Ap Biology Chapters 22-24: Evolution

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Aristotle and Natural Theology

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believed that all living forms could be arranged on a scale, or ladder, of increasing complexity "scale of nature"
-each form of life has its own allotted rung - species are perfect, unchanging and do not evolve
-opposed any concept of evolution

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Natural Theology - 1700s

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-beliefs dedicated to discovering the creator;s plan by studying nature

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Carolus Lineus

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discovered order in the diversity of life, which was the objective of natural theology
-taxonomy
-implied no evolution kinship

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taxonomy

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naming and classifying all forms of life
-a major objective of natural theology was to classify species to reveal the steps of the scale of life that God created

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Hutton : gradualism

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-earth's geological features: profound change is a slow but continuous process

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Charles Lyell : uniformitarianism

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-incorporated Hutton's theory and added that geologic processes have occurred through out history

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two conclusions that influenced Darwin

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1. if geologic change results from slow continuous events, then Earth must be very old
2. very slow and subtle change persisting over long periods of time can add up to substantial changes

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George Cuvier

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-proposed catastrophes and repopulations from other regions over time will result in a new species
-studied fossils, sedimentary rock, paleontology

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Jean-Baptiste Lamarck

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-organisms become adapted to environment; suggested that any characteristic that a parent acquired over its lifetime would be passed on to it offspring

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catastrophism

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extinction by catastrophe
-results in a region being repopulated by species immigrating from other areas

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fossils placed in an evolutionary context

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-Lamarck compared fossils to current species and used them to explain how specific adaptations evolve in response to environment

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Lamarck

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-claimed that organisms adapted to their environments by acquiring traits
-said that next generations inherited the acquired the traits

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Darwin's Theory of Evolution

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-naturalist aboard the HMS beagle
-sailed to Galapogos isalands
hypothesis: common descent does occur
: natural selection results in adaptation to the environment

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Voyage of the HMS Beagle

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-invited to travel around the world
-22 yrs old
-1831-1836
-main mission was to chart the South American coastline
-stopped in the Galapagos Islands

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Galapagos

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-recent volcanic origin
-most animal species on the islands live nowhere else in the world, but they resemble animals on the South American mainland

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Galapagos birds

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22 of 29 species of birds on the island are endemic
-one particular group, the finches, was studied by Darwin
-he discovered many different types of finches, all originally from the mainland but adapted to the island habitats

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Darwin's Finches

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-difference in beaks
-associated with eating different foods
-survival and reproduction of beneficial adaptations to foods available on islands

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Darwin's Conclusion on finches

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-small populations of original South American finches landed on island
-variation in beaks enabled individuals to gather food successfully in different environments
-over many different generations, the populations of finches and changed anatomically and behaviorally
-accumulation of advantageous traits in population
-emergence of different species

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Darwin's primary observations

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1. geology and fossils
-agreed with Lyell that massive geological changes on Earth were caused by slow continuous change
--concluded that Earth is old enough for descent with modification to occur
2. Biogeography
-study of organisms around the world (Galapagos)
--concluded : adaptations to the environment can cause diversification including the origin of new species

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Darwin's Dilemma

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-after returning, Darwin reassessed his observations while on his voyage
-he began to perceive the origin of new species and adaptation to the environment
-by 1840, still not published, poor health, worked out major ideas about natural selection
-1844: long essay but reluctant to publish, asked his wife to publish if he died
-Lyell advised Darwin to publish b/c he feared someone else might publish first

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Alfred Russel Wallace

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-a young naturalist working the East Indies, had written a short manuscript with a new idea
-he asked Darwin to evaluate his ideas and pass it along for publication
-he had developed a theory of natural selection almost identical to Darwin's

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Origin of Species

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Darwin's book was published in 1859
-gave great attention to the diversity of organisms
-laid out in detail the evidence that supported the theory of evolution by natural selection

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2 Major Points in Origin of Species

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1. descent from ancestral species
2. natural selection

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natural selection

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populations of organisms can change over generations if individuals have certain heritable traits that leave more offspring than other individuals
-result: evolutionary adaptation where inherited characteristics enhance organisms survival and reproduction in certain environments

