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Evidence of Evolution
What Evidence Supports Evolution?
Since Darwin’s time, scientists have found a great deal
of evidence that supports the theory of evolution.
Fossils, patterns of early development, similar
body structures, and similarities in DNA and
protein structures all provide evidence that
organisms have changed over time.
Fossils By examining fossils, scientists can infer the
structures of ancient organisms. Fossils show that, in
many cases, organisms that lived in the past were very
different from organisms alive today. The millions of
fossils that scientists have collected are called the
fossil record. The fossil record provides clues about
how and when new species evolved and how
organisms are related.
Similarities in Early Development Scientists also
infer evolutionary relationships by comparing the
early development of different organisms. For
example, the organism in this picture look similar
during the early stages of development. All four
organisms have a tail. They also have a row of tiny
slits along their throats. The similarities suggest that
these vertebrate species are related and share a
common ancestor.
Discussion questions:
1. What are the 4 types of evidence that supports
evolution?
2. What are fossils?
3. How do fossils support the theory of evolution?
4. How do patterns of early development of
different organisms support the theory of
evolution?
Similarities in Body Structure An organism’s body
structure is its basic body plan, which in vertebrates
includes how bones are arranged. Fishes, amphibians,
reptiles, birds, and mammals all have an internal
skeleton with a backbone. This similarity provides
evidence that these animal groups all evolved from a
common ancestor.
Similar structures that related species have inherited
from a common ancestor are known as homologous
structures. In the picture you can see some examples
of homologous structures. These include a bird’s
wing, a dolphin’s flipper, and a dog’s leg.
Some fossils show structures that are homologous
with structures in living species. For example,
scientists have recently found fossils of ancient whalelike creatures. The fossils show that the ancestors of
today’s whales had legs and walked on land. This
evidence supports other evidence that whales and
other vertebrates share a common ancestor that had a
skeleton with a backbone.
Discussion questions:
1. How are the homologous structures similar?
2. How are they different?
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3. Why do you think the
homologous structures
shown in the diagram
evolved differently?
Similarities in DNA and Protein Structure Why
do some species have similar body structures and
development patterns? Scientists infer that the
species inherited many of the same genes from a
common ancestor.
embryos, and body structure. For example, DNA
comparisons show that dogs are more similar to
wolves than to coyotes. Scientists had already
reached this conclusion based on similarities in the
structure and development of these three species.
Recall that genes are segments of DNA. Scientist’s
compare the sequence of nitrogen bases in the DNA
of different species to infer how closely related the
two species are. The more similar the DNA
sequences, the more closely related the species are.
The DNA bases along a gene specify what type of
protein will be produced. Therefore, scientists can
also compare the order of amino acids in a protein to
see how closely related two species are.
Discussion questions:
1. What does DNA tell you about how similar two
species are?
In most cases, evidence from DNA and protein
structure has confirmed conclusions based on fossils,
2. In addition to studying DNA itself, what else do
scientists study to compare the DNA of different
organisms? What does this tell scientists about
DNA?
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