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Advanced Biology: Bahe & Deken

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Evolution

Chapter 6


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6.1 Genetic change

Each species present on earth todayrepresents a long chain of evolution andeach of these species plays a uniqueecological role in the earth’s communitiesand ecosystems. These species,communities, and ecosystems are alsoessential for future evolution as the earthcontinues its long history of environmentalchange. Understanding how earth’s speciesevolved and the nature of their niches (orbiological roles) is vital to understanding theeffects of human actions on wild species andprotecting species from prematureextinction.

According to scientific evidence, the majordriving force of adaptation to changes inenvironmental conditions is biologicalevolution (or just evolution). Evolution isthe change in a population’s genetic makeup(gene pool) through successive generations.The theory of evolution asserts that allspecies descended from earlier, ancestralspecies. This widely accepted scientifictheory explains how life has changed overthe past 3.7 billion years and why life is sodiverse today.

Biologists use the term microevolution todescribe the small genetic changes thatoccur in a population. The termmacroevolution is used to describe long-term, large-scale evolutionary changesthrough which new species are formed fromancestral species (speciation) and otherspecies are lost through extinction.

The first step in evolution is thedevelopment of genetic variability in apopulation. Recall that genetic informationin chromosomes is contained in varioussequences of nucleotides in DNAmolecules. Genes found in chromosomes

are segments of DNA coding for certaintraits that can be passed on to offspring.

A population's gene pool is the set of allgenes in the individuals of the population ofa species. Microevolution is a change in apopulation’s gene pool over time. There arefive conditions that can cause a deviation inthe gene pool; mutations, no gene flow,nonrandom mating, genetic drift, andnatural selection. Only natural selectionresults in adaptations to the environment.

Although members of a population generallyhave the same number and kinds of genes, aparticular gene may have two or moredifferent molecular forms, called alleles.Sexual reproduction leads to a randomshuffling or recombination of alleles. As aresult, each individual in a population has adifferent combination of alleles.

Genetic variation in a population startsthrough mutations, those random changesin the structure or number of DNAmolecules in a cell. Radioactivity, X rays,and various natural and human-madechemicals can cause mutations. Mutationscan also occur from random mistakes in thegenetic code when DNA molecules arecopied each time a cell divides andwhenever an organism reproduces. Onlymutations that occur in reproductive cells,like eggs and sperms, are passed on tooffspring and thus contribute to the processof evolution.

Most mutations are harmful and alter traitsso that an individual cannot survive. Somemutations are harmless and rarely a mutationis beneficial. The result of mutations is newgenetic traits that give the organisms and itsoffspring better chances for survival andreproduction, under current environmentalconditions or when the environmentchanges.


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Remember, mutations are random andunpredictable. They are the only source oftotally new genetic raw material. They arerare events. Once alleles are created bymutation, new alleles can be shuffledtogether or recombined randomly to createnew combinations of genes in populations ofsexually reproducing species.

The movement of alleles betweenpopulations by migration of breedingindividuals is called gene flow. Continuousgene flow makes gene pools similar andreduces the possibility of allele frequencydifferences among populations of a species.Gene flow tends to decrease the geneticdiversity among populations, causing theirgene pools to become more similar.Without gene flow populations will tend tobecome more and more dissimilar until theyare so dissimilar that gene flow can longeroccur because the differences in the alleleswill no longer allow successful matingbetween them.

Random mating occurs when individualspair by chance and not according to theappearance or behavior of a possible mate.Of course random mating is the exceptionnot the rule. Most animals choose theirmates based on genes, appearance, orbehavior – nonrandom mating. Sexualselection occurs when males compete forthe right to reproduce, and females choose tomate with males that have a particular trait.The elaborate tail of a peacock may havecome about because peahens choose to matewith males with such ornate tails.Inbreeding is another example ofnonrandom mating because inbreeding doesnot change the frequencies of alleles in apopulation.

Genetic Drift occurs when chance eventschange the proportion of alleles in a

population. Genetic drift can occur in bothlarge and small populations, but a largepopulation will most likely be less effectedby such changes. Genetic drift is a randomprocess, and therefore it is not likely toproduce the same results in differentpopulations.

Sometimes a species may come close toextinction because of a natural disaster (e.g.,earthquake or fire) or because ofoverhunting, overharvesting, and habitatloss. It is as if most of the population hasstayed behind and only a few survivors havepassed through the neck of a bottle. Thebottleneck effect prevents the majority ofgenotypes from participating in theproduction of the next generation.

