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Natural Selection •! Levels of Analysis in Ethology –! Proximate –! Ultimate (Evolutionary) Tinbergen •! Natural Selection –! Darwin –! Natural Selection –! Adaptation/Functionality Darwin Levels of Analysis in Ethology •! •! •! •! •! Example: Why do male monkeys fight? Niko Tinbergen 1963 “On Aims and Methods in Ethology” Not mutually exclusive Answer questions about WHY behaviors occur Four levels of analysis –! Proximate Mechanisms •! Causation •! Development (“Ontogeny”) –! Ultimate (Evolutionary) Mechanisms •! Phylogeny •! Function Causation •! •! •! •! •! •! •! Sensory systems Signals Neurobiology Hormones Motivation Pheromones Social cues Herring gulls Development “Ontogeny” means development •! •! Age and Experience –! Physical/mental change and growth –! Learning is a change in an animal's behavior in a particular situation attributable to its previous experience of the situation Development Harlowe’s studies on rhesus social development Reared in cage alone Reared in cage with other monkeys Phylogeny •! Evolutionary history and relations to other species •! How does the behavior compare with similar behavior in related species? •! How might the behavior have arisen through the process of past evolution? Function •! Did the behavior evolve? •! Why did the behavior evolve? •! Does the behavior impact on the animal's chances of survival and reproduction? •! Better: how did the trait impact the relative rate of reproduction of the animal’s ancestors in the past? •! Did the behavior have a functional role—a purpose—in reproduction in the past? •! Is the behavior an adaptation? •! Did the behavior evolve by natural selection? •! zcf Function Primate Examples Grooming langurs Female gibbon calling Howler eating young leaves Summary: Two Categories •!Proximate Mechanisms (within an organism’s life) –!Causation –!Development (“Ontogeny”) •!Ultimate (Evolutionary) Mechanisms (over generations) –!Phylogeny –!Function Levels and NS: Overview •! Levels of Analysis in Ethology –! Proximate –! Ultimate (Evolutionary) Tinbergen •! Natural Selection –! Darwin –! Natural Selection –! Adaptation/Functionality Darwin Darwin’s Two Main Contributions •! Carried out the necessary research to conclusively document that evolution has occurred •! Discovered the process by which complex, functional design originates in living things: natural selection Charles Darwin (1809-1882) Darwin’s Life •! Family –! English –! moderately wealthy (mom was a Wedgewood) –! Dad influenced his career options •! Education –! Started in medicine at 16 –! Switched to theology at Cambridge –! Interested in the scientific ideas of geologist Adam Sedgwick and naturalist John Henslow –! At first, didn’t believe evolution occurred –! Far more interested in biology than theology when he graduated The Beagle •! Five-year voyage on the H.M.S. Beagle (1831-1836) at age 22 with Captain Robert Fitzroy •! Galapagos Islands Darwin’s Influences Charles Lyell (1797-1875): geologist who popularized ‘uniformitarianism’ Darwin’s Influences Thomas Malthus (1766-1834) was an economist who observed that more individuals are born than survive to reproduce; individuals are thus in a ‘struggle for existence,’ that is, competition "The elephant is reckoned the slowest breeder of all known animals, and I have taken some pains to estimate its probable minimum rate of natural increase; it will be safest to assume that it begins breeding when 30 years old and goes on breeding until 90 years old; if this be so, after a period from 740 to 750 years there would be nearly 19 million elephants descended from this first pair.” (Darwin) So, some individuals will reproduce, and others will not. Question: are “winners” a random selection, or do some individuals have an advantage over others? Darwin’s Influences •! One pair of mice is capable of producing a litter of six offspring as many as six times a year. Within six weeks, each offspring can produce litters of their own. Darwin’s Influences Artificial Selection (selective Breeding For particular traits) Darwin’s Influences Comparative Anatomy Vertebrate forelimb Darwin’s Influences Fossils Darwin’s Influences Geographic distribution of traits: beaks were well-adapted to local environments on the islands Adaptive Radiation Adaptive Radiation in Galapagos Finches Darwin’s Influences •! •! •! •! •! •! Geology (Lyell) Within-species competition (Malthus) Artificial selection (breeders) Comparative anatomy Paleontology (fossils) Geographic distribution of traits (finches) ...Natural Selection Darwin’s Short Definition “I have called this principle, by which each slight variation [in a trait], if useful, is preserved, by the term Natural Selection.” - From The Origin of Species Natural Selection •!Natural selection is the process by which favorable traits that are heritable become more common in successive generations of a population of reproducing organisms, and