Chapter 11: Evidence for Evolution PDF

Chapter 11: Evidence for Evolution SCB 101 Prof. Calkins  Evolution: a change in the overall characteristics of a group of organisms (populations) over multiple generations Populations evolve, individuals do not. Evolution Populat...

Chapter 11: Evidence for Evolution SCB 101 Prof. Calkins  Evolution: a change in the overall characteristics of a group of organisms (populations) over multiple generations Populations evolve, individuals do not. Evolution Population: a group of individuals of the same species living in a defined area  Natural selection: process by which individuals with advantageous inherited characteristics for a particular environment survive and reproduce at a Mechanism higher rate than do individuals with other, less useful characteristics s of Evolution Genetic Drift: the frequency of a neutral mutation (no positive or negative effects) randomly increases in a population. Evolution by Natural Selection Natural selection: Those individuals that survive long enough to reproduce will pass on their characteristics to their offspring, who continue to reproduce and pass on the advantageous characteristics. In other words, whoever has the most kids wins! Dead individuals do not pass on traits, so whoever survives LONGER will have more kids. Natural Selection Birds with larger beaks can eat large, tough seeds After a drought, ONLY large seeds are available Therefore, birds with larger beaks will be able to consume enough food to survive and reproduce The offspring in the next generation will then have larger beaks than the previous due to natural selection  Direct observation through artificial selection Evidence Fossil evidence Shared characteristics among living organisms for Similarities and differences in DNA Evolution Biogeographic evidence Common patterns of embryo development Artificial Selection Artificial selection: biological evolution for desired traits caused by humans performing selective breeding Selective breeding: process by which humans determine which individuals with desired characteristics will mate Fossils Fossils: the mineralized remains or impressions of formerly living organisms The Fossil Record The fossil record: Enables biologists to reconstruct the history of life on Earth Provides some of the strongest evidence that species have evolved over time Contains excellent examples of how major new groups of organisms arose from previously existing organisms called transitional fossils Transitional fossils: evidence of species with some similarities to the ancestral group and some similarities to the descendant species The ages of fossils correspond to their depth or distance from the surface of Earth: Older fossils are found in deeper, older rock layers This helps us ‘age’ different fossils to determine WHEN they existed  Recap: Q1: What is the general definition of a fossil? Fossils are the mineralized remains of formerly living organisms or the impressions of formerly living organisms. Q2: How are the ancestors of modern whales different from their present form? They became larger, they lost their back limbs, and their front limbs became proportionally smaller. Q3: What is meant by the term “transitional fossil” when referring to the fossil record? Intermediate forms of fossils are fossils of species with some similarities to the known extinct ancestral group and some similarities to the descendant or currently living species. They can be thought of as “missing links” in evolution. Ex: Whale Ancestors J. G. M. “Hans” Thewissen discovered that the broken ear bone of a 50-million-year-old deerlike mammal named Indohyus looks more like a whale ear than that of any living land mammal.  Thewissen and his team identified more than 400 bones that belonged to Indohyus. Putting together the They assembled a skeleton and had an artist’s depiction of Indohyus Evolution ‘puzzle’ illustrated. The bones and fossils they found were more similar to water-dwelling mammals than to land-dwellers. Ex: Whale Ancestors The features of the fossils provided additional evidence that Indohyus was a relative of whales: Ear bone Oxygen isotopes in teeth that match water-going mammals today Large crushing molars for eating plants, similar to hippos and muskrats Thick, heavy bones like other water-dwelling mammals Adaptive Traits Modern animals that live in shallow water have thick bones. Helps prevent them from floating Enables them to dive quickly Adaptive trait/ adaptation: a feature that gives an individual improved function in a competitive environment  Echolocation in bats is an adaptive trait used for catching insects in the dark. Adaptations take Stick insects avoid detection by predators by physically and behaviorally many forms mimicking the plants they live on.  Recap: Q1: What is an adaptation? A feature that gives an individual improved function in a competitive environment Q2: Why does this thick-bone adaptation suggest a water-dwelling lifestyle? Fossil animals with thick bones are presumed to have been water dwellers because almost all currently living water-dwelling animals have thick bones. Q3: How did this adaptation likely increase survival or reproduction in Indohyus? Thick bones probably enabled Indohyus to forage on the bottoms of lakes or ponds more efficiently than could species with lighter bones that had to work harder to stay submerged. A feeding advantage could have enabled Indohyus to eat more, live longer, and have a higher reproductive rate (producing more babies that survived) than those with lighter bones. Shared Characteristics among Living Organisms Many shared characteristics result from organisms sharing traits that evolved from a common ancestor. Common ancestor: an organism from which many species have evolved Common descent: the sharing of a common ancestor by two or more different species Shared Characteristics of Mammals All mammals share these characteristics: 1) Have hair or fur 2) Breathe air 3) Have mammary glands 4) Give birth to live young 5) Maintain a constant internal body temperature (warm-blooded) These characteristics