Descent with Modification Part A: Darwin & Natural Selection Chapter 19 Descent with Modification Part A: Darwin & Natural Selection

What you must know: Several examples of evidence for evolution from different scientific disciplines and how each supports change of populations over time. The difference between structures that are homologous and those that are analogous, and how this relates to evolution. The role of adaptations, variation, time, reproductive success, and heritability in evolution.

Descent with Modification Theme: Evolutionary change is based on the interactions between populations & their environment which results in adaptations (inherited characteristics) to increase fitness Define: Evolution Descent with modification (Darwin) Change over time in the genetic composition of a population from generation to generation

Carolus Linnaeus = founder of taxonomy binomial nomenclature: genus, species Domain – Kingdom – Phylum – Class – Order – Family - Genus – Species Dear King Philip Came Over For Good Spaghetti Classification based on anatomy & morphology Carolus Linnaeus 1707-1778

Slow & subtle changes in organisms  big change Hutton: geologic change results from slow & gradual, continuous process Lyell: Earth’s processes same rate in past & present  therefore Earth is very old Slow & subtle changes in organisms  big change James Hutton 1726-1797 Charles Lyell 1797-1875

Lamarck Published theory of evolution (1809) Jean-Baptiste de Lamarck 1744-1829 Lamarck Published theory of evolution (1809) Use and Disuse: parts of body used  bigger, stronger (eg. giraffe’s neck) Inheritance of Acquired Characteristics: modifications can be passed on Importance: Recognized that species evolve, although explanation was flawed

Charles Darwin (1809-1882) English naturalist 1831: joined the HMS Beagle for a 5-year research voyage around the world Collected and studied plant and animal specimens, bones, fossils Notable stop: Galapagos Islands

Darwin waited 30 years before publishing his ideas on evolution Alfred Russell Wallace – published paper on natural selection first (1858) Charles Darwin (1859): On the Origin of Species by Means of Natural Selection Mechanism for evolution is Natural Selection Darwin didn’t use “evolution”, but rather “descent with modification”

Descent With Modification Organisms descended from an ancestor that lived in the remote past “I think …” (Darwin’s sketch)

Darwin’s Overall Conclusions Variation exists in every population which may have been inherited and the result of a mutation Production of more individuals (overproduction of offspring) than can be supported by the environment leads to a struggle for existence among individuals Only a fraction of offspring survive each generation Survival of the Fittest Adaptation: Individuals who inherit characteristics (adaptations) that are most fit (suitable/favorable) for their environment are likely to leave more offspring than less fit individuals Called fitness High survival = more offspring = more fit Descent with Modification: Over time these adaptations will increase in the population.

Natural Selection Adaptations enhance an organism’s ability to survive and reproduce in specific environments Eg. Desert fox - large ears, arctic fox - small ears

Natural Selection Artificial Selection Nature decides “Man” decides Works on individual Selective breeding Inbreeding occurs eg. beaks eg. dalmations Therefore, if humans can create substantial change over short time, nature can over long time.

Key Ideas of Natural Selection: Competition for limited resources results in differential survival. Evolutionary Fitness: Individuals with more favorable adaptations are more likely to survive and produce more offspring, and pass traits to future generations If environment changes or individuals move to new environment, new adaptations and new species may arise. Populations evolve, not individuals.

Recap main ideas of natural selection: Evolution is change in species over time. There is overproduction of offspring, which leads to competition for resources. Heritable variations exist within a population. These variations can result in differential reproductive success. Over generations, this can result in changes in the genetic composition of the population. Remember: Individuals do NOT evolve! Populations evolve.

