10.2 15 Darwin s Theory Observations of Evolution What is Evolution? Study of how things change over time
10.2 15 Darwin s Theory Observations of Evolution Theories of Evolution - Lamarck Jean Baptiste Lamarck (1744 1829) Law of Use and Disuse - parts of the body that are used become more developed - unused body parts become smaller and eventually disappear Law of Inheritance of Acquired Characteristics - organisms can pass traits acquired during their lifetime to their offspring - ex. giraffe evolution
10.2 15 Darwin s Theory Observations of Evolution Theories of Evolution - Lamarck Lamarck s explanation of how giraffes evolved long neck: 1) In order to reach higher leaves, giraffes stretch their necks and acquire long necks. (Law of Use and Disuse) 2) They can pass their acquired long neck trait to their offspring. (Law of Inheritance of Acquired Characteristics) 3) Eventually, all giraffes have long necks over time. Lamarck s explanation was believed to be invalid.
10.2 15 Darwin s Theory Observations of Evolution Theories of Evolution - Darwin Charles Darwin (1809-1882) - traveled on HMS Beagle to Galapagos Islands observing and collecting samples of organisms
10.2 15 Darwin s Theory Observations of Evolution Theories of Evolution - Darwin Darwin observed that: 1) the Galápagos Islands were close together but had very different climates. 2) the characteristics of many animals and plants varied noticeably among the different islands of the Galápagos. (ex: 14 species of finches) Warbler finch Cactus finch Woodpecker finch Sharp-beaked finch Small insectivorous tree finch Small ground finch Large insectivorous tree finch Vegetarian tree finch Insect eaters Bud eater Cactus eater Seed eaters Medium ground finch Large ground finch
10.2 15 Darwin s Theory Observations of Evolution Theories of Evolution - Darwin Darwin wondered if finches living on different islands had once been members of the same species. These separate species would have evolved from an original South American ancestor species.
10.2 15 Darwin s Theory Observations of Evolution Theories of Evolution - Darwin Darwin s conclusions: variations in beaks differences in beaks in the original flock adaptations to foods available on islands natural selection for most fit over many generations, the finches were selected for specific beaks & behaviors offspring inherit successful traits accumulation of winning traits: both beaks & behaviors separate into different species
10.2 15 Darwin s Theory Observations of Evolution Theories of Evolution - Darwin Darwin collected the preserved remains of ancient organisms, called fossils. Some of those fossils resembled organisms that were still alive. Others looked completely unlike any creature he had ever seen. ancient Armadillo present day Armadillos
10.2 15 Darwin s Theory Observations of Evolution Theories of Evolution - Darwin Darwin published the book The Origin of Species in 1859 (32 years after the end of his voyage). Darwin proposed the Theory of Evolution by Natural Selection: individuals with traits best suited for a specific environment survived and passed on these traits to their offspring.
10.2 15 Darwin s Theory Observations of Evolution Theories of Evolution - Darwin How would Darwin have explained the evolution of giraffe s long neck differently than Lamarck? Based on Darwin s theory of natural selection: 1) Long neck giraffes were better suited for reaching higher leaves and survived better. 2) More long neck giraffes survived over time and passed on the long neck traits to their offspring. 3) Short neck giraffes died out because they could not compete with the long neck giraffes.
10.2 15 Darwin s Theory Observations of Evolution Several key insights led to Darwin s idea for natural selection. Darwin noticed domesticated plants and animals seemed to show traits that were not found in their wild relatives. Breeders of these domesticated plants and animals select the desired traits (instead of the environment). neck feathers crop tail feathers
10.2 15 Darwin s Theory Observations of Evolution Several key insights led to Darwin s idea for natural selection. Artificial selection is the process by which humans select traits through breeding. (aka selective breeding )
10.2 15 Darwin s Theory Observations of Evolution Several key insights led to Darwin s idea for natural selection. Darwin compared processes in nature to artificial selection. In artificial selection, human selects the desired traits; while in natural selection, environment (or nature) selects the desired traits. In nature, there is always struggle for survival because of limited resources of food, water, and shelter.
10.2 15 Darwin s Theory Observations of Evolution Natural selection explains how evolution can occur. There are four main principles to the theory of natural selection. 1) Overproduction: OVERPRODUCTION A jaguar may produce more offspring than they can survive due to struggle for survival.