The extreme genetic similarity found incheetahs is believed to be due to abottleneck. In a study of 47 differentenzymes, each of which can come in severaldifferent forms, all the cheetahs had exactlythe same form. This demonstrates thatgenetic drift can cause alleles to be lost froma population. What caused the cheetahbottleneck is not known. Today, cheetahssuffer from relative infertility because of theintense inbreeding that occurred after thebottleneck.

The founder effect is an example of geneticdrift in which rare alleles, or combinationsof alleles, occur at a higher frequency in apopulation isolated from the generalpopulation. The founding individualscontain only a fraction of the total geneticdiversity of the original gene pool. Whichparticular alleles are carried by the foundersis dictated by chance alone.

6.2 Natural Selection

Charles Darwin described natural selectionas a process that occurs when some


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individuals of a population have geneticallybased traits that increase their chances ofsurvival and increases their ability toproduce viable offspring. Three conditionsare necessary for evolution of a populationby natural selection to occur:

1. These must be natural variability fora trait in a population.

2. The trait must be heritable, meaningit must have a genetic basis so that it can bepassed from one generation to another.

3. The trait must somehow lead todifferential reproduction, meaning it mustenable individuals with the trait to leavemore offspring than other members of thepopulation.

Natural selection causes any allele or set ofalleles that results in a beneficial trait tobecome more common in succeedinggenerations and causes other alleles tobecome less common. A heritable trait thatenables organisms to better survive andreproduce under a given set ofenvironmental conditions is called anadaptation.

When faced with a change in environmentalconditions, a population of a species caneither adapt to the new conditions by naturalselection, migrate to an area with morefavorable conditions, or become extinct.

The peppered moth ofEngland demonstrates aclassic example ofmicroevolution. Beforethe industrial revolutionin the mid-1800s, thespeckled light-gray formof the peppered mothwas much more commonthan the dark-gray form.When these night-flyingspeckled moths rested onlight gray lichens living

on trees during the day, their colorcamouflaged them from their bird predators.During the industrial revolution, soot andother pollutants from factory smokestacksbegan killing lichens and darkening trees.As a result, the dark form of moth becamethe common one, especially near industrialcities. In this new environment, the darkform of moth blended in with the blackenedtrees, whereas the light form of moth washighly visible to predators. Through naturalselection, the dark form began to surviveand reproduce at a greater rate than its light-colored kin.

Biologists recognize three types of naturalselection:

Directional natural selection: If theenvironment favors one end of the range of acharacteristic, individuals with those traitswill become more common that themidrange forms. The peppered moth is anexample of directional selection. Otherexamples include the evolution of geneticresistance to pesticides among insects and toantibiotics among disease-carrying bacteria.Directional selection is most common whenenvironmental conditions are changing orthe population migrates to a new habitatwith different environmental conditions.


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Stabilizing natural selection: If theenvironment selects against both endsof a range of a characteristic, theaverage form will predominate. Forexample, very big human head size atbirth is selected against because thosebabies have an increased likelihood ofnot passing through the birth canal.Very small heads are also selectedagainst because of decreasedfunctionality of the child. Mosthuman babies’ heads fall within avery narrow range at birth.Stabilizing selection is most commonwhen the environment changes verylittle and most members of thepopulation are well adapted to thatenvironment.

Disruptive natural selection: Ifthe environment favorsindividuals at both ends of thespectrum and selects againstindividuals with intermediatetraits this will cause both of theextreme phenotypic groups toarise in the population. This typeof selection is most commonwhen the environment isheterogeneous and patchy. Forexample, if the soil has darkpatches interspersed with lightrocky outcrops, snails of light anddark colors are favored and snailswith medium coloration areselected against.


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Use the underlined words from sections 6.1and 6.2 to fill in the crossword puzzlebelow.

Name:


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6.3 Coevolution

Interactions between species can also resultin microevolution in each of the populations.When populations of two different speciesinteract over a long time, changes in thegene pool of one species can lead to changesin the gene pool of the other species. Thisprocess is called coevolution.

For example, suppose some owls becomebetter at hunting mice. Because of geneticvariation, certain mice will have traits thatallow them to escape or hide from theirpredators and they will pass these traits on tosome of their offspring. However, a few ofthe owls may also have traits, such as bettereyesight or quicker reflexes, that allow themto hunt the better-adapted prey successfully.They would pass these traits on to theiroffspring. Speed, agility, claws, fangs, andambush tactics all counter the defensemechanisms of prey.

