Chapter 22: Descent with Modification

Theory of Evolution Change through time – Descent with modification – Genetic changes of a population through time Explains Biodiversity – Variety of life forms, with adaptations to specific environments – Form=Function Explains relationship between living organisms – How organisms are related by descent from common ancestors

Theory of Evolution Pattern of Evolution – Observations from natural world – Collected from variety of fields Biology, geology, physics, chemistry Process of Evolution – Mechanisms causing change Unifying theory of biology – Explains and connects observations from natural world

Types of Evolution Microevolution= change in the gene pool of a population over many generations 4 Methods of Microevolution – Mutations May be deleterious or neutral – Natural Selection Process in which individuals with favorable inherited traits are more likely to survive and reproduce – Genetic Drift= chance events cause genetic changes from one population to the next – Gene Flow= individuals or gametes move to a different population

Natural Selection and Mutation

Classification of Species Before 1700s, major belief was organisms did not change through time but were “perfect” and “permanent” – Greek philosopher Aristotle= arranged species on a scala naturae Simple to complex Viewed species as fixed, non-changing 1700s: Carolus Linnaeus= founder of taxonomy – Branch of biology concerned with classifying organisms – Developed the binomial format for naming species Homo sapiens

Classification of Species In the mid-1700s, studies of fossils found evidence of life-forms different from those currently living Early 1800s, French naturalist Jean Baptiste Lamarck explained the differences in fossil records by proposing organisms evolved through time

Fossil Record Primarily based on imprints or remains left in sedimentary rock – Relative ages of fossils can be determined based on their position in rock layers – Radiometric dating allows for more precise aging of fossils – Whole organisms can also be preserved in mediums preventing decomposition Insects in resin Wooly mammoth frozen in ice Documents change of organisms through time Documents large number of extinct species

Classification of Species Lamarck proposed: – Organisms could change its traits by using or not using certain body parts – These changes could be passed to offspring Not supported by genetics

Charles Darwin Born in 1809 Life-long naturalist After college, joined the crew of the HMS Beagle to explore and map parts of the South American coastline – Collected specimens of South American plants and animals HMS Beagle in port

The Galápagos Islands NORTH AMERICA ATLANTIC OCEAN Chile SOUTH AMERICA AFRICA EUROPE Great Britain Equator PACIFIC OCEAN Malay Archipelago AUSTRALIA Tasmania New Zealand Brazil Argentina Cape Horn Andes Mtns. Cape of Good Hope PACIFIC OCEAN Charles Darwin: Voyage of HMS Beagle

Figure 22.5c The Galápagos Islands PACIFIC OCEAN Pinta Marchena Genovesa Equator Santiago Daphne Islands Fernandina Isabela Santa Cruz Santa Fe San Cristobal Española Kilometers Florenza Pinzón

Charles Darwin During voyage, made 2 important observations: – Animals and plants had characteristics specific to the environment they inhabited – Organisms on islands were similar but different from organisms on mainland Darwin perceived adaptation to the environment and the origin of new species as closely related processes

Figure 22.6 (a) Cactus-eater (b) Insect-eater (c) Seed-eater

Charles Darwin

1844: wrote an essay on natural selection as the mechanism of descent with modification – Did not introduce his theory publicly 1858: Received manuscript from Alfred Russell Wallace – Developed a theory of natural selection similar to Darwin’s Darwin quickly finished The Origin of Species and published it the next year

Charles Darwin 1859: The Origin of Species was published Provided evidence of “descent with modification” – Current species came from a succession of ancestors – As descendants spread into new habitats, modifications (adaptations) accumulated as a result of new environmental factors – Resulted in new species and increased diversity Proposed mechanism for evolution – Natural selection

Charles Darwin In the Darwinian view, the history of life is like a tree with branches representing life’s diversity Darwin’s theory meshed well with the hierarchy of Linnaeus

Figure 22.8 Hyracoidea (Hyraxes) Sirenia (Manatees and relatives) † Deinotherium † Mammut † Platybelodon † Stegodon † Mammuthus Elephas maximus (Asia) Loxodonta africana (Africa) Loxodonta cyclotis (Africa) † Moeritherium † Barytherium 60 Millions of years ago Years ago

Artificial Selection Darwin noted that humans have modified other species by selecting and breeding individuals with desired traits – Artificial selection

Figure 22.9 Brussels sprouts Kale Selection for leaves Selection for axillary (side) buds Selection for apical (tip) bud Cabbage Broccoli Kohlrabi Wild mustard Selection for stems Selection for flowers and stems

Darwin drew two inferences from two observations Observation #1: Members of a population often vary in their inherited traits Inference #1: Individuals whose inherited traits give them a higher probability of surviving and reproducing in a given environment tend to leave more offspring than other individuals

Darwin drew two inferences from two observations Observation #2: All species can produce more offspring than the environment can support, and many of these offspring fail to survive and reproduce Inference #2: This unequal ability of individuals to survive and reproduce will lead to the accumulation of favorable traits in the population over generations

Natural Selection Unequal reproduction is the essential part of natural selection Individuals with characteristics allowing them to be better at… – getting food – escaping predators – tolerating environment – attracting mates – …will survive longer and potentially produce more offspring with the adaptive characteristic

Natural Selection Explains the match between organisms and their environment…

3 Key Points to Evolution by Natural Selection Individuals do not evolve, populations evolve – Evolution occurs as adaptations accumulate in populations over several generations Natural selection only works on heritable traits with variation in the population – Acquired traits are not passed to offspring Evolution is not working towards a specific goal or “perfect” organisms – Natural selection results from an organism interacting with a specific environment – Characteristics favorable in one environment may not be favorable in another

