Presentation on theme: "Ch. 5 Evolution APES Mrs. Sealy. I. Origins of Life How do we know? Chemical analysis: chemists have conducted lab experiments to show how simple organic."— Presentation transcript:
Ch. 5 Evolution APES Mrs. Sealy
I. Origins of Life How do we know? Chemical analysis: chemists have conducted lab experiments to show how simple organic compounds could have been created. Radioactive dating: radiocarbon, radiometric dating with radioactive rocks and fossils
Electrical sparks simulating lighting provide energy to synthesize organic compounds Sample for chemical analysis Cooled water containing organic compounds Cold water Condenser Electrode Water vapor H2OH2O CH 4 CO 2 N2N2 NH 3 H2H2 H2OH2O Fig. 5.3, p. 104
Life evolved in two phases over the course of 4.7-4.8 billion years Chemical evolution of organic molecules and polymers Biological evolution from single celled prokaryotic bacteria to multi-cellular eukaryotic organisms
Chemical Evolution Formation of the Earths Crust: 4.6 to 4.7 billion years ago a cloud of cosmic dust condensed into planet earth which soon turned molten due to radioactive decay and meteorite impacts. As cooling took place a thin crust developed. Formation of the earths seas: volcanic eruptions and comet impacts brought water vapor that rained down on earth to create the sea
Chemical Evolution (cont.) Small organic molecules form in the seas: from eroded minerals from rocks 4.4 billion years ago the first atmosphere was formed. The main components were believed to be: CO 2, N 2,H 2 O, CH 4, NH 3, H 2 S, HCL, no oxygen This mixture is often to as: The primordial stew
Chemical Evolution (cont.) Large organic molecules form in the seas: energy from lightening, heat from volcanoes, and UV light and the chemicals in the atmosphere combined to form the first large organic molecules such as amino acids and carbs. Another theory is that these large molecules formed in hydrothermal vents. First protocells form in the seas: these new compounds washed into the seas and sat for millions of years to form the first DNA and protocells
Formation of the earths early crust and atmosphere Small organic molecules form in the seas Large organic molecules (biopolymers) form in the seas First protocells form in the seas Single-cell prokaryotes form in the seas Single-cell eukaryotes form in the seas Variety of multicellular organisms form, first in the seas and later on land Chemical Evolution (1 billion years) Biological Evolution (3.7 billion years) Fig. 5.2, p. 103
Biological Evolution 3.5 to 3.8 billion years ago, well below the surface of the sea away from harmful UV radiation the first prokaryotic cells formed: PROKARYOTIC 2.3 to 2.5 billion years ago the first cyanobacteria appear and they: photosynthesize 2.0-2.1 billion years ago oxygen: formed from cyanobacteria 1.2 billion years ago we see the first eukaryotic cells arrive, which could reproduce sexually and produce a wide variety of organisms 400-500 million years ago we see: the first land plants and animals How do we know what organisms were around: –Fossil record –Radiometric dating of rocks near the fossils
Fig. 5.4, p. 105 Fossils present but rare Evolution and expansion of life Fossils become abundant Plants invade the land Age of reptiles Age of mammals Insects and amphibians invade the land Modern humans (Homo sapiens) appear about 2 seconds before midnight Recorded human history begins 1/4 second before midnight Origin of life (3.6–3.8 billion years ago)
Evolution Heritable changes in a populations genetic make-up through successive generations An overwhelming majority of biologists believe that this is the best explanation for the changes that have occurred over the last 3.7 billion years and also for why life on earth today is so diverse. The theory of evolution is based on the idea that all species descended from other species http://www.hippocam pus.org/Biology
1 st generation 2 nd Generation GG, Gg = green beetle gg = brown beetle Evolution= shift in gene frequency in a population
Macroevolution long term, large scale evolutionary changes among a group or species. One species leads to the appearance of many other species.
Genetic persistence: The inheritance of DNA molecules from the origin of the first cells through all subsequent lines of descent which is the basis of the unity of life
Genetic divergence Long term changes in lineages of species, which are the basis of the diversity of life
Genetic losses The steady background extinction or relatively abrupt catastrophic loss of lineage
Microevolution: the small genetic changes that a population experiences How does microevolution work?