Plants in a population may also evolvedefenses, such as camouflage, thorns, orpoisons, to counter against efficientherbivores (who are really predators ofplants) just like prey animals that haveevolved protective armor, spines, or externalglands that produce noxious chemicals. Inturn, some herbivores in the population mayhave genetic characteristics that enable themto overcome these plant defenses andproduce more offspring than those withoutsuch traits. During coevolution, adaptationfollows adaptation in an ongoing, long-term“arms race” between individuals ofinteracting populations of different species.

Another example of coevolution is theinteraction between the caterpillar of thebutterfly Heliconius and a tropical vine,Passiflora. Passiflora produces toxicchemicals that protect its leaves from beingeaten by most insects but Heliconius

caterpillars have evolved digestive enzymesthat break down the toxins. As a result,Heliconius gains access to a food source thatfew other insects can eat. These caterpillarswould be a selective force for Passifloravines that have other defenses besides thetoxins. The leaves of some species ofPassiflora vines produce yellow sugardeposits that look like Heliconius eggs.Female Heliconius butterflies avoid layingtheir eggs on leaves that already have eggs.Presumably, this is an adaptation thatensures an adequate food supply foroffspring, since only a few caterpillars willhatch and feed on any one leaf. Because thebutterfly often mistakes the yellow sugardeposits for eggs, Passiflora species withthe deposits are more likely to escapepredation by Heliconius caterpillars.

As stated above, stationary plants haveevolved physical defenses such as spinesand thorns as well as chemical toxins. Somechemicals you may be familiar with includestrychnine from a tropical vine, morphinefrom the opium poppy, nicotine fromtobacco, mescaline from peyote cactus,tannins from oaks, and many substances weuse as flavorings but are toxic to predators(such as cinnamon, cloves and mint).

Animals have evolved a diverse array ofdefenses against predators. Mechanicaldefenses, such as the porcupine’s sharpquills, are obvious. Like plants, animals canhave chemical defenses. Animals withchemical defenses are often brightly colored.The bright colors and markings of poison-arrow frogs in tropical rain forests warn ofdeadly alkaloids in the frog’s skin. In someparts of South America, human hunters tiptheir arrows with poisons from these frogs tobring down large mammals. Camouflage isan especially common type of defense in theanimal kingdom.


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Mimicry is another effective defensemechanism. The honeybee has a stingerarmed with a toxic chemical defense. Theflowerfly is a non-stinging insect that lookslike the honeybee. Many predators learn toavoid the harmful bee and may not attackthe harmless flowerfly because it is mistakenfor a honeybee. This type of mimicry,where a tasty speciesmimics an unpalatable one,is called Batesian mimicry.For this type of mimicry tobe effective, the mimic mustbe considerably lessabundant than the species itcopies; otherwise, predatorswould learn that, forexample, yellow insects thatlook like bees are goodrather than bad to eat.Another example is theharmless robber fly thatresembles the bumblebeeeven though the two are notclosely related. A well-known example of Batesianmimicry is the viceroy butterfly, whichcontains no toxic substances but has astriking resemblance to the monarchbutterfly, which enables it to capitalize onthe monarch's unpalatability.

The milkweed leaves on which the monarchcaterpillar feeds contain several substancesthat are toxic to vertebrates. The larva storesthese within its body and thus becomesunpalatable to vertebrate predators. Thechemicals remain in the body even aftermetamorphosis, so that adults areunpalatable as well. When a blue jay eats aportion of a monarch butterfly that had fed(in its larval stage) on poisonous milkweedthe blue jay will immediately vomit.Following this episode, the blue jay willrefuse to eat any other monarch offered to it.

In Mullerian mimicry, two unpalatablespecies mimic one another. The wasp calledthe yellow jacket and the bee called thecuckoo bee both have stingers that releasetoxic chemicals and look very similar. Bothgain adaptive advantage because predatorswill learn quickly to avoid any prey with thisappearance.

6.4 Niche

If asked what role a certain species such as asquirrel plays in an ecosystem, an ecologistwould describe its niche, the species’ way oflife or function in an ecosystem. A species’niche involves everything that affects itssurvival and reproduction. A niche is thesum total of its use of the biotic and abioticresources of its habitat where it lives. Forthe squirrel, its niche would include thetemperature range within which it survives,the source and amount of water it drinks, thetime of the day when it feeds, the types offood it consumes, the acorns it buries forwinter use, and the leaves it carries to thetree branches for its nest.