10.2 15 Darwin s Theory Observations of Evolution Natural selection explains how evolution can occur. 2) Variation: heritable differences among individuals. VARIATION Jaguar 1 Jaguar 2 Jaguar 1 = larger jaws and teeth Jaguar 2 = smaller jaws and teeth
10.2 15 Darwin s Theory Observations of Evolution Natural selection explains how evolution can occur. 3) Adaptation: a feature that allows an organism to better survive in its environment ADAPTATION Jaguars with larger jaws and teeth have better adaptations for eating shelled reptiles, so they are more likely to survive and reproduce better. (survival of the fittest)
10.2 15 Darwin s Theory Observations of Evolution Natural selection explains how evolution can occur. 4) Descent with Modification: Over time, natural selection will produce more individuals with the adaptations that are better suited for a particular environment. DESCENT with MODIFICATION Larger jaws and teeth become the more common traits in the population. So jaguars descendants showed modification, or change, over time.
10.2 15 Darwin s Theory Observations of Evolution Modern Day Example of Natural Selection Industrial Melanism of peppered moths - Industrial Revolution in Europe during 1850s affected the natural selection on colors of the peppered moths - As the environment changed, the moths that could camouflage themselves had better chances of survival and reproduction. Year % dark % light 1848 5 95 1895 98 2 1995 19 81
10.2 15 Darwin s Theory Observations of Evolution Modern Day Example of Natural Selection early 1800s = pre-industrial England low pollution lichen on trees = light colored bark light colored moths survived better late 1800s = industrial factories = soot coated trees killed lichen = dark colored bark dark colored moths survived better mid 1900s = pollution controls clean air laws return of lichen = light colored bark light colored moths survived better again
10.2 15 Darwin s Theory Observations of Evolution Natural selection acts on distributions of traits. A normal distribution, represented by a bell-shaped curve, is generally found in a typical population. highest frequency near mean value frequencies decrease toward each extreme value Traits not undergoing natural selection have a normal distribution.
10.2 15 Darwin s Theory Observations of Evolution Natural selection can change the distribution of a trait in one of three ways. 1) Stabilizing Selection - favors intermediate phenotype - reduces variations
10.2 15 Darwin s Theory Observations of Evolution Natural selection can change the distribution of a trait in one of three ways. 2) Directional Selection - favors phenotype at one extreme - leads to rapid evolution
10.2 Darwin s Observations Natural selection can change the distribution of a trait in one of three ways. 3) Disruptive Selection - favors both extreme phenotypes; intermediate phenotype is eliminated - leads to evolution of two new species
10.2 16 Evolution Darwin s of Observations Populations Natural selection acts on different phenotypes in a population. Genetic variation leads to phenotypic variation. The greater the genetic/phenotypic variations in a population increases the chance that some individuals will survive Genetic variation is stored in a population s gene pool. - gene pool = all the genes in all individuals in a population
10.2 16 Evolution Darwin s of Observations Populations Allele frequencies measure genetic variation. measures how common allele is in population can be calculated for each allele in gene pool As allele frequencies and gene pools change over time, the population evolve.
10.2 16 Evolution Darwin s of Observations Populations Genetic variation comes from several sources. Mutation is a random change in the DNA of a gene. can form new allele can be passed on to offspring if in reproductive cells Sexual reproduction results in new combinations of alleles. (crossing-over, independent assortment) usually occurs during meiosis parents alleles arranged in new ways in gametes
10.2 16 Evolution Darwin s of Observations Populations Genetic variation results in different types of adaptations. Adaptation = variations that improve an organisms chance for survival and reproduction. Physical Adaptation 1) Chemical: poison, toxin (ex: skunk) 2) Mechanical: Camouflage = adaptive coloration; blend in with the environment Mimicry = resemble another species 3) Structural: protective body forms (ex: fangs, claws, spines)
10.2 16 Evolution Darwin s of Observations Populations Genetic variation comes from several sources. Behavioral Adaptation - actions taken by an organism to prolong survival (ex: hiding, running, migration, hibernating)
10.2 16 Evolution Darwin s of Observations Populations There are five factors that can lead to evolution. 1) Genetic drift - changes allele frequencies due to random chance. - Genetic drift causes a loss of genetic diversity. - It is most common in small populations.
10.2 16 Evolution Darwin s of Observations Populations A population bottleneck can lead to genetic drift. It occurs when an event drastically reduces population size. The bottleneck effect is genetic drift that occurs after a bottleneck event. The founding of a small population can lead to genetic drift. It occurs when a few individuals start a new population. The founder effect is genetic drift that occurs after start of new population.
