Chapter 24 Evolution by Natural Selection 24 1 The Evolution of Evolutionary Thought Plato and Typological Thinking Claimed every animal was a perfect creation by God Might deviate slightly but similar to a shadow on the wall Typological thinking Based on the idea that species are unchanging types and that variations within species are unimportant or even misleading Bible book of Genesis Eventually began to break down Aristotle and the Great Chain of Thinking Linear scheme Species were organized into a sequence based on increasing size and complexity Humans at the top Characteristics of species were fixed didn t change over time Central claims Species are fixed types Some species are higher in the sense of being more complex or better than others Lamarck and the Idea of Evolution as Change through Time Formal theory of Evolution Species are not static but change over time Pattern component initially based on great chain Simple organisms at base by spontaneous generation Evolve by moving up the chain over time Always producing larger and more complex organisms Ladder of life into an escalator Change through time via inheritance of acquired characteristics Eventually abandoned it Darwin and Wallace and Evolution by Natural Selection Evolution occurs bc traits vary among individuals and certain traits leave more offspring than others Variation among individuals in a pop was the key to understanding the nature of species Population thinking Revolutionary for several reasons Overturned idea that species are unchanging Replaced typological thinking w population thinking Scientific 24 2 The Pattern of Evolution Have Species Changed through Time Descent with modification o o o o Darwin Species that lived in the past are the ancestors of the things living today Species and their descendants change through time Descendent species are modified Pattern component of natural selection o o Species change through time Species are related by common ancestry Evidence for Change through Time Fossils fossil records Extant species o o Those species living today o Geological time scale A sequence of named intervals called eons eras and periods Represent the major events in earth s history Based on observations on rock formation Sedimentary rocks Form from sand or mud Radiometric dating based on Observed decay rates of parent to daughter atoms The ratio of parent to daughter atoms present in newly formed rocks The ratio of parent to daughter atoms present in a particular rock sample The geological record indicated the earth was much much older than the 6000 years claimed by proponents of the theory of special creation o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o Earth is about 6 4 billion years old Earliest signs of life appear in rocks that formed 3 4 3 8 billion yrs ago All the fossil records indicate over 99 of the species that ever existed are extinct Transitional feature a trait in a fossil species that is intermediate btwn those of older and younger species Vestigial trait a reduced or incompletely developed structure that has no function or reduced function but clearly similar to structured in closely related species Species are dynamic Evidence of Descent from a Common Ancestor Similar species are found in the same geographical area Homology A similarity that exists in species bc they both inherited the trait from a common ancestor Ex human hair dog fur Genetic homology Occurs in DNA sequences Development homology Recognized in embryos Structural homology Similarity in adult morphology or form These 3 levels of homology interact Genetic homologies cause the developmental homos observed in embryos which then leads to structural homos seen in adults This is why you can test drugs on mice and animals first before people genetic homo The theory of evolution by natural selection predicts that homologies will occur If species were created independently of one another these types of similarities would not occur Evolution s Internal Consistency the Importance of Independent Datasets Internal consistency the observation that data from independent sources agree in supporting predictions made by a theory Ex whales dolphins some have vestigial hip and limb bones Whales gradually evolved from a terrestrial ancestor Descent with modification Much more successful and powerful theory 24 3 The Process of Evolution How Does Natural Selection Work Darwin s 4 Postulates The individual organisms that make up a population vary in the traits they possess shape size Some of the trait differences are heritable can be passed down to offspring In each generation many more offspring are produced than can possibly survive only some can survive long enough to reproduce and some will produce more than others The subset of individuals that survive best and produce the most offspring is not a random sample of the population instead individs w certain heritable traits are more likely to survive and reproduce Natural selection occurs when indivds w certain traits produce more offspring than do individs w o those traits The individuals are selected naturally by the environment The frequency of these selected traits increases with each generation Darwin s condensed statements Evolution by natural selection occurs when 1 heritable variation leads to 2 differential reproductive success Fitness Adaptation Biological fitness the ability of an individual to produce surviving offspring relative to that ability in other individuals in the population Adaptation a heritable trait that increases the fitness of an individual in a particular environment relative to individuals lacking the trait Adaptations increase fitness 24 4 Evolution in Action Recent Research on Natural Selection Case Study 1 How did Mycobacterium tuberculosis become resistant to antibiotics Receeded in importance in early 1900s because Advances in nutrition made people better able to fight it off quickly The development of antibiotics allowed physicians to stop even advanced infections TB surged in many countries in 1980 The strains were largely resistant to antibiotics Patient history He had an active TB infection and given antibiotics for 6 weeks No more infection Readmitted and had the infection again given many antibiotics Died 10 days later his bacteria was resistant to drugs o Mutation in a bacterial gene confers resistance by a chain of events By chance one of the bacteria had a point mutation C T and these offspring would normally stay at