Darwin’s Theory of Evolution Chapter 15 Darwin’s Theory of Evolution
Section 15-1 – Puzzle of Life’s Diversity Biological Diversity – variety of living things How did all these organisms come to be? How are they related? Evolution - change over time; the process by which modern organisms have descended from ancient organisms Change in a population of organisms over generations
I. Voyage of the Beagle Charles Darwin Born 1809 Attended Cambridge - Studied natural history, geology After college, joined the crew of the H.M.S. Beagle. His observations & collected data led to him proposing evolutionary theory
II. Darwin’s Observations Patterns of Diversity Plants & animals seemed remarkable well suited to their environment Types of organisms are found in only certain areas of the world Argentina & Australia have grasslands. So why don’t they have the same organisms living there?
Living Organisms & Fossils Darwin also collected fossils (remains of ancient organisms) What are some different types/examples of fossils? Some fossils resembled current, living organisms, while others looked completely different Why had some species disappeared? How are they related to living species?
The Galapagos Islands Found 13 species of finches that were similar except for their beaks Each Island had different food sources, requiring different beaks! Also noticed different species of land tortoises on different islands. The shape of a tortoise’s shell differed from island to island. See pg. 371, Figure 15-3
(a) Cactus-eater (b) Insect-eater (c) Seed-eater Figure 22.6 Figure 22.6 Three examples of beak variation in Galápagos finches. (c) Seed-eater
Section 15-2: Ideas that shaped Darwin’s Thinking The Beliefs of the Time Earth & all life had only been created a few thousand years ago No organisms had changed, but the robin had always been a robin As fossils record grew, adjustments to beliefs began Periods of creation occurred following catastrophic events that killed off many forms of life
II. An Ancient Changing Earth James Hutton Proposed theory of Gradualism where by Earth’s features were created (& changed) gradually by natural processes over time Mountain building, valleys, canyons, oceanic ridges, etc. occur over millions of years Proposed Earth was much older than a few thousand years.
Charles Lyell Before his journey, Darwin was given Lyell’s book, Principles of Geology Incorporated gradualism into uniformitarianism, which states that geologic processes operate today just as they did for most of Earth’s history Influenced Darwin! If the Earth could change over time, might life change too? If so, life would change slowly, over millions of years, just like the Earth.
Jean Babtiste de Lamark – 1st to hypothesize on evolution Similar species descended from a common ancestor. Meaning all similar species come from one ancient species. New species develop through the passing of acquired traits, which are traits not determined by genes, but by the environment.
According to Lamark, species acquire traits because/by: All organisms acquire traits that help them live more successfully in their environment Using/not using certain parts of their body to change the size/shape of organs
Are acquired traits passed on? NO Ex: A water acquired webbed-feet by stretching the membrane between its toes. Every offspring of this bird will have webbed feet. Ex: A person is blinded in an accident. This acquired trait will be passed on to offspring. Does this make sense? NO Are acquired traits passed on? NO
Lamark’s theories Disproved/Proved Acquired Traits are not passed on to offspring, only genetic traits are! Similar species do tend to share a common ancestor and organisms do change over time.
Darwin applied this concept to plants/animals. Thomas Malthus – observed that babies were born faster than people or dying If the human population grows unchecked, living space & food will become insufficient. Darwin applied this concept to plants/animals. 1 maple tree produces 1000’s of seeds a year Not all survive = many offspring die before reproducing What factor(s) determines who survives & who doesn’t?
Section 15-3: Darwin’s Theory of Evolution I. The Race to publish Alfred Wallace also proposed a theory on evolutionary change, sent the essay to Darwin Drove Darwin to write out and publish his theory ……. before Wallace. 1859, published On the Origin of Species: By Means of Natural Selection
Natural Variation & Artificial Selection Natural variation is differences among individuals of a species in nature This variation could be inherited. Darwin noted that breeders used variation to improve their crops, livestock through a technique called selective breeding. Darwin termed this process as artificial selection Nature provides the variation, and humans select those variations that they find useful.
Evolution by Natural Selection Struggle for Existence Members of each species struggle to exist by competing for food, living space, etc.
Survival of the Fittest Fitness: ability of an individual to survive and reproduce in its specific environment The fitness is the result of adaptations, inherited characteristic that increases an organism's chance of survival. Anatomical/structural, characteristics, organism’s physiological processes or functions, or complex features (behaviors).
Darwin referred to the survival of the fittest as Natural Selection Successful adaptations = organisms become better suited to their environment = better able to survive & reproduce. Unsuccessful characteristics = organisms not well suited to their environment (low levels of fitness) = death or few offspring.
Natural Selection The traits being selected increase over time & contribute to an organism's fitness in its environment. Takes place without human control or direction. Cannot be seen directly; it can only be observed as changes in a population over generations.
Descent with Modification – Each living species has descended, with changes, from other species over time As a result, species today look different from their ancestors. Also implies that all living organisms are related to one another. Common Descent: All species—living & extinct—were derived from common ancestors a single “tree of life” links all living things.
Darwin’s Tree of Life
IV. Evidence of Evolution Fossil Record Fossils formed in different rock layers showed that organisms have changed over time. Fossils from sequential rock layers could show how a species changed and produced a new species!
Geographic Distribution of Living Species Darwin’s finches in the Galápagos were similar, yet different from one another & also different from a similar species on the mainland. Darwin’s finches could have descended with modification from a common mainland ancestor.
Entirely different species of animals living in similar environments can have similar structures/behaviors descended from different ancestor. Living under similar ecological conditions, being exposed to similar pressures of natural selection, they ended up evolving common features. Regardless of appearance, two species are closely related when they share a common ancestry.
Anatomical Evidence Homologous structures: Body parts with same basic structure but different function Structures have different mature forms but develop from same embryonic tissues Indicates common ancestry Foreleg – same set of bones for vertebrate.
Anatomical Evidence Analogous Structures - Body parts with similar function but different structure Indicates NO common ancestry e.g. wings if insect and wings of bat
Anatomical Evidence Vestigial Structure: structure reduced in size No known function Left over from other structure e.g. tailbone for humans
Embryological Evidence – Compares development of embryos Similar embryologycommon ancestry. Embryo looks similar for longer period = more closely related species Embryonic cells develop in same order and pattern to produce tissues and organs which produce homologous structures
Biochemical Evidence The sequence of amino acids that make up proteins are similar similar DNA strandsorganism show evolutionary relationship. e.g. Humans and Chimpanzees (97% similar)