Evolution Objectives
Evolution – change in the genetic make-up of a population.
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How do we measure genetic make-up?
o Allele frequency – the number of each allele (A or a) in a population.
How do we measure evolution?
o Measure the allele frequency over many generations
o If the allele frequency changes (drastically), the population has evolved.
o If the allele frequency stays the same, the population remains in genetic
equilibrium.
How does a population stay in genetic equilibrium?
o Following the 5 Rules described by Hardy and Weinberg
 Big Population
 No Migration
 No Mutations (Special characteristics)
 Equal chance of survival
 Blind mating
So, how does the genetic make-up change?
o Break the rules. The more rules the population breaks and the more severely they
are broken, the faster evolution goes.
o There are 2 Basic ways population’s genetic make-up changes
 Natural Selection:
 First, there are 3 characteristics of all populations.
o Ability to overproduce – populations want to grow!
o Competition for food, space, mates… a struggle for
survival.
o Variation – not all members look or behave the same
because of some genetic differences (many alleles)
 Natural selection describes that certain variants in the population
survive and reproduce better than others.
 Given time (generations) the population will have a greater
number of alleles from those that were better adapted (more fit)
to the environment. This is how populations evolve.
 Genetic Drift
 Sometimes, population’s genetic make-up can change without
natural selection (randomly). This is called genetic drift.
 This happens most frequently when populations go from real big
to real small for some reason (mass extinctions or mass
migrations).
 This can also happen randomly by some external reason.
 Both are involved with changing the population’s make-up, but Natural
Selection has the greatest effect.
Can these processes be used to describe how the many different organisms seen today
came into being?
o Yes – this leads us to the Theory of Evolution, which is all life on Earth has
come from changes that are passed on from previously existing organisms.
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o But since we can’t go back in time to see these changes happen, we need to look
for evidence.
o There are 2 lines of evidence:
 Evidence for a common ancestor
 Evidence for change over time
o Evidence of a common ancestor
 Homologous structures – bird wing, whale flipper, human arm all have
similar bone structure. All these organisms share a common vertebrate
ancestor.
 Homologous development – related species will look more similar in
early stages of development – compare the embryos of many vertebrates
 Homologous biochemistry – all life on earth uses the same genetic code
(A, T, G, and C). Compare the amino acid sequence or gene sequence of
related individuals and you will see more similarities.
o Evidence of change over time
 Fossil record – shows us what life looked like at various stages of Earth’s
history. It shows that some species are extinct now and some look very
different than their ancestors.
 Vestigial structures – structures that are “left-over” from evolution – like
the pelvis of a whale.
 Analogous structures – shows that with similar selection (convergent
evolution), evolution will produce similar structures – for example: wing
of bird and wing of butterfly (not related but have similar structure).
 Symbiosis – relationships between unrelated species – they have selected
for each other (coevolution). Prey having camouflage to hide from
predator, flowers smelling nice to attract bees are examples.
How has life changed over time?
o Life first evolved 3.8 billion years ago.
o Life first appeared as prokaryotes and remained like that until about 1 billion
years ago.
o Animals were seen about 500 million years ago.
o Dinosaurs lived in a span of 200 million years and went extinct about 65 million
years ago.
o Modern Humans were first seen less than 1 million years ago.