Nature of Sciencereview of terms Science a way of knowing about the natural world Law a description of how a natural phenomenon will occur under certain circumstances Ex. Keplers Law of planetary Motion Fact a natural phenomenon repeatedly confirmed by observation. A fact is assumed to be true. It takes Venus 225 days to go around the sun Nature of Scienceterms Theory a well substantiated explanation of some aspect of the natural world that typically incorporates many confirmed observations, laws, and successfully verified hypothesis. Theory of evolution Hypothesis a possible and testable statement about a natural phenomenon If a plant isnt watered then the plant will die. Science Before Darwin Ideas that shaped Darwins Thinking James Hutton Processes that changed the earth are the same forces shaping the earth presently. Most geological processes operate extremely slowly Charles Lyell Darwin read his book Principles of Geology Lyell proposed that geological features could be built up or torn down over long periods of time Scientists must explain past events in terms of processes that they can observe Darwin became convinced the Earth was much older than believed at that time If the earth could change over time, might life change as well? Jean Baptiste Lamarck ( ) The first to recognize that living things have changed over time, and proposed a hypothesis for this process. His hypothesis was incorrect. Lamarck believed that the long neck of giraffes evolved as generations reached for higher leaves. They used their necks more. Thomas Malthus Darwin read his essay written in 1798 Wrote that human populations are able to increase faster than the food supply. Controlled by famine, disease, or war Darwin observed this applies to animals and plants as well If all offspring of a species would survive, they would overrun the world What factors determine which offspring survive and reproduce, and which do not? Darwins Journey Darwins Theory of Evolution Who is Charles Darwinthe voyage of the Beagle Wrote On the Origin of Species By Means of Natural Selection Published years after his return home PBS Evolution Who was Charles Darwin Darwins Return Home Darwin didnt publish his findings until 23 years later! He was given an incentive when he received a manuscript from Alfred Wallace. Wallace wrote about the exact same ideas that Darwin had. Evolution at a Glance The changes, over time, in organisms Deals with a very specific type of change Changes in the frequencies of different genes (made up of alleles), within a species. What causes changes to genes? What sorts of things happen when gene frequencies change? What is gene frequency? We know genes determine traits We know genes are inherited Alternative versions of a trait are called alleles Some alleles are dominant and some are recessive. Within a population scientists can actually measure the frequency, or how often a particular gene appears in a population. Changes in Gene Frequency Evolution on the smallest scale Example: A population of Beetles half have the gene for brown color, the gene frequency is 50% half have the gene for green color, its gene frequency is 50% Several years later the gene frequency changes the brown color gene is now at 75% the green color gene is at 25% the frequencies are changing, and evolution has happened. Campbell bio: ch 23 bioflix mechanisms of evolution The Origin of Species To explain how and why evolution occurred, Darwin needed a mechanism. A scientific explanation Darwin realized that most organisms do not survive and reproduce He wanted to know which individuals do survive and reproduce Today this mechanism explains how gene frequencies could change over generations Natural Selection The mechanism to explain descent with modification Changes to an organism through generations Not all individuals have an equal chance of contributing to the next generation Some are selected for and some are selected against. Natural Selection is the driving force. Darwin Gains insight into Natural Selection through Artificial Selection Artificial Selection Plant and animal breeders use artificial selection or selective breeding to choose the best traits Humans select the natural variations they find useful Cows that produce more milk, the fastest horses, etc. This has produced many diverse organisms that look different from their ancestors. Artificial Selection Figure Terminal bud Lateral buds Brussels sprouts Cabbage Flower cluster Leaves Cauliflower Flower and stems Broccoli Wild mustard Kohlrabi Stem Kale All domesticated animals, livestock and crops have been produced this way! PBS dangerous idea #4 Artificial SelectionA Question? If variations could be selected for and against by humans, then couldnt this also happen naturally in nature? This selection would then affect how organisms looked over time. Evolution by Natural Selection Under what conditions does natural selection occur? The Struggle for Existence Variation and Adaptation Differential Reproductive Success Survival of the Fittest (lets discuss) Survival of the Fittest Makes it sound like only the strong survive and the weak die away. Darwin didnt coin this phrase. Herbert Spencer did Fitness is all about how an organism reproduces and passes its genes on to the next generation. In fancy terms its called differential reproductive success Or how successful an individual is at producing offspring Youtube cuttlefish mating trick https://www.youtube.com/watch?v=OEqsgwyvtqc Observation #1: For any species, population sizes would increase exponentially if all individuals that are born reproduced successfully Figure 22.8 Observation #2: Nonetheless, populations tend to be stable in size Except for seasonal fluctuations Observation #3: Resources are limited Inference 1: Production of more individuals than the environment can support, leads to a struggle for existence among individuals of a population, with only a fraction of their offspring surviving Natural Selection-Conditions 1. The Struggle for Existence Organisms produce more offspring than can survive. Only a small fraction of these offspring survive to reproduce. Members compete for Food Living space Other necessities of life Natural Selection Struggle for Existence Which individuals come out on top? Observation #4: Members of a population vary extensively in their characteristics No two individuals are exactly alike Figure 22.9 Observation #5: Much of this variation is heritable Inference #2 Survival depends in part on inherited traits Individuals whose inherited traits