Descent with Modification: A Darwinian View of Life PDF

Chapter 22 Descent with Modification: A Darwinian View of Life © 2021 Pearson Education, Inc.  This Malaysian orchid mantis (Hymenopus coronatus) closely resembles the flower on which it rests, waiting for unwary prey to com...

Chapter 22 Descent with Modification: A Darwinian View of Life © 2021 Pearson Education, Inc.  This Malaysian orchid mantis (Hymenopus coronatus) closely resembles the flower on which it rests, waiting for unwary prey to come within its reach. Other mantises have diverse shapes and colors that have evolved in different environments—yet all mantises also share certain features, such as grasping forelimbs, large eyes, and six legs © 2021 Pearson Education, Inc. Figure 22.1a © 2021 Pearson Education, Inc. Figure 22.1b CONCEPT 22.1: The Darwinian revolution challenged traditional views of a young Earth inhabited by unchanging species Publication of The Origin of Species by Charles Darwin in 1859 started a scientific revolution—the era of evolutionary biology Darwin’s ideas developed gradually, through the influence of other’s works and his own travels © 2021 Pearson Education, Inc. © 2021 Pearson Education, Inc. Figure 22.2 Endless Forms Most Beautiful Shared characteristics among different species illustrate the unity of life – For example, insect species in the order Mantodea (mantises) all have bulging eyes, and a flexible “neck” Different species also have differing characteristics – For example, mantis species differ in size, shape, and color © 2021 Pearson Education, Inc.  Mantises illustrate three key observations about life: – Organisms are adapted for life in their biotic and abiotic environments – The many shared characteristics (unity) of life – The diversity of life © 2021 Pearson Education, Inc.  Evolution refers to the process by which species accumulate differences from their ancestors as they adapt to different environments over time This definition is summarized by Darwin’s phrase descent with modification © 2021 Pearson Education, Inc.  Evolution can be viewed as both a pattern and a process – Pattern is revealed by scientific data showing that life has evolved over time – Process consists of the mechanisms that cause the pattern of change © 2021 Pearson Education, Inc. Scala Naturae and Classification of Species Greek philosopher Aristotle (384–322 BCE) believed that species were fixed (unchanging) He arranged species on a scale of increasing complexity called the scala naturae In the 1700s, scientists interpreted adaptations as evidence of design by a Creator © 2021 Pearson Education, Inc.  Carolus Linnaeus (1707–1778) developed a nested classification system grouping similar species into increasingly inclusive categories He also developed the binomial format for naming species (for example, humans are Homo sapiens) Both of these systems are still in use today © 2021 Pearson Education, Inc. Ideas About Change over Time Darwin drew from the study of fossils, remains or traces of organisms from the past Many fossils are found in sedimentary rock, which appears in layers called strata © 2021 Pearson Education, Inc. © 2021 Pearson Education, Inc. Figure 22.3  Paleontology, the study of fossils, was developed in large part by Georges Cuvier (1769–1832) Cuvier observed that older strata contain fossils less similar to current organisms than more recent strata He also observed that, from layer to layer, new species appear while others disappear © 2021 Pearson Education, Inc.  Cuvier speculated that boundaries between strata represent sudden catastrophic events Darwin was also influenced by scientists proposing that slow, continuous processes caused change on Earth © 2021 Pearson Education, Inc.  James Hutton (1726–1797) proposed that Earth’s geologic features were formed gradually – For example, valleys being formed by rivers Charles Lyell (1797–1875) proposed that the same geologic processes operate today as in the past, at the same rate © 2021 Pearson Education, Inc.  Darwin reasoned that the Earth must be older than the widely accepted age of a few thousand years If true, gradual processes could also account for substantial biological change © 2021 Pearson Education, Inc. Lamarck’s Hypothesis of Evolution Jean-Baptiste de Lamarck (1744–1829) proposed two principles to explain evolutionary change – Use and disuse: body parts used extensively become larger and stronger, unused parts deteriorate – Inheritance of acquired characteristics: modifications acquired in one’s lifetime can be passed to offspring This mechanism is not supported by experimental evidence © 2021 Pearson Education, Inc. Figure 22.4 © 2021 Pearson Education, Inc. CONCEPT 22.2: Descent with modification by natural selection explains the adaptations of organisms and the unity and diversity of life By the early 19th century, it was still generally thought that species were created, and remained unchanged However, doubts were beginning to gather © 2021 Pearson Education, Inc. Darwin’s Research Charles Darwin (1809–1882) had a consuming interest in nature throughout his life He studied medicine (unsuccessfully) and then switched to theology at Cambridge University After graduation, he took a position as naturalist on a five-year, worldwide voyage on the HMS Beagle © 2021 Pearson Education, Inc. The Voyage of the Beagle During his travels on the Beagle, Darwin collected specimens of South American plants and animals He noted that fossils resembled living species from the area in which they were found, and living species resembled other species from areas nearby © 2021 Pearson Education, Inc.  