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CHAPTER 15
Evolution is the process by which modern organisms have descended from ancient organisms.
1. Darwin’s Voyage
• 1831-- H.M.S. Beagle voyages around the world
• collected plant, animal and fossil specimens
2. Darwin's Observations
• Same habitats, such as grasslands, did not always have the same species.
• Galápagos Islands are close together but have very different climates & very different organisms.
3. Darwin’s Hypothesis Animals on different islands were once members of the same species from South America
Scientist who influence Darwin’s Thinking
1. Hutton and Lyell
• Earth is many millions of years old
• processes for change still operate
2. Jean-Babtiste Lamarck's Evolution Hypotheses
• living things have changed over time.
• all species were descended from other species.
• organisms were adapted to their environments.
Lamarck proposed that by selective use or disuse of organs, organisms acquired beneficial traits or lost
detrimental traits during their lifetime. These traits could be passed on to offspring. Over time, the species
changed.
Lamarck did not know:
• how traits are inherited.
• that an organism’s behavior has no effect on its heritable characteristics.
3. Population Growth
• 1798 -- Thomas Malthus
• More people are born than die.
• If there is no war, famine, or disease to control growth the population will grow unchecked.
• Eventually resources will run out.
Darwin applied this to plants and animals.
Publication of On the Origin of Species
Alfred Wallace independently proposed the same idea as Darwin in 1858.
On the Origin of Species published in 1859
• proposed natural selection.
• presented evidence for evolution
NATURAL SELECTION
1. Organisms produce more offspring than can survive.
There is a struggle for existence. Individuals compete for limited resources.
2. Variations exist in offspring
3. Variations are inherited
Mutations are new sources of variations – can be lethal, neutral or beneficial
4. Variations that provide a competitive advantage and aid survival are called ADAPTATIONS.
Adaptations can be behavioral or physical
Adaptations evolve in response to environmental conditions
Abiotic – climate, water, nutrients
Biotic – escaping predation, obtaining food, courtship
Adaptations enable organisms to become better suited to their environment and better able to survive &reproduce
5. Animals with better variations survive to reproduce passing on those traits – SURVIVAL OF THE FITTEST
Differential reproduction –some individuals are prolific and some fail to reproduce
Most fit, best suited individuals with the best adaptations survive and reproduce more. Species changes over time.
Fitness - the ability of an individual to survive and reproduce in its environment, fitness is the result of adaptations
Selective Pressure – condition which causes certain individuals to reproduce more than others
(example: fast predators – these would cause the fastest prey to survive and reproduce more)
Natural selection - NATURE applies the selective pressure
Traits evolve that are advantageous to survival
Generally a slow process
Artificial selection - PEOPLE apply the selective pressure (aka Selective Breeding)
Organisms with desired traits are selected by people for breeding
Generally a fast process
Descent With Modification = Each living species has descended, with changes, from other species over time.
Common descent = all living organisms are related to one another.
Evidence of Evolution
Organisms have been evolving on Earth for millions of years.
1. The Fossil Record – scientist document life has changed over time.
2. Geographic Distribution of Living Species – Island Biogeography
3. Homologous Body Structures - Structures that are different but develop from the same embryonic tissues
4. Vestigial Organs - organs so reduced in size that they are just vestiges/traces of homologous organs in other species.
5. Similarities in Embryology - the same groups of embryonic cells develop in the same order and in similar patterns to
produce the tissues and organs of all vertebrates.
6. Biochemistry – DNA and similar proteins (cytochrome c for cellular respiration and blood proteins)
Evolutionary Theory
Scientific advances in many fields of biology, geology, and physics have confirmed and expanded most of Darwin’s
hypotheses.
CHAPTER 16
How Common Is Genetic Variation?
Variation in biochemical processes may not be readily apparent. Many traits have heterozygous genotypes.
population= a group of individuals of the same
species that interbreed.
gene pool = all genes (and their alleles) in a
population.
relative frequency = how often an allele occurs in a
gene pool compared to other alleles - expressed as a
percent.
