Week 3 Evolution PDF

NATS113|MCDR LESSON OBJECTIVES NATS113|MCDR Origins of Evolutionary ideas How intellectuals formed ideas of evolution as we know today. NATS113|MCDR +A new era of biology began in 1859 when Charles Darwin published The Origin of...

NATS113|MCDR LESSON OBJECTIVES NATS113|MCDR Origins of Evolutionary ideas How intellectuals formed ideas of evolution as we know today. NATS113|MCDR +A new era of biology began in 1859 when Charles Darwin published The Origin of Species which focused biologists’ attention on the great diversity of organisms. +Darwin noted that current species are descendants of ancestral species. +Evolution can be defined by Darwin’s phrase: descent with modification. +Evolution can be viewed as both a pattern and a process. NATS113|MCDR NATS113|MCDR IMPORTNANT NAMES IN EVOLUTION + Carolus Linnaeus was the founder of taxonomy, the branch of biology concerned with classifying organisms. + Paleontology, the study of fossils, was largely developed by French scientist Georges Cuvier. + The study of fossils helped to lay the groundwork for Darwin’s ideas. + Fossils are remains or traces of organisms from the past, usually found in sedimentary rock, which appears in layers or strata. + Lamarck hypothesized that species evolve through use and disuse of body parts and the inheritance of acquired characteristics. NATS113|MCDR During his travels on the Beagle, Darwin collected specimens of South American plants and animals. He observed adaptations of plants and animals that inhabited many diverse environments. NATS113|MCDR DARWIN’S FOCUS ON ADAPTATION + Darwin’s interest in geographic distribution of species was kindled by a stop at the Galápagos Islands near the equator west of South America. + Darwin perceived adaptation to the environment and the origin of new species as closely related processes. + Recent biologists have concluded that speciation is indeed what happened to the Galápagos finches. NATS113|MCDR On the Origin of Species: +Darwin developed two main ideas: + Descent with modification explains life’s unity and diversity. + Natural selection is a cause of adaptive evolution. +Darwin noted that humans have modified other species by selecting and breeding individuals with desired traits, a process called artificial selection. +Darwin then described four observations of nature and from these drew two inferences. NATS113|MCDR  DARWIN’S OBSERVATIONS + Observation #1: Members of a population often vary greatly in their traits. + Observation #2: Traits are inherited from parents to offspring. + Observation #3: All species are capable of producing more offspring than the environment can support. + Observation #4: Overproduction leads to competition for food or other resources. + The individuals best adapted to their environment will survive and reproduce. NATS113|MCDR INTERFERENCES: DESCENT WITH MODIFICATION +Inference #1: Individuals whose + Darwin was influenced by Thomas inherited traits give them a higher Malthus who noted the potential for probability of surviving and human population to increase faster than food supplies and other reproducing in a given resources. environment tend to leave more + If some heritable traits are offspring than other individuals. advantageous, these will accumulate in the population, and this will +Inference #2: This unequal ability increase the frequency of individuals of individuals to survive and with those adaptations. reproduce will lead to the + This process explains the match accumulation of favorable traits in between organisms and their environment. the population over generations. NATS113|MCDR  Evidences of Evolution Biogeography, Fossil Records, DNA sequences, Homology and Embryology NATS113|MCDR 1 FOSSILS NATS113|MCDR 2 ANATOMICAL AND MOLECULAR HOMOLOGIES NATS113|MCDR 2 NATS113|MCDR  Convergent evolution is the evolution of similar, or analogous, features in distantly related groups. Analogous traits arise when groups independently adapt to similar environments in similar ways. The Darwinian concept of an evolutionary tree of life can explain homologies. Evolutionary trees are hypotheses about the relationships among different groups. NATS113|MCDR  3 BIOGEOGRAPHY Darwin’s observations of biogeography, the geographic distribution of species, formed an important part of his theory of evolution. ❑ Islands have many endemic species (found only in that part of the world and nowhere else). Darwin postulated that endemic species are often closely to species on the nearest mainland or island. ❑ Earth’s continents were formerly united in a single large continent called Pangaea, but have since separated by continental drift. ❑ An understanding of continent movement and modern distribution of species allows us to predict when and where different groups evolved. NATS113|MCDR Mechanisms of Evolution Artificial and natural selection, genetic drift and mutation NATS113|MCDR Overview: The Smallest Unit of Evolution Natural selection acts on individuals, but only populations evolve. +Genetic variations in populations contribute to evolution. +Microevolution is a change in allele frequencies in a population over generations. +Two processes, mutation and sexual reproduction, produce the variation in gene pools that contributes to differences among individuals.  1 Mutation +The effects of point mutations can vary: +Mutations in noncoding regions of DNA are often harmless. +Mutations are changes in the +Mutations in a gene might not nucleotide sequence of DNA. affect protein production because of redundancy in the genetic code. +Mutations cause new genes +Mutations that result in a change and alleles to arise. in protein production are often harmful. +Only mutations in cells that +Mutations that result in a change produce gametes can be in protein production can passed to offspring. sometimes increase the fitness of the organism in its environment. +A point mutation is a change in one base in a gene. 2 Sexual Reproduction +Sexual reproduction can shuffle existing alleles into new combinations. +In organisms that reproduce sexually, recombination of alleles is more important than mutation in producing the genetic differences that make adaptation possible. Hardy-Weinberg equation tests whether a sexually reproducing population is evolving A population is a localized The five conditions for group of individuals (a species nonevolving in an area) capable of interbreeding and producing populations are rarely fertile offspring. met in nature: +A gene pool consists of all the No mutations alleles for all loci in a Random mating population. No natural selection +A locus is fixed if all individuals Extremely large in a population are population homozygous for the same No gene flow allele. 