Chapter 8.1 Scientific Contributions to a Theory of Evolution -in the 1600s, scholars in Europe began to use a system of empirical studies—observation and experiment to form ideas, to explain the natural world -John Ray (1627-1705) was the first scientist to carry out an empirical study on the natural world—he developed a classification system for plants and animals based on physiology -later, Carolus Linnaeus (1707-1778) expanded this system -this system helped scientists of the time recognize and think about similarities and differences between organisms Georges-Louis Leclerc, Comte de Buffon (1707-1788) -Buffon noted the similarities between humans and apes, and speculated that they might have a common ancestor -he also suggested that the Earth was much older than 6000 years old The Science of Paleontolo Paleontology gy -a fossil is the preserved remains of a once-living organism -Mary Anning (1799-1847) discovered the first plesiosaur, an aquatic reptile -Georges Cuvier is credited with developing the science of paleontology of paleontology—the study of ancient life through the examination of fossils -he noted that in each stratum (layer of rock) is characterized by a unique group of fossil species -also found that the deeper (older) the stratum, the more different the species are from the modern species -he found evidence that new species appeared and others disappeared over the passage of time—showed that species could become extinct -Cuvier proposed the idea that Earth experienced many destructive natural events that were violent enough to have killed numerous species—this idea is known as catastrophism -he suggested that these catastrophes corresponded with the boundaries between the strata -he used this idea to explain the appearance of fossils of species that did not exist anymore Charles Lyell (1797-1875) -rejected catastrophism catastrophism -he proposed uniformitarianism, uniformitarianism, which states that geological processes operated at the same rates in the past as they do today -theorized that slow, subtle processes could happen over a long period of time and could result in substantial changes -meaning, the forces that built and eroded mountains took over the same rate of time as today -inspired famous naturalist, Charles Darwin Jean Baptist Lamarck (1744-1829) -he observed the changes in species over time as a “line of descent”—in which a series of fossils (from older to more recent) led to a modern species -hypothesized that organisms would become progressively better adapted to their env ironments -his idea was called the inheritance of acquired species—the idea that characteristics acquired during an organism’s lifetime can be passed on to its offspring -he also had another idea called use and disuse, where body parts that were not used would eventually disappear -also noted that an organisms adaptations to the environment resulted in characteristics that could be i nherited by the environment Charles Darwin (1809-1882) -in 1831, Darwin went on an expedition on the HMS Beagle, a British survey ship -primary purpose was to map the coast of South America and also provided him with the opportunity to explore the natural history of various countries -his observations later on contributed to his theory of evolution—a theory explaining how life has changed, and
-evolution is the process of genetic change in a population over time -his main observations were: •the rodents from South America were structurally similar but significantly different f rom rodents from other continents •the fossils of extinct animals had many similarities to some of the living, modern species •finches and other animals observed in the Galapagos closely resembled the animals he had observed on the west coast of South America •the species in the Galapagos varied slightly between islands Darwin, Wallace, and the Theory of Evolution by Natural Selection -Russel Wallace, another English naturalist, reached conclusions that were similar to Darwin’s -they accepted that populations changed changed as time passed, but were still unsure of how they change -an economist, Thomas Malthus, proposed that populations produced far more offspring than their environment could support—then the populations would eventually be reduced due to starvation or disease -this led Darwin to develop his idea of the survival of the fittest —the idea that the organisms that are the fittest leave the most offspring, so those organisms win the struggle for survival -he also proposed that all life descended from some unknown organism and as descendants of this organism spread out over different habitats, they developed adaptations that helped them better survive in their l ocal environment -his ideas are as summarized as: •Organisms produce more offspring than can survive. Therefore, they compete for limited resources •individuals of a population vary extensively, and much of this variation i s heritable •individuals that are better suited to local conditions survive to produce more offspri ng •processes for change are slow and gradual -Darwin did not use the word evolution; instead, he called it descent with modification -he felt that using the word evolution implied progress and natural selection does not demonstrate progress; it has no set direction
Chapter 8.2 Sources of Evidence for Evolution Fossils: Evidence for the History of Life -fossil records are the remains and traces of past life that are found in sedimentary rock; it reveals the history of life on Earth and the kinds of organisms that were alive in the past -can be used to examine organisms over 500 million years ago -first record of fossils were from 3.5 billion billi on years ago Evidence from the Fossil Record -the fossil record provides the following evidence: •fossils in young layers of rock are much more similar to species alive today than fossils found in deeper layers of rock •fossils appear in chronological order in the rock layers (younger, newer layers/older, deeper l ayers) •not all organisms appear in the fossil reco rd at the same time Evidence from Transitional Fossils -transitional fossils are fossils that show intermediary links between groups of organisms -help link the past with the present -for example, scientists have found fossilized whales from 36 to 35 million years ago -these fossils link present day whales to their ancestral past -the whales from 36 million years ago had small hind limbs, but li ved a completely aquatic life -the characteristic would be useless—are called vestigial structures, structures , a structure that is a reduced version of a structure that was functional in the organism’s ancestors
Evidence from Biogeography -biogeography is the study of the past and present geographical distribution of organisms -Darwin and Wallace’s observations were heavi ly based on biogeography -they have observed that: •geographically close environments are more likely to be populated by related species than locations that are far apart but environmentally similar
•animals found on islands often closely re semble animals found on the closest continent—this suggests that the island animals have evolved from mainland m ainland migrants and the populations would change by becoming adapted to the conditions of their new environment
•fossils of the same species can be found on the coastline of neighbouring continents—evidence of the supercontinent, Pangea Evidence from Anatomy -despite the difference functions of vertebrate forelimbs (flying, swimming, etc), all vertebrate forelimbs contain the same set of bones -this is because the basic vertebrate forelimb originated with a common ancestor -homologous structures are structures that have similar structural elements and origin but may have different functions (human arm, bat wing, etc) -the structures all have similar components, such as: the number of bones, muscles, l igaments, tendons and blood vessels -how these components are arranged can be suited for different functions -analogous structures are body parts of organisms that perform similar functions but do not have a common evolutionary origin -they evolve in species of different origin that live in similar ecological units (e.g. bird wings vs. insect wings) Evidence from Embryology -embryology is the study of early, pre-birth stages of an organism’s development -embryos of different organisms exhibit similar stages of embryonic development -for example, all vertebrate embryos have paired pouches—in fish, the pouches develop into gills whereas i n humans, the pouches develop into the ears and throat -the similarities between embryos in related rel ated groups (such as vertebrates) point to a common ancestral origin Evidence from DNA -scientists can determine how closely related two organisms are by comparing their DNA -if two species have similar patterns in their DNA, this indicates that these DNA sequences must have been inherited from a common ancestor -by studying gene sequences, scientists have determined that dogs are related to bears and whales and dolphins are related to hoofed animals such as cows and deer
