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Neo Darwinian Evolution
Human Biology and Forensics
Introduction
• There are many different models of evolution,
but for this class we are going to learn about
Neo-Darwinian evolution
• Darwin believed that natural selection was the
primary way certain individuals were able to
survive and pass on their traits, but there are
other things working.
Four Forces of Evolution
• Primary Forces
– Mutation
– Natural Selection
• Secondary Forces
– Gene Flow
– Genetic Drift
Mutation
• Mutation provides variation
• If there was no variation, then there could be
no new traits
• If there were no new traits, then changes in
environment could quickly lead to extinction.
Mutation
• This has to do with genetics
• Darwin didn’t know a lot about genetics,
coming out at the same time
• Most are deleterious, some are beneficial
• Ultimate source of variation
• 1 error per billion pairs; 3 per egg/sperm; 6
per zygote
Natural Selection
• Individuals with trains that are more favorable
for the environment are more likely to survive,
reproduce and pass on their traits
• This leads to changes and maybe even new
species
• Darwin saw this as most important
• Differential births and deaths
Natural Selection
• Types of Natural Selection
• Directional selection
• Stabilizing
• Diversifying
Macroevolution
• If enough changes accumulate in a population,
you can get a new species.
Rates of Natural Selection
• Gradualism:
– Speciation occurs gradually
• Punctuated Equilibrium:
– Speciation has periods of no change & fast change
Types of Natural Selection
• Anagenesis:
– One species changes into one species
• Cladogenesis:
– One species changes into more than one species
Gene Flow
• Two populations that were previously isolated
now can interbreed
• Allows for exchange of genes and reduces
genetic diversity between the two groups;
increases within
• Very important now
Genetic Drift
• HARD TO UNDERSTAND
• Genes are observed in terms of percentages
– For example if you have 5 individuals
– That makes 10 alleles for eye color (2 each)
– If there are 7 alleles for brown and 3 for blue then
70% (.7) alleles are brown and 30% (.3) are blue
Genetic Drift
• The smaller the population the more likely for
RANDOM fluctuations in gene pool of offspring
• For example
– You have 50% chance of heads and 50% chance of tails
– However, if you only flip the coin a few times, you will
likely get something other than 50% and 50%
– This will change distribution of traits in future
generations
Genetic Drift
• In smaller populations, genes are more likely to
DRIFT and change gene pool in future generations
• Very import in early human evolution
Comparing Gene Flow & Genetic Drift
Gene Flow
Within Group
Variation
Between Group
Variation
Genetic Drift
OTHER MODELS OF EVOLUTION
• Lamarck
• Kimura
• Ohta
Lamarck
• Organisms adjust to the environment
• Spontaneous Generation (Abiogenesis) – life
from non life
• Inheritance of Acquired Characteristics
(bacteria, genetic engineering)
• Vitalism: inner drive for perfection
Kimura
• Rate of change depends on mutation rate
• Believed that genetic drift had more to do
with evolution than natural selection
• Evolution depended on mutation on natural
selection
Ohta
• Nearly neutral
• Less on natural selection
• More on mutation and genetic drift