A niche of a species is more than just itshabitat, or the physical location, where it


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lives. Ecologists often say that a niche islike a species’ occupation whereas thehabitat is like its address.

The attributes of a species’ niche are theadaptations it has acquired throughevolution. These adaptations allow thespecies to survive and reproduce moreeffectively under a given set ofenvironmental conditions.

For conservation, understanding a species’niche can help prevent premature extinctionand help evaluate the environmental changeswe make in terrestrial, land, and aquaticecosystems. For example, how will theniches of various species be changed byclearing a forest, plowing up a grassland,filling in a wetland, or dumping pollutantsinto a lake or stream?

As described before niches can be used toclassify species as generalists or specialists.Generalist species have broad niches. Theycan live in many different places, eat avariety of foods and tolerate a wide range ofenvironmental conditions. Some examplesof Missouri generalists are flies,cockroaches, mice, rats, white-tailed deer,raccoons, coyotes, copperheads, catfish, andhumans.

On the other hand, specialists have narrowniches. They might be able to live only inone type of habitat, eat only one or a fewtypes of food, and/or tolerate only a narrowrange of environmental conditions.Specialists are more prone to extinctionwhen environmental conditions change. Afew examples of specialists include tigersalamanders, which can breed only infishless ponds so their larvae will not beeaten; red-cockaded woodpecker, whichcarve nest holes almost exclusively in old (atleast 75 years) longleaf pines; spotted owls,which need old-growth forests in the Pacific

northwest for food and shelter; and giantpandas, which feed almost exclusively onvarious types of bamboo.

When environmental conditions are fairlyconstant, as in a tropical rain forest,specialists have an advantage overgeneralists because they have fewercompetitors. However, under rapidlychanging environmental conditions, thegeneralist is usually better off than thespecialist.

Competition between members of two ormore different species for food, space, orany other limited resource is calledinterspecific competition. As long ascommonly used resources are abundant,different species can share them. Thisallows each species to come close tooccupying the fundamental niche it wouldoccupy if there were not competition.

A species’ fundamental niche is the fullpossible range of physical, chemical, andbiological conditions and resources it couldtheoretically use if there were no directcompetition from other species. But in aparticular ecosystem, species often competewith one another for one or more of thesame resources. Therefore, the niches ofcompeting species at least partly overlap.The more they overlap, the more theycompete with one another.

In order to avoid competition for the sameresources (food, sunlight, water, soilnutrients, space, nesting sites, and goodplaces to hide), a species usually occupiesonly part of its fundamental niche. This isits realized niche. By analogy, you may becapable of being study body president ofJohn Burroughs School (your fundamentalniche) but competition from others maymean you may become only president of thebasket-weaving club (your realized niche).


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A classic study on barnacles of the NorthAtlantic seacoast demonstrates clearly thesetypes of niches and the role competitionplays in structuring a community. Twospecies of barnacles, Balanus andChthamalus, grow on rocks that are exposedduring low tide. Both feed on particlessuspended in seawater at high tide. They areattached as adults but have free-swimminglarvae that may settle and begin to developon almost any rock surface. This attachmenton rocks, the amount of exposure toseawater and air, and interactions with otherspecies are all part of the barnacle’s niche.

If Chthamalus is the only type of barnacleliving in a community, it will occupy rocksurfaces all the way from the high tide lineto the low tide zone. If Balanus is the onlytype present, it will only occupy the rocksurface from low tide to about half way tohigh tide because Balanus is more prone todrying out in the air during low tide. IfBalanus and Chthamalus are both living in acommunity, Balanus will displace theChthamalus individuals on the lower half ofthe rock. Researchers concluded that theupper limit of Balanus’ distribution is setmainly by the availability of water whereasthe lower limit of Chthamalus’ distributionis set by competition.

Interspecific competition can also lead toextinction of one population in thatparticular area. Another classic experimentillustrates this concept. In 1934, Russianecologist G.E. Gause studied the growth oftwo Paramecium species in the lab. Hegrew each species, Paramecium aurelia andParamecium caudatum in separate cultureswith a constant amount of bacteria addedeach day as food. Each population grewrapidly and then leveled off at what wasapparently the carrying capacity of theculture. They demonstrated typical logisticgrowth.