It is the development of genetic variability in a population A populations gene pool is the sum total of all genes possessed by the individuals of the populations species
Microevolution is a change in the species gene pool over time
Members of a population have different molecular forms of the same gene called alleles. Sexual reproduction leads to a shuffling of alleles. As a result each individual has a different combination of alleles. This is called genetic variability
Microevolution works through a combination of four processes: every Mutation, natural selection, gene flow, genetic drift
Mutation: The source for all new alleles (genes) is mutations, which are random changes in the structure of DNA molecules in a cell. Adaptation: any genetically controlled trait that helps an organism survive and reproduce under a given set of environmental conditions Every so often a mutation is beneficial and the result is a new genetic trait that will ensure the survival of offspring better Mutations are rare
Natural Selection Differential reproduction: because of random shuffling or recombination of genes, certain individuals may by chance have one or more beneficial adaptations that allow them to survive under various environmental conditions. As a result they are more likely to reproduce than individuals that do not have such adaptations.
Natural selection does not create favorable genes; instead it favors some individuals over others by acting on genes already in the gene pool. Natural selection occurs when the combined effects of adaptation and differential reproduction result in a particular beneficial gene becoming more common in succeeding generations
Three types of Natural Selection: Directional: it pays to be different: changing environmental conditions cause gene frequencies to shift so that individuals with traits at one end of the normal range become more common than midrange species
Directional Natural Selection Natural selection New averagePrevious average Number of individuals Coloration of snails Proportion of light-colored snails in population increases Number of individuals Snail coloration best adapted to conditions Average Coloration of snails Fig. 5.6a, p. 110 Average shifts
Stabilizing: it pays to be average: in a stable environment species that have abnormal genes have no advantage and tend to be eliminated.
Stabilizing Natural Selection Coloration of snails Light snails eliminated Dark snails eliminated Number of individuals Coloration of snails Snails with extreme coloration are eliminated Number of individuals Average remains the same, but the number of individuals with intermediate coloration increases Fig. 5.6b, p. 110 Natural selection
Diversifying: it doesnt pay to be normal: when environmental conditions favor individuals at both extremes of the genetic spectrum and sharply reduce the number of mid-range individuals.
Number of individuals with light and dark coloration increases, and the number with intermediate coloration decreases Coloration of snails Number of individuals Snails with light and dark colors dominate Diversifying Natural Selection Coloration of snails Number of individuals Light coloration is favored Dark coloration is favored Intermediate-colored snails are selected against Fig. 5.6c, p. 110 Natural selection
Gene Flow: Movement of genes between populations
Genetic drift: involves change in a genetic composition of a population by chance and is important in small populations
Co evolution When populations of two different species interact over a long time, changes in the gene pool of one species can lead to changes in the gene pool of the other species. For example:
An Example of evolution by natural selection: The peppered moths of England During the industrial revolution. http://www.echalk.co.uk/Science/Bi ology/PepperedMoth/Peppered_ MothWEB.swf
Coevolution Coevolution can occur between animals that have a symbiotic relationship as well those who have a predator prey relationship Coevolution gone awry
Ecological Niches and Adaptation Ecological niche: the species way of life or the functional role of the species in an ecosystem. For example: a. types of resources used b. range of tolerance c. how it interacts with components of the ecosystem d. its role in flow of energy and matter cycling
Fundamental vs realized niche Fundamental niche vs. realize niche: Your fundamental niche is all the possible conditions that you can live under. Your realized niche is how you are actually living. For example: you may be capable being a star, but competition keeps you from getting the job
Region of niche overlap Generalist species with a broad niche Generalist species with a narrow niche Niche breadth Niche separation Number of individuals Resource use Fig. 5.7, p. 111
Generalist species vs. Specialist species Generalist: have very broad niches and eat a variety of foods and can live in a variety of places under differing conditions. For example cockroach Specialist: narrow niche, may only be able to live in one type of habitat or eat only one type of food. For example: panda bear –Is it better to be a generalist or a specialist?
Speciation Two species arise from one species in response to changes in environmental conditions. The mechanism for speciation occurs in two phases –Geographic isolation: occurs when two populations of a species becomes physically separated for long periods –Reproductive isolation: occurs as mutation and natural selection occur independently in two separated populations of the same species. Eventually, the changes are so great that two groups will no longer interbreed.
