Download Theory of Evolution Evidence

Theory of Evolution
Bio. Standard 3.4.1
Key Concepts
• What was the early atmosphere like?
• How do experiments suggest first “cells” may
have evolved?
• How did early conditions affect the type of
organisms that developed?
How did life on Earth begin?
• The current scientific thinking is based on a
relatively small amount of evidence, so it is
likely that these ideas will change
• Earth is about 4.6 billion years old and started
as pieces of cosmic debris that collided and
stuck together; these and subsequent
collisions produced enough heat to melt the
entire planet
• The molten Earth STRATIFIED (layered)
according to density, while radioactive
elements in the interior generated enough
heat to keep the interior molten
• The least dense elements, hydrogen and
nitrogen, along with hydrogen cyanide, carbon
dioxide, carbon monoxide, hydrogen sulfide,
and water, formed the first atmosphere
• About 3.8 billion years ago, Earth’s surface
cooled enough for water to remain a liquid;
rain produced oceans, which were brown with
dissolved iron, that covered much of the globe
Atoms do not assemble themselves into
complex organic molecules or living cells on
Earth today for a number of reasons
1. oxygen is very reactive and would destroy
many kinds of organic molecules not protected
within cells
2. as soon as organic molecules appeared,
something (bacteria) would probably eat them
• MILLER AND UREY suggested how mixtures of
the organic compounds necessary for life
could have arisen from simpler compounds
present on a primitive
Earth
• While Miller and Urey’s simulations of Earth’s
early atmosphere were not accurate, similar
experiments based on more current
knowledge have also produced organic
compounds, including cytosine and uracil
• About 200 to 300 million years after liquid
water could exist on early Earth, cells similar
to modern bacteria were common-but how
might these cells have originated?
• PROTEINOID MICROSPHERES can form under
certain conditions when large organic
molecules form tiny bubbles
• While microspheres are not living cells, they
do have selectively permeable membranes and
a simple means of storing and releasing
energy, suggesting that structures similar to
these may have acquired more and more
characteristics of living cells over time
A number of discoveries about RNA suggests that
RNA may have existed before DNA
1. RNA can help DNA replicate
2. some RNA sequences process messenger RNA
after transcription
3. some RNA sequences catalyze chemical reactions
4. some RNA sequences can grow and duplicate
themselves
How simple RNA-based forms of life led to the
system of DNA-directed protein synthesis that exists
now is still unclear
• MICROFOSSILS-microscopic fossils-of
prokaryotes that resemble modern bacteria
have been found in rocks more than 3.5 billion
years old; these must have evolved in the
absence of oxygen
• Over time, photosynthetic bacteria evolved and began
producing oxygen, as evidenced by formation of iron
oxide, which precipitated to the ocean floor
• As oxygen gas accumulated in Earth’s atmosphere,
concentrations of methane and hydrogen sulfide
decreased, and the ozone layer formed
• The rise of oxygen in the atmosphere drove some life
forms to extinction, while other life forms evolved new,
more efficient metabolic pathways that used oxygen for
respiration; anaerobic organisms were forced into a few
airless habitats
• About 2 billion years ago, prokaryotic cells
began evolving internal cell membranes; the
end result was ancestral eukaryotic cells
• Then other prokaryotes began entering these
ancestral eukaryotic cells and began living
inside the larger cells in a symbiotic
relationship
• ENDOSYMBIOTIC THEORY suggests that
eukaryotic cells formed from a symbiosis
among several different prokaryotic
organisms
• Ex. prokaryotes that performed cellular
respiration became mitochondria;
prokaryotes that performed photosynthesis
became chloroplasts
Evidence of endosymbiotic theory includes
1. DNA similar to bacterial DNA in chloroplasts and
mitochondria
2. ribosomes in chloroplasts and mitochondria
similar to bacterial DNA
3. chloroplasts and mitochondria reproduce by
binary fission when cells containing them divide
during mitosis
• Some time after eukaryotic cells arose, those
cells began to reproduce sexually, which
greatly sped the process of evolution-but
how?
• Most prokaryotes reproduce asexually, which
restricts genetic variation
• Sexual reproduction shuffles genes so that the
probability of more favorable combinations of
genes is increased, increasing the chances of
evolutionary change in a species due to natural
selection
• A few hundred million years after evolution of
sexual reproduction, multicellular organisms
evolved from single-celled organisms, which
allowed for a great increase in diversity
Evidence of Common Ancestry
• Fossil evidence
• Biochemical similarities
• Anatomical structures (homologies)
Common Ancestry
• The evolutionary relationship between many
organisms can be traced back to a common
ancestor. A common ancestor is an individual
from which two or more related species could
have evolved. With the passage of time,
organisms change and diverge from their
common ancestor to form new species
Biochemistry
• DNA, RNA, the genetic code and protein
synthesis are similar in all organisms. The
greater the genetic and molecular similarity
between species, the closer their common
ancestor. Humans and chimpanzees have 98%
of their genes in common. The remaining 2%
is what distinguishes these two species from
each other.
• Diabetics can use insulin from cows and pigs
because insulin from these animals is almost
identical to human insulin. In addition,
hemoglobin in humans, which has almost 600
amino acids, is almost identical to hemoglobin
in all other vertebrates. This similarity in
chemical structure demonstrates that all
vertebrates can be traced back to a common
ancestor.
Anatomical Structures
Embryo Similarities
Vestigial Organs
• structures or organs that seem to serve no
useful function
ex. human tailbone. The vestigial tailbone in
humans is homologous to the functional tail of
other primates.
Macroevolution
• Large-scale evolutionary patterns and
processes that occur over long periods of time
Species
that are
Unrelated
Related
form
in
Interrelationshiops
Similar
environments
can undergo
Coevolution
under
under
in
in
Intense
environmental
pressure
Small
populations
Different
environments
can undergo
can undergo
can undergo
can undergo
Convergent
evolution
Extinction
Punctuated
equilibrium
Adaptive
radiation