How Populations Evolve

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Chapter 13

• How Populations Evolve

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Charles Darwin and The Origin of Species

• Species arose from succession of ancestors thru
  process of descent with modification
  evolution
• Life evolves by natural selection
• Population changes arise from heritable traits
  that leave more offspring than those without the
  trait
• increase in frequency of traits suited to
  environment
• Evolution genetic composition of population has
  changed over time

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Camouflage Evolutionary Adaptations
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Historical Perspective

• Origins was vastly different than thoughts of
  the time
• Many thought the Earth was young and populated
  by unrelated species so Darwin shook things up
• Idea of Fixed Species ancient Greeks thought
  life arose from water and simple life forms
  preceded more complex but Aristotle held that
  species are fixed and not evolved also enforced
  by the Judeo-Christian interpretation of Book of
  Genesis

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Lamarck and Evolutionary Adaptations

• 1700s Buffon suggested that the Earth is much
  older than 6000 years from studying fossil
  records saw similarities between animal fossils
  and current animals
• Lamarck in 1766 suggested that life evolves
  adaptation which is the refinement of
  characteristics that allow organisms to perform
  successfully in environment
• proposed that by using or not using its body
  parts it passes traits on to offspring
• thought that they passed on the power they
  developed in their beaks to crack seeds to their
  children

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Voyage of the Beagle

• Darwin traveled around the world to help chart
  the coastline of South America and to catalogue
  the animal and plant life there as well as
  fossils
• very different from Europe even in the areas
  that were similar in temperature and environment
• everything was distinctly South American

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Galapagos Islands

• Intrigued by geographic distribution of organisms
  on the island
• have organisms seen nowhere else but similar to
  those on mainland South America
• Plants and animals had to come from somewhere but
  adapted to the islands
• some finches are unique to one island while
  others are distributed across several islands
• different beak types to eat the seeds available
  on the island

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Principles of Geology

• Darwin read this book and realized that the
  mountains pushed up following earthquakes
• made sense then why he found fossils of sea
  snails in the Andes probably from the marine
  floor prior to mountain formation

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Natural Selection

• Mechanism by which evolution occurs
• descendants of earliest organisms spread to
  various habitats and over millions of years
  accumulate different modification or adaptations
  to the diverse ways of life
• descent with modification changes in genes that
  gave an organism an edge over those without the
  change

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History Is Analogous to a Tree

• Branch from a single trunk
• Each branch is a common ancestor to all branches
  from that point on

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Evidence of Evolution

• Biological evolution has left observable marks
• 5 lines of evidence for evolution
• 1 is historical and the other 4 encompass
  historical vestiges of evolution in modern life

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1. Fossil Records

• Found in sedimentary rocks carried by water and
  pile up leading to identifiable strata newer on
  top
• Organisms can also be swept away and deposited in
  the layers age of samples can be determined by
  layer
• Fossil records ordered sequence of fossils as
  they appear in rock layers geological time
• prokaryotes at about 3.5 billion years and move
  up to eukaryotic cells

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Fossil Records

• Oldest vertebrates are fish like, then
  amphibians, reptiles and finally mammals
• Evidence for birds descending from a branch of
  dinosaurs
• Fossilized whales that connect to land dwelling
  ancestors

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2. Biogeopraphy

• Geographic distribution of species
• Darwin noted species on Galapagos resemble South
  American species rather that distant islands
• Australia has more marsupials (pouched animals)
  than placental animals
• can raise placental animals here to point of
  ecological and economic nuisances no natural
  predators
• marsupials evolved on island continent in
  isolation from placental mammals

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3. Comparative Anatomy

• Compare body structures between different species
• Similar structures among species like wrist
  bones
• each limb has different function and evolved from
  some common ancestor otherwise wouldnt see
  such similar structure

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Homology

• Homology is defined as sharing similar
  characteristics like homologous chromosomes
• common ancestry
• Vestigial organs remnants of structures that
  served an important function but no longer need
  some skeletons of some snakes retain evidence of
  pelvis and leg bones of walking ancestors
• our appendix is vestigial from when we where
  mainly herbivores

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4. Comparative Embryology

• Complex anatomical structures in early
  development
• all organisms have structures called gill pouches
  fish, frogs, snakes, birds, apes and all
  vertebrates look more alike than different
• make more changes as each organism develops
• gill pouch in fish gills in humans ears and
  throat

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5. Molecular Biology

• Possess DNA sequence that closely resembles
  another species inherit from a relatively
  recent ancestor
• less nucleotides in common probably not closely
  related
• share common ancestor all organisms use DNA,
  RNA and genetic code for amino acids making up
  proteins

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Natural Selection

• Finches on Galapagos Island colonized from the
  mainland and after many generations they became
  so dissimilar that they have become different
  species
• biggest difference is their beaks based on food
  available

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Theory of Natural Selection

• All species tend to produce excessive numbers of
  offspring
• hope a small percentage will find a home and live
  to reproduce
• Variation among population
• much is heritable siblings share more things in
  common than unrelated individuals

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Connections

• Darwin connected the 2 concepts
• organisms overproduce offspring
• individuals have variations in the same
  population
• Leads to the inference of differential
  reproductive success leads to accumulations of
  favored traits in a population over generations -
  evolution

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Natural Selection in Action

• Pesticide resistance is not caused by the
  pesticide but rather it selects organisms
  resistant to pesticide that are already in the
  population
• Natural selection depends on time and place
  favors characteristics in varying populations
  that fit the current environment

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Environmental Factors

• Environmental factors vary and an adaptation for
  one environment may be good but in a different
  environment it may be bad or have no consequence
• DDT resistance gene in flies cause the flies to
  grow slower but in the presence of DDT it becomes
  a reproduction benefit allowing the flies to
  survive over the ones without the gene