Evolutionary Patterns Chapter 23 – Flashcards

classify biological diversity. A century later, Charles Darwin recognized this pattern as the expected outcome of a process of "descent with modification," or evolution

Just as a tree sprouts new branches on old ones and adds rings to a thickening trunk, the pattern of nested similarities among species strongly indicates a process of descent with modification and the accumulation of change. This history of descent with branching is called "and is much like the genealogy that records our own family histories."

First is the nested pattern of similarities found among species on present-day Earth. The second is the historical pattern of evolution recorded by fossils.

the point where a branch splits called this. it represents the common ancestors from which the descendant species diverged ( separate from another route)

is to recognize and name groups of individuals as species, and, subsequently, to group closely related species into the more inclusive taxonomic group of the genus, and so on up through the taxonomic ranks—species, genus, order, class, phylum, kingdom, domain. It also provides us with a hierarchical classification of species in more and more inclusive groups, giving us a convenient way to communicate information about the features each group possesses. So, if we want to tell someone about a small animal we have seen with fur, mammary glands, and extended finger bones that permit it to fly, we can give them this long description, or we can just say we saw a bat

the study of evolutionary and genetic relationships among organisms. The other is taxonomy, the classification of organisms.ims to discover the pattern of evolutionary relatedness among groups of species or other groups by comparing their anatomical or molecular features, and to depict these relationships as a phylogenetic tree.

is a hypothesis about the evolutionary history, or phylogeny, of the species. explore the relatedness of particular groups of individuals, populations, or species.provides information about evolutionary relationships among vertebrates are built from careful analyses of the morphological and molecular attributes of the species or other groups under study.

Two species, or groups of species, are considered to be closest relatives if they share a common ancestor not shared by any other species or group.Groups that are more closely related to each other than either of them is to any other group, like lungfish and tetrapods, are called hylogenetic hypotheses amount to determining this type of group relationships because the simplest phylogenetic question we can ask is which two of any three species (or other groups) are more closely related to each other than either is to the third

Closeness of relationship is then determined by looking to see how recently two groups share a common ancestor. Shared ancestry is indicated by a

with taxonomy providing a formal means of naming groups. In recent decades, biologists have worked to integrate evolutionary history with taxonomic classification.

meaning that all members share a single common ancestor not shared with any other species or group of species. In Fig. 23.2, the tetrapods are monophyletic because they all share a common ancestor not shared by any other taxa. Similarly, amphibians are monophyletic.

group includes some, but not all, of the descendants of a common ancestor. Early zoologists separated birds from reptiles because they are so distinctive, but feathers and other unique features of birds do not tell us about their relationship to other vertebrates. In fact, many features of skeletal anatomy and DNA sequence strongly support the placement of birds as a sister group to the crocodiles and alligators.

if in order to separate a group from the rest of the phylogenetic tree you need only to make one cut, the group is monophyletic. If you need at least two cuts to separate the group from the tree, it is paraphyletic.

Groupings that do not include the last common ancestor of all members are called

e monophyletic groups include all descendants of a common ancestor and only the descendants of that common ancestor. This means that monophyletic groups alone show the evolutionary path a given group has taken since its origin. Omitting some members of a group, as in the case of reptiles and other paraphyletic groups, can provide a misleading sense of evolutionary history. By using monophyletic groups in taxonomic classification, we effectively convey our knowledge of their evolutionary history.

losely related species group together on a single branch of the tree of life. In the vocabulary of formal classification, closely related species are grouped into a

Closely related genera, in turn, belong to a larger, more inclusive branch of the tree—they are classified as a

closely related families, in turn, form an order, orders form a class, classes form a phylum (plural, phyla), and phyla form a kingdom,

Biologists today commonly refer to the three largest limbs of the entire tree of life as The Eukarya, or eukaryotes; Bacteria; and Archaea, or archaeons

