Biology and the Tree of Life

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Biology and the Tree of Life

• Chapter 1

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Unity and Diversity of Life
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Unity and Diversity of Life

• Scope of biology is immense
• Huge variety of life forms with many diversifying
  characteristics
• Two unifying concepts
• Cell theory
• Theory of evolution by natural selection

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Cell Theory

• In the late 1660s, Robert Hooke and Anton van
  Leeuwenhoek were the first to observe cells.
• By the 1800s there were enough observations to
  make the generalization that all organisms were
  made of cells

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Cell Theory

• The cell theory states that all organisms are
  made of cells and all cells come from preexisting
  cells.
• Based on inductive reasoning
• Hooke and van Leeuwenhoek showed that all
  organisms are made of cells
• Louis Pasteur proved that cells arise from cells
  and not by spontaneous generation

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Cell Theory

• Implicated that
• All single-celled organisms in a population are
  related to a single common ancestor
• And all cells in a multi-cellular organism also
  descend from a single ancestral cell

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The Evolution of Life
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Theory of evolution by natural selection

• In 1858, Darwin and Wallace proposed that all
  species are related by descent from a common
  ancestor.
• Theory of evolution states that
• Species change over time and are related to one
  another.
• Natural selection is the process by which
  evolution occurs

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Natural Selection

• Individuals of the same species living in the
  same area at the same time constitute a
  population.
• Two conditions must be met for natural selection
  to occur in a population
• Individuals in the population must differ from
  one another for some heritable trait(s)
• Differential reproductive success due to
  heritable traits.

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Natural Selection

• In natural selection, as the individuals with the
  favorable traits increase in frequency, a
  populations characteristics will change over
  time
• In artificial selection, individuals in a
  population are selected for mating based on
  particular traits. Repeating this process over
  generations results in a population with altered
  characteristics

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Artificial Selection
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Artificial Selection

• Allows breeding for particular characteristics
• Brassica oleracea- broccoli, cabbage, kale,
  brussell sprouts
• All the same species, just different cultivars
• Same with dogs and cats

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Classifying Life
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Classifying Life

• Linnaeus taxonomic system for classifying
  organisms, each organism is given a unique
  two-part scientific name consisting of the genus
  and the species.
• Linnaeus system is hierarchical with nested
  taxa. The taxonomic levels from least to most
  specific are kingdom, phylum, class, order,
  family, genus, and species

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Classification of Man
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Classification of Man
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Classification of Organisms

• Linnaeus proposed a two kingdom system
• Plant and animal
• An alternative five-kingdom system based on
  phylogeny was proposed in the 1960s
• Monera, Protista, Animalia, Plantae, and Fungi

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Molecular Classification

• Carl Woese and colleagues studied small subunit
  rRNA, as a means for understanding the
  evolutionary relationships among groups of
  organisms.
• Closely related species should have rRNA
  sequences that are more similar than those from
  distantly related species
• rRNA sequences can be used to produce a
  phylogenetic tree

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Molecular Classification

• The tree of life indicates three major groups of
  organisms the eukaryotes (Eukarya) and two
  groups of prokaryotesthe Bacteria and the
  Archaea.
• Woese proposed a new taxonomic level called the
  domain. Each of the three domains (Bacteria,
  Archaea, and Eukarya) includes several related
  kingdoms)

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The Tree of Life
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Experimenting with Biology
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Hypothesis Driven Science

• In science, inquiry that asks specific questions
  involves the proposing and testing of
  hypothetical explanations, or hypotheses
• A hypothesis is a tentative answer to a
  well-framed question, an explanation on trial
• Makes predictions that can be tested

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Hypothesis-Driven Science

• Example
• Hypothesis All human males
• have a Y sex chromosome.
• Prediction If this hypothesis is correct,
• Experiment and I test all human males,
• Predicted result these males should have the Y
  sex chromosome.

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Example Dead Batteries
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Hypothesis Driven Science

• A scientific hypothesis must have two qualities
• It must be testable
• It must be falsifiable
• Is an idealized process of inquiry
• No amount of testing can prove a theory beyond a
  shadow of a doubt
• Most scientific endeavors do not follow the
  scientific method to the letter
• Often the research gets redirected or changed all
  together

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Experimental Design

• A good scientific experiment must have three
  parts
• A control group to check for other factors that
  might influence the results
• experimental conditions that are controlled to
  eliminate extraneous variables
• the test is repeated to reduce the effects of
  random variation (sample size).