Evolution. Life’s Adaptations Over Time. Can a Species Change Over Time?. All breeds of dog are descended from the wolf. (they are domesticated wolves!) Genus: Canis Species: lupus All of the different breeds of dog have been produced by controlling how they reproduce. .
Evolution Life’s Adaptations Over Time
Can a Species Change Over Time? • All breeds of dog are descended from the wolf. (they are domesticated wolves!) Genus:Canis Species:lupus • All of the different breeds of dog have been produced by controlling how they reproduce.
Artificial Selection • Many plants and animals humans use have been domesticated over time from their wild ancestors. • Examples: cats, dogs, cattle, chickens, wheat, corn… • Domesticated plants and animals have been produced by selective breeding (or artificial selection) • What is artificial selection? • Selecting which varieties of a species breed or reproduce from generation to generation • By doing so, we encourage some characteristics (traits) and discourage other traits over time. • Characteristics selected for become abundant. • Characteristics selected against become rare or extinct.
Another Example of “Selection” • Observation: There are crabs found off the coast of Japan which look like a Samurai warrior. • Problem: Why are there crabs with Samurai warrior faces on their shells and why are they found only off the coast of Japan? The “Heike Crab”
Variation and Adaptation • Variation: an inherited trait that makes an individual different from other members of its species • Result from permanent changes (mutations) in an organism’s genes • Gene changes are inherited by offspring • Adaptation: a variation that makes an organism better suited to its environment • Changes in color, shape, behavior, chemical makeup • Good examples: camouflage, defenses
Two Examples of Adaptation • Having a striped coat makes these species very successful • in their environments. • What makes this variation an adaptation? (Why are stripes • important?) • Would albinoanimals be rare or abundant in the wild? Why?
Ideas About Evolution What is meant by the term evolution? • In general, the word evolution refers to any process of change over time. • Examples of things evolving or changing over time: • Changes in culture: customs, languages, technology • Changes in nature: habitats, climate, environment • Studies indicate that the Earth’s environments have changed greatly over millions of years. • How have living things changed along with their environments and adapted to new conditions?
What is a Species? • Millions of species of plants, animals, and other organisms are found on Earth today. • What is meant by the term species? • A species is a group of organisms that share similar characteristics and can reproduce among themselves. • Four examples species (out of several million): • Apis mellifera (honey bee) • Acer saccharum (sugar maple) • Panthera leo (African lion) • Homo sapiens (human being)
What is Evolution? Evolution • Refers to changes in the inherited characteristics of a species over time Theories of Evolution • Propose that existing life forms have evolved from earlier forms over long periods of time Why is evolution important in the study of life (biology)? • Explains why there are differences among the millions of species of living things on Earth • Explains why species in the past (now extinct) were very different from species found on Earth today • Explains the diversity of life on Earth (biodiversity) as well as the relationships between all living things
Lamarck’s Hypothesis: An Early Idea of Evolution • In 1809, Jean Baptiste de Lamarck proposed a hypothesis for why evolution occurs: • Hypothesis: Maybe characteristics (or traits) developed or acquired during life are inherited by their offspring. • He called his hypothesis the “Inheritance of Acquired Characteristics” • For example: muscles built by exercise giraffes stretching their necks • Why was Lamarck’s idea rejected?
Darwin’s Model of Evolution • In 1831, the H.M.S. Beagle sailed from England to explore the South American coast. • On board was a young naturalist named Charles Darwin. • Darwin was fascinated by the varieties of plants and animals he found during the voyage. • During the journey, he recorded observations about the strange organisms he found in the Galapagos Islands.
Darwin’s Observations Marine Iguana Galapagos Tortoises Flightless Cormorant Darwin’s Finches
Darwin’s Finches • Darwin observed 13 similar species of finches, with variations in body size, beak shape, and eating habits. • Darwin hypothesized that all 13 species descended from a similar species of finch found on the mainland. • Like all living things, finches produce more offspring than could possibly survive. • In a large population, there must be competition for food, habitats, and other resources. Those best adapted are most likely to survive, reproduce, and pass on their traits. • Finches with the best beak shapes for the available food survive longer and therefore produce more offspring. • Darwin reasoned that after many generations, these groups of finches might become separatespecies.