EVOLUTION is any change in the relative frequency
of alleles in a population
Sources of Genetic Variation
1. Mutations=change in the DNA code caused by mutagens (radiation, heat, chemicals). Do not always affect the
phenotype.
2. Gene Shuffling
Biggest source of variation. Crossing-over increases the number of genotypes that can appear in offspring.
Sexual reproduction produces different phenotypes, but it does not change the relative frequency of alleles in a
population.
Single-Gene and Polygenic Traits
The number of phenotypes produced for a given trait depends on how many genes control the trait.
A single-gene trait is controlled by one gene
Polygenic traits are controlled by two or more genes.
that has two alleles. Variation in this gene
Polygenic traits can have many genotypes and phenotypes.
leads to only two possible phenotypes.
Widow’s peak is dominant over the allele
for a straight hairline, but widow’s peak may
be less common in a population.
Height in humans is a polygenic trait.
A bell-shaped curve is typical of polygenic traits.
A bell-shaped curve is also called normal distribution.
Evolution is any change over time in the relative frequencies of alleles in a population.
Populations, not individual organisms, can evolve over time.
Natural selection on single-gene traits can lead to changes
in allele frequencies and thus to evolution.
Red lizards visible few survive & reproduce
Black lizards warm up faster on cold days
have energy to avoid predators
survive & produce more offspring
The allele for black color will increase in relative frequency.
Natural selection on polygenic traits can affect the distributions of phenotypes in any of three ways:
Directional Selection
Stabilizing Selection
Disruptive Selection
Individuals at one end of the curve have
higher fitness than individuals in the middle or
at the other end.
Birds with larger beaks have higher fitness
and average beak size increases.
Individuals near the center of the curve
have higher fitness than those at either
end – the curve narrows and stays at its
current position. Human babies born at
an average mass are more likely to
survive than babies born much smaller
or larger than average.
Individuals at the upper and lower ends of the curve
have higher fitness than those near the middle. If
natural selection is strong and long enough, the curve
will split, creating two distinct phenotypes. If averagesized seeds become scarce, two groups will result - one
will eat small seeds and one will eat large seeds.
Genetic Drift - A random change in allele frequency.
In small populations a chance event might cause some
individuals to survive over others. This can cause an allele
to become common in a population.
Founder Effect - Genetic drift may occur when a few
individuals colonize a new habitat. If they have alleles in
different relative frequencies than the parent population, the
new population will be genetically different.
Evolution Versus Genetic Equilibrium
Hardy-Weinberg principle = allele frequencies in a population will remain constant (genetic equilibrium) unless one or
more factors cause those frequencies to change.
To maintain genetic equilibrium from generation to generation you need:
1. Random Mating
Each individual has an equal chance of reproducing and passing on alleles
(In nature, random mating is rare -- mates are often chosen for certain traits.)
2. Large Population
Genetic drift is more likely to occur in small populations.
3. No Movement Into or Out of the Population
Immigration introduces new alleles and emigration removes alleles.
To keep allele frequencies constant, there can be no mixing with other populations.
4. No Mutations
If genes mutate, new alleles may be introduced into the population, and allele frequencies will change.
5. No Natural Selection
All genotypes in the population must have equal probabilities of survival and reproduction.
No phenotype can have a selective advantage over another.
Speciation = the formation of a new species.
A species = a group of similar organisms that breed to produce fertile offspring.
The gene pools of two populations must become separated for them to become new species.
Reproductive Isolation – two populations are unable to interbreed
1. Behavioral Isolation - different courtship rituals or reproductive behavior
2. Geographic Isolation - separation by geographic barriers such as rivers or mountains, ranges do not overlap
3. Temporal Isolation - reproduce at different times
CHAPTER 17
Fossil record
• all information about past life
• incomplete
• shows changes over time
• Paleontology = study of fossils
• Fossil Formation - Dead organisms are buried by layers of sediment, which forms new rock.