He then grew the two species together in thesame culture dish. This time, P. aureliaapparently had a competitive edge inobtaining food and P. caudatum was drivento extinction in the culture. Gauseconcluded that the two species are so similarthat they compete for the same limitingresources and cannot coexist in the sameplace. One will use the resources moreefficiently and thus reproduce more rapidly.Even a slight reproductive advantage willeventually lead to local elimination of theinferior competitor. Gause’s ideas weretermed the competitive exclusion principle.This research has been supported by otherlab and field experiments using other animalspecies.

Essay Questions(answer on a separate sheet of paper)

1. Describe an example of coevolutionbetween predator and prey. Are thereecological relationships other thanpredator/prey interactions that areshaped by coevolution between twospecies? Give an example.

2. What is the difference betweenBatesian mimicry and Mullerianmimicry?

3. What is the difference between afundamental niche and a realized niche?

4. When Gause cultured Parameciumaurelia and Paramecium caudatumtogether, P. caudatum was invariablydriven to extinction. When P. aurelia andP. bursaria were cultured together inanother experiment, however, both wereable to coexist for months. What kinds ofsimilarities and differences must there beamong the three species? What do youthink would happen if P. caudatum and P.bursaria were cultured together? Why?


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6.5 Speciation

Under certain circumstances, naturalselection (part of microevolution) can leadto an entirely new species (part ofmacroevolution). In this process, calledspeciation, two species arise from one.

The most common mechanism of speciation,especially among animals, takes place intwo phases. First, geographic isolationoccurs when groups of the same populationof a species become physically separated forlong periods of time. For example, part of apopulation might migrate in search of foodand then begin living in another area underdifferent living conditions. Populations mayalso become separated by physical barrierssuch as mountain ranges, streams, lakes, androads, or by a drastic geologic event such asa volcanic eruption or earthquake, or when afew individuals are carried to a new area bywind, water, or birds.

The second phase of speciation isreproductive isolation. It occurs whenmutation and natural selection operateindependently in two geographically isolatedpopulations and change the allelefrequencies in different ways. If thisdivergence continues long enough,

members of the isolated populations maybecome so different in genetic makeup thatthey cannot interbreed or if they do, theycannot produce live, fertile offspring. Whenthis occurs, one species has become two,and speciation has occurred throughdivergent evolution.

For rapidly reproducing organisms, this typeof speciation may occur within just a fewhundred years. However, for most speciessuch speciation takes from tens of thousandsto millions of years. Because of this hugetime scale, it is difficult to observe anddocument the appearance of new species.As a result, there are many controversialhypotheses about the details of speciation.

After speciation, the second processaffecting the number and types of species onearth is extinction. When environmentalconditions change, a species must eitherevolve to become adapted, move to a morefavorable area if possible, or cease to exist,which means, to become extinct.

Over the 3 billion years that life has existedon earth, speciation and extinction havebeen affected by several major factors. Thecontinental drift of the continents overmillions of years, the gradual climate


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changes caused by continental drift andslight shifts in the earth’s orbit around thesun, and rapid climate change caused bycatastrophic events, such as large volcaniceruptions, huge meteorites and asteroidscrashing into the earth and releasing largeamounts of methane trapped beneath theearth’s floor. These all have affected theevolution and survival of species. Some ofthese events create dust clouds that shutdown or sharply reduce photosynthesis longenough to eliminate huge numbers ofproducers, and in turn, the consumers thatfed on them.

Extinction is the ultimate fate of all species,just as death is for all individual organisms.Biologists estimate that 99.9% of all thespecies that have ever existed are nowextinct.

As local environmental conditions change, acertain number of species disappear at a lowrate, called background extinction. Incontrast, mass extinction is a significantrise in extinction rates above the backgroundlevel. It is a catastrophic, widespread, oftenglobal, event in which large groups ofexisting species(25 to 75%) arewiped out. About5 periods of massextinctions ofvarying scales haveoccurred in thepast 500 millionyears.

A mass extinctioncrisis for onespecies is anopportunity foranother. Theexistence ofmillions of speciestoday means that

speciation, on average, has kept ahead ofextinction. Evidence shows that the earth’smass extinctions have been followed byperiods of recovery called adaptiveradiations in which numerous new speciesevolve to fill new vacated ecological nichesin changed environments. Fossil recordssuggest that it takes 5 million years or morefor adaptive radiations to rebuild biologicaldiversity after a mass extinction ordepletion.