3 Natural selection, genetic drift, and gene flow can alter allele frequencies in a population Three major factors alter allele frequencies and bring about most evolutionary change Natural Selection: Differential success in reproduction results in certain alleles being passed to the next generation in greater proportions by the more fit individuals. Genetic drift: describes how allele frequencies fluctuate randomly from one generation to Genetic drift tends to reduce genetic variation through the next. losses of alleles. More on genetic drift The bottleneck effect is a sudden reduction in +The founder effect population size due to a change in the environment, such as a natural disaster. The resulting gene pool may occurs when a few no longer be reflective of the original population’s gene pool. If the population remains small, it may be individuals become further affected by genetic drift. isolated from a larger population. +Allele frequencies in the small founder population can be different from those in the larger parent population. Gene Flow: Immigration & Emigration +Gene flow consists of the movement of alleles among populations. +Alleles can be transferred through the movement of fertile individuals or gametes (for example, pollen). +Gene flow tends to reduce differences between populations over time. +Gene flow is more likely than mutation to alter allele frequencies directly. NATURAL SELECTION: RELATIVE FITNESS + The natural selection phrases “struggle for existence” and “survival of the fittest” are misleading as they imply direct competition among individuals. + Reproductive success is generally more subtle and depends on many factors. + Relative fitness is the contribution an individual makes to the gene pool of the next generation, relative to the contributions of other individuals. Directional selection favors individuals at one end of the phenotypic range. + Selection favors certain genotypes by Disruptive selection favors individuals at both acting on the phenotypes of certain extremes of the phenotypic range. organisms. Stabilizing selection favors intermediate variants and acts against extreme phenotypes. Speciation, Microevolution and Macroevolution +Speciation, the origin of new species, is at the focal point of Darwin’s evolutionary theory. +Evolutionary theory must explain how new species originate and how populations evolve. +Microevolution consists of adaptations that evolve within a population, confined to one gene pool. +Macroevolution refers to In the Galápagos Islands Darwin discovered plants evolutionary change above the and animals found nowhere else on Earth species level. The Biological Species Concept emphasizes reproductive isolation +Biologists compare morphology, physiology, biochemistry, and DNA sequences when grouping organisms. The biological species concept states that a species is a group of populations whose members have the potential to interbreed in nature and produce viable, fertile offspring; they do not breed successfully with other populations. Reproductive Isolation = Barriers to Interbreeding Speciation can take place with or without geographic separation +Speciation can occur in two ways: +Allopatric speciation: geographic barrier separates populations. +Sympatric speciation: no geographic barrier  Allopatric (“Other Country”) Speciation Allopatric (“Other Country”) Speciation In sympatric speciation, speciation takes place in geographically overlapping populations. Polyploidy is the presence of extra sets of chromosomes due to accidents during cell division. An autopolyploid is an individual with more than two chromosome sets, derived from one species. An allopolyploid is a species with multiple sets of + In allopatric speciation, gene flow is interrupted chromosomes derived from different species. or macroevolution is the cumulative effect of many speciation and extinction events. Polyploidy is common in plants. Many important crops (oats, cotton, potatoes, tobacco, and wheat) are + reduced when a population is divided into polyploids. geographically isolated subpopulations … A geographic barrier separates the original population. + Separate populations may evolve independently through mutation, natural selection, and genetic drift. + Reproductive isolation between populations generally increases as the distance between them increases. + Barriers to reproduction are intrinsic; separation itself is not a biological barrier. Hybrid zones provide opportunities to study factors that cause reproductive isolation +A hybrid zone is a region in which members of different species mate and produce hybrids. +A hybrid zone can occur in a single band where adjacent species meet. +Hybrids often have reduced The distribution of hybrid zones can be more fitness compared with parent complex if parent species are found in multiple habitats within the same region. species.  Hybrid Zones over time +When closely related species meet in a hybrid zone, there are three possible outcomes: + Reinforcement -- Strengthening of reproductive barriers reducing gene flow. + Fusion -- Weakening of reproductive barriers with eventual fusion into one species. + Stabilizing -- Continued formation of hybrid individuals.  + Broad patterns in speciation can be studied using the fossil record, The Time Course of morphological data, or molecular data. Speciation + The fossil record includes examples of species that appear suddenly, persist essentially unchanged for some time, and then apparently disappear + Niles Eldredge and Stephen Jay Gould coined the term punctuated equilibrium to describe periods of apparent stasis (no change) punctuated by brief periods of rapid change. + The punctuated equilibrium model contrasts with a Darwinian model of gradualism: slow continuous change over time in a species’ existence. Let’s discuss: Why can’t evolution create perfect organisms? NATS113|MCDR