Transcript Macroevolution: How Do Species Evolve?

Macroevolution: How Do
Species Evolve?
Chapter 17
Macroevolution
• The origin, multiplication and extinction of
species and higher groups of organisms.
• Speciation – the formation of new
species.
• The species seen on the Galapagos
islands had all descended from mainland
species, but had changed over time and
become unique to each island.
What is a species?
• Over 1.7 million species identified.
• Most of these species were named and
grouped according to a few observable
(physical) characteristics
• Morphological species
“Think about it, Ed….The class Insecta contains 26 orders,
almost 1,000 families, and over 750,000 described species --but I can’t shake the feeling we’re all just a bunch of bugs.”
Biological Species Concept
• Species are groups of actually or
potentially interbreeding populations,
which are reproductively isolated from
other such groups.
• No matter how extensive the phenotypic
variation, individuals will remain members
of the same species as long as their form,
physiology and behavior permit them to
interbreed and produce fertile offspring.
Problems with the biological
species concept.
• What about organisms that reproduce
asexually (yeast, bacteria, etc.)?
• What about extinct organisms?
• What about organisms that interbreed
sometimes but not others?
• Now can use DNA fingerprinting.
Reproductive Isolation
• Geographic or physical isolation
• Evolve separate adaptations
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There are two major barriers to gene flow
between species:
1. Prezygotic barriers
1. Before or during fertilization
2. Postzygotic barriers
1. Occur after fertilization
Prezygotic barriers
• Temporal isolation – separation by time
– Cicada
• One species breeds every 13 years
• Another species breeds every 17 years
• Overlap every 221 years.
Prezygotic barriers
• Ecological isolation – adapted to
different microevironments in the same
habitat.
• Behavioral isolation
– Mating rituals
– Vocalizations
• Mechanical isolation - incompatibility of
body parts
Prezygotic barriers
• Gametic isolation – gametes are
incompatible at a molecular level
– Pollen
– Enzymes in sperm
Postzygotic barriers
• Zygote either dies or fails to reproduce
successfully.
• Hybrid inviability – embryo dies
• Hybrid sterility – offspring infertile
• Hybrid breakdown – offspring of hybrids
weak or sterile.
Patterns of descent
• Divergent evolution – one species of
organisms changes into two
• Convergent evolution – independent
development of similar features in
separate groups of organisms
– Wings
– Blood antifreeze proteins
• Adaptive radiation – ( a form of divergent
evolution) a single species gives rise to
several, very differently adapted species.
– Finches in the Galapagos
– Most dramatic cases occur on islands
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Reproductive isolation
Distinctive selection pressures
Small population size
Smaller number of species leaves more ecological
niches open
– Plants also radiate
• Darwin believed evolution was very
gradual
• Others believed in jumps or saltations
• “hopeful monsters” – flounders
• Organisms may not change for long
periods (stasis) and then evolve rapidly –
punctuated equilibrium
Prebiotic Evolution
Chapter 18
Until about 300 years ago people believed in
the idea of spontaneous generation –
that life comes from non-living material.
1668 Francesco Redi proved that magots
did not come from rotting meat.
Could microorganisms arise spontaneously?
1864 Lois Pasteur finally disproved this idea.
How did life arise on Earth?
1. “panspermia” – life arrived here from
outer space
– Not a testable hypothesis
2. Prebiotic evolution – life arose from nonliving matter
For prebiotic evolution to take place,
conditions on the early Earth must
have been very different
1. The atmosphere contained virtually no
free oxygen
2. There was no life on Earth
3. Life had 300 million years to get its act
together
• The early Earth’s atmosphere probably
had hydrogen gas, ammonia, methane,
and traces of carbon dioxide and hydrogen
sulfide.
– No rust
– No ozone – UV radiation may have been a
driving force
– Heat from the earth and lightning also
provided energy to make chemical bonds
• Organic molecules could have come from
comets, asteroids or meteors.
• Either way, oceans may have been full of
organic molecules.
• More complex molecules needed more
help to form, probably on clay and metal
ions at the edges of oceans.
• Can make peptides of up to 50 amino
acids in length.
First information carrying molecule
• Was probably RNA since it does not need
enzymes or a primer
– RNA can act as an enzyme
Cyanobacteria