During an earthquake in Chile, Darwin observed the uplift of rocks by several meters He inferred that rocks containing fossils of ocean organisms in the Andean Mountains must have been raised there by many similar earthquakes © 2021 Pearson Education, Inc.  On the Galápagos Islands, Darwin collected many similar, but different species of birds, some unique to individual islands, others found on multiple islands Animals unique to the islands resembled species on the nearby mainland of South America Darwin hypothesized that species from the mainland colonized and then diversified on the islands © 2021 Pearson Education, Inc. Figure 22.5 © 2021 Pearson Education, Inc. Darwin’s Focus on Adaptation Darwin observed many examples of adaptations during the voyage of the Beagle Adaptations are inherited characteristics that enhance an organism’s survival and reproduction in specific environments © 2021 Pearson Education, Inc.  Darwin perceived that new species could arise from ancestral forms through gradual accumulation of adaptations This process formed the diverse group of Galápagos finches © 2021 Pearson Education, Inc. Figure 22.6 © 2021 Pearson Education, Inc.  Darwin proposed natural selection as an explanation for adaptation Natural selection is a process in which individuals with certain inherited traits tend to survive and reproduce at higher rates because of those traits © 2021 Pearson Education, Inc.  Darwin wrote down his ideas in 1844, but did not publish out of concern they would cause an uproar He continued to compile supporting evidence In June 1858, Alfred Russel Wallace (1823–1913) sent Darwin a manuscript describing a nearly identical hypothesis of natural selection © 2021 Pearson Education, Inc.  Papers by both Wallace and Darwin were presented to the Linnean Society of London on July 1, 1858 Darwin quickly finished The Origin of Species and published it the next year Within a decade, most scientists were convinced that life’s diversity is the product of evolution © 2021 Pearson Education, Inc. Ideas from The Origin of Species Descent with modification by natural selection explains three broad observations: – The unity of life – The diversity of life – The ways organisms are suited to life in their environments © 2021 Pearson Education, Inc. Descent with Modification Darwin used descent with modification to describe his view of life By this view, all organisms are related by descent from a common ancestor that lived in the past Related organisms living in different habitats gradually accumulated diverse modifications to fit them to specific ways of life © 2021 Pearson Education, Inc.  Darwin viewed the history of life as a tree, with multiple branchings from a common trunk – Labeled branches represent groups of organisms living in the present day – Unlabeled branches represent extinct groups – A fork represents the most recent common ancestor of all lines of evolution branching from that point © 2021 Pearson Education, Inc. Figure 22.7 © 2021 Pearson Education, Inc.  Large morphological gaps between related groups are explained by branching and extinction events – For example, living elephant species are similar because they split from a recent common ancestor – The extinction of seven older species helps explain the dissimilarity between elephants and their nearest living relatives, hyraxes and manatees © 2021 Pearson Education, Inc. Figure 22.8 © 2021 Pearson Education, Inc. Artificial Selection, Natural Selection, and Adaptation Humans modify species through artificial selection, breeding only individuals with desired traits Crops, livestock animals, and pets often bear little resemblance to their wild ancestors © 2021 Pearson Education, Inc. Figure 22.9 © 2021 Pearson Education, Inc.  Darwin drew two inferences from two observations – Observation #1: Members of a population often vary in their inherited traits – Observation #2: All species can produce more offspring than the environment can support, and many of these offspring fail to survive and reproduce © 2021 Pearson Education, Inc. Figure 22.10 © 2021 Pearson Education, Inc. Figure 22.11 © 2021 Pearson Education, Inc.  Inference #1: Individuals with inherited traits that increase survival and reproduction in an environment tend to produce more offspring than other individuals Inference #2: The unequal ability of individuals to survive and reproduce will lead to the accumulation of favorable traits in the population over generations © 2021 Pearson Education, Inc.  