• Relative Dating = estimating a fossil’s age by comparing it with fossils in other rock layers (oldest=bottom, recent=top)
index fossil = a species that is recognizable and that existed for a short period but had a wide geographic range.
• Radioactive Dating Using half-lives to determine the absolute age of a sample
half-life = the length of time required for half of the radioactive atoms in a sample to decay.
In radioactive dating, scientists calculate the age of a sample based on the amount of remaining radioactive isotopes
it contains.
Geologic Time Scale
Formation of Earth
relatively small amount of evidence, gaps and uncertainties - scientific ideas about the origin of life will likely change
Four billion years ago, Earth cooled, rocks formed - millions of years later, volcanic activity
About 3.8 billion years ago, Earth’s surface cooled, water remained liquid and oceans covered much of the surface.
The First Organic Molecules
In the 1950s, Stanley Miller and Harold Urey simulated conditions on
the early Earth in a laboratory setting.
The Puzzle of Life's Origins
Evidence suggests that 200–300 million years after Earth had liquid
water, cells similar to modern bacteria were common.
Evolution of RNA and DNA Several hypotheses suggest:
Some RNA sequences can help DNA replicate under the right conditions.
Some RNA molecules can even grow and duplicate themselves.
RNA might have existed before DNA.
Free Oxygen
microfossils (microscopic fossils) of unicellular prokaryotes over 3.5
billion years old. This life evolved without oxygen.
2.2 billion years ago, photosynthetic bacteria oxygen into the oceans.
Next, oxygen gas accumulated in the atmosphere.
Origin of Eukaryotic Cells - The Endosymbiotic Theory
Eukaryotic cells arose from living communities formed by prokaryotic organisms.
Prokaryotes that use oxygen to generate energy-rich molecules of ATP evolved into mitochondria.
Prokaryotes that carried out photosynthesis evolved into chloroplasts.
Sexual Reproduction and Multicellularity
Asexual reproduction:
exact copies of the parent cell
restricts genetic variation to mutations in DNA
Sexual reproduction:
offspring different from parents
increased probability that favorable combinations are produced
increased chance of evolutionary change from natural selection
Macroevolution - large-scale evolutionary patterns and processes that occur over long periods of time.
1. Extinction
 More than 99% of all species that have ever lived are now extinct.
 Current thinking - mass extinctions caused by several factors
 Mass extinctions have provided ecological opportunities for organisms that survived and
resulted in bursts of evolution that produced many new species
2. Adaptive Radiation
 a single species or a small group of species
evolves into several different forms
 Darwin's finches - more than a dozen species
evolved from a single special
 larger scale – extinction of dinosaurs resulted in
the adaptive radiation of mammals
3. Convergent Evolution
 unrelated organisms come to resemble one another is called convergent evolution
 Examples - sharks, dolphins, seals, and penguins.
 Analogous structures -look and function similarly but are made up of parts that do not share a common
evolutionary history , Examples: dolphin’s fluke and a fish’s tail fin.
4. Coevolution
 two species evolve in response to changes in each other over time
 examples: parasites and hosts, flowers and pollinators
5. Punctuated Equilibrium
Gradualism
Biological change
slow and steady
(Darwin
hypothesized this)
Punctuated equilibrium
Long stable periods are
interrupted
by brief
periods of more rapid
change
Evolution has often proceeded at different rates for different organisms at different times during the history of life on Earth.
Both patterns have been found in different organisms, suggesting that both models may apply in different cases.
6. Developmental Genes and Body Plans
 Changes in genes for growth and
differentiation during embryological
development could produce changes in body
shape and size.
Species options to New Situations
1. Readaptation – depends on
 Rate and degree of change: fast rate + high degree of change = not enough time to evolve
Slow rate and small degree of change is the best
 Genetic variability in starting population: large genetic variability is the best = lots of genes to choose from
 Biotic Potential: high reproduction and recruitment the best
 Size of organism: larger generally need more resources, have smaller populations and reproduce slower
Small organisms can generally evolve faster
(Fly v.s. Panda bear)
 Geographic distribution: if the distribution is large, changing conditions may only affect a part of the population
2. Migration
 Move to other areas
 Not always an option
3. Extinction – 99% of all species that ever existed are extinct
CHAPTER 32 Primates
1. Fingers, Toes, and Shoulders
Can run along tree limbs, climb and swing from branches due to arms that can rotate around a strong shoulder joint.
