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Chapter 10: The Origin and Diversification of Life on Earth Understanding biodiversity Lectures by Mark Manteuffel, St. Louis Community College Learning Objectives Be able to describe how: Biodiversity leads to long-term stability in an ecosystem. Life on earth most likely originated from nonliving materials. Species are the basic units of biodiversity. Evolutionary trees help us conceptualize and categorize biodiversity. Be able to describe: Macroevolution and the diversity of life. An overview of the diversity of life on earth. Why do we care about biological diversity? • Diversity-stability hypothesis proposes that an ecosystem with high biodiversity is better able to survive disturbances than an ecosystem with low biodiversity. • Other benefits? – – – – Plants/producers Medicines Foods Fibers/products 10.1 Complex organic molecules arise in nonliving environments. The 4-Stage Hypothesis for the Origin of Life explains the origin of organic molecules and how cooperation and polymerization led to the evolution of the first prokaryotic cell. Follow the slides – your book doesn’t cover Stage 2: Abiotic Synthesis of Organic Polymers Stage 1: The Formation of Small Molecules Containing Carbon and Hydrogen The Urey-Miller Experiments Stage 1: Abiotic Synthesis of Organic Monomers (small molecules containing carbon and hydrogen) The first demonstration that complex organic molecules could have arisen in earth’s early environment – Recall repeatability in science – These experiments have been repeated again and again and have produced all 20 amino acids, several sugars, lipids, and nucleotides. Stage 2: Abiotic Synthesis of Organic Polymers • Researchers have observed polymerization of organic monomers in various situations. • By dripping solutions of organic monomers onto hot sand or rock, the heat vaporizes the water and concentrates the monomers. • Some of the monomers spontaneously bond together via dehydration synthesis without the aid of enzymes or other cellular equipment. 10.2 Cells and self-replicating systems evolved together to create the first life. RNA appears on the scene. RNA can catalyze reactions necessary for replication. Here it gets a little more speculative. Some researchers believe enzymes were required. Stage 3: Origin of Self-Replicating Molecules • Laboratory experiments have shown that short RNA molecules can assemble spontaneously. Original “gene” RNA monomers Formation of short RNA polymers: simple “genes” Assembly of a complementary RNA chain (pairing rules are G with C and A with U) Complementary chain serves as template for making copy of original “gene” Stage 4: The Development of a Membrane, Enabling Metabolism, and Creating the First Cells Membranes numerous aspects of metabolism possible. make Lipids self-assemble into membrane enclosed droplets. 10.3 What is a species? Species is a Latin word meaning “kind” or “appearance”, but many times we cannot tell simply by appearance alone. Biological Species Concept Species: different kinds of organisms Species are natural populations of organisms that: • interbreed with each other or could possibly interbreed • cannot interbreed with organisms outside their own group (reproductive isolation) Two Key Features of the Biological Species Concept: 1) actually interbreeding or could possibly interbreed 2) “natural” populations Barriers to Reproduction 1) Prezygotic barriers 2) Postzygotic barriers Prezygotic Barriers Make it impossible for individuals to mate with each other – before the mating attempt or Make it impossible for the male’s reproductive cell to fertilize the female’s reproductive cell – after the mating attempt Prezygotic barriers include: Courtship rituals – behavioral isolation Physical differences – habitat isolation, temporal isolation, and mechanical isolation Physical or biochemical factors involving gametes – gametic isolation Mating behaviors may be complex… slug sex video? Postzygotic Barriers Occur after fertilization – Are backup mechanisms that operate should interspecies mating actually occur and produce hybrid zygotes – Offspring fail to develop normally – Prevent the production of fertile offspring Hybrids • Postzygotic barriers include: – Hybrid inviability = offspring die before they can reproduce. – Hybrid sterility = The mule is sterile. Horse Mule (hybrid) Donkey Figure 14.7 10.4 How do we name species? A scientific name for a particular species consists of two parts (binomial nomenclature): 1) genus 2) specific epithet (species name) Hierarchical System Inclusive categories at the top… …leading to more and more exclusive categories below. 10.5 Species are not always easily defined using the biological species concept. 10.6 How do new species arise? Speciation One species splits into two distinct species. Occurs in two distinct phases Requires more than just evolutionary change in a population Allopatric Speciation Speciation with geographic isolation Speciation without Geographic Isolation The individual with four sets can no longer interbreed with any individuals having only two sets of chromosomes Self-fertilization or mating with other individuals that have four sets can occur. Asexual reproduction and selffertilization are much more common in plants. 10.7 The history of life can be imagined as a tree. The tree reveals the evolutionary history of every species and the sequence of speciation events that gave rise to them. This tree is only a working hypothesis and is revised as new evidence is revealed. Most evolutionary trees are constructed using fossil, structural, and more and more molecular evidence. 10.9 Similar structures don’t always reveal common ancestry. Recall analogous vs. homologous structures Because appearances are sometimes deceptive, molecular evidence is generally more reliable. 10.10 Macroevolution is evolution that goes beyond the species level. Short-term and Long-term Results Microevolution Macroevolution 10.11 The pace of evolution is not constant. In some cases, the fossil record reveals rapid periods of evolutionary change punctuated by longer periods with little change. In others cases, species may change at a more gradual, but consistent, pace. 10.12 Adaptive radiations are times of extreme diversification. When a small number of species diversifies into a much larger number of species. Evolutionary Innovations • What accounts for the evolution of biological novelty like flight in birds and human intelligence? Birds are derived from a lineage of earthbound reptiles. Developed from flightless ancestors, but how? • Exaptation – Involves a structure that evolves in one context and gradually becomes adapted for other functions. – Is one mechanism for novel features to arise gradually. – Natural selection can only refine a structure in the context of its current utility, it does not predict future change. – In birds, did feathers or lightweight bones come first? The first flights may have been glides or extended hops. Feathers are also used for warmth. Evolutionary Innovations • A subtle change in developmental genes can have profound effects. • Paedomorphosis – Is the retention of juvenile body features in the adult – Probably played a role in human evolution Neoteny: Human and Chimpanzee skull development: Chimpanzee fetus Chimpanzee adult Extending the juvenile process of brain development helps the human brain grow larger . Human fetus Human adult Figure 14.17 • Earth was born 4.5 billion years ago – Prokaryotes - 3.5 billion years ago – Oxygen production 2.5 billion years ago – Single-celled eukaryotic organisms - 1.7 billion years ago – Multicellular organisms – 1 billion years – Animal diversification – 570 million – Plants and fungi move to land – 475 million 10.14 All living organisms are divided into one of three groups. 10.15 The bacteria domain has tremendous biological diversity. 10.16 The archaea domain includes many species living in extreme environments. 10.17 The eukarya domain consists of four kingdoms.