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Evidence of Evolution

Section 2 of Darwin's Theory
by

Christopher Landry

on 27 February 2015

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Transcript of Evidence of Evolution

Changes Over Time
- Evidence of Evolution -

Objectives
Interpreting the Evidence
Modern-day organisms can provide clues about evolution. Fossils, patterns of early development, and similar body structures all provide evidence that organisms have changed over time.
Fossils
Similarities in Development
Similarities in Early Development
Similarities in Body Structure
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.
By comparing organisms, scientists can infer how closely related the organisms are in an evolutionary sense. Scientists compare body structures and DNA sequences.
Scientists make inferences about evolutionary relationships by comparing the early development of organisms.
If one was to compare an adult fish, salamander, chicken, and opossum, one would say they look quite different. But during their early stages of development, they share similarities.
All four organisms have a tail and a row of tiny slits along their throats. These similarities suggest that these vertebrate species are related and share a common ancestor.
An organism's body structure is its basic body plan, such as how its bones are arranged. Fish, amphibians, reptiles, birds, and mammals, for example, all have a similar body structure.
They all have an internal skeleton with a backbone. This is why scientists classify all five groups of animals together as vertebrates.
Presumably, these groups all inherited these similarities in structures that related species have inherited from a common ancestor are called homologous structures.
Sometimes scientists find fossil evidence that supports the evidence provided by homologous structure.
What evidence supports the theory of evolution?
Inferring Relationships
Scientists infer that species with similar body structures and development patterns inherited many of the same genes from a common ancestor.
Recall that genes are made of DNA. By comparing the sequences in the DNA of different species, scientists can infer how closely related the species are.
The more similar the sequences, the more closely related the species are. Recall also that the DNA bases along a gene specify what type of protein will be produced.
Scientists can also compare the order of amino acids in a protein to see how closely related two species are.
How do scientists infer evolutionary relationships among organisms?
Combining Evidence
In many cases, evidence from DNA and protein structure has confirmed conclusions based on fossils, embryos, and body structure.
Sometimes, however, scientists have changed their hypotheses about species relationships.
Branching Trees
Scientists have combined the evidence from DNA, protein structure, fossils, early development, and body structure to determine the evolutionary relationships among species.
Scientists use the combined evidence of species relationships to construct branching trees. A branching tree is a diagram that shows how scientists think different groups of organisms are related.
New Species
A new species can form when a group of individuals remains isolated from the rest of its species long enough to evolve different traits.
Isolation, or complete separation, occurs when some members of a species become cut off from the rest of the species.
How do new species form?
Full transcript