Biologists use characteristics of organisms to figure out their relationships. Similarities among organisms are particularly important in that similarities sometimes suggest shared ancestry. However, a key principle of constructing trees is that only some similarities are actually useful. Others can in fact be misleading.

are the anatomical, physiological, or molecular features that make up organisms. To be useful for phylogenetic reconstruction, they must vary among but not within species and have a genetic basis

In general, characters have several observed conditions, called n the simplest case, a character can be present or absent—lungs are present in tetrapods and lungfish, but absent in other vertebrate animals. Commonly, however, multiple character states are apparent—petals are a character of flowers, for example, and their arrangement can be considered a character state. Flowers can have many petals arranged in a helical pattern, many petals arranged in a whorl, few petals arranged in a whorl, or few petals fused into a tube.

Characters that are similar because of descent from a common ancestor are said to b

The character state was present in the common ancestor of the two groups and retained over time (common ancestry), or the character state independently evolved in the two groups as an adaptation to similar environments (convergent evolution).

Not all similarities arise in this way, however. Think of wings, a character exhibited by both birds and bats (which are mammals). Much evidence supports the view that wings in these two groups do not reflect descent from a common, winged ancestor but rather evolved independently in the two groups. Similarities due to independent adaptation by different species are said to be They are the result of convergent evolution.

its homologies

However, it turns out that only some homologies are useful. For example, character states that are unique to a given species or other monophyletic group can't tell us anything about its sister group. They evolved after the divergence of the group from its sister group and so can be used to characterize a group but not to relate it to other groups. Similarly, homologies formed in the common ancestor of the entire group and therefore present in all its descendants do not help to identify sister-group relationships among the groups under consideration.

What we need to develop hypotheses of evolutionary relationship are homologies shared by some, but not all, of the members of the group under consideration. These are shared derived characters and are called

Thus, the presence of lungs provides one piece of evidence that lungfish are the sister group of tetrapods. Phylogenetic reconstruction on the basis of synapomorphies is called

. For comparison, we have a species that we believe is outside this ingroup—that is, it falls on an earlier branch of the tree—and so is called

that is, choosing the simpler of two or more hypotheses to account for a given set of observations. In systematics, this suggests counting character changes on a phylogenetic tree to find the simplest tree for the data (the one with the fewest number of changes). Each change corresponds to a mutation (or mutations) in an ancestral species, and the more changes or steps we propose, the more independent mutations we must also hypothesize.

using anatomical features as characters, but increasingly, tree construction relies on molecular data. The amino acids at particular positions in the primary structure of a protein can be used as characters, as can the nucleotides at specific positions along a strand of DNA.

From genealogy to phylogeny, tracing mutations in DNA or RNA sequences has revolutionized the reconstruction of historical genetic connections

simply provide more details. Indeed, for microbes and viruses, there is very little morphology available, so molecular information is critical for phylogenetic reconstruction in these microscopic taxa. Once a gene or other stretch of DNA or RNA with suitable levels of variation is identified in two or more species, sequences are obtained and aligned to identify homologous nucleotide sites.

Rather than comparing the sequences of a few genes, we compare the sequences of entire genomes.

The descendants of a recent common ancestor will have had relatively little time to evolve differences, whereas the descendants of an ancient common ancestor have had a lot of time to evolve differences. Thus similarity (or low distance) indicates the recency of common ancestry.

Today, the single largest library of taxonomic information is the National Institutes of Health's genetic data storage facility, called gives users access to more than 100 billion observations (mostly nucleotides) collected under more than 400,000 taxonomic names.

The sequence of changes on a tree from its base to its tips documents evolutionary changes that have accumulated through time. Trees suggest which lineages are older than others, and which traits came first and which followed later. Proper phylogenetic placement thus reveals a great deal about evolutionary history, and it can have practical consequences as well. For example, oomycetes, microorganisms responsible for potato blight and other important diseases of food crops, were long thought to be fungi because they look a lot like some fungal species.

provides a powerful tool for evolutionary analysis and is useful across timescales ranging from months to the entire history of life, from the rise of epidemics to the origins of metabolic diversity. Few other breakthroughs in science have had as broad an impact as that of phylogenetic systematics and the new sources of molecular data that have carried it so far.

