Transcript Evidence of Homology

What causes the "struggle for existence"?
Which animal has INCREASED fitness?
Living in a dry,
wooded area in the
fall season…..
Living in
north
Canada…in
the winter
time….
What are these called??
What is it called when humans
intervene and create changes in a
population?
“descendants” of wild mustard
Evidence of Homology
• Homology: the similarity in characteristics that has resulted
from common ancestry
• Structures develop from same embryonic tissues
Homologous structures
Homologous structures
• Certain structures are similar in different animals – but
used for different functions
– This similarity is evidence for a common ancestor
• Forelimbs on different animals have similar bone
structures even though they function very differently
Vestigial traits
Not all homologous structures serve important functions.
The traits of many animals are so reduced in size that they
are just vestiges, or traces, of homologous traits in other
species.
Embryology
• There are similarities in development for many organisms
• Early embryos look very similar, even for animals that look vary different
as adults
MORE EVIDENCE…..of a
common ancestor
Comparative embryology
• Development of embryo tells an evolutionary
story
– similar structures during development
all vertebrate embryos have a “gill
pouch” at one stage of development
EMBROLOGY
Shows evidence of common ancestry.
Different species in
the same Class (like
mammals) often have
very similar embryos,
even if the adult forms
are quite different.
The forelimbs might be legs in an ancestral species, but
would be modified as flippers, arms, wings, etc. at a late
stage in development; but the pattern in the embryonic
stage would remain similar if not unchanged.
Embryology in plants
• Similarities in seedlings of very different kinds of plants suggests a
common ancestry among plants as well
Homology in DNA
Different organisms have similar genes
The more DNA sequences species have in
common, the more closely related they are in
evolutionary time (the more recently they
diverged from a common ancestor).
Homology in DNA
• A comparison of the
sequences of dozens of
genes that are found in
humans and other
primates demonstrates
the same pattern of
relationship
Homology in DNA
• DNA sequence comparisons in a wide variety of organisms support
hypotheses of common descent that are implied by physical similarities
Evidence from Biogeography
Similar, but unrelated species evolve in similar
environments.
African deserts do contain several species of plants that
resemble cacti, but are from a different family
Fossils tell a story…
the Earth is old
Life is old
Life on Earth has changed
Name another piece of
evidence for common ancestry!
Evidence for common ancestry.
Evidence from the
Fossil Record
• Over time, the organic material in living things that have been
buried degrades and is replaced by minerals, forming fossils
– This is a relatively rare since it can happen under only certain
circumstances
Fossil Record Evidence
• By the early 1800s fossils remnants of dinosaur were
being studied
• Darwin predicted that evidence for evolution between
humans and modern apes would come from the fossils of
human ancestors
Fossil Record Evidence
 Fossils of hominins – humans and human ancestors – provide another
source of evidence on common descent
 A key anatomical difference between humans and other primates –
bipedal locomotion versus traveling on all fours – is studied by looking
at hominin fossils
Fossil Record Evidence
• Homo neanderthalensis – Neanderthal man, the first hominin
fossil was found in Germany in 1856
• Homo erectus – standing man – found in Java in 1891
• Australopithecus afarensis – first fossil hominin found in Africa
Fossil Record Evidence
•
•
•
•
“Lucy,” a fossil hominin found in Africa
Australopithecus afarensis type
The fossil skeleton is almost complete
Evidence that this hominin walked upright
• Radiometric dating uses the decay of radioactive elements in the fossils to
determine age
• Based on the half-life, scientists can estimate the age of materials like rock
• The age of the fossil is calculated based on the age of the rocks
around it
• Fossils found in specific age layers of rock are given an age dating that
is consistent with that age layer
• Ardepithecus ramidus - 5.2 to 5.8 million years old
Jaw of Ardepthecus ramidus
Ardepithecus ramidus
• The common ancestor of humans and chimpanzees
• The connection between humans and chimps has not been supported by
fossil evidence
• The common ancestor of humans and chimpanzees has not been identified
by fossil evidence
– Some critics of evolution cite this in saying that the relationship
between apes and humans remains unproven
• The theory of common descent stands in spite of the lack of fossil of the
common ancestor
– Finding fossilized evidence between any two species extremely
difficult
– Strong support of common descent exists in intermediate forms
between modern organisms and ancestors
• Other fossil records – including that of horses – support common descent
as well
• Do the preceding observations enable us to reject any of
the three hypotheses that compete with common
descent?
– Static model
– Transformation
– Separate types
• States that no changes have occurred
• Rejected because:
– Radiometric data – Earth is older than 10,000 years
– Fossil record shows changes
• States that organisms are separate and change separately
• Rejected because:
– DNA is similar
– Anatomy is similar
– Existence of vestigial structures
• States that there are separate ancestors for separate species
• Rejected because:
– DNA similarities
– Translation process similarities
– Existence of mitochondria for all eukaryotic cells
• Scientists favor the theory of common descent because it
is the best explanation for how modern organisms came
about

The theory of evolution provides the best explanation for
how different types of organisms can look very different,
while sharing a genetic code and many cellular aspects