unfavorable traits that are heritable become less common. •!Over time, this process can result in adaptations that specialize organisms for particular ecological niches and may eventually result in the emergence of new species. Natural Selection Assumption 1: Reproducing entities exist. Natural Selection Assumption 2: Variations exist, and they can be passed on to offspring (heritable variation). Natural Selection Assumption 3: Variations have reproductive consequences. Natural Selection Result: over time, the entire population will come to possess the reproductively superior variation. Natural Selection After thousands of generations…adaptations Adaptation here: camouflage Natural Selection •! Assumption 1: Reproducing entities exist. •! Assumption 2: Variations exist, and they can be passed on to offspring (heritable variation). •! Assumption 3: Variations have reproductive consequences. •! Result: over time, the entire population will come to possess the reproductively superior variation— adaptations. Darwin’s “Influences” Why did he wait so long to publish his theory of natural selection? Alfred Russel Wallace (1823-1913) Example: Finches at Daphne Major Darwin’s Biggest Scientific Problem •!Darwin realized that natural selection for specific traits could lead to changes in species through time. •!However, Darwin lacked information on how these traits were passed from generation to generation. Genetics Mendel was the first to explore the units of inheritance: genes. Gregor Mendel (1822-1884) What do GENES do? They control the production specific PROTEINS in living things… By stringing up small amino acid molecules into long protein strands… Protein –! the stuff living things are made of (e.g., collagen, enzymes, etc.) –! Proteins are long molecules that are folded over upon themselves –! The components of protein molecules are smaller molecules called amino acids (AAs) Amino Acids •! There are 20 kinds of AAs that make up all the proteins that organisms have –! alanine, asparagine, aspartic acid, cysteine, glutamic acid, glutamine, glycine, proline, serine, tyrosine, (essentials:) arginine, histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine •! AAs are made of limited elements: Hydrogen, Oxygen, Nitrogen, Carbon, and Sulfur (S only in methionine and cysteine) atoms only Amino Acids •! •! •! AAs are small molecules, but when strung up and folded over on themselves to form a protein, they can be quite large AAs are attached by peptide bonds This protein is 5 AAs long Amino acid ‘strand’ Each AA is like a bead on a necklace; electrochemical interactions among neighboring AAs cause the strand to fold over on itself in specific ways. The folded strand is a protein. Different AA sequences will make different proteins. Protein •! Proteins interact with other substances (including other proteins) in specific ways that are determined by their electrochemical properties. •! There are only 20AAs out there—a finite number (though in actuality the story is more complex than this) •! Different lengths and permutations of the AAs that make up AA strands can lead to countless varieties of proteins Protein Functions •! Structural proteins (collagen in skin, keratin in hair and nails, proteins that make up muscle tissue, etc.) •! Transport proteins (hemoglobin is a blood cell protein that transports oxygen to body tissues) •! Enzymes: proteins that catalyze (speed up) chemical reactions in the body •! Immune functions •! Signaling functions: E.g., neurons in your brain communicate with each other; these neurons are proteins (and other substances) From where do we get amino acids? Food! •! Foods are typically living (or formerly living) substances… •! What substances are in our food? Lichtenstein 1962 “Meat” One organism’s bodies becomes Another organism’s body… Living thing Organ/Tissue/Cells Protein AA to be restrung up into some protein needed by the eater’s body, as directed by the eater’s genes AA strand Proteins to AAs •! •! •! •! •! •! •! •! We eat the tissues of other organisms (plant tissue, meat, etc.) These tissues are made of proteins The proteins are cow muscle proteins or plant part proteins (such as cellulose) Your body is made of human muscle protein, hair protein, cornea protein, various neural proteins, etc. Cow muscle protein is different from human hair protein; how does the transformation happen? Answer: your digestive system breaks down the cow muscle protein into its constituent AAs Those AA molecules are the raw material that is used to build the proteins your body needs; they get restrung up into new “YOUR HAIR” proteins But how do they get restrung up into YOUR HAIR proteins? Amino Acids to Proteins …genes Genes •! •! •! •! •! •! •! Proteins Genes determine what proteins get built from those raw AA molecules Genes are protein-coding units of DNA You eat proteins of other living things, and break the protein into amino acids; then, genes in your DNA re-string those