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Evolution
Species Changing over time
Charles Darwin
• Evolution by Means of Natural Selection
Reasons for Change
• Mutation
A mutation could cause parents with genes
for bright green coloration to have offspring
with a gene for brown coloration. That
would make the genes for brown beetles
more frequent in the population.
•Migration
Some individuals from a
population of brown beetles
might have joined a
population of green beetles.
That would make the genes
for brown beetles more
frequent in the green beetle
population.
Reasons for Change
• Genetic Drift
Natural Selection
Imagine that green beetles are easier
for birds to spot (and hence, eat).
Brown beetles are a little more likely
to survive to produce offspring. They
pass their genes for brown coloration
on to their offspring. So in the next
generation, brown beetles are more
common than in the previous
generation.
Imagine that in one generation, two
brown beetles happened to have
four offspring survive to reproduce.
Several green beetles were killed
when someone stepped on them
and had no offspring. The next
generation would have a few more
brown beetles than the previous
generation—but just by chance.
These chance changes from
generation to generation are
known as genetic drift.
Natural Selection Principles
• Principle of overproduction: Organisms are
capable of producing huge numbers of offspring
• Principle of variation: offspring have hereditary
physical variations in phenotype & genotypes
• Principle of competition: offspring must
compete for limited resources
• Principle of differential reproduction:
Organisms whose phenotypic characters allow
them to best compete for limited resources will
leave the most genes to succeeding populations.
Artificial Selection
• Long before Darwin, farmers and breeders used the idea of
selection to cause major changes in the features of their
plants and animals. Farmers and breeders allowed only the
plants and animals with desirable characteristics to
reproduce, causing the evolution of farm stock. This
process is called artificial selection because people
(instead of nature) select which organisms get to
reproduce.
•As shown here,
farmers have
cultivated
numerous popular
crops from the wild
mustard, by
artificially selecting
for certain
attributes.
Genetic Variation
•
Mutations are changes in the DNA. A single mutation can
have a large effect, but in many cases, evolutionary change
is based on the accumulation of many mutations.
•
Gene flow is any movement of genes from one population
to another and is an important source of genetic variation.
•
Sexual reproduction can introduce new gene combinations
into a population.
Survival of the fittest!
• Those individuals best suited to exploiting
the various factors of the environment will,
by definition, leave more genes to
succeeding generations than those that
are less suited for their environment!
Speciation
• Geographic isolation is a common way for the process of
speciation to begin: rivers change course, mountains rise,
continents drift, organisms migrate, and what was once a
continuous population is divided into two or more smaller
populations, but it doesn’t even need to be a physical barrier
like a river that separates two or more groups of
organisms—it might just be unfavorable habitat between the
two populations that keeps them from mating with one
another.
Types of evolution
Convergent, divergent, co-evolution
Coevolution is likely to
happen when different
species have close
ecological interactions
with one another.
These ecological
relationships include:
This is the product of coevolution: the
plants would not have evolved hollow
thorns or nectar pores unless their
evolution had been affected by the ants,
and the ants would not have evolved
herbivore defense behaviors unless their
evolution had been affected by the plants.
– Predator/prey and
parasite/host
– Competitive species
– Mutualistic species
• Divergent evolution is
the process of two or
more related species
becoming more and
more dissimilar.
In convergent evolution, on
the other hand, unrelated
species become more and
more similar in appearance
as they adapt to the same
kind of environment.
Cladogram
Phylogenic tree
Tree of Life
Dating!!!
•
1. Radiometric dating relies on half-life decay
of radioactive elements to allow scientists to
date rocks and materials directly.
•
2. Stratigraphy provides a sequence of events
from which relative dates can be extrapolated.
•
3. Molecular clocks allow scientists to use the
amount of genetic divergence between
organisms to extrapolate backwards to estimate
dates.
Fossil record
Have many good fossil records to show
evolutionary relationships of organisms. Not
complete for all species because of the
process of becoming a fossil.
Archaeopteryx
Whales
Anatomy
Homologous
Structures: a
structure that
serves different
functions in two
species, but is
derived from a
common
ancestral
structure
Analogous
Structures : a
structure that serves
the same function in
two species, but is
NOT derived from a
common ancestral
structure
vestigial
structures
have
marginal, if
any use to
the organims
Embryology
A
B
C
D
E
F
Which of these is the human???
G
H
Embryology
Biochemical evidence
Cell Membranes
are similar in all
living organisms
There are only
20 amino
acids that
make up all of
the proteins
needed to
make EVERY
living thing on
the planet
ALL DNA in prokaryotes &
eukaryotes is made of A, G, T, C
ATP is the fuel for ALL
living cells!
Human Evolution
It is important to
remember that:
• Humans did not evolve
from chimpanzees. Humans
and chimpanzees are
evolutionary cousins and
share a recent common
ancestor that was neither
chimpanzee nor human.
• Humans are not “higher” or
“more evolved” than other
living lineages. Since our
lineages split, humans and
chimpanzees have each
evolved traits unique to their
own lineages.