Adaptive radiation not only occurs aftermass extinctions up new environments butany time a new and diverse environment isexposed. Isolated island chains with diversehabitats are often the sites of adaptiveradiations. The Galapagos Islands off thenorthwestern coast of South America is oneof the most famous examples of this rapidspeciation event. The four-island chain wasborn from underwater volcanoes andthrough the process of succession eventuallyhas become home to many plants andanimals.


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Questions

1. Distinguish between microevolution and macroevolution.

2. Explain the importance of geographical isolation in the formation of a species.

3. Explain how could speciation take place without geographical isolation.

4. In the diagram to the right each letterrepresents a distinct species of bird. Each numberrepresents the sequential order of a migration or aspeciation event. What process does this diagramexplain? How does it explain this process?

Name:


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6.7 Taxonomy

In order to describe and understand life’sdiversity, we need a system of classification.Biologists organize these collective groupsinto a classification, an arrangement oflarger groups that are subdivided intosmaller groups, each reflecting their degreeof evolutionary relatedness. Classificationshelp us to catalog and describe life’sdiversity, which is the first step on the wayto understanding the Earth’s great diversity.

Any collective group of similar organisms,such as insects or orchids, is called a taxon,and taxonomy is the study of how these taxa(plural of taxon) are recognized and howclassifications are made. In a biologicalclassification, species are grouped intosuccessively more inclusive groups, or‘higher taxa’: related species are groupedinto genera (singular; genus), relatedgenerea into families, related families intoorders, related orders into classes, relatedclasses into phyla (singular; phylum), andrelated phyla into kingdoms, such as theanimal or plant kingdoms.

For example, human beings constitute the

species Homo sapiens. Homo sapiens isgrouped together with Homo erectus andcertain other fossil species into the genusHomo. (A genus always has a one-wordname that is capitalized; a species has a two-word name in which the first word is thename of the genus; after the two-word namehas been introduced, the genus maysubsequently be abbreviated, for example,H. sapiens. Both genus and species namesshould either be italicized or underlined.)The genus Homo is grouped together withthe extinct genera Australopithecus and afew others into the family Hominidae. Thisfamily is included in the order Primates,which also includes apes (Pondigae),monkeys (Cebidae and Cercopithecidae),and lemurs (Lemuridae). The primates aregrouped together with rodents (Rodentia),carnivores (Carnivora), bats (Chiroptera),whales (Cetacea), and over two dozen otherorders into the class Mammalia, whichincludes all warm-blooded animals with hairor fur that feed milk to their young.Mammals are one of several classes in thephylum Chordata, a group that includes allvertebrates (animals with backbones) and afew aquatic relatives such as the sea squirtsand amphioxus. The Chordata and several


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dozen other phyla are together placed in theanimal kingdom (Animalia). Animals areone of the several kingdoms.

An important goal of classification is tosummarize and communicate what we knowabout taxa. Good classification shoulddescribe the variation among taxa,summarizing both their differences and theirsimilarities. Early classification systemswere mainly based on physical structures,and members of each group werecategorized based on their visiblecharacteristics.

Another goal of classification is to describeevolution. In order to describe all thedifferent descendants of some ancientspecies, we clearly need some collectivename for the group. Such a group is called aclade (from a Greek word, meaning branch),and the study of branching patterns inevolution, from common ancestors to theirdescendents, is therefore called cladistics.

On a family tree like that shown below, aclade consists of any branching point,representing an ancestor, and all the lines

branching from it above, representing itsdescendents. Traditionally, most cladeswere formed by comparing the physicalcharacteristics of each species. Todaymolecular biology provides further evidencethat can be used to construct classifications.The DNA sequences or protein sequencesfrom different species can be compared.Molecular analysis prevents the grouping ofanimals that arose from convergentevolution (similar looking animals that arenot evolutionarily related) from belonging tothe same clade. Convergent evolution is anevolutionary phenomenon in which similaradaptations evolve independently in lineagesnot closely related. Resemblance resultingfrom convergent evolution is calledanalogy, and is usually the result of animalsliving in separate locations but fulfilling asimilar niche. For example, the wings ofbats and birds are analogous.


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Use words from the ENTIRE chapter to complete the crossword puzzle below.

Name:


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