Biology - Principles of Evolution | Biology

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Study GuideBiology–Principles of Evolution1. History of the Theory of Evolution1.1 What Is Evolution?Evolution means change over time. In biology, it refers to changes in the characteristics of apopulation of organisms across manygenerations. These changes do not happen all at once. Instead,they occur slowly over long periods of time.1.2 Early Ideas About EvolutionThe idea of evolution is very old. Ancient Greek philosophers were already thinking about how livingthings might be connected. Some believed that all organisms were related in some way, even if theconnection was distant.One famous Greek philosopher, Aristotle, suggested the idea of a “ladder of life.” According to thisview, simple organisms were at the bottom, and more complex organisms were at the top. Hebelieved life moved step by step from simple forms to more advanced ones.1.3 Religious Views and CreationismNot everyone agreed with these ideas. Many religious leaders believed in creationism, which is basedon the biblical account of creation in the Book of Genesis. They argued that all living things werecreated exactly as they are now.One religious scholar, James Ussher, even calculated the exact time of creation. He claimed thatEarth was created on October 26, 4004 B.C., at 9 a.m.1.4 Discoveries in Geology Challenge Old BeliefsAs science progressed, geologists began to question the idea that Earth was only a few thousandyears old. Their studies suggested that Earth must be much older.

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Study Guide•In 1785,James Hutton proposed that Earth was shaped by slow, natural processes such aserosion, earthquakes, and uplift.•In the early 1800s, Georges Cuvier estimated that Earth was about 6,000 years old.•By 1830, Charles Lyell presented strong evidence showing that Earth was several millionyears old.These discoveries made scientists more open to the idea that life could also change over long periodsof time.1.5 Lamarck’s Early Theory of EvolutionDuring this period, French zoologist Jean-Baptiste Lamarck proposed an early theory of evolution. Hebelieved organisms developed new traits in response to changes in their environment.Lamarck suggested the idea of “use and disuse.” He argued that body parts used often becamestronger, while unused parts became weaker. For example, he believed giraffes developed longnecks because they stretched their necks to reach high leaves.Lamarck also believed in “acquired characteristics,” meaning traits gained during an organism’slifetime could be passed on to offspring. This idea was widely accepted for many years.1.6 Charles Darwin and the Voyage of the BeagleCharles Darwin was the son of an English doctor and became a naturalist. He traveled aboard theship H.M.S.Beagle, visiting South America and other distant regions.During this journey, Darwin carefully observed plants and animals. He was especially fascinated bythe finches and tortoises of the Galapagos Islands, located about 200 miles west of Ecuador. Henoticed that different islands had different species, even though the islands were close together. Thismade him wonder how new species could develop in such isolated places.1.7 Influence of Population GrowthAfter returning to England in 1838, Darwin continued thinking about evolution. He was stronglyinfluenced by Thomas Malthus’sEssay on the Principle of Population.

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Study GuideMalthus explained that populations tend to produce more offspring than can survive. Becauseresources are limited, individuals must compete to live and reproduce. Darwin realized this idea couldapply to plants and animals as well. This insight became a key part of his theory.1.8 Wallace and the Theory of Natural SelectionIn 1858, another English naturalist, Alfred Russel Wallace, independently developed a theory ofevolution very similar to Darwin’s. Wallace shared his ideas with Darwin through letters.The two scientists decided to present their ideas together to the scientific community in London. Thisjoint presentation helped introduce the theory of evolution by naturalselection.1.9 On the Origin of SpeciesIn 1859, Darwin published his most famous book,On the Origin of Species by Means of NaturalSelection, or the Preservation of Favoured Races in the Struggle for Life. Today, it is commonlyknown asThe Origin of Species.This book clearly explained Darwin’s theory and provided strong evidence for evolution. It becameone of the most important scientific works ever written and permanently changed how peopleunderstand life on Earth.2. Evidence for EvolutionInOn the Origin of Species, Charles Darwin did more than just propose a theory. He also presentedstrong evidence to support evolution. His goal was to convince the scientific community that evolutionis real and that species change over time. Darwin used observations from many different areas ofscience to build his case.2.1 Paleontology: Evidence from FossilsOne major source of evidence for evolution comes frompaleontology, the study of fossils. Fossilsare preserved remains or traces of ancientorganisms, such as bones, shells, teeth, or footprints. Bystudying fossils, scientists learn about life that existed millions of years ago.

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Study GuidePaleontology supports evolution because it shows that modern organisms descended from earlierforms. Fossils found in deeper rock layers are usually simpler and less diverse. As scientists examinehigher rock layers, they find fossils that look more like organisms living today.This pattern suggests that life began with fewer and simpler organisms and gradually became morecomplex over time. The oldest fossils represent ancestors, while the most recent fossils resemblepresent-day species.2.2 Comparative Anatomy: Similar Structures, Shared OriginsAnother strong line of evidence comes fromcomparative anatomy, which compares body structuresof different organisms.Darwin noticed that the forelimbs of humans, porpoises, bats, and other animals are built in verysimilar ways, even though they are used for different purposes. For example:•Humans use forelimbs for lifting and grasping•Porpoises use them for swimming•Bats use them for flyingDarwin explained that these similar structures likely came from a common ancestor. Over time, theywere modified to meet the needs of different organisms. These changes are examples of adaptations.