Artificial vs. Natural Selection • In artificial selection, humans choose which variations are most favorable. Darwin studied this. In the selective breeding of dogs, we select individuals with certain features we like and allow them to reproduce and pass on their traits. • In nature, the most favorable variations are those that ensure survival in the natural environment. Individuals with favorable variations survive and pass on their traits. Darwin called this “natural selection.”
Principles of Natural Selection 1. 2. 3. 4. 5. All organisms produce more offspring than can survive. Differences, or variations, occur among individuals of a species. Variations are passed on to offspring: they are inherited. Some variations are helpful. Individuals with helpful variations survive and reproduce better than those without these variations. Over time, the offspring of individuals with helpful variations make up more of a population and eventually become a separate species.
How Fast Does Evolution Occur? • It takes hundreds, thousands, or millions of generations for a new species to evolve. • Gradualism Model • describes evolution as a slow, ongoing process • fossil record shows intermediate forms and gradual changes • Punctuated Equilibrium Model • mutation of a few genes results in the appearance of a new species in a relatively short period of time • fossil record shows few (if any) intermediate forms • explains fast development of penicillin-resistant bacteria
Gradualism The evolution of the horse shows gradual changes over the last 60 million years.
Punctuated Equilibrium? • Many species of moth in England began to become • darker in the 19th century. Above is the “Peppered Moth.” • In 1849, a rare coal-black mutant moth was found near • Manchester, England (a very industrial area). • Within a century, this black variety increased to 90% of • the moth population in this area. How?
Fossil Clues About Evolution • Different types of fossils found in sedimentaryrocks show evidence that species evolved. • Examples of fossils: • footprints, imprints, casts • mineralized bones (like dinosaurs) • frozen fossils (mammoths) • insects trapped in amber (fossilized tree sap) • Complex forms of life occur in younger rocks; simpler forms of life in older rocks. • Fossils indicate gradual changes in living things, from simpler to more complex forms, over time.
Fossil Evidence: Feather Imprints Archaeopteryx – a primitive bird, Jurassic Period (150 million years ago)
Fossil Evidence: Dinosaur Bones Tyrannosaurus and Triceratops: Dinosaur Predator and Prey Western U.S., 70 million years ago
Fossil Evidence: Footprints Dilophosaurus tracks 180 million years old Dinosaur State Park Hartford, Connecticut Laetoli hominid footprints 3.2 million years old Tanzania, East Africa
Fossil Evidence: Amber Insects trapped in tree sap (fossilized into amber) 5 million years ago, Baltic region, Europe
Fossil Evidence: La Brea Tar Pits Extinct mammoth trapped in natural tar 40,000 years ago La Brea Tar Pits, Los Angeles, California
Why does the fossil record have gaps? • Fossils provide an incomplete rock record. • Fossils are rare: most organisms do not become fossils. • Weathering and erosion destroy much of the fossil record over time. • Some species may evolve rapidly (punctuated equilibrium), so few fossils may exist.
How Are Fossils Dated? • Fossil age can be determined by two basic methods: • Relative Dating • A fossil’s age depends on its location in the rock layers • Younger rock layers are found above older rock layers • “Relative” age can be determined (younger or older) • Radiometric Dating • Radioactive elements in rocks decay over time • By comparing the amounts of radioactive and nonradioactive element in a rock, age can be determined: radioactivity is a kind of “clock” • Example: Carbon-14 dating
Relative Dating • The limestone is known to be • 200 million years old. • The sandstone is known to be • 350 million years old. • Fossils found in the shale layer • could be: • a) 150 million years old • b) 200 million years old • c) 250 million years old • d) 400 million years old • That’s relative dating!!