Most have opposable thumb and big toe allowing them to hold objects in their hands or feet.
2. Well-Developed Cerebrum
Complex behaviors including social behaviors (adoption of orphans, warfare between rival primate troops).
3. Binocular Vision
Eyes face forward with overlapping fields of view. Merging images from both eyes gives depth perception and 3D view.
The two main groups of primates are
prosimians and anthropoids.
Prosimians - small, nocturnal primates with large eyes
adapted to seeing in the dark
Examples: bush babies, lemurs, lorises, and tarsiers.
Anthropoids - humanlike primates
Examples: Humans, apes and most monkeys
This group split into two major branches as drifting
continents moved apart.
New World monkeys
• live almost entirely in trees.
• long, flexible arms to swing from branches.
• prehensile tail, can coil around branches like a hand
Old World monkeys and great apes
• live in trees but lack prehensile tails.
• Great apes, also called hominoids, include gibbons, orangutans, gorillas, chimpanzees, and humans.
Hominid Evolution
Between 6 and 7 million years ago, the hominoid line gave rise to hominids.
 began to walk upright and
 developed thumbs adapted for grasping.
 developed large brains
 skull, neck, spinal column, hipbones, and leg
bones changed shape enabling bipedalism
(freed both hands to use tools)
 evolved an opposable thumb for grasping
The hominid family includes modern humans.
Hominids displayed a remarkable increase in brain size, especially in an
expanded cerebrum—the “thinking” area of the brain.
Early Hominids
At present, the hominid fossil record includes 20 separate hominid species
• Ardipithecus
• Australopithecus - A. afarensis = Lucy 1M tall
• Paranthropus –
• Kenyanthropus – 2001 skull in Kenya, small brain, traits of both chimpanzees and Homo fossils, new genus
• Homo
All are relatives of modern humans, but not all are human ancestors.
In 2002, paleontologists working in the desert in north-central Africa discovered another
skull.
• Called Sahelanthropus, it is nearly 7 million years old.
• If it is a hominid, it would be a million years older than any hominid previously
known.
• It had a brain like a modern chimp and a flat face like a human.
The hominid fossil record dates back 7
million years, close to the time that DNA
studies suggest for the split between
hominids and the ancestors of modern
chimpanzees.
The Genus Homo
 first fossils about 2.5 million years old.
 found with tools, called the species Homo habilis, which means “handy man.”
 2 mya, Homo ergaster appeared - bigger brain and downward-facing nostrils like modern humans.
 At some point, either H. ergaster or a related species named Homo erectus began migrating out of Africa through the
Middle East. Evidence suggests that hominids left Africa in several waves
 It is not certain where and when Homo sapiens arose.
One hypothesis, the multi-regional model, suggests that modern humans evolved independently in several parts of
the world from widely separated populations of H. erectus.
Another hypothesis, the out-of-Africa model, proposes that modern humans evolved in Africa between 200,000–
150,000 years ago, migrated out to colonize the world, and replaced the descendants of earlier hominid species.
Modern Homo sapiens
over the past 500,000 years involves two main groups:
Earliest called Homo neanderthalensi lived in Europe and Asia 200,000–30,000 years ago, they made stone tools
and lived in organized social groups
Other group is Homo sapiens—people whose skeletons look like those of modern humans.
50,000–40,000 years ago some populations of H. sapiens seem to have changed their way of life – better tools,
cave paintings, ritualistic burials
About 40,000 years ago, Cro-Magnons appeared in Europe.
By 30,000 years ago, Neanderthals had disappeared from Europe and the Middle East.
Since that time, our species has been Earth’s only hominid.