Natural Selection: Summary Individuals with certain heritable characteristics survive and reproduce at a higher rate than other individuals Natural selection increases the adaptation of organisms to their environment over time If an environment changes over time, natural selection may result in adaptation to these new conditions and may give rise to new species

Evidence of Natural Selection: Response to Introduced Plant Species Soapberry bugs use their mouthparts to feed on seeds within fruits Southern Florida: feed on balloon vine with large fruit – Longer beaks Central Florida: feed on goldenrain tree with small fruit – Shorter beaks Correlation between fruit size and beak size also observed in Louisiana, Oklahoma, and Australia Soapberry bug with beak inserted in balloon vine fruit

Figure 22.13b On native species, southern Florida Museum-specimen average On introduced species, central Florida Number of individuals Beak Beak length (mm) RESULTS 9

In all locations, beak size has evolved in populations that feed on introduced plants – Fruits smaller or larger than native fruits Evolution by natural selection In Florida, this evolution in beak size occurred in less than 35 years Evidence of Natural Selection: Response to Introduced Plant Species

Evidence of Natural Selection: Antibiotic resistant bacteria Staphylococcus aureus is commonly found on people – S. aureus became resistant to penicillin in 1945, two years after it was first widely used One strain, methicillin-resistant S. aureus (MRSA) is a dangerous pathogen – S. aureus became resistant to methicillin in 1961, two years after it was first widely used

Evidence of Natural Selection: Antibiotic resistant bacteria Methicillin= inhibits a protein used by bacteria in their cell walls – MRSA bacteria use a different protein in their cell walls When exposed to methicillin, MRSA strains are more likely to survive and reproduce than nonresistant S. aureus strains – MRSA strains are now resistant to many antibiotics

Evidence of Natural Selection: Antibiotic resistant bacteria Antibiotic Applied Most bacteria killed, High resistance strains remain Reproduction Final population composed of high resistance strains

Evidence of Natural Selection: Antibiotic resistant bacteria Natural selection does not create new traits – Works on existing traits already present in the population – Mutations are raw material for natural selection to act on Local environment determines which traits will be selected for or selected against in any specific population

Evidence of Natural Selection: Comparative Anatomy Homology= similar characteristics resulting from a common ancestor Homologous structures= similar structure in features even if function is different Example: Vertebrate Forelimbs

Figure Humerus Radius Ulna Carpals Metacarpals Phalanges Human Cat Whale Bat

Evidence of Natural Selection: Comparative Anatomy Comparative embryology reveals anatomical homologies not visible in adult organisms

Evidence of Natural Selection: Comparative Anatomy Vestigial structures= remnants of features with served important functions in the organism’s ancestors

Evidence of Natural Selection: Molecular Biology Homologies also occur at the molecular level – Genes shared among organisms inherited from a common ancestor

Evidence of Natural Selection: Molecular Biology Evolutionary history contained in an organism’s DNA Closely related species will have more similarities in DNA than distantly related species Darwin proposed all life forms are related – Supported by molecular biology – All organisms use same genetic language- DNA and RNA – Same genetic code for nearly all organisms – Humans and bacteria share homologous genes

Evidence of Natural Selection: Evolutionary Trees Evolutionary trees= hypotheses about the relationships among different groups – Form nested patterns in evolutionary trees Made using different types of data – Anatomical similarities – DNA sequence data

Figure Branch point Lungfishes Amphibians Mammals Lizards and snakes Crocodiles Ostriches Hawks and other birds Feathers Amnion Digit- bearing limbs Homologous characteristic Tetrapods Amniotes Birds

Evidence of Natural Selection: Evolutionary Trees Convergent evolution= evolution of similar, or analogous, features in distantly related groups – Arise when groups independently adapt to similar environments in similar ways Convergent evolution does not provide information about ancestry

Evidence of Natural Selection: Biogeography Biogeography= geographic distribution of species Island animals resemble species on closest mainland more than they resemble species on islands closer and farther away Explanation: Animals on islands migrated from mainland, natural selection changed animals over time into separate species – Galapagos Finches – Marsupials in Australia

Evidence of Natural Selection: Biogeography Alfred Russel Wallace (1823–1913) – Father of biogeography Best known as the co-discoverer of the principles of natural selection with Darwin Main contribution was the study of species distributions across large spatial scales

Evidence of Natural Selection: Biogeography Wallace (1860) observed that animals can vary considerably over very short distances – Could not be explained until continental drift was proposed Continental drift from movement of Earth’s plates explains the distributions of some species Type of macroevolution

Types of Evolution Macroevolution= change in groups above the level of species, often results in new taxonomic groups Methods of Macroevolution – Adaptive radiation= periods of change when many new species originate from a common ancestor – Mass extinctions= large number of species go extinct within a relatively short amount of time 5 mass extinctions have occurred through geological time with 50% or more species lost – Plate tectonics and Continental drift= movement of Earth’s plates

Mass Extinction Event

Evidence of Natural Selection: Biogeography

Endemic species= species that are not found anywhere else in the world Islands have many endemic species – Closely related to species on the nearest mainland or island Darwin explained that species on islands gave rise to new species as they adapted to new environments

Evolution is a Theory In science, theory accounts for many observations and data – Attempts to explain and connect a huge variety of phenomena Darwin’s theory of evolution by natural selection – integrates diverse areas of biological study – stimulates many new research questions Ongoing research adds to our understanding of evolution