Two examples of a nested pattern of similarity among organisms are (1) a dog and a wolf are more similar to each other than either is to a cat, and (2) a dog, a wolf, and a cat are more similar to each other than they are to a turtle.

to calibrate phylogenies in terms of time. It is one thing to infer that mammals diverged from the common ancestor of birds, crocodiles, lizards, and turtles before crocodiles and birds diverged from a common ancestor (see Fig. 23.7), but another matter to state that birds and crocodiles diverged about 220 million years ago, whereas the lineage represented today by mammals branched from other vertebrates about 100 million years earlier.

The evolutionary relationship between birds and crocodiles highlights Not only do fossils record past life, they also provide our only record of extinct species. The phylogeny in Fig. 23.7 contains a great deal of information, but it is silent about dinosaurs. Fossils demonstrate that dinosaurs once roamed Earth, and details of skeletal structure place birds among the dinosaurs in the vertebrate tree. Indeed, some remarkable fossils from China show that the dinosaurs most closely related to birds had feathers

place evolutionary events in the context of Earth's dynamic environmental history. Again, dinosaurs illustrate the point.

re the remains of once-living organisms, preserved through time in sedimentary rocks. If we wish to use fossils to complement phylogenies based on modern organisms, we must understand how fossils form and how the processes of formation govern what is and is not preserved.

the fossil record of marine life is more complete than that for land-dwelling creatures because marine habitats are more likely than those on land to be places where sediments accumulate and become rock. Thus, trees and elks living high in the Rocky Mountains have a low probability of fossilization, whereas clams and corals on the shallow seafloor are commonly buried and become fossils.s

Many animals leave tracks and trails as they move about or burrow into sediments. These from dinosaur tracks to the feeding trails of snails and trilobites, preserve a record of both anatomy and behavior (Fig. 23.13).

to the rocks. Most biomolecules decay quickly after death. Proteins and DNA, for example, generally break down before they can be preserved, although, remarkably, a sizable fraction of the Neanderthal genome has been pieced together from DNA in 40,000-year-old bones.

for example, 505 million years ago, during the Cambrian Period, a sedimentary rock formation called the accumulated on a relatively deep seafloor covering what is now British Columbia.

Fossils record the evolution of life on Earth. They eventually mapped out the

laboratory measurements indicate that half of the 14C in a given sample will decay to nitrogen in 5730 years, a period called its

to date wood and bone. As shown in Fig. 23.17, cosmic rays continually generate 14C in the atmosphere. Through photosynthesis, carbon dioxide that contains 14C is incorporated into wood, and animals also incorporate small amounts of 14C into their tissues when they eat plant material. After death, the unstable 14C in these materials begins to break down, losing an electron to form 14N, a stable isotope of

today, for example, the continents are distributed widely over the planet's surface, but 290 million years ago they were clustered in a supercontinent called

now known from 11 specimens splayed for all time in fine-grained limestone, lived 150 million years ago. Its skeleton shares many characters with dromaeosaurs, a group of small, agile dinosaurs, but several features—its pelvis, its braincase, and, especially, its winglike forearms—are distinctly birdlike. this clearly suggests a close relationship between birds and dinosaurs, and phylogenetic reconstructions that include information from fossils show that many of the characters found today in birds accumulated through time in their dinosaur ancestors

and other skeletons in rocks deposited 375 to 362 million years ago record an earlier but equally fundamental transition: the colonization of land by vertebrates. Phylogenies show that all land vertebrates, from amphibians to mammals, are descended from fish. As seen in F

spelled the end of many previously important groups of species, but they opened up new possibilities for evolution.

