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Evolution: Classified as "descent with modification" meaning that animals undergo speciation over time. Darwin claims every organism shares a common ancestor. Organisms closest on the tree of life are more closely related.

Evidence: Organisms having ANATOMICAL SIMILARITIES shows that they must be related. Anatomic Similarities are classified in three ways:

Homologous Structures: Homologous structures are structures that are similar in terms of their anatomy and physicality, but have adapted independently to help each organism that has that structure survive in their specific environment. In other words, homologous structures are similar anatomically but different in function. AKA, Divergent Evolution.

Ex: The forelimbs of whales, humans, and birds. All of these animals have the same forelimb structure, but the forelimbs of each animal does something different. For example, humans use it to grab things with their hands, whales use them to swim in the ocean, and birds use them to fly.

* Homologous structures is evidence for evolution because it suggests that even animals that are vastly different from one another share a common ancestor that passed down the similar anatomical structure.

Vestigal Structures: Vestigial Structures are anatomical structures that organisms have, but they do not perform any particular function in the organism's body. They are homologous to structures that OTHER organisms use.

Ex: The human tailbone which has no particular function in humans. Humans are said to be descended from monkeys, which DO indeed use their tailbones.

* Vestigial structures suggest evolution and speciation because the vestigial structures may have once had use in the common ancestor of organisms, but have developed to not have the same use due to speciation. Animals that still use the structures would, in this case, be more closely related to the common ancestor.

Analogous Structures: Anatomical structures that look similar and have similar functions, but DO NOT suggest common ancestry. In other words, they look the same and have the same function, but the structures have evolved independently. They are the same due to the same selective pressures. AKA Convergent Evolution.

Ex: The Arctic Fox and Ptargamin Bird both live in the Arctic Tundra and have white fur/feathers. They likely DO NOT share a common ancestor, but they both live in the same environment and need white fur in order to blend in and avoid being detected by their predators, so they display the same phenotype.

* Although analogous structures are more a testament to the process of Natural Selection, DNA similarities and embryological similarities tell us more about evolution.

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Embryology: Embryology is the study of embryos and their similarities. Embryos of almost all organisms look so similar in the womb that it is hard to tell them apart. The traits of some organisms appear in the early embryos of another organism, and then disappear as the embryo matures and grows into a baby.

Ex: Human embryos have gills slits (for breathing underwater). Fish embryos also have gill slits. Since fish have to breath under-water, the gills DO develop in the mature fish embryo, but they disappear before birth in the human embryo.

* This supports evolution because it shows that because ALL organisms share so much embryological similarity, they must all have a common ancestor that whos phenotype was like the un-matured early embryos.

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DNA/Molecular Similarities: All living organisms are made up of DNA, and surprisingly the genome of all of these organisms is more or less the same. Furthermore, the chemical processes of DNA replication and gene expression use similar cell technology and processes.

Ex: All organisms have DNA polymerase. Although the DNA pol is slightly different in terms of each organism (Due to Natural Selection and Selective Pressures), it has the same function in all organisms: to aid in DNA replication by adding nucleotides.

* This is clear evidence that all organisms must have shared a common ancestor with the same basic DNA structure and one which conducted the same DNA processes. DNA similarities do not help scientists discover how exactly the organisms are related, it simply shows that they ARE related.

The more similar DNA of two organisms, the more closely related they are.

Homologous/Orthologous Genes: When two organisms share a sequence of related genes. Can show how closely related two organisms are.

Ex: Humans, cows, chickens and chimpanzees share the gene that codes for insulin. The gene is 98% similar in humans and chimps and only 64% similar in humans and chickens; shows that humans are more closely related to chimpanzees than chickens.

* This is evidence for evolution because all organisms shared a common ancestor that passed on that specific gene.

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Biogeography: Relates the geographical location of some species back to evolution. Approximately 2 Billion years ago the super-continent pangea hosted organisms. The organisms before the tectonic plates divided are seen all across the world. However, organisms seen after the break-up of Pangea are in small clusters. Some areas that are split geographically (Allopatric Speciation) have organisms that are not visible in any other areas of the world.

