The Fossil Record Similarities in Development Similarities ......Evidence of Evolution ... E.g. bat...
Transcript of The Fossil Record Similarities in Development Similarities ......Evidence of Evolution ... E.g. bat...
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Evidence of Evolution
◼ The Fossil Record
◼ Similarities in Development
◼ Similarities in Body Structure
◆ Homologous structures
◆ Vestigial structures
◆ (Analogous structures)
◼ Biochemical Compounds
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The Fossil Record
◼ Fossils preserve evidence of past life forms
◆ Hard parts (shell, bone) preserved better
◆ Chancy process
◆ Quality varies
◼ Fossils trapped in sedimentary rock layers: age of layers can be determined
Further reading: textbook section 13-3
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The Fossil Record
Further reading: textbook section 13-3
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◼ Embryo: organism at early stage of development
◼ Similarities of vertebrate embryos → similar genes at work responsible for patterning of body segments
◼ Mutations that disrupt development are lethal; selected against
◼ Early developmental stages retained evolutionarily
Similarities in Development
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◼ Homologous Structures: body structures that
appear different and meet different needs, but have
common origin. Indicates common ancestry.
Similarities in Body Structure
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◼ Vestigial Organs: organs that serve no useful
function in an organism
◆ E.g. humans: wisdom teeth, appendix,
tailbone, tonsils
◆ E.g. pelvic bone in whale and snake, eyes in
star-nosed mole
Similarities in Body Structure
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◼ Analogous Structures: structures that appear
similar and have similar functions, but the
evolutionary origin is different. These organisms
DO NOT share a common ancestor.
◆ E.g. bat wing and butterfly wing
◆ E.g. mimicry in wing patterns
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◼ Darwin was not aware of biochemical evidence
◼ Some biochemical compounds conserved
evolutionarily: essential and/or ‘as good as it gets’
◆ DNA/RNA as genetic material
◆ Cytochrome c (used in mitochondrial electron transport
chain)
◆ Rubisco in all photosynthetic organisms (Calvin cycle)
Biochemical Compounds
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Biochemical Compounds
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◼ Darwin was not aware of biochemical evidence
◼ Some biochemical compounds conserved
evolutionarily: essential and/or ‘as good as it gets’
◆ DNA/RNA as genetic material
◆ Cytochrome c (used in mitochondrial electron transport
chain)
◆ Rubisco in all photosynthetic organisms (Calvin cycle)
Artificial/natural selection only works on variation that
already exists. Variation on essential components likely
to be bad (selected against).
Biochemical Compounds
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Analogy to TechnologyNot testable
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Analogy to TechnologyNot testable
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Descent with Modification
◼ Living organisms evolved through gradual
modification of earlier forms – descent from a
common ancestor
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Summary of Darwin’s Theory
1) Variation exists in nature: individuals differ from one another in their traits
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Summary of Darwin’s Theory
2) Struggle for Existence
◼ Because more organisms are produced than
can survive, each species must struggle for
resources
◼ Each organism is unique: each has
advantages and disadvantages in the
struggle for existence
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Summary of Darwin’s Theory
2) Survival of the fittest
◼ Individuals best suited for the environment
are most successful at surviving and
reproducing; they pass on their traits
(adaptations)
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Summary of Darwin’s Theory
3) Evolution
◼ Frequency of variants of traits in a species
or population changes over time
◼ “Process by which modern organisms have
descended from ancient organisms”
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Summary of Darwin’s Theory
4) Descent with Modification/Common
Ancestry
◼ Species alive today descended with
modification from species that lived in the
past
◼ All organisms on earth are united into a
single family tree of life by common
descent
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MISCONCEPTIONS
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#1: “Individuals adapt or mutate in order
to survive/reproduce in the environment”
◼ No! This sounds Lamarckian.
◼ New adaptations or mutations only very rarely
arise, and never with a ‘purpose’ or ‘goal’…only
randomly
◼ No adaptation or mutation occurs during lifetime;
you must be born with it (it is inherited from your
parents)
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#2: “Natural selection occurs
because of variation in fitness”
◼ Variation = different types, different traits,
different “variants” in population
◼ Variation in traits → variation in fitness →
different individuals survive and reproduce more
◼ Selection acts on the variation in traits that already
exists
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#3: “Natural selection only happens
when environment changes”◼ Natural selection is happening all the time; the key
is an individual’s ability to survive and reproduce
(its fitness)
◼ Sometimes the environment is stable (in
equilibrium)…frequencies of traits unlikely to
shift
◆ E.g. brown and white mice living happily together
◼ Sometimes environment changes. When change
occurs, the frequency of certain traits is likely to
shift
◆ E.g. frequency of white mice decreases
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#4: “After natural selection, new
traits/adaptations appear”
◼ New adaptations or mutations only very rarely
arise, and never with a ‘purpose’ or ‘goal’…only
randomly
◼ The only result of natural selection is that the
variants who are most fit, pass on their traits more;
overall there is a change in frequency of these
traits to favour the most adaptive traits (i.e. those
that increase fitness)
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#5: “Unfit individuals do not
reproduce”
◼ They may still reproduce, but they reproduce less
than the more fit individuals
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#6: “Long lifespan helps them look
after offspring”
◼ Longer lifespan linked to more offspring (higher
reproductive rate)
◼ May be related to offspring care, but not
necessarily
◆ E.g. humans must live long to take care of
young
◆ E.g. plants, coral, jellyfish, fish do not take care
of young (generally)