Thomas Malthus wrote about the capacity of human populations to increase faster than critical resources Darwin recognized this capacity in all species Only a fraction of offspring complete development and reproduce; the rest are starved, eaten, unmated, diseased, or intolerant of physical conditions © 2021 Pearson Education, Inc.  If advantageous traits increase the number of offspring that survive and reproduce, then they will appear at higher frequency in the next generation – For example, offspring may inherit a trait that helps them escape predators or obtain food © 2021 Pearson Education, Inc.  Over time, natural selection by predators, lack of food, or adverse conditions can increase the proportion of favorable traits in the population Even slight advantages gradually accumulate in the population, while less favorable variations diminish In this way, organisms become better suited for life in their environment © 2021 Pearson Education, Inc. Key Features of Natural Selection Individuals with certain heritable traits survive and reproduce at a higher rate than other individuals Natural selection increases the frequency of adaptations that are favorable in an environment If the environment changes, natural selection may drive adaptation to new conditions, giving rise to new species © 2021 Pearson Education, Inc. Figure 22.12 © 2021 Pearson Education, Inc.  Individuals do not evolve; it is the population that evolves over time Natural selection can only increase or decrease heritable traits that are variable in a population The environment varies from place to place and over time; favorable traits vary with the environment © 2021 Pearson Education, Inc. CONCEPT 22.3: Evolution is supported by an overwhelming amount of scientific evidence New discoveries continue to fill the gaps identified by Darwin in The Origin of Species Four types of data document the pattern of evolution – Direct observations – Homology – The fossil record – Biogeography © 2021 Pearson Education, Inc. Direct Observations of Evolutionary Change Biologists have documented evolutionary change in thousands of scientific studies Two examples include natural selection in response to introduced species and the evolution of drug- resistant bacteria © 2021 Pearson Education, Inc. Natural Selection in Response to Introduced Species Herbivores often have adaptations to help feed efficiently on their primary food source – For example, soapberry bugs use a long “beak” to feed on seeds embedded within the fruits of various plants © 2021 Pearson Education, Inc.  Feeding is most effective when beak length is closely matched to seed depth within the fruit – In southern Florida, soapberry bugs feed on native balloon vines with large fruit; they have long beaks – In central Florida, they feed on introduced golden rain trees with smaller fruit; they have shorter beaks © 2021 Pearson Education, Inc. Figure 22.13 © 2021 Pearson Education, Inc.  Correlation between fruit size and beak size has also been found in Louisiana, Oklahoma, and Australia In all cases, longer beaks evolved when bugs fed on the larger fruit of introduced plants In Florida, evolution in beak size occurred in less than 35 years © 2021 Pearson Education, Inc. The Evolution of Drug-Resistant Bacteria The bacterium Staphylococcus aureus occurs on the skin or nasal passages of about one in three people Certain strains, called methicillin-resistant S. aureus (MRSA), are pathogens that can cause potentially fatal infections – For example, clone USA300 can cause “flesh-eating disease” © 2021 Pearson Education, Inc. Figure 22.14 © 2021 Pearson Education, Inc.  In 1943 penicillin became the first widely used antibiotic to treat bacterial infections Penicillin resistance evolved in S. aureus by 1945 A new antibiotic, methicillin, was introduced in 1959 Methicillin resistance evolved in S. aureus by 1961 © 2021 Pearson Education, Inc.  Methicillin works by inhibiting an enzyme used by bacteria to produce cell walls MRSA bacteria are able to use a different enzyme that is not affected by methicillin Resistance increases in the presence of methicillin because MRSA strains are more likely to survive and reproduce than nonresistant strains © 2021 Pearson Education, Inc.  Multidrug-resistant strains have evolved through the exchange of resistance genes between individuals Resistance is now spreading faster than new antibiotics are being discovered A new antibiotic, “teixobactin,” discovered in 2015, shows promise for treating resistant pathogens © 2021 Pearson Education, Inc.  Natural selection does not create new traits; it selects for traits already present in the population Evolution by natural selection can occur rapidly in species with short generation times Natural selection favors traits that are advantageous in the current, local environment © 2021 Pearson Education, Inc. Homology Homology, similarity resulting from common ancestry, is another type of evidence for evolution Related species can have characteristics that have an underlying similarity yet function differently © 2021 Pearson Education, Inc. Anatomical and Molecular Homologies Homologous structures are anatomical resemblances that represent variations on a structural theme present in a common ancestor – For example, the forelimbs of all mammals have the same arrangement of bones, but different functions © 2021 Pearson Education, Inc. Figure 22.15 © 2021 Pearson Education, Inc.  