Evidence for Evolution: Direct Observations Homology Fossil Record Biogeography

Evidence for Evolution 1. Direct Observations 2. Homology 3. Fossil Record 4. Biogeography

Evidence for Evolution: 1. Direct Observations Examples: Insect populations become resistant to pesticides (DDT) Antibiotic-resistant bacteria (MRSA) Peppered moth (pollution in city vs. country)

The Rise of MRSA (methicillin-resistant Staphylococcus aureus)

Evidence for Evolution: 2. Homology Homology: characteristics in related species can have underlying similarity even though functions may differ Examples: Homologous structures: similar anatomy from common ancestors (eg. forelimbs of human/cat/whale/bat) Embryonic homologies: similar early development (eg. vertebrate embryos with tail & pharyngeal pouches) Vestigial organs: structures w/little or no use (eg. flightless bird wings) Molecular homologies: similar DNA and amino acid sequences

Homologous Structures

Embryonic Development

Vestigial Structures

Molecular Homologies Compare DNA and amino acid sequences

Convergent Evolution Distantly related species can resemble one another Similar problem, similar solutions! Analogous structures: similar structures, function in similar environments Eg. Torpedo shape of shark, penguin, & dolphin

Evidence for Evolution: 3. Fossil Record Fossils = remains or traces of organisms from past Found in sedimentary rock Paleontology: study of fossils Show evolutionary changes that occur over time and origin of major new groups of organisms Ankle bones

Prokaryotes (oldest fossils)  eukaryotes (fish – amphibians – reptiles – birds – mammals) Transitional forms = links to modern species

Evolutionary Tree

Evidence for Evolution: 4. Biogeography Biogeography = geographic distribution of a species Species in nearby geographic areas resemble each other Continental drift and Pangaea explains similarities on different continents Endemic species: found at a certain geographic location and nowhere else Eg. Marine iguanas in the Galapagos

Island Biogeography

Galapagos Tortoises

(evolutionary history) Systematics: classifying organisms and determining their evolutionary relationships Taxonomy (classification) Systematics Phylogenetics (evolutionary history)

Morphology (homologous structures) Tools used to determine evolutionary relationships: Fossils Morphology (homologous structures) Molecular evidence (DNA, amino acids) Who is more closely related? Animals and fungi are more closely related than either is to plants.

What kind of organism is this? Legless conditions evolved separately  analogous structures evolved by convergent evolution What kind of organism is this?

Taxonomy: classifying and naming organisms Ordered division of organisms based on similar/different characteristics Dear King Philip Came Over For Good Spaghetti Each category at any level is called a taxon.

Binomial nomenclature (Genus species) Naming system developed by Carolus Linnaeus

Phylogenetic Tree Branching diagram that shows evolutionary history of a group of organisms

Branch lengths can represent genetic change

Branch lengths can indicate time

Constructing Phylogenetic Trees Divergent vs. Convergent Evolution Sorting homology from analogy

Cladogram: diagram that depicts patterns of shared characteristics among groups Clade = group of species that includes an ancestral species + all descendents Shared derived characteristics (evolutionary novelties) are used to construct cladograms Turtle Leopard Hair Amniotic egg Four walking legs Hinged jaws Vertebral column Salamander Tuna Lamprey Lancelet (outgroup) Cladogram Shared ancestral characteristic (of all vertebrates) = vertebral column Shared derived characteristic of mammals = hair

Constructing a phylogenetic tree A 0 indicates a character is absent; a 1 indicates that a character is present.

Draw a phylogenetic tree based on the data below Draw a phylogenetic tree based on the data below. Draw hatch marks on the tree to indicate the origin(s) of each of the 6 characters.

Answer:

Principle of maximum parsimony: use simplest explanation (fewest DNA changes) to construct phylogenetic tree – “keep it simple” The first tree is the most parsimonious  fewest changes in bases

Molecular clock for mammals Molecular clocks: measure evolutionary change based on regions of genome that appear to evolve at constant rates Estimate date of past evolutionary events Eg. Origin of HIV infection in humans= 1930’s Molecular clock for mammals Origin of HIV-1 M

3 Domains: Bacteria, Archaea, Eukarya Tree of Life 3 Domains: Bacteria, Archaea, Eukarya Based on sequence data for rRNA and other genes

Common Ancestry of All Life Forms Elements conserved across all 3 domains: DNA and RNA are carriers of genetic info Universal genetic code (codons  amino acids) Conserved metabolic pathways

Conserved elements in Eukaryotes: Cytoskeleton Membrane-bound organelles Linear chromosomes Endomembrane systems (including nuclear envelope)

Horizontal Gene Transfer Movement of genes between different domains Exchange of transposable elements, plasmids, viral infections, fusion of organisms Trees are complex! Phylogenetic trees are hypotheses subject to change based on available data