Evolution: Direct Evidence • Fossil evidence supports the idea that evolution has occurred in the past. • Direct evidence supports the idea that evolution is occurring today: • Plant breeding • Development of antibiotic-resistant bacteria • Rapid evolution of pesticide-resistant insects • Rapid mutation of the HIV virus • The “Peppered Moth” is a also a good example
Evolution: Indirect Evidence Besides fossils and modern studies of changes in species, there are many examples of indirectevidence for evolution: • Embryology: the study of embryos (unborn young) and their development shows similarities among all vertebrate species (animals with backbones) • Homologous structures: similar body parts in related species can indicate that two or more species share common ancestors • Vestigialstructures: structures that don’t seem to have a function but might once have functioned in an ancestor • DNA: similarities in DNA between species provides evidence for how closely related they are
Embryology Similarities in the developing embryos of these organisms provide indirect evidence that they shared ancestors.
Homologous Structures Homologous structures in these organisms (limb bones) are indirect evidence that they evolved from a common ancestor.
Vestigial Structures • Vestigial structures in whales (hip and leg bones) have • no function in modern whales. This is indirect evidence that • whales descended from mammals that lived on land. • (Remember: whales are mammals, not fish!) • Vestigial structures in humans include: • appendix, tailbone, (what about ear muscles?)
DNA Similarities • The greater the similarity in DNA between different species, the • fewer variations (traits) separate them. This is indirect evidence of • how recently two species shared a common ancestor. • Comparing DNA indicates that apes and humans are genetically • very similar. Which species is our closest relative in the animal • kingdom? How recently may we have shared a common ancestor?
Evolution of Primates • Mammals (a class) are vertebrates that give birth to live young, have hair, and feed their young with milk. • Primates (an order) are mammals that share the following features or traits: • Opposable thumbs • Binocular vision • Rotating forelimbs • Flexible shoulders • Primates are divided into two groups (or families): • Prosimians (lemurs and tarsiers) • Anthropoids (monkeys, apes, and humans)
Hominids • Hominids were humanlike primates that appeared in Africa about 4 to 6 million years ago. • Hominids shared some characteristics with apes, but had different adaptations: • ate both meat and plants (omnivores) • walked upright on two legs • larger brains than apes
Early Human Ancestors Australopithecus fossils: (East Africa, 4 to 2 million years ago) Homo habilis fossils: (East Africa, about 2.5 to 1.5 million years ago) Homo erectus fossils: (Europe, Asia, Africa, about 1.5 MYA to 400,000 years ago) Homo sapiens fossils: Neanderthals in Europe (adapted to ice-age climate) (became extinct about 30,000 years ago) Cro-Magnon in Europe, Asia, Africa thought to be direct ancestors of modern humans (10,000 to 40,000 years ago)
Review Questions • What is artificial selection? Can you give an example? • What is the difference between a variation and an adaptation? • What is the definition of evolution? • What is a species? • Describe Lamarck’s hypothesis for how evolution occurs. • What are the five principles of natural selection? • How fast does evolution occur? Describe the two models of evolution that describe the speed of evolution and give examples of each. • What are some different types of fossils? • Describe the two methods of dating fossils. • Describe four examples of indirect evidence for evolution. • What are the characteristics of primates? • What are hominids? What are their characteristics? • Describe the differences between the different human ancestors. • What is the meaning of the species name “Homo sapiens?” • Can you describe some specific examples of adaptation and evolution we discussed in class?
References: Massachusetts Curriculum Framework Learning Standards Evolution and Biodiversity 10. Give examples of ways in which genetic variation and environmental factors are causes of evolution and the diversity of organisms. 11. Recognize that evidence drawn from geology, fossils, and comparative anatomy provide the basis of the theory of evolution. 12. Relate the extinction of a species to a mismatch of adaptation and the environment. Changes in Ecosystems Over Time 17. Identify ways in which ecosystems have changed throughout geologic time in response to physical conditions, interactions among organisms, and the actions of humans. Describe how changes may be catastrophes such as volcanic eruptions or ice storms. 18. Recognize that biological evolution accounts for the diversity of species through gradual processes over many generations. From “Life Science (Biology), Grades 6-8,” Massachusetts Science and Technology/Engineering Curriculum Framework, Massachusetts Department of Education, May 2001.