were first seen in the earliest common ancestor of mammals, and have continued to persist and evolve in today’s mammals too. Homologous Traits Homologous traits are: Similar structures in organisms of common descent Traits that were inherited from a common ancestor Traits that will begin to look different over time SHARED traits across living organisms  Recap: Q1: What is meant by the term “common ancestor”? A common ancestor is the species from which at least two currently living species both descended Q2: Why are homologous structures among organisms evidence for evolution? Homologous structures are parts of an organism that have changed in size or specific form over time but are easily determined to be the same structure in the ancestral species from which the organism evolved. Species with homologous traits are all related by originally coming from an ancestor with those specific structures. Q3: Aside from skeletal structural similarities, what other commonalities among organisms might be considered homologous? Any traits that are shared by related organisms and also shared in an ancestor could be homologous traits. Some examples include mammary glands, egg laying, structures to extract oxygen from air or water, and the use of DNA as the genetic material. Vestigial Traits Vestigial traits: another type of trait that many organisms have because of a common descent These features are inherited from a common ancestor, but are no longer useful. They may appear as reduced or degenerated parts whose function is hard to discern.  Recap: Q1: Why are vestigial structures among organisms evidence for evolution? Vestigial structures are evidence for evolution because they are shared among related species that all have a common ancestor. Goose bumps in humans are one example. In our furry ancestors, goose bumps fluffed the fur, thereby increasing its insulating effects and helping the animals to keep warm. Q2: Why might vestigial structures still exist if they are no longer useful (think about natural selection)? Only traits that harm an organism’s ability to survive and reproduce disappear from the fossil record, because organisms having these traits die and do not reproduce. Traits that are merely useless and not harmful will persist in the organisms that have them. They may diminish because these structures are no longer needed and do not give organisms a selective advantage, but the organisms survive and reproduce just as well with or without them. Similarities and Differences in DNA All living organisms on Earth use DNA as their hereditary or genetic material. All living organisms on Earth use the same genetic code to build proteins. The universality of the genetic code is one of the strongest pieces of evidence that all living things evolved from a common ancestor. Similarity between DNA sequences points to common ancestors among species. And how closely related they are Pseudogenes Like vestigial structures, pseudogenes are genes that code for proteins we no longer make. They are there, but not functional Humans lack the enzyme to synthesize vitamin C, BUT we have a mutation of the gene that codes for the enzyme. Non-primates have the functioning version  Recap: How is the similarity in the DNA sequence of related organisms evidence for evolution? Since all living things use the same nucleotides in DNA, we can assume that they all EVOLVED from a common ancestor. The changes in DNA sequences in populations over time create the changes in traits that drive evolution. We can map the changes that occur in populations or species by looking at sequence similarity and re-creating a family tree. The more related a species is to another species, the more similar the DNA sequences are. Humans and chimps are more similar in DNA sequence than are humans and mice. Biogeography Biogeography of a species: the geographic locations where its fossils are or will be found Biogeography of whale fossils matches the pattern predicted by evolution: All early species of whales that lived in rivers and lakes, but did not swim in the ocean, are found near India and Pakistan. All fully aquatic protocetids are geographically much more widespread because they were good swimmers.  Recap: Can we use biogeographic evidence to support evolution without using fossil evidence? Give examples. Yes. We can use the current locations of living organisms that are related to support evolution by biogeography. For example, members of the primate family are found on almost all the continents on Earth, suggesting that their common ancestor lived at the time of Pangaea Embryonic Development Embryonic development: how an organism develops from a zygote into its full form at birth Similarities in different organisms show that characteristics arose through evolutionary modifications of traits from common ancestors. Example: gill slits and tails during development of humans  Recap: Why are the similarities among organisms during early development evidence for evolution? Similarities between organisms during early development suggest that they have a common ancestor whose early development occurred in the same or similar manner. All vertebrates go through similar stages of development in the early embryo. Many invertebrate organisms also share the same steps in embryonic development. Review: There are animals that have DNA sequences for genes for some of the same proteins as humans do. What does this suggest? a. Long ago, these animals crossbred with humans. b. Humans and these animals evolved via common descent from a common ancestor. c. Nothing, this is just a coincidence. Review: Which of the following is NOT evidence for evolution by natural selection? a. similarities in embryonic development of different animals b. the increase in the size of finch beaks after a drought c. the great diversity of domestic dogs d. humans, whales, and bats (and others) having armlike structures with five digits Review: If a homologous trait is no longer useful in a specific organism, then it is referred to scientifically by what term? a. vestigial b. analogous c. adaptive d. transitional