Ex: Australia has always been a separate island from the rest of the world. Therefore, Australia contains the only marsupials (such as koalas) which carry their young in a pouch. Most other mammal species in the rest of the world keep their young in the placenta. Marsupials were alone and therefore evolved independently of other organisms.

Animal species on islands are diverse due to the different ecosystems and niches of each island, but they share similarities with mainland organisms. This means mainland organisms were once the ancient common ancestors of the island variations of species.

* This is evidence for evolution because it shows that when supercontinents still existed, animals on different islands after separation underwent speciation, but shared similarities between the mainland organisms they descended from.

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Fossils: Fossils are the remains of organisms and are often located in sedimentary (layered) rock. Not all animals fossilize.

Fossil Record: An incomplete record detailing the timeline of the fossils. Fossil dating helps to determine when the organisms were alive.

Fossils are contained in layers of sedimentary rock called strata which provide a timeline. Older layers with older fossils, and thus older animals and possinle common ancestors are located at the bottom. Newer layers are located at the top and have newer fossils.

Radiometric Dating: Measures radioactive decay of elements that can tell how old the fossils are.

Fossils document the history of living organisms and show the change and evolution of those organisms over time. Similarities in fossils over the years are noticed by the scientists. When fossils contain similarities, this suggests that the older organisms were probably the ancestors of the younger fossils found at the top.

You can construct a large family tree looking at fossils, dating back millions of years to an original common ancestor.

Changes in the physical and anatomical features over time can reflect the adaptations that animals encountered as their environment changed over time.

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Evolution is NOT "Just a Theory." Many scientists reduce the "Theory" of Evolution to just a hypothesis. It is important to remember that "theory" and "hypothesis" are not interchangeable. A hypothesis is an educated guess based off of a case study or information. A theory is different as it has been tested rigorously and VERIFIED. It explains a large set of observations.

The Theory of Evolution through Natural Selection has so much evidence (including Anatomical, Embryological, DNA, Biogeographical, and Fossils) that it is said to be describing FACTS about our living world and the way that organisms grow, adapt, and evolve over time.

Therefore, the "theory" of evolution holds great validation.

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Individuals DO NOT evolve, rather it is the POPULATIONS themselves of species that evolve over time. Although individuals do change over their lifetime, these are rather called "developments" but they are not referred to as the organism evolving.

Evolution is better described as evolution of a SPECIFIC trait. For example, bacteria undergo evolution when they have the trait of antibiotic resistance. The indvidual bacterium itself does not evolve, but rather, the entire population evolves through expression of that trait. SEVERAL individuals contribute to the overall evolution, not just a singular organism.

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Evolution DOES NOT explain the origin of life, but rather how life that already pre-existed evolved over time. The most basic unit of life is the cell; evolution, while it may shed some light on the topic, does not explain WHERE this basic unit of life came from. It is sometimes possible to connect evolution to the "evolution" of a cell, but there is not enough information to explain where a cell came from. Evolution generally focuses on larger populations and how organisms are related to one another, not how organisms were created.

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Organisms DO NOT evolve knowingly, but rather the populations naturally evolve as a result of changes in the surrounding environment. In other words, evolutions is not intentional; organisms do not decide to evolve if they need to.

Furthermore, traits do not appear out of nowhere, traits are already present within the population. This is because one trait MUST be selected OVER another trait, meaning that it already has to be present in a larger amount and at a genetic level at which it can be passed down. For instance, bacterial populations that exhibit antibiotic resistance do not all mutate to do this, rather this trait already exists in some and depending on the environment, it will be naturally selected to become expressed in the majority if needed.

Species do not generally make an effort to "improve" over time. Evolution can't exactly "improve" or "better" a species because the environment is constantly changing. There is no telling if one trait that is beneficial at one point will be beneficial many years down the line as the environment undergoes changes. Therefore, "survival of the fittest" is not about which organism is better, stronger, or faster. It is rather about how well an organism is adapted to survive and reproduce in that specific environment.