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Thomas Malthus

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-connected natural selection and overpopulation and recognized the "struggle for existence"
-the capacity to overproduce= characteristics of all species
-environmental factors filter heritable variations

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Darwin's Explanation for Natural Selection

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1. members of a population exhibit random, but inherited variations
-can be harmful or helpful
2. there is s struggle for existence
- competition for resources is inevitable
3. organisms differ in their reproductive success
-fitness = who can produce the greatest number of offspring
4. natural selection can result in adaptation to a local environment

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Resistance to Evolutionary Views

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-the Origin of Species was radical- challenged prevailing scientific views that had been taugh for centuries
-Darwin's views contrasted thoughts (that Earth was only a few 1000 years old and populated by unchanging forms of life individually made in single week by a Creator

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descent with modification

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unity of life, related through descent of unknown ancestors, over millions of years - accumulated modifications (adaptations)
-most branches of evolution lead to dead end : about 99% of all species that have ever lived are extinct

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Essence of Darwin's Ideas

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natural selection
-variation exists in population
-overproduction of offspring
-competition/struggle for existence
-differential survival
-differential reproduction

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artificial selection

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-the breeding of domesticated plants and animals
-humans have modified species by selecting individuals with desired traits
-products often bear little resemblance to ancestors
-accomplished in short periods of time

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Population

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group of interbreeding individuals belonging to a particular area and sharing a common geographic area
-smallest unit that can survive
-occurs when proportions of heritable variations in a population happens over generations

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evidence of evolution

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1. fossil record
-transitional fossils show common anscentry
2. biogeography
-study the range and distribution of plants and animals
3. homology
-anatomical similarities resulting from common ancestry
-homologous structure, embryological structures, molecular homologies

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microevolution

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evolution that occurs within a population

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population genetics

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studies variations in gene pools

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gene pool

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total of all the alleles in the pop.

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gene flow

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1. movement of alleles among populations by migration
2. increases variations
3. continued gene flow decreases diversity and gene pools can become smaller
4. can prevent specific speciation from occurring

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In order for evolution to stop :

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1. no migration
2. random mating
3. no natural selection
4. large population
5. no net mutating

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Assortative mating (non-random mating)

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1. non-random mating - individuals choose their mates
2. inbreeding is mating between relatives to a greater extent than by chance
- inbreeding does not change the allele frequencies
-however, inbreeding decreases the proportion of heterozygotes
-in human populations, inbreeding increases frequency of recessive abnormalities
3. assortative mating occurs when individuals mate with those that have the same phenotype
4. sexual selection occurs when males compete for the right to reproduce and the female selects the males of a particular phenotype

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genetic drift

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refers to changes in allele frequencies, usually in small populations
-occurs when founders start a new population or after a bottleneck

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bottleneck effect

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cause by a sever reduction in population, reduces overall diversity

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founder effect

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an example of genetic drift where rare alleles or combinations occur in higher frequency in a population isolated from the general population

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types of selection

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1. directional
2. stabilizing
3. disruptive
4. sexual

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directional selection

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-one phenotype is favored over another
-causes a shift in the overall appearance of the species

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stabilizing selection

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-occurs en extreme phenotypes are eliminated and the intermediate phenotype is favored

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disruptive selection

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-occurs when extreme phenotypes are favored and can lead to more than one distinct form

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sexual selection

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-"special case" of natural selection
-acts on an organism's ability to obtain or successfully find a mate and have offspring

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maintenance of variations

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-populations that lack variety may find it difficult to adapt to changing conditions
-mutations and recombination occurs
-gene flow
-natural selection

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Prezygotic isolating mechanism

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habitat isolation
-different habitats
temporal isolation
-mating season
behavioral isolation
-courtship behaviors
mechanical isolation
-genitalia mismatch
gamete isolation
-sperm unable to reach egg

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Allopatric speciation

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-populations separtated geographically
-variations accumulate
-reproductive isolation
-separates the population

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sympatric speciation

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-occurs when members of a single population develops a difference without geographic isolation

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adaptive radiation

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-a single ancestral species becomes several diff. species

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regulatory genes

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Pax 6 : controls development of both comera type compound in eye
Tbx 5 : controls development of limbs
Hox : control # and appearance of repeated structures along main body axis