Download Evolution: An Introduction

Evolution: An Introduction
A Scientific Theory
• Must make predictions.
• Must be in agreement with the evidence and
be the best explanatory model.
• Must be verifiable – potentially falsifiable
(capable of being tested).
A Scientific Theory is NOT “flawed” or
invalid when…
• It cannot account for an observation
• It is incomplete
• A particular piece of evidence cannot be
found
ALL Scientific Theories are Incomplete
What is the Theory of Evolution?
• Evolution is the process in which significant
changes to genetic traits of a species occur
over successive generations
i.e. any shift in the gene pool of a population
End Result:
• The adaptation of a species to its environment
• Individuals cannot evolve – populations are
the smallest unit that can evolve
What Drives Evolution?
(1) Mutations
– Mutations are not related to the present needs of an
organism but are merely the result of chance.
(2) Sexual Reproduction
– Results in recombination of 1000s of different alleles
– E.g. an individual of a species with 20 000 genes that
is heterozygous at only 10% of these loci could
produce 220000 different allelic recombination in their
gametes
Somatic Mutation
• Happens in a body cell (e.g. skin and stomach
cells)
• Are the cause of some cancers
• Not passed on to the next generation
Germ-like Mutation
• Occurs in the cells that give rise to gametes
(sperm and egg cells)
• Are heritable (which means that they can be
passed on to the offspring)
Are all mutations harmful?
Why or Why not?
• Not all mutations are harmful
• Some are beneficial by providing a selective
advantage (i.e. organism is favoured in terms of
survival and reproduction)
• Other mutations are neutral – no effect on
organism’s fitness (ability to reproduce), but may
become critical for survival later if the
environment changes
Why are harmful mutations not passed
on to the next generation?
• Most harmful mutations typically reduce an
organism’s fitness and don’t live long enough
to pass on their traits
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