10.2 16 Evolution Darwin s of Observations Populations 2) Gene flow - movement of alleles from one population to another - changes the allele frequencies in a gene pool immigration = movement into the population emigration = movement out of the population
10.2 16 Evolution Darwin s of Observations Populations 3) Mutation - permanent change in DNA Positive mutations help an organism better adapt to its environment Harmful mutations organism dies and removes gene from population
10.2 16 Evolution Darwin s of Observations Populations 4) Sexual selection - selects for traits that improve mating success.
10.2 16 Evolution Darwin s of Observations Populations 5) Natural selection - selects for traits advantageous for survival.
10.2 16 Evolution Darwin s of Observations Populations The isolation of populations can lead to speciation. Speciation = the rise of two or more species from one existing species. A species is a group of organisms that breed with one another and produce fertile offspring. Populations become isolated when there is no gene flow. Isolated populations adapt to their own environments. Genetic differences can add up over generations.
10.2 16 Evolution Darwin s of Observations Populations The isolation of populations can lead to speciation. Types of Isolation: 1) Geographical Isolation - isolated by physical barriers (ex: continental drift, earthquake, volcano) 2) Behavioral Isolation - differences in courtship and mating behaviors 3) Temporal Isolation - timing of reproductive periods prevents mating
10.2 16 Evolution Darwin s of Observations Populations Evolution through natural selection is not random. Natural selection can have direction. The effects of natural selection add up over time.
10.2 16 Evolution Darwin s of Observations Populations Convergent evolution describes evolution toward similar traits in unrelated species.
10.2 16 Evolution Darwin s of Observations Populations Divergent evolution describes evolution toward different traits in closely related species. kit fox red fox ancestor
10.2 16 Evolution Darwin s of Observations Populations Species can shape each other over time. Two or more species can evolve together through coevolution. evolutionary paths become connected species evolve in response to changes in each other coevolution can occur in beneficial or competitive relationships.
10.2 16 Evolution Darwin s of Observations Populations Adaptive Radiation - Many species evolve from one species ancestral species diversifies into many descendent species descendent species usually adapted to wide range of environments
10.2 16 Evolution Darwin s of Observations Populations Species can become extinct. Extinction is the elimination of a species from Earth. occur at roughly the same rate as speciation usually affects a few species in a small area caused by local changes in environment
10.2 17 The Darwin s History Observations of Life Evidence for evolution came from several sources. 1) Fossils records provides a record of the earth s past life forms offers the most direct evidence for evolution shows a pattern of development of early ancestors to their modern descendants
10.2 17 The Darwin s History Observations of Life fossil preserved or mineralized remains (bone, petrified tree, tooth, or shell) or imprint of an organism that lived long ago fossil record is incomplete many organisms lived in places where fossils could not form there are gaps in the record
10.2 17 The Darwin s History Observations of Life 2) Biochemical Evidence changes in DNA/amino acid/protein sequences - closely related organisms have similar DNA/ amino acid/protein sequences and this also suggests common ancestry.
10.2 17 The Darwin s History Observations of Life Example: studying differences in hemoglobin between species
10.2 17 The Darwin s History Observations of Life 3) Comparative Anatomy comparison of anatomy can reveal basic structural similarities (even though the functions may be very different) indicating common ancestry Human hand Mole foot Bat wing
10.2 17 The Darwin s History Observations of Life Homologous Structures - same structures but used for different functions through evolution - ex. forelimbs in vertebrates all have the same basic bone structure - have common ancestors(closely related)
10.2 17 The Darwin s History Observations of Life Analogous Structures - different structures but used for same functions through evolution - ex. bird wings, bat wings, insect wings - DO NOT have common ancestors( not closely related) Fly wing Bat wing
10.2 17 The Darwin s History Observations of Life Vestigial Structures - structures that are reduced in size through evolution - either have no use or have a less important function than they do in other related organisms - provide evidence of an organism s evolutionary past - ex. hindlegs in whales, appendix in humans
10.2 17 The Darwin s History Observations of Life 4) Comparative Embryology comparing embryos of related organism shows similar developmental patterns - similar in embryos, but different in adult forms
10.2 17 The Darwin s History Observations of Life - ex: the embryos of all vertebrates have similar characteristics during early development all develop a tail, backbone, buds that become limbs, and pharyngeal pouches.