Download NOTES Ch. 15 Evolution

NOTES Ch. 15 – Evolution
Charles Darwin
 degree in theology, studied medicine and the sciences
 sailed five years on the HMS Beagle
 influenced by Charles Lyell’s book “Principles of Geology” which
proposed that the Earth was millions of years old
On the Beagle
 observed marine life high in the Andes Mountains
 unearthed giant fossil versions of smaller living mammals
 saw how earthquakes could lift rocks great distances quickly
 on the Galapagos Islands he noticed that each island had a different
variety of finches and other animals
 Darwin looked at his specimens after the voyage and noticed that they
were different from European species but more closely resembled South
American species. Therefore populations changed after they reached the
Galapagos.
 Darwin hypothesized that new species could appear gradually through
small changes in ancestral species.
Thomas Malthus
 suggested that if left unchecked, human population would outgrow its
food supply and lead to a struggle for existence. Darwin thought that
through the struggle for existence some competitors would be better
equipped to survive. These organisms would survive to reproduce.
Artificial Selection and Natural Selection
 Darwin looked at selective breeding as a possible mechanism for the
evolution of species he saw in the Galapagos. Used when breeders
develop new breeds of dogs or new strains of crops.
 Darwin inferred that if humans could change species through artificial
selection then perhaps the same process works in nature, and through
this happening over long periods of time, new species could develop.
-Artificial Selection -
-Natural Selection-
Darwin’s FOUR basic principles:
1. Variation: Individuals in a population show differences (or variations).
2. Heritability: Variations can be inherited
3. Overproduction: Organisms have more offspring than can survive on
available resources.
4. Reproductive Advantage: Variations that increase reproductive success
will have a greater chance of being passed on.
 Natural Selection is considered the mechanism by which evolution takes
place.
 Evolution – Any change in heritable traits within a population, across
generations. Biologists use the term evolution to define the cumulative
changes in groups of organisms over time.
Natural Selection does not mean Evolution!
Natural Selection is the mechanism for evolution!
Individuals DO NOT evolve, Populations evolve!
EVIDENCE OF EVOLUTION
 A theory provides an explanation for a natural phenomenon based on
observations.
 The theory of evolution states that all organisms have descended from a
common ancestor.
1. The fossil record
 fossils show similarities and differences between organisms living
today and in the past. Transitional fossils contain features shared by
different species. i.e. Certain dinosaur fossils show feathers of modern
birds and teeth and bony tails of reptiles.
2. Comparative anatomy
 Homologous structures – anatomically similar structures – indicate the
structures were inherited from a common ancestor.
 Vestigial structures – reduced forms of functional structures in other
organisms.
- Vestigial Structure-
-Vestigial Structure-
 Analogous structures – structures used for the same purpose but not
inherited from a common ancestor.
o Show that functionally similar features can evolve in similar
environments.
3. Comparative embryology
 Vertebrate embryos exhibit homologous structures but become totally
different structures in adult forms.
4. Comparative biochemistry
 The more closely related the species are, then they will share a greater
number of shared amino acid sequences.
 all organisms share DNA and RNA – since all organisms share these
molecules, it indicates that these molecules evolved early in the history
of life and have been passed down to all organisms.
5. Geographic distribution
 animals are more similar to species it lives near showing a common
ancestor.
Adaptation – a trait that increases an organism’s chances for reproductive
success.
Camouflage – morphological adaptations that allow them to blend in with their
environments. More camouflaged individuals survive enabling them to survive
and reproduce.
Mimicry – morphological adaptations where one species evolves to resemble
another species. Usually occurs when a harmless species evolves to look like a
harmful species.
Antimicrobial resistance – species of bacteria that originally were killed by
antibiotics have developed drug resistance.
Hardy-Weinberg Principle – In the absence of forces, allelic frequency in a
population will not change and evolution will not occur. In order to change
allelic frequencies need to be acted upon by a force.
Genetic drift – any change in allelic frequencies that result from chance. More
pronounced in smaller populations.
 Founder effect – a small sample of a population settles in a location
separated from the rest of the population.
 Bottleneck – occurs when a population declines to a very small number
then rebounds. Population is genetically similar and results in
decreased diversity. (i.e. cheetahs, humans)
Gene Flow – New organisms may enter a population by migration from another
population. If they mate within the population, they can bring new alleles to the
local gene pool. It is rare to have no gene flow. Few populations are truly
isolated.
Nonrandom mating – mating is usually NOT random. Individuals mate with
those in close proximity increasing chance of favoring homozygous traits.
Mutation – random change in genetic material. While some mutations cause
harm and can be lethal, others can be beneficial and selected for.
How does natural selection alter phenotypes:
1. Stabilizing Selection – eliminates extremes, favors average
2. Directional Selection – one extreme is favored (peppered moth)
3. Disruptive Selection – removes average traits, favors both extremes
Sexual Selection – A natural selection operating on factors that contribute to an
organism’s mating success. Large differences in males and females. (male
peacocks, fireflies)
Speciation – process whereby some members of a population change so much
that they can no longer produce fertile offspring with members of the original
population. A population must diverge and become reproductively isolated.
a. allopatric speciation –(most common) physical barrier divides a
population into two or more populations. (mountain ranges, wide rivers)
b. sympatric speciation – occurs without a physical barrier
Patterns of Evolution:
Adaptive Radiation (divergent evolution) – one species gives rise to many new
species due to new ecological opportunities. Rise of mammals following
extinction of dinosaurs.
Coevolution – species evolve in close relationship with other species.
Sometimes mutualistic, can be parasitic.
Convergent evolution – unrelated species evolve similar traits even though they
live in different parts of the world due to similar ecology and climate.
Rate of speciation
a. gradualism – evolution occurs in small, gradual steps
b. punctuated equilibrium – rapid spurts of genetic change cause species
to diverge quickly.