amino acids into proteins that YOU need to survive and reproduce Bodies are made of proteins (fat and carbs and water are essentially there to service these proteins) Genes also code for enyzmes, which are proteins that regulate everything, including development Other parts of DNA do not code for proteins, and have either no function (e.g. “hitchhiker DNA), or function for self-regulation, and other tasks—take advanced biology classes to learn about these very cool things DNA does What’s DNA? DNA •! Deoxyribonucleic acid •! A long molecule with a small number of constituent molecules •! Shape is a “double helix”—think of a ladder that is twisted DNA •! •! •! •! •! •! •! •! A sugar-phosphate “backbone,” (I.e., the “sides” of the ladder), and “rungs made up of paired nucleic acids There are 4 nucleic acids: adenine (A), thymine (T), cytosine (C), and guanine (G) Note these are not AAs A only bonds to T C only bonds to G A-T and C-G bonds are weak Sugar-phosphate bonds are strong Lots of “zipping” action Genes to Proteins •! Protein synthesis •! An elegant process that we do not have time to discuss thoroughly in this class •! Upshot: the sequence of nucleotides in DNA determines the sequence of AAs in protein manufacture (nucleic acid sequence maps to AA sequence, but not one-to-one, and redundancy is built into the system) •! In other words, your DNA determines what proteins get built out of the AAs that your body extracts from the foreign proteins you eat Genes Proteins Bodies + DNA molecule Amino acid molecules Cell parts, cells, and tissues Amino acid strand Organ Protein Body Natural Selection •! That was Darwin’s influences, •! A stripped-down tutorial on NS •! A brief overview of genes and molecular genetics •! Now, common misconceptions regarding natural selection Important Point •! A common misconception when thinking about natural selection is that there is a competition or a struggle for existence among members of different species •! E.g., thinking about rabbits vs. foxes •! Or thinking about a species vs. the many environmental circumstances that it encounters, including other species Not just getting food from the environment... Getting more food than other members of your species Not just avoiding predators… Avoiding predators better than other members of your species Not just avoiding parasites… Parasitic micro-organisms: roundworm, protozoan, bacterium, fungus, yeast Avoiding parasites better than other members of your species do (mange; a funny website: http://www.giantmicrobes.com/) Not just getting good living spaces... Wedge tail eagle nest Getting better living spaces than other members of your species (‘strumming,’ Riechert & Hammerstein) Funnel spider Stay Away from Funnel Spiders Don’t think of it as the environment (which includes other species) vs. the mouse Think of it as mouse vs. mouse in an environment (which includes other species) Mouse vs. mouse •! In any population, not all individuals survive to reproduce. Found place to live. Out-competed other mice for food. Found a mate. Successfully avoided predators. Reproduced successfully. His kids inherited his genes and the traits those genes build. No place to live. No food. Couldn’t find a mate. Predator ate him. Did not reproduce. His nonexistent kids did not inherit his genes and the traits those genes build. Important for mammals, and highlights the importance of within-species competition to exist and to reproduce: getting more or better mates than other same-sexed members of your species Male red deer Within-species Competition: The Bear and the Campers Still within-species competition, even here, where different species are still in different niches even though they are all eating the same fallen gazelle (1st cheetah, 2nd lions, 3rd hyenas, 4th vultures, next bugs…) (Back to Tinbergen’s Levels of Analysis) Trying to understand the Functional Level of Analysis: Adaptation/Functionality •! What is an adaptation? •! Adaptations are functional mechanisms that have been designed by the process of natural selection to serve specific problems related to survival and reproduction. •! Functional mechanisms have properties and features that were designed by natural selection. •! What is a function? Adaptation/Functionality Functions are mechanisms that solve specific problems. Adaptation/Functionality Functions are specific mechanisms that solve specific problems. Adaptation/Functionality Functional mechanisms have specific design features that solve specific problems. Most configurations will not solve the problem. Adaptation/Functionality •! Functional mechanisms contain considerable information about the problems they were designed to solve. •! A mechanism’s design features can often tell us what the function of it is •! “Reverse engineering” Reverse Engineering •! The process of discovering the technological principles of a human made device, object or system through analysis of its structure, function and