give them a high probability of surviving and reproducing are likely to leave more offspring than other individuals Inference #3: This unequal ability of individuals to survive and reproduce will lead to a gradual change in a population, with favorable characteristics accumulating over generations Natural Selection-Conditions 2. Variation and Adaptation There is variation in nature Arises through sexual reproduction and mutation Certain variations called Adaptations increase an individuals chance of surviving and reproducing. Adaptation any inherited characteristic that increases an organisms ability to survive and reproduce. Sources of Variation Adaptations What can be an Adaptation Structural Adaptations Teeth and claws Rose thorns, porcupine quills Mimicry A harmless species has adaptations that result in a physical resemblance to a harmful species camouflage Physiological adaptations changes in metabolic processes Resistance to pesticides (insects and plants) Bacterial resistance to antibiotics Behaviors Defensive behaviors-mothers protecting young Running from predators Natural Selection-Conditions 3. Differential Reproductive Success Fitness- how successful an organism is at getting its genes into the next generation How successful are you at reproducing Nothing to do with how buff an organisms is Fitness is key to the process of evolution Individuals that are not well suited, die or leave fewer offspring Differences in adaptations affect an individuals fitness If one individual produces twice as many offspring as the next, all other things being equal, its twice as fit Natural Selection The Process by which organisms with variations most suited to their local environment survive and leave more offspring. It only acts on inherited traits Adaptations dont have to be perfect-just good enough Doesnt always move in a fixed direction Evidence Supporting The Theory of Evolution Sources of evidence come from Fossils anatomical Embryology DNA The Fossil Record Fossils are the preserved remains of ancient organisms How do fossils provide evidence of evolution? They provide a record of early life and evolutionary history Show that the earth has changed over time and new species arise from existing species The evolutionary path that led to todays camel The transition to life in the sea Transitional Fossils Provide evidence for how species have changed over time. These are intermediate forms between older species and their more modern descendants Archaeopteryx (intermediate between dinosaur and birds) Anatomical Structural similarities is evidence that organisms evolved from a common ancestor It would be unlikely for so many animals to have similar structures if each species arose separately All are mammals Anatomical evidence- Homologous structures Structures that may have different form and functions but similar tissue Share an evolutionary relationship Structures that have similar functions but different components in two unrelated organisms Do not have a common evolutionary origin. Show that the organisms evolved separately. Have adapted to similar environments Example: Wings Or fins of fish and dolphin (swimming in water) Anatomical evidence- Analogous structures Vestigial structures Organs, or body parts, that are so reduced in size or function that they are merely traces of homologous organs in other species These organs do not serve important functions. Examples of Vestigial structures Hind limbs of whales Tiny bones in snakes that were once legs Miniature tailbones at the base of a human spine (once supported a tail) The human appendix is a vestigial organ Similarities in Embryology Embryonic cells develop in the same order and similar patterns. It is the shared features in the young embryos that suggest evolution from a distant, common ancestor Ex. All limbs develop from the same clump of cells All embryos have a tail and pharyngeal pouches. In fish, these pouches develop into the supports for the gills, while in mammals, reptiles and birds they develop into parts of ears, jaws and throat. Zebra fish What organism? Universal Genetic Code (DNA) Nearly all organisms share DNA, similar proteins and genes ATP powers cellular respiration and photosynthesis Examples cytocrome c, an enzyme occurs in almost all organisms Utah.edu all living things are related How can changes occur Mutations can cause differences in otherwise similar DNA sequences Occur at a certain rate Indicate how long tow lineages have evolved independently The more common sequences, the more recent a common ancestor The greater the differences, the more time has passed between two species Evolutionary trees Comparing gene sequences Hemoglobin Comparisons Between Humans and Other Vertebrates Humans are more closely related to primates than other vertebrates. Their difference is only one amino acid Anatomical resemblances among species Are generally reflected in their molecules, their genes, and their gene products Figure Species Human Rhesus monkey Mouse Chicken Frog Lamprey 14% 54% 69% 87% 95% 100% Percent of Amino Acids That Are Identical to the Amino Acids in a Human Hemoglobin Polypeptide Closely related species have a larger proportion of DNA and proteins in common than do more distantly related species Biogeography The geographic distribution of species Influenced by continental drift The slow movement of Earths continents over time Islands generally have many species of plants and animals that are endemic Meaning they are found nowhere else in the world Yet island species are closely related to species from the nearest mainland or neighboring island Islands are colonized by species from the nearest mainland Natural selection results in the evolution of populations a population is a group of interbreeding individuals of the same species in a common geographic area Evolution is measured only as change in the relative proportions of variations in a population over time Natural selection affects only those traits that are heritable Natural selection depends on the specific environmental factors present in a region at a given time If the environment changes, different adaptations will be favored In Summary Darwins theory of evolution by natural selection Integrates diverse areas of biological study and stimulates many new research questions Evolution can sometimes occur more quickly than Darwin originally hypothesized. New species can arise within a few thousand years Evolutionary biologists now recognize that natural selection is not the only mechanism responsible for evolution.