More than 90% of all genera recorded in late Permian oceans disappeared, especially animals like corals and sponges with heavy skeletons. There is no compelling evidence for meteorite impact, so geologists have hypothesized that this mass extinction resulted from the

Five great mass extinctions occurred over the past 500 million years, but only the two at the end of the Permian and Cretaceous Periods so thoroughly changed the course of evolution.

The diversity of life we see today is the result of evolutionary processes playing out over geologic time. Evolutionary process can be studied by experiment, both in the field and in the laboratory, but evolutionary history is another matter. There is no experiment we can do to determine why the dinosaurs became extinct—we cannot rerun the events of 65 million years ago, this time without the meteorite impact. The history of life must be reconstructed from evolution's two great patterns: the nested similarity observed in the forms and macromolecular sequences of living organisms, and the direct historical archive of the fossil record.`

The great advantage of reconstructing evolutionary history from living organisms is that we can use a full range of features—skeletal morphology, cell structure, DNA sequence—to generate phylogenetic hypotheses. The disadvantage of using comparative biology is that we lack evidence of extinct species, the time dimension, and the environmental context. This, of course, is where the fossil record comes into play. Fossil evidence has strengths and limitations that complement the evolutionary information in the living organisms. We can use phylogenetic methods based on DNA sequences to infer that birds and crocodiles are closely related, but only fossils can show that the evolutionary link between birds and crocodiles runs through dinosaurs. And only the geologic record can show that mass extinction removed the dinosaurs, paving the way for the emergence of modern mammals. Paleontologists and biologists work together to understand evolutionary history. Biology provides a functional and phylogenetic framework for the interpretation of fossils, and fossils provide a record of life's history in the context of continual planetary change.

phylogenetic based on morphological or molecular comparisons of living organisms make hypotheses about the timing of evolutionary changes through Earth history. We humans are a case in point. As discussed in more detail in Chapter 24, comparisons of DNA sequences suggest that chimpanzees are our closest living relatives. This is hardly surprising, as simple observation shows that chimpanzees and humans share many features. However, among other differences, chimpanzees have smaller stature, long arms that facilitate knuckle-walking (the arms help support the body as the chimpanzee moves forward), a more prominent snout, and larger teeth. Fossils painstakingly unearthed over the past century show that the morphological features that mark us as human accumulated through a series of speciation events. Six to seven million years ago, when the human and chimpanzee lineages first split, the two newly diverged taxa looked much more alike than humans and chimpanzees do today.he agreement of comparative biology and the fossil record can be seen at all scales of observation. Humans form one tip of a larger branch that contains all members of the primate family. Primates, in turn, are nested within a larger branch occupied by mammals, and mammals nest within a still larger branch containing all vertebrate animals, which include fish. This arrangement predicts that the earliest fossil fish should be older than the earliest fossil mammals, the earliest fossil mammals should be older than the earliest primates, and the earliest primates older than the earliest humans. This is precisely what the fossil record shows (Fig. 23.22). The agreement between fossils and phylogenies drawn from living organisms can be seen again and again when we examine different branches of the tree of life or, for that matter, the tree as a whole. All phylogenies indicate that microorganisms diverged early in evolutionary history, and mammals, flowering plants, and other large complex organisms diverged more recently. The tree's shape implies that diversity has accumulated through time, beginning with simple organisms and later adding complex macroscopic forms. The geologic record shows the same pattern. For nearly 3 billion years of Earth history, microorganisms dominate the fossil record, with the earliest animals appearing about 600 million years ago, the earliest vertebrate animals 520 million years ago, the earliest tetrapod vertebrates about 360 million years ago, the first mammals 210 million years ago, the first primates perhaps 55 million years ago, the oldest fossils of our own species a mere 200,000 years ago. Similarly, if we focus on photosynthetic organisms, we find a record of photosynthetic bacteria beginning at least 3500 million years ago, algae 1200 million years ago, simple land plants 470 million years ago, seed plants 370 million years ago, flowering plants about 140 million years ago, and the earliest grasses 70 million years ago. In Part 2, we explore the evolutionary history of life in some detail. Here, it is sufficient to draw the key general conclusion: The fact that comparative biology and fossils, two complementary but independent approaches to reconstructing the evolutionary past, yield the same history is powerful evidence of evolution.

