B5 - Developing Theories to Explain Change (Updated 2024) PDF

B5 - Developing Theories to Explain Change I can… Discuss the importance of sexual reproduction with regards to individual variation and evolution Compare Lamarckian and Darwinian explanations of evolutionary change Use evidence to explain the evolution of modern species from ancestr...

B5 - Developing Theories to Explain Change I can… Discuss the importance of sexual reproduction with regards to individual variation and evolution Compare Lamarckian and Darwinian explanations of evolutionary change Use evidence to explain the evolution of modern species from ancestral forms Developing Theories to Explain Change Scientific hypothesis: Provides one possible answer to a question or possible explanations for an observation ○ Needs to be tested to determine validity (truth) Hypotheses that consistently lead to successful predictions and explanations can be synthesized into general statements that explains a broad range of observations, called a scientific theory Historical Theory Greek philosophers, Plato and Aristotle, believed that life existed on Earth in a perfected and unchanging form Before 18th century, widely believed that living things were “fixed” and stayed the same generation after generation. In the second half of 18th century, scholars began to speculate about the issue of evolution Developing Theory of Natural Selection Developed over many centuries Because of influence of Roman Catholic Church in Europe, few evolutionary theories developed in 1700s Georges-Louis Leclerc, Comte du Buffon (1749) Noted similarities between humans and apes Speculated that they have a common ancestor Suggested Earth was much older than 6000 years old (was a common belief) Georges Cuvier (1813) Georges Cuvier published his Essay on the Theory of the Earth, in which he studied ancient life through the examination of fossils Cuvier found that different groups of fossil species could be found in different layers of rock, and that the deeper (older) the stratum, the more dissimilar the species are from modern life Found evidence that new species appeared and others disappeared as time passed Showed species could become extinct Hypothesized that destructive natural events (ex. floods, volcanic eruptions) killed numerous species Charles Lyell (1830) Rejected ideas of evolutions - natural disasters Suggested that geological processes that occur on Earth are slow, meaning Earth was quite old Theorized that slow, subtle processes could happen over longer periods of time and could result in substantial changes Jean Baptiste Lamarck (early 1800s) Thought that characteristics that were acquired during an organism's’ lifetime could be passed onto offspring Called this “Inheritance of Acquired Characteristics” ○ Ex. Giraffes stretching to reach higher leaves results in offspring getting taller His theory was rejected Charles Darwin In 1831, Darwin travelled aboard the HMS Beagle on a voyage to survey the coast of South America Made numerous observations regarding organisms he saw along the way Named the “Father of Evolutionary Theory” Darwin’s Observations In South America, Darwin observed unusual fossil species that resembled giant variations of the sloths and armadillos living in the same region He suspected that the living forms might have descended from the fossilized species He noted that species living in the South American tropics did not resemble those living in the African tropics ○ Did those species evolve independently? Darwin’s Observations The harsh landscape of the Galapagos Islands is home to 13 very similar species of finches that are found nowhere else on Earth Most closely resembled species living in a very different habitat on the coast of South America Did they all evolve from a single species that had arrived in the Galapagos from South America? Alfred Russel Wallace At the same time that Darwin was studying his observations, Wallace was studying organisms in South America and Malaysia Theory of Evolution by Natural Selection Darwin and Wallace were influenced by Thomas Malthus’ Essay on Principles of Population, which stated: Populations produced more offspring than environment could support. Darwin and Wallace reasoned that competition for limited resources would select for favorable traits (traits that increased chance of survival and reproduction) ○ As time passed, a greater proportion of population would have these beneficial traits as they improved their chances of surviving and reproducing ○ Process is called natural selection Evolution Over time, populations of the same species that are exposed to different environmental pressures can become so genetically different that they can no longer interbreed ○ They diverge to become two separate species - this process is known as evolution Evolution: The process by which new species come into being ○ Natural selection is the mechanism by which evolution occurs Further Evidence for Evolution 1. Fossils 2. Patterns of distribution 3. Anatomy 4. Embryology 5. Molecular biology 6. Genetics 1. Fossils Found in layers of rocks near surface, appear to be much more closely related to modern species than fossils found in older layers Not all organisms appear in fossil record at the same time, which indicates that different species evolved at different times Changes were slow and took millions of years Transitional fossils: Found to fill in gaps to the fossil record and link different species together 2. Patterns of Distribution Biogeography: Study of past and present geographical distribution of organisms Closely related species are almost never found in exactly the same location/habitat Examples of biogeographical evidence: 1. Animals in inlands resemble animals on closest mainland. 2. Geographically close environments carry related species, which aren’t found in further, but environmentally similar area 3. Similar fossils can be found on coasts of neighboring continents 3. Comparative Anatomy Many closely related organisms have common homologous structure: structures that have same origin and general elements, but different functions ○ Point to a common ancestor Analogous structure: Body parts with similar functions but different evolutionary origins The bones shown above have very similar ○ Don’t lend evidence to evolution arrangements, but they all have different uses. 4. Embroyology Embryos of different organisms exhibit similar stages of embryonic development Points to common ancestral origin Embryology is possibly the most important evidence of evolution, as it demonstrates how tiny changes in protein signalling during development can result in large-scale anatomic change. 4. Embryology In the early weeks of development, human embryos possess a tail and gill slits (similar to chicken and fish embryos) The embryonic tail serves no function and eventually serves as a tailbone (coccyx) ○ Provides stability and weight distribution when sitting 5. Molecular Biology Technologies have been developed to identify DNA and protein molecules ○ Provide evidence to support idea of common ancestry and evolution through natural selection All cells consist of: ○ Membranes filled with water ○ Genetic material ○ Protein ○ Lipids and carbohydrates Enzymes control biochemical reactions 6. Genetics When Darwin proposed theory of extinction, little was understood regarding genetics Genetic evidence and understanding of heredity have led to understanding that: ○ Species pass on their traits to offspring using genetic material ○ Genetic materials can randomly change (mutations), leading to variation in traits DNA analysis has also been used to trace the movement of the human species across the globe.