Transcript Chapter 5
Chapter 5 Evolution and Biodiversity: Origins, Niches, and Adaptation The Origin of Life • How did life emerge on Earth? • Chemical analysis and radioactive elements in rocks and fossils • Simple inorganic compounds formed amino acids (proteins), simple sugars (carbs) and DNA/RNA Most widely-accepted hypothesis • Organic molecules needed for life came from inorganic chemicals in the Earth’s atmosphere -energy from lightning -heat from volcanoes -intense UV light -other forms of solar radiation Scientific Experiments • Since 1953 • Placed mixtures of gases (in early atmosphere) into closed containers • Subjected gases to sparks (lightning) and heat • Building blocks (necessary for life) formed H2O Water vapor CH4 Electrode CO2 N2 NH3 Electrical sparks simulating lighting provide energy to synthesize organic compounds H2 Condenser Cold water H2O Sample for chemical analysis Cooled water containing organic compounds Are there other possibilities? • Organic molecules formed from… 1. Dust particles in space that reached earth on meteorites or comets 2. Deep within the earth 3. Hydrothermal vents (cracks in ocean floor, lead to chambers of molten rock) REGARDLESS… • Organic molecules accumulated and underwent chemical reactions for several hundred million years • Led to formation of proteins, RNA, and other polymers that formed protocells • Protocells could take up materials from environment, grow, and divide Earth Developed in 2 Phases 1. Chemical evolution: organic molecules and chemical reactions to form protocells -1 billion years 1. Biological Evolution: single-celled prokaryotes single-celled eukaryotes multicellular organisms -3.8 billion years Chemical Evolution Formation of the earth’s early crust and atmosphere Small organic molecules form in the seas Large organic molecules form in the seas First protocells form in the seas Biological Evolution Single-cell prokaryotes form in the seas © 2004 Brooks/Cole – Thomson Learning Single-cell eukaryotes form in the seas Multicellular organisms form, first in the seas and later on land How do we know what organisms lived in the past? • Fossils!: mineralized or petrified replicas of skeletons, bones, teeth, shells, seeds, etc. 1. Physical evidence of organisms 2. Internal structures Fossil record is incomplete! We have 1% of species believed to have ever lived! What is Evolution? • Evolution: The change in a population’s genetic makeup (gene pool) through successive generations • Theory of Evolution: all species developed from earlier, ancestral species Macro- and Microevolution • Microevolution: small genetic changes that occur in a population • Macroevolution: long-term, large-scale evolutionary changes through which… 1. new species are formed from ancestral species 2. other species are lost through extinction Remember… • Genetic information in chromosomes is contained in DNA • Genes (on chromosomes) represent certain traits that may be passed to offspring • Gene pool: set of all genes in individuals of a population • Alleles: different forms of a gene (dominant or recessive) Mutations • Genetic variability originates through mutation: random changes in the DNA in a cell. • Mutations happen in two ways: 1. DNA is exposed to radioactivity, X-rays, mutagens 2. Random mistakes when DNA is copied (cell division) Sometimes, mutations are beneficial Microevolution • Microevolution: change in a population’s gene pool over time • Summary of microevolution: genes mutate, individuals are selected, populations evolve Natural Selection • Occurs when individuals have traits that increase their chances of survival • Needs 3 conditions: 1. Natural variability for a trait 2. Trait must be heritable 3. Must lead to differential reproduction (individuals with trait leave more offspring than individuals without trait) Let’s think about the moths again… 1. Variability: 2 color forms 2. Heritability: color form was geneticallybased 3. Differential reproduction: greater survival and reproduction by one color When environment changes… Population may: 1. Adapt to new conditions through natural selection 2. Migrate to an area with better conditions 3. Become extinct 3 Types of Natural Selection 1. Directional: changing environmental conditions select individuals who are not the norm so that their type makes up more of the population (“it pays to be different”) 2. Stabilizing: gets rid of individuals on both extremes (“it pays to be average”) 3. Diversifying: favors individuals with uncommon traits and reduces average individuals (“it does not pay to be normal”) Snail coloration best adapted to conditions Average Natural selection Number of individuals Number of individuals Directional Natural Selection New average Coloration of snails Proportion of light-colored snails in population increases Previous average Average shifts Coloration of snails Light snails eliminated Dark snails eliminated Coloration of snails Natural selection Number of individuals Number of individuals Stabilizing Natural Selection Snails with extreme coloration are eliminated Coloration of snails Average remains the same, but the number of individuals with intermediate coloration increases Intermediate-colored snails are selected against Light coloration is favored Dark coloration is favored Coloration of snails Natural selection Number of individuals Number of individuals Diversifying Natural Selection Snails with light and dark colors dominate Coloration of snails Number of individuals with light and dark coloration increases, and the number with intermediate coloration decreases Coevolution • Changes in the gene pool of one species leads to changes in gene pool of the other Example: plants evolve defenses (camouflage, thorns, poison) effective against herbivores Herbivores evolve immunity against these traits Ecological Niches • Niche: role of a species in an ecosystem (like an occupation) • Habitat: physical location (like an address) 2 types of niches: 1. Fundamental niche: potential and theoretical niche (without competition, etc) 2. Realized niche: actual niche How do new species evolve? • Speciation: two species arise from one • Geographic isolation: groups of the same population become physically separated and undergo different evolution Ex. mountain range, volcano, earthquake Leads to reproductive isolation Northern population Arctic Fox Early fox population separates Adapted to cold through heavier fur, short ears, short legs, short nose. White fur matches snow for camouflage. Different environmental conditions lead to evolution into two different species. Southern population Gray Fox Adapted to heat through lightweight fur and long ears, legs, and nose, Which give off more heat. LAURASIA 120° 80° 40° 80° 120° 120° 80° 80° 120° GONDWANALAND 135 million years ago 225 million years ago NORTH AMERICA EURASIA AFRICA 120° 80° SOUTH AMERICA INDIA MADAGASCAR 120° 120° 0° 40° AUSTRALIA ANTARCTICA 65 million years ago Present 120°