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Study Guide2.3 Vestigial Organs: Structures with No Current UseDarwin also pointed out that some organisms have body parts that no longer serve a useful purpose.These are calledvestigial organs.In humans, vestigial structures include:•The appendix•Fused tail vertebrae (the coccyx)•Wisdom teeth•Muscles that move the ears and noseDarwin suggested that these structures were useful to ancestors but became unnecessary afterenvironmental changes. Over time, they shrank or lost their function. For example, the appendix mayonce have helped digest certain foods, and the coccyx may be the leftover remnant of a tail.2.4 Embryology: Similarities in Early DevelopmentDarwin also found evidence for evolution by studying embryos.Embryologyis the branch of biologythat focuses on embryos and their development.He observed that embryos of complex animals—such as humans, chickens, frogs, reptiles, and fish—look very similar during early stages of development. These similarities suggest that these organismsshare a common ancestor.In early development, many embryos have:•Gill slits•A two-chambered heart•A tail with musclesAs development continues, the embryos become more distinct and take on the unique features oftheir species. This pattern supports the idea that organisms share inheriteddevelopmental pathwaysthat were modified over time.

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Study Guide2.5 Comparative Biochemistry: Molecular SimilaritiesAlthough Darwin did not know much about biochemistry, modern science has revealed powerfulevidence at the molecular level.Comparative biochemistryexamines similarities in chemicalprocesses among living organisms.Scientists have discovered that:•Nearly all organisms use the same methods to capture and use energy•Proteins are built from the same amino acids•DNA and RNA carry genetic information in all living things•The genetic code is almost identical across speciesThese shared biochemical features strongly suggest that all life forms are related and descendedfrom common ancestors.2.6 Domestic Breeding: Evolution Guided by HumansDarwin also learned fromdomestic breeding, where humans selectively breed plants and animals toproduce desired traits.For example:•Pigeon breeders created many different pigeon varieties from a single ancestral type•Farmers developed new crop varieties through selective breedingDarwin realized that if humans could cause noticeable changes in species over a short time, naturecould do the same over long periods. This idea helped him understand how evolution could occurnaturally.2.7 Geographic Distribution: Location MattersDarwin was especially fascinated by where organisms live, a field known asgeographic distribution.While studying the Galapagos Islands, he noticed that many species—especially finches—were foundnowhere else in the world. He identified 13 different finch species, all unique to the islands.

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Study GuideDarwin concluded that these finches likely evolved from a single ancestral group that arrived on theislands long ago. Because the islands were isolated, the finches evolved into different species overmany generations.Similar patterns are seen elsewhere:•Alligators are found only in certain regions•Australia and New Zealand have unique animals due to long-term isolationThese observations support the idea that isolation and environment play important roles in evolution.3. Quiz Evidence for Evolution1.QuestionWhich of the following statements does paleontology NOT support?Answer Choices•Fewer kinds of organisms existed in past eras.•Modern organisms descended from common ancestors.•Organisms were probably more complex during past eras.Correct AnswerOrganisms were probably more complex during past eras.Why This Is CorrectPaleontology studies fossils to understand life in the past. Fossil evidence shows thatearlyorganisms were generally simpler, and complexity increased over time through evolution.Paleontologydoes supportthat fewer kinds of organisms existed in the past and that modernorganisms descended from common ancestors. However, itdoes not supportthe idea thatorganisms were more complex in earlier eras.2.QuestionWhich ofthe following statements about fossils is FALSE?

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Study GuideAnswer Choices•Fossils from the deeper layers are the ancestors of current forms.•Fossils from the upper layers are the ancestors of modern forms.•Fossils from the uppermost rock are most likecurrent forms.Correct AnswerFossils from the upper layers are the ancestors of modern forms.Why This Is CorrectIn rock layers,deeper layers are olderand contain earlier organisms that can be ancestors ofmodern species.Upper layers are youngerand usually contain organisms that are more similar topresent-day forms.Therefore, fossils in theupper layers are not ancestorsof modern organisms—they are closer intime and represent later or more recent forms.3.QuestionWhich comparative anatomy example does NOT support the theory of evolution?Answer Choices•Bats, humans, and cats have similarly constructed forelimbs and thus suggest a commonancestor.•The genus of legless lizards are no longer considered lizards and are now part of the snakegenus.•Vestigial organs are structures that are no longer necessary for survival and are thusgradually becoming nonfunctional and reduced in size.Correct AnswerThe genus of legless lizards are no longer considered lizards and are now part of the snakegenus.

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Study GuideWhy This Is CorrectComparative anatomy focuses onstructural similarities and differencesbetween organisms toshow evolutionary relationships.•Similar forelimb structures in bats, humans, and cats arehomologous structures, whichsupport common ancestry.•Vestigial organs show evidence ofevolutionary change over time, supporting evolution.However, reclassifying legless lizards into the snake genus is based ontaxonomic classification,not direct anatomical comparisons used as evidence in comparative anatomy. Therefore, thisexample doesnotsupport the theory of evolution through comparative anatomy.4.QuestionEmbryology does NOT suggest which of the following?Answer Choices•Developmental mechanisms are evolutionarily modified in a way that is unique to anorganism’s way of life.•Developmental mechanisms are unique for everydifferent type of life and share nocommonalities.•Human embryos pass through embryonic stages inherited from their ancestors.Correct AnswerDevelopmental mechanisms are unique for every different type of life and share nocommonalities.Why This Is CorrectEmbryology shows that many organisms sharesimilar early developmental stages, which suggestscommon ancestry. These shared patterns indicate that developmental mechanisms arenotcompletely unique, but are modified over time to suit different lifestyles.Therefore, the statement claiming that developmental mechanisms shareno commonalitiesis falseand isnot supportedby embryological evidence.

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