operation. It often involves taking something (e.g., a mechanical device, electronic component, or software program) apart and analyzing its workings in detail Reverse Engineering Reverse Engineering Reverse Engineering (Note: same functions, different design) Eating leaves •! Colobines vs. howlers Adaptation/Functionality Lungs were designed by natural selection to oxygenate blood. Adaptation/Functionality How do you identify an adaptation? (1)! Design Analysis (2) Comparative method Analysis of Design Harvey dissected the heart and learned that the heart functions to pump blood by examining what he saw: chambers, strong muscles that expand and contract the chambers, arteries through which blood leaves a chamber and gets to other tissues in the body, valves to keep it from flowing backwards, etc. Analysis of Design Adaptations show evidence of: •! Precision •! Economy •! Efficiency •! Constancy •! Complexity •! Reliability George Williams Analysis of Design •! Problems: –! It is subjective…but let’s be reasonable –! Adaptations are not always perfectly-designed, hindering our ability to see, for sure, what their functions are (human spine) –! Function of adaptations is not always obvious, even though we KNOW they are adaptations (human bipedalism) The Comparative Method icthyosaur Marlin Dolphin The Comparative method: A primate example •! Testes to body ratio •! Low in gorillas, where females only mate with one male while fertile •! High in chimps, where females mate with multiple males while fertile •! Humans: somewhere in the middle •! What does this tell us about the sexual behaviors of our human ancestors? Adaptation/Functionality What kinds of functions will evolve? •! Precisely those functions that facilitate, or enable, reproduction, both directly (uteruses) and indirectly (hearts). •! These functions are called adaptations. •! An organism can be thought of an integrated set of adaptations. Functional Level of Analysis in Ethology (Tinbergen) •! Did the behavior evolve? •! Why did the behavior evolve? •! Does the behavior impact on the animal's chances of survival and reproduction? •! Better: how did the trait impact the relative rate of reproduction of the animal’s ancestors in the past? •! Did the behavior have a functional role—a purpose—in reproduction in the past? •! Is the behavior an adaptation? •! Did the behavior evolve by natural selection? Behaviors as adaptations? •! The link: neurons •! Brain cells and their linkages are made of protein—proteins built by genes—and are thus subject to the process of natural selection •! Brain activity causes behavior (recall the requirements for being a member of the animal kingdom; recall also sea squirts) The Modern Evolutionary Synthesis •! A union of ideas from different branches in biology that provides a logical account of the physical process of evolution; links are made over time with regard to: –! 1850s-1890s: Darwin’s ideas –! Early 1900s: Mendel’s work was rediscovered and incorporated –! Starting in 1920s: work by population geneticists Haldane, Wright, Morgan, and others –! Further advances in the understanding of DNA (Watson, Crick, and Franklin) in mid 1900s –! Those ideas, combined, comprise the Modern Synthesis –! Today, the synthesis is accepted by most working biologists •! …In later 1900s: ideas elaborated by Hamilton, Maynard-Smith, Dawkins, Williams, Trivers, and others Both Design Analysis ~AND/OR~ The comparative method “Survival of the Fittest” •! •! Some think the phrase explains why gazelles are eaten by cheetahs--cheetahs are more "fit" so they "survive.” Problematic terms and meanings: –! Survival? Nope, it is actually reproduction that is relevant--salmon die to spawn; birth kills 1/100 women in regions without access to medical care; men risk their lives in fights over women; male praying mantises are eaten alive by the female during copulation –! Fittest? The strongest? The fastest? What about the rodent-like mongrels that survived the meteor that killed off the dinosaurs 65 million years ago? –! Fittest? Fittest what? Fittest species? Fittest individual? Fittest genes? Fittest ecosystem of intracting species? •! If you interpret the words to their more specific meanings, and do so accurately, it ceases to be problematic. Dawkins uses but he is quite explicit about exactly those terms mean: replication (i.e., reproduction/copying) and thus "survival," over generations, of a particular sequence of DNA (such sequences of DNA are the "replicators"); the DNA molecule itself does not survive, but the ORDER of it's nucleotide molecules does. !"#$%$&' “For the good of the species” -Thought experiment: who would reproduce more, an organism that incurred a cost on its own reproduction to benefit others in its species, or one that hurt others to benefit its own reproduction? What would the next generation look like? -Wynne-Edwards vs. Lack’s studies of egg-laying in birds, and interpretations of the data in Dawkins