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Evolution & Natural Selection
First thoughts on the idea…
• “Acquired Traits”
– If you want it you
can make yourself
have it
• Once a structure is
modified it is passed
onto offspring
Next to hypothesize….Charles Darwin
• “Natural Selection”
• Organisms best suited to their environment
reproduce more successfully than other
organisms, increasing favorable traits.
• is a gradual change in a species over time
that is caused by natural selection.
Why change?
• Environment causes
species to change
• Species with traits
that help it adapt to
its environment
have more offspring
and pass those traits
to them
• These species have
greater “FITNESS”
So what EVIDENCE do we have?
• 1 - Homological Structures
• Same embryonic structures that have been
• 2 – Analogous Structures
• Structures that look similar and have the same
function, but they are not embryologically
similar – they are not from a common ancestor
• 3 – Vestigial Structures
• Structures that are no longer useful, but were
useful for our ancestors.
• 4 – Similarities in Embryology
• Early stages of different vertebrate are VERY
• 5 – Similarities in Macromolecules
• Amino acid sequence – the more difference
there is between the sequences the longer it
has been since there was a common ancestor
• The change of two or more species in close
association with each other
Convergent Evolution
• When the environment selects for similar
features, even though ancestors are very
Divergent Evolution
• Two or more related
species become
more and more
dissimilar, due to
changing habitats.
• Can eventually
result in new
Artificial Selection
Adaptive Radiation
• When many different species evolve from one