Adapted to heat through lightweight fur and long ears, legs, and nose, which give off more heat. Adapted to cold through heavier fur, short ears, short legs, short nose. White fur matches snow for camouflage. Gray Fox Arctic Fox Different environmental conditions lead to different selective pressures and evolution into two different species. Spreads northward and southward and separates Southern population Northern population Early fox population Fig. 5.8, p. 113
Convergent evolution: Two separate species will evolve separately to create animals with similar characteristics. Species that have similar niches tend to evolve similar sets of traits in response similar environmental conditions. For example:
Divergent evolution: speciation creates separate species
Extinction When environmental changes occur species either evolve or cease to exist and their genetic material is permanently lost. Extinction patterns have been caused by large-scale movements of the continents and gradual climate changes like those from meteors and volcanoes. All species inevitably disappear Background extinction is the low rate that species constantly disappear. It is the normal level. Approx. 3 species per year Mass extinction: an abrupt rise in extinction rates above the background rate. It is catastrophic, global and often results in 25% to 70% loss of species There are have been five previous mass extinctions and we are currently in the six mass extinction, which is being caused by humans.
– Speciation minus extinction equals biodiversity – Although extinction is a natural process, humans have sped up the process and we have lost a lot of genetic material – This mass extinction is different from previous extinctions in the following ways: – 1. First time it has ever been caused by one species – 2. This is the fastest it has every happened – 3. Adaptive Radiation will be slow after because we are destroying habitats
Ordovician: 50% of animal families, including many trilobites Devonian: 30% of animal families, including agnathan and placoderm fishes and many trilobites. Permian: 90% of animal families, including over 95% of marine species; many trees, amphibians, most bryozoans and brachiopods, all trilobites. Triassic: 35% of animal families, including many reptiles and marine mollusks. Cretaceous: up to 80% of ruling reptiles (dinosaurs); many marine species including many foraminiferans and mollusks. Current extinction crisis caused by human activities. Many species are expected to become extinct within the next 50–100 years. Species and families experiencing mass extinction Bar width represents relative number of living species Extinction Millions of years ago PeriodEra Paleozoic Mesozoic Cenozoic Quaternary Tertiary Cretaceous Jurassic Triassic Permian Carboniferous Devonian Silurian Ordovician Cambrian Today 65 180 250 345 500 Extinction Fig. 5.10, p. 115
Adaptive Radiation Adaptive radiation: an extinction of one species is an opportunity for another species and after a mass extinction there is a period in which numerous new species can evolve Speciation and extinction affects biodiversity:
How does Macroevolution occur? A. Macroevolution is concerned with how evolution takes place above the level of species and over long periods of time and shows how small changes can lead to the eventual creation of many different species, genera and families. B. Gradualist model: theory that says macro evolutionary change occurs over many millions of years C. Punctuated Equilibrium: opposing theory that says there are long periods of relatively punctuated with brief periods of very rapid changes. D. In reality it is probably a combination of both
Common Misconceptions about Evolution Survival of the fittest is often misinterpreted as survival of the strongest. In biological terms fitness is a measure of reproductive success and the ones with the most descendants are the fittest. Natural selection is not "tooth and claw competition. Humans evolved from apes, this is not true. Apes and humans have a common ancestor from which both are descended. Nature has a grand plan in which species become progressively more perfect, natural selection is random and there is no goal of perfection.
1) Before 5 mya: In Africa, our ancestral lineage and the chimpanzee lineage split. 2) Before 4 mya: The hominid Australopithecus anamensis walked around what is now Kenya on its hind legs. 3) >3 mya: Australopithecus afarensis ( Lucy ) lived in Africa. 4) 2.5 mya: Some hominids made tools by chipping stones to form a cutting edge. There were perhaps four or more species of hominid living in Africa. 5) 2 mya: The first members of the Homo clade, with their relatively large brains, lived in Africa 6) 1.5 mya: Hand axes were used. Also, hominids had spread out of Africa and into much of Asia and Europe. These hominids included the ancestors of Neanderthals (Homo neanderthalensis) in Europe and Homo erectus in Asia. 7) 100,000 years ago: Human brains reached more or less the current range of sizes. Early Homo sapiens lived in Africa. At the same time, Homo neanderthalensis and Homo erectus lived in other parts of the Old World. 8) 50,000 years ago: Human cultures produced cave paintings and body adornment, and constructed elaborate burials. Also, some groups of modern humans extended their range beyond Africa. 9) 25,000 years ago: Other Homo species had gone extinct, leaving only modern humans, Homo sapiens, spread throughout the Old