Download Evolutionary Theory

Ideas on the Origin of Life
 Pasteur showed that life was not spontaneously
created from non living material, so how do scientists
account for organisms emerging from nonliving
material?
 Chemical evolution: the gradual formation of life from
nonliving chemicals
The Oparin-Haldane Hypothesis
 Since free oxygen destroys organic molecules as fast as
they are formed, Alexander Oparin suggested that
with energy from lightning and heat from volcanoes,
chemicals could combine to form complex organic
molecules.
 J.B.S. Haldane suggested that the sun could react to
form these compounds to make virus-like organisms.
The Miller-Urey Experiment
 Stanley Miller and Harold Urey tested part of the







Oparin-Haldane hypothesis
in 1953
Application: the experiment
indicated that if the
atmosphere was made up of
these gases, it could have
formed basic organic
compounds.
Alternate Ideas
 Other scientists believe that the Earth’s early
atmosphere was made up of mainly carbon dioxide.
 Scientists do not agree what the early atmosphere
contained so scientists have come up with two
alternative explanations.
 1. chemical reactions occurred in deep sea vents.
However, heat could have destroyed those molecules
 2. Panspermia: life originated in outer space. A
meteorite could have carried organic material to Earth.
Obstacles to Chemical Evolution
 The basic-single celled organism is extremely complex
Cell membrane
DNA
 DNA is the information to make life. How did DNA
form? Scientists have been unable to form proteins
without enzymes.
 The DNA double helix is too complex to have formed
by natural processes.
The First Cell
 Aerobic- existing with oxygen
 Anaerobic- existing without oxygen
 Heterotrophic – unable to make food
 Autotrophic – able to make food from the sun or other
chemicals
 Prokaryote – cell with no nucleus
 Eukaryote – cell with a nucleus and other membranebound organelles.
The First Cell
 First cell is thought to be anaerobic, heterotrophic,
and prokaryotic.
 Endosymbiotic Theory attempts to explain the origin
of mitochondria and chloroplasts in eukaryotic cells.
Natural Selection
 Natural Selection – a process that favors organisms
that are best adapted to their environment.
Example 1
 A wild rabbit population that lives in a densely wooded
area has genes that can produce white offspring, brown
offspring, or black offspring. How could
environmental factors and natural selection affect
which trait for fur color occurs most often?
 Natural selection does not produce new traits. It only
favors traits already present.
Natural selection in three ways
 Natural selection affects the distribution of genes in a
species in three ways.
Stabilizing Selection
 Natural Selection which favors average individuals in a
population
 Example: If an insect is larger than average, it is more
visible to animals. If it is too small, it may not be able
to capture and eat its prey.
Directional Selection
 Favors organisms with an extreme form of a trait.
 Example: Galapagos finches. During droughts, food is
scarce. Finches with larger beaks are better suited for
survival and reproduction so the average beak size
increases.
Disruptive Selection
 Favors organisms with extremes in both directions and
eliminates the middle.
 Example: If only very large or very small seeds were
available to a species of bird, then the birds with large
and small beaks would be advantageous. The birds
with average size beaks would decrease.
Consider a flying beetle which is
introduced to a new tropical island.
 Only the beetle with the darkest bodies thrive
 The smallest beetles cannot compete for food. The
largest beetles are easy prey for birds.
 The beetles with the smallest wings thrive in rotten
tree trunks. The beetles with the largest wings thrive
along the coastline.
Mutations change the genetic code
 If a mutation occurred in a population of wild rabbits
who were brown, what would happen to a animal that
had a mutation causing it to be white?
Adaptations in animals
 Cats: have claws that help them catch prey.
 Pointed teeth that help them tear apart their food.
Example
 A mutation occurs in a plant that causes its leaves to
taste bitter. In what kind of environment would this
mutation be beneficial and more likely passed on to
future generation?
The gene pool
 Gene pool: The total number of different genes
available to a species.
 The more diverse a population is (the more genes), the
better that species is able to adapt to their
environment.
Example 1
 How would the environment affect the gene pool if a
wild rabbit population of brown, white, and black fur
lived in a densely wooded environment?
Example 2
 Sometimes by mere chance, traits could occur more
frequently than others. (genetic drift). If a species of
insect can have white or brown eyes, and both are
equally beneficial, then just by chance more insects
are born with brown eyes during a season. How would
this affect the gene pool?
 Would genetic drift affect small or large populations
more?
Example 3
 A mouse species lives on a small island. A hurricane
kills 80% of all life on the island including the mice.
How might this affect the gene pool?
Example 4
 Organisms with a high rate of mutation have a better
chance of survival in a changing environment. Why?
 A bacteria culture is started. After treating the culture
with an antibiotic, only 2% of the culture survives. If
the culture is left to repopulate, how will it likely
respond to future treatment?
Speciation
 Speciation: the formation of new species.
 Example: If a population gets divided by some natural
event like a volcano or separated by a land mass, the
two populations can no longer breed together. The
newer and smaller population would breed with each
other and eventually form new traits and new species.
This is called geographic isolation.
 Other ways species will not breed with each other
include their reproductive cycles could be different or
their behavior or courtship rituals are different.
Similarities in species
 Homologous vs Analogous structures
 Homologous structures: Different species with similar
structures with different functions
Analogous structures
 Structures that have similar functions but have
different structures
Vestigial Organs
 Organs that seem to have no useful purpose.
Types of Evolution
 Divergent: species formed from a common ancestor
 Convergent: unrelated species evolving similar
characteristics
 Coevolution: two species evolving together.
Divergent
Convergent
Coevolution