The nested pattern of similarities seen among organisms is a result of descent with modification and can be represented as a phylogenetic tree. The order of branches on a phylogenetic tree indicates the sequence of events in time. Sister groups are more closely related to one another than they are to any other group. A node is a branching point on a tree, and it can be rotated without changing evolutionary relationships. A monophyletic group includes all the descendants of a common ancestor, and it is considered a natural grouping of organisms based on shared ancestry. A paraphyletic group includes some, but not all, of the descendants of a common ancestor. A polyphyletic group includes organisms from distinct lineages based on shared characters, but it does not include a common ancestor. Organisms are classified into domain, kingdom, phylum, class, order, family, genus, and species.

Characters, or traits, existing in different states are used to build phylogenetic trees. Homologies are similarities based on shared ancestry, while analogies are similarities based on independent adaptations. Homologies can be ancestral, unique to a particular group, or present in some, but not all, of the descendants of a common ancestor (shared derived characters). Only shared derived characters, or synapomorphies, are useful in constructing a phylogenetic tree. Molecular data provide a wealth of characters that complement other types of characters in building phylogenetic trees. Phylogenetic trees can be used to understand evolutionary relationships of organisms and solve practical problems, such as how viruses evolve over time.

Fossils are the remains of organisms preserved in sedimentary rocks. The fossil record is imperfect because fossilization requires burial in sediment, sediments accumulate episodically and discontinuously, and fossils typically preserve only the hard parts of organisms. Radioactive decay provides a means of dating rocks. Archaeopteryx and Tiktaalik are two fossil organisms that document, respectively, the bird-dinosaur transition and the fish-tetrapod transition. The history of life is characterized by rare mass extinctions, including the extinction at the end of the Cretaceous Period 65 million years ago in which the dinosaurs (other than birds) became extinct, and the extinction at the end of the Permian Period 252 million years ago, the largest documented mass extinction in the history of Earth.

Phylogeny makes use of living organisms, and the fossil record supplies a record of species that no longer exist, absolute dates, and environmental context. Data from phylogeny and fossils are often in agreement, providing strong evidence for evolution.

Two examples of a nested pattern of similarity among organisms are (1) a dog and a wolf are more similar to each other than either is to a cat, and (2) a dog, a wolf, and a cat are more similar to each other than they are to a turtle.

monophyletic groups are groups in which all members share a single common ancestor not shared with any other species or group of species, like amphibians. Paraphyletic groups include some, but not all, of the descendants of a common ancestor, like birds being excluded from the "reptile" group even though there is evidence that they share a common ancestor. A polyphyletic group does not include the last common ancestor of all members, like putting bats and birds in a single "flying vertebrates" group.

The levels of classification are as follows: species, genus, family, order, class, phylum, kingdom, and domain.

A homologous trait is one that results from shared ancestry, such as an amniotic egg and lungs. An analogous trait is a similarity that results from convergent evolution, such as bird and bat wings or echolocation.

Synapomorphies, or shared derived characters between some members of a group, are useful in building phylogenetic trees because the homologies are shared by some but not all of the members of the group. If an entire group shared the same homologous trait, we would not be able to construct a meaningful phylogenetic tree.

Three types of fossils are skeletal fossils, where the hard parts of the organism such as the skeleton are fossilized, trace fossils, where the tracks or trails of an animal are fossilized, and molecular fossils, where an organism's DNA or proteins are left.

For an organism to be fossilized it must be buried and have features that resist decay after death. Not all organisms meet these two criteria, so they do not become fossils and lead to gaps in the fossil record.