Comparative embryology reveals anatomical homologies not visible in adult organisms – For example, all vertebrate embryos have a post- anal tail and pharyngeal arches – The arches develop into structures with very different functions in adults from different vertebrate groups © 2021 Pearson Education, Inc. Figure 22.16 © 2021 Pearson Education, Inc.  Vestigial structures are remnants of features that served a function in the organism’s ancestors – For example, snakes arose from ancestors with legs; the skeletons of some snakes retain vestiges of pelvis and leg bones © 2021 Pearson Education, Inc.  Molecular homologies include the genetic code shared by all life and specific genes that are shared between vastly different organisms In some species, homologous genes may acquire new functions, or lose function entirely Similarities in such genes are evidence of inheritance from a common ancestor © 2021 Pearson Education, Inc. Homologies and “Tree Thinking” Characteristics shared by many species date to a deep ancestral past; homologies that evolved more recently are shared only within smaller groups – For example, tetrapods, like all vertebrates, have a backbone – Unlike other vertebrates, all tetrapods also have limbs with digits © 2021 Pearson Education, Inc.  Evolutionary trees are diagrams that reflect hypotheses about the relationships among groups Homologies form nested patterns on the tree Relatedness is determined by the recent common ancestor, not the proximity of groups on the tree Evolutionary trees show relative timing of events, not actual dates © 2021 Pearson Education, Inc. Figure 22.17 © 2021 Pearson Education, Inc.  Evolutionary trees are made using many different data sets, including both anatomical and DNA sequence data Well-supported trees can be used to make predictions about organisms © 2021 Pearson Education, Inc. A Different Cause of Resemblance: Convergent Evolution Convergent evolution is the evolution of similar, or analogous, features in distantly related groups Analogous traits arise not through common ancestry, but through independent adaptation to similar environments – For example, the sugar glider is an Australian marsupial that superficially resembles the flying squirrel, a North American eutherian © 2021 Pearson Education, Inc. Figure 22.18 © 2021 Pearson Education, Inc. The Fossil Record The fossil record provides evidence of the extinction of species, the origin of new groups, and changes within groups over time – For example, the fossil record supported the DNA- based hypothesis that cetaceans are close relatives of even-toed ungulates © 2021 Pearson Education, Inc. Figure 22.19 © 2021 Pearson Education, Inc.  Fossils can document important transitions, such as the transition from land to sea in the ancestors of cetaceans © 2021 Pearson Education, Inc. Figure 22.20 © 2021 Pearson Education, Inc.  Fossil evidence shows that living cetaceans and even-toed ungulates are more different from each other than were earlier members of these groups – For example, Pakicetus, an early cetacean, closely resembles Diacodexis, an early even-toed ungulate © 2021 Pearson Education, Inc. Figure 22.21 © 2021 Pearson Education, Inc. Biogeography Evidence from biogeography, the scientific study of the geographic distribution of species, provides support for evolution © 2021 Pearson Education, Inc.  Species distributions are influenced by continental drift, the gradual movement of Earth’s landmasses – For example, 250 million years ago, all landmasses formed a single large continent called Pangea – By 20 million years ago, they had drifted apart to form the continents near their present locations © 2021 Pearson Education, Inc.  Understanding continental drift and modern species distribution helps predict when and where different groups evolved – For example, freshwater fish in the family Galaxiidae live in South America and Australia, separated by wide stretches of open ocean – All three species share an ancestor dating back to the time that these continents broke away from Pangea © 2021 Pearson Education, Inc. Figure 22.22 © 2021 Pearson Education, Inc. What Is Theoretical About Darwin’s View of Life? In science, a theory accounts for many observations and data, and attempts to explain and integrate a great variety of phenomena Darwin’s theory of evolution by natural selection integrates diverse areas of biological study and stimulates many new research questions Ongoing research adds to our understanding of evolution © 2021 Pearson Education, Inc. Figure 22.UN01a © 2021 Pearson Education, Inc. Figure 22.UN01b © 2021 Pearson Education, Inc. Figure 22.UN02 © 2021 Pearson Education, Inc. Figure 22.UN03 © 2021 Pearson Education, Inc.