection: a mechanism for how evolution occurs common descent: an inference that proposes all living things are related and share one comon ancestor Charles Darwin Alfred Wallace  Darwin on evolution "As many more individuals of each species are born than can possibly survive; and as, consequently, there is a frequently recurring struggle for existence, it follows that any being, if it vary however slightly in any manner profitable to itself, under the complex and sometimes varying conditions of life, will have a better chance of surviving, and thus be naturally selected. From the strong principle of inheritance, any selected variety will tend to propagate its new and modified form." - Charles Darwin, On the Origin of the Species "Therefore I should infer from analogy that probably all the organic beings which have ever lived on this earth have descended from some one primordial form, into which life was first breathed." - Charles Darwin, On the Origin of the Species, p. 484 Evidence of Evolution  Evidence for evolution The following lines of evidence support evolution because they are exactly what we would expect to see if evolution were true. We will examine evidence from the fossil record homologous structures convergent evolution developmental homologies molecular homologies biogeography  Fossil record: evolution of tetrapods from fish Fossils are still the only way to uncover and identify ancestral organisms By arranging fossils of closely related organisms by date, one can reconstruct possible evolutionary scenarios Below is an example of a possible scenario for the evolution of tetrapods from ancient fish The Tiktaalik is a transitional form because it possesses intermediate features between those of fish and tetrapods: its skull and its wrists The progression of forelimbs from fish to early tetrapods Tiktaalik rosea fossil Tiktaalik rosea reconstruction  Fossil record: evolution of whales from land mammals Below is a possible evolutionary scenario of cetaceansrevealing that modern whales evolved from land mammals As cetaceans evolve, nostrils can be seen progressively moving to the top of the skull, giving rise to blowholes in present-day whales (Bryde‘s whale)  Fossil record: evolution of whales from land mammals The fossil record also shows the progressive loss of hind-limbs in whales Some extant whales possess vestigial hips, which supports the model that whales evolved from land-dwelling mammals Vestigial structures are structures derived from an ancestor that no longer possess the original function of the ancestral structure (typically degenerated) (Bryde‘s whale) Fossil record: evolution of whales from land mammals https://youtu.be/lIEoO5KdPvg  Homologies A homology is a similarity in two or more organisms that is derived/ inherited from their common ancestor Homologies can exist at the structural or molecular level Structural homologies are similarities between external (scales, feathers, hair, etc.) or internal (bones, teeth, etc.) structures of two or more organisms Developmental homologies are structural homologies that appear only during embryonic development Molecular homologies are similarities between the nucleotide sequence (DNA) or amino acid sequence (protein) of two or more organisms Similarities in bone structure of Similarities in amino acid sequence of the p53 protein of different forelimbs of different organisms organisms  Structural homologies As evolution would predict, species that are closely related share a greater number of similar structures/traits than species that are distantly related These similarities are derived from their common ancestor and are referred to as homologous structures/traits (contrast with analogous structures on next slide) Thus, homologous structures are evidence of relatedness For example, the forearms of tetrapods, while serving different functions, possess homologous forearm bones that were derived from their common tetrapod ancestor  Convergent evolution Not all similar traits are evidence of relatedness… similar traits may evolve independently in different lineages These traits are referred to as analogous structures/traits and make it difficult to determine relatedness of organisms Analogous structures arise when similar selective pressures select for similar traits in different organisms, a phenomenon called convergent evolution Example: the streamlined body of sharks and dolphins are analogous traits that evolved independently in each lineage via convergent evolution Vertebrates Tetrapods Mammals = evolution of streamlined bodies  Convergent evolution Another classic example of convergent evolution is bioluminescence Bioluminescence is the ability of living organisms to produce light to attract mates, prey, or beneficial organisms When comparing bioluminescent organisms, it becomes clear that bioluminescence has evolved independently in hundreds of different organisms Bioluminescent fireflies Bioluminescent fungi Bioluminescent phytoplankton  Homologous vs Analogous Features It helps to think of family trees when thinking about evolution Homologous traits are similar traits derived from a common ancestor Like similar traits in siblings – derived from common ancestor (parents) Analogous traits are similar traits that were not present in the common ancestor that arose independently in each lineage Like your celebrity doppelganger – not derived from common ancestor, instead, arose independently Siblings: Chris and Liam Hemsworth Doppelgangers: Alejandro D’Brot and Pavarotti  Developmental Homologies Related organisms share considerable structural homologies during embryonic development which often give rise to entirely different structures in the adult stages Example: All vertebrate embryos (including humans) exhibit pharyngeal arches (green) and a bony tail (blue) as embryos, which give rise to different structures Summed up by the phrase “ontogeny recapitulates phylogeny” – the ancestral lineage of an organism is seen throughout its fetal development Human embryo at 4 weeks Human embryo at 4 weeks Early-stage skate embryo  Molecular Homologies Molecular homologies are similarities between the nucleotide sequence (DNA) or amino acid sequence (protein) of two or more organisms Organisms that are more closely related (and therefore share a more recent common ancestor) will share a greater similarity of DNA sequences or protein sequences Just what you would expect if evolution were true! Look at the chart below comparing the percentage of identical amino acids between the p53 protein in humans and the p53 protein in other organisms. Which are more closely related to humans: chickens or dogs?  Evidence from Molecular Homology The great ape phylogenetic tree shown below was created by comparing the nucleotide sequence of protein-coding genes of great apes The phylogenetic tree built using molecular data is consistent with the phylogenetic tree built with the morphological data More recently, scientists have been able to sequence DNA from Neanderthals and Denisovans (extinct human relatives) and, not surprisingly, human DNA is more similar to Neanderthal and Denisovan DNA than it is to chimp DNA  Biogeography Biogeography is the multi-disciplinary study of the distribution of organisms across space and time The geographical distribution of organisms is what you would expect if organisms were evolving along with continental drift Example: why do marsupials exist only in Australia and South America? Fossil and genetic evidence suggest all extant marsupials descend from a common ancestor in South America Some of these marsupials migrated to Australia ~50 million years ago via Antarctica while they were connected Marsupial distribution Marsupial migration present day ~50 million years ago  Island biogeography As evolution would predict, organisms that become stranded on islands evolve to become different than their mainland counterparts Why? Climate, resources, and predators on islands are different than those of the mainland, which influence the evolution of these organisms vs Chaco tortoise from Chile Galapagos giant tortoise (closest relative) vs Lace monitor from Australia Komodo dragon (closest relative)