The relative timescale of past events can be determined by the location of the fossil in the Earth's surface since a fossil's age is related to how deep into the Earth's layers the fossil is found. The absolute timescale can be determined by measuring isotope decay, since unstable isotopes decay at a particular, known rate. Carbon, uranium, and lead are all used to date fossils.

Archeopteryx is a fossil organism that shows the transition from bird to dinosaur, and Tiktaalik is a fossil organism that shows the transition from fish to tetrapod in the fossil record. Transition fossils are significant because they give us evolutionary clues of morphological and physiological phylogenetic shifts through time.

Mass extinctions have shaped the ecological landscape by removing the dominant species in an ecosystem and thereby changing the competitive landscape of the remaining organisms. The survivors of this altered ecosystem live and reproduce, thus introducing new mutations into the population.

-Phylogenetics trees contain a lot of information about the inferred evolutionary relationships between a set of viruses. Decoding that information is not always straightforward and requires some understanding of the elements of a phylogeny and what they represent. Here is an example (fictional) phylogeny as it may be presented in a journal article: We can start with the dimensions of the figure. In this figure the horizonal dimension gives the amount of genetic change. The horizonal lines are branches and represent evolutionary lineages changing over time. The longer the branch in the horizonal dimension, the larger the amount of change.

A group composed of a collection of organisms, including the most recent common ancestor of all those organisms and all the descendants of that most recent common ancestor. A monophyletic taxon is also called a clade. Examples : Mammalia, Aves (birds), angiosperms, insects, etc.

A group composed of a collection of organisms, including the most recent common ancestor of all those organisms. Unlike a monophyletic group, a paraphyletic taxon does not include all the descendants of the most recent common ancestor. Examples : Traditionally defined Dinosauria, fish, gymnosperms, invertebrates, protists, etc.

A group composed of a collection of organisms in which the most recent common ancestor of all the included organisms is not included, usually because the common ancestor lacks the characteristics of the group. Polyphyletic taxa are considered "unnatural", and usually are reclassified once they are discovered to be polyphyletic. Examples : marine mammals, bipedal mammals, flying vertebrates, trees, algae, etc.

In everyday life, people look like one another for different reasons. Two sisters, for example, might look alike because they both inherited brown eyes and black hair from their father. On the other hand, two people attending an Elvis impersonators' convention may look alike because they are both wearing rhinestone studded suits and long sideburns. The similarity between the sisters is inherited, but the similarity between the Elvis impersonators is not. -Biological similarity It works the same way in biology. Some traits shared by two living things were inherited from their ancestor, and some similarities evolved in other ways. These are called homologies and analogies

traits inherited by two different organisms from a common ancestor -Ancestral organism shared by two or more descendent lineages — in other words, an ancestor that they have in common. For example, the common ancestors of two biological siblings include their parents and grandparents; the common ancestors of a coyote and a wolf include the first canine and the first mammal.

similarity due to convergent evolution, not common ancestry -Process in which two distinct lineages evolve a similar characteristic independently of one another. This often occurs because both lineages face similar environmental challenges and selective pressures.

Derived character state shared by different lineages. - allow us to identify monophyletic groups, because if a character is shared by two lineages, we assume that it was inherited from their most recent common ancestor

Fossils give us information about how animals and plants lived in the past. -by studying the fossil record we can tell how long life has existed on Earth, and how different plants and animals are related to each other. Often we can work out how and where they lived, and use this information to find out about ancient environments.

If an isotope (forms of chemical elements that differ in the number of neutrons in their atomic nuclei) is radioacitve, it will break down naturally into a lighter element called a decay product. This process occurs at a predictable rate and can be used to determine how old an object is. - is a technique used to find how old an object is.

1. Morphological Data: - Number of spines in the fins of various fish species - Size or shape of a bony projection on the femur 2. Behavioral Data: - Pitch or duration of frog or bird calls 3. Molecular Data: - LDH isoenzyme patterns discerned from starch gel electrophoresis - DNA or protein sequences