Chapter 8 Flashcards
Evolution
the change in genes of a population on Earth over time
Evolution
the change in genes of a population on Earth over time
Microevolution
the changes in one gene pool of a population over generation
Macroevolution
speciation, the formation of an entirely new species
Individuals never
change or evolve
What is the smallest group that can evolve?
population
Population
consists of all the members of one species in 1 place
There are 6 areas of scientific study that provide evidence for evolution
Fossil record Comparative anatomy Comparative biochemistry Comparative embryology Molecular biology biogeography
Fossil Record
reveals existence of species that have become extinct or have evolved into other species.
Fossil record shows us
- 99% of all organisms that ever lived on earth are now extinct
- Prokaryotic cells are the oldest fossils and were the first organisms to develop on Earth
- Earth is about 4.6 billion years old (we know through studies of radioactive dating and half-life)
Paleontologists have discovered many transitional fossils
that link older extinct fossils to modern species
Archaeopteryx is a fossil that shows
both reptile and bird characteristics
Hyracotherium (Eohippus), the ancient horse
is an ancestor of the modern horse, Equus
Comparative Anatomy
organisms that have similar anatomical structures are related to each other and share a common ancestor
Example of comparative anatomy
Ex. comparing dental structures in chimps and humans demonstrates that we are related + share a common ancestor
Comparative Anatomy:
Homologous structures
the same internal bone structure although the function of each varies , homologous structures are examples of divergent evolution
Examples of homologous structures
the wing of a bat, the lateral fin of a whale, and the human arm show that we are all mammals and diverged from a common ancestor
Comparative Anatomy:
Analogous Structures
have the same function but not the same underlying structure, the similarity is superficial and reflects adaptation to a similar environment
Analogous structures are not evidence of
a common origin or ancestry but of convergent evolution
Example of Analogous Structures
Ex. bat’s wing and a fly’s wing have the same function but diff underlying structure
Comparative anatomy:
Vestigial Structures
structures that are remnants of an earlier active structure, such as the appendix, they are evidence that animals have evolved
Example of Vestigial Structures
Appendix is an example of a structure needed when our ancient ancestors ate a different diet
Comparative Biochemistry
organisms that have a common ancestor will have common biochemical pathways
The more closely related organisms are to each other, the more
similar their biochemistry is.
Examples of comparative biochemistry
Ex. humans and mice are both mammals, this relationship is the reason medical researchers can test new medicines on mice and extrapolate the results to humans
Comparative Embryology
closely related organisms go through similar stags in their embryonic development because they evolved from common ancestor
Example of comparative embryology
Ex. all vertebrate embryos go through a stage in which they have gill pouches on the sides of their throats, in fish, pouches develop into gills. In humans, they develop into eustachian tubes that connect the middle ear with the throat
Molecular Biology:
Since all aerobic organisms contain cells that carry out respiration and require ETC
they also all contain the necessary polypeptide, cytochrome c.
A comparison of the amino acid sequence of cytochrome c among different organisms shows
which are most closely related
Example of molecular biology
Cytochrome c in human cells is identical to that of a chimp but differs from that of a pig and is vastly different than that found in paramecia or oak leaves
Biogeography
theory of continental drift states that about 250 million years ago, the continents were locked together in a single super-continent known as Pangaea which separated into 7 continents over the course of the next 150 million years.
The study of the location of fossils confirms the theory that
marsupials migrated by land from South America across Antarctica to Australia before those 2 became separate continents about 55 million years ago
-as a result most of the world’s marsupials are isolated in australia
Lamarck was
a contemporary of Darwin
Lamarck was
a contemporary of Darwin
Lamarck’s theory focused on
inheritance of acquired characteristics and use and disuse → stated that individual organisms change in response to their environment
Lamarck’s theory focused on
inheritance of acquired characteristics and use and disuse → stated that individual organisms change in response to their environment
Example of Lamarck theory
Giraffe developed a long neck because it ate leaves of the tall acacia tree for nourishment and had to stretch to reach them and passed the acquire trait to their offspring
-widely accepted theory in the early 19th century
Darwin
a naturalist who developed the theory of natural selection → explains how populations evolved and how new species develop
What did Darwin publish?
Published “On the Origin of the Species” in 1859
Darwin’s Theory of Natural Selection
1 “Sub-Theory”
Populations tend to grow exponentially, to overpopulate, and exceed their resources→ developed this after reading Malthus who published a treatise on population growth, disease, and famine in 1798
Darwin’s Theory of Natural Selection
2nd Sub-Theory
Overpopulation results in competition and a struggle for existence
Darwin’s Theory of Natural Selection
3rd Sub-Theory
In any population, there is variation and an unequal ability of individuals to survive and reproduce → no one understood genetics or mutation which would have given a base for understanding variation ( had Medel and Hugo de Vries respectively been more ‘popular’)
Darwin’s Theory of Natural Selection
Only best-fit individuals survive and get to pass on their traits to offspring→ survival of the fittest. The degree of fitness is measured by the ability of an individual to survive and to reproduce in its environment.
Evolution occurs as
advantageous traits accumulate in a population
What’s the weakest part of Darwin’s theory?
His inability to explain the sources of diversity of a population
How the Giraffe Got Its Long Neck:
According to Darwin’s theory
Ancestral giraffes = short necked → length varied between individuals
According to Darwin’s theory of the giraffe’s long neck :
Since population of animals competing for limited food supply increased:
taller individuals and a better chance of surviving than those with shorter necks
Darwin: Over time, proportion of giraffes in the population with longer necks increased until only long-necked giraffes existed
correct theory:average length of the neck in the population changed not an individual animal
Until 1845 in England, most peppered moths
were light colored; few dark ones could be found
How the Peppered Moth Changed from Light to Dark
Increasing industrialization→ increased pollution→ some and soot made all plants + roots black
By the 1950s all moths in the industrialized regions were dark and only a few were light
Before industrial revolution
light moths were camouflaged and dark moths were easy prey for predators (birds)
After industrial revolution
dark moths were camouflaged and had the selective advantage
After 100 yrs dark replaced light in the population
this darkening is due to industrialization and is referred to as industrial melanism
No single individual moth changed but the
frequency of an allele (for color) in the population changed
Natural selection can produce
very rapid shifts in populations
Examples of rapid shifts in populations
Only a few years after the discovery of antibiotics, bacteria appeared that were resistant to these drugs
Appearance of antibiotics did not induce mutations for resistance, it just
killed susceptible bacteria
Only resistant individuals survived to reproduce –>
next gen was resistant to antibiotic they were exposed to
An entire population of bacterium can ‘become’
resistant to a certain antibiotic in a matter of months
individual bacteria do not evolve
the population evolves
Current treatment for AIDS
Current treatment is a cocktail of drugs including AZT, which slows the progression of the disease
One reason we have not been able to cure aids:
Some patients have been taking cocktail for years and the virus that causes AIDS suddenly becomes resistant and patient quickly sickens
AIDS virus has the ability to mutate and evolve rapidly
viruses that are susceptible to the drugs become inactivated, while those that have mutated are resistant.
The virus is able to
survive + reproduce an entire population that is resistant
A new flu vax must be developed every year because
the flu virus evolves so rapidly
Types of Natural Selection
3 types of natural selection that can alter
frequency of inherited traits in 3 different ways
3 Types of Natural Selection
Stabilizing selection, diversifying or disruptive selection, and directional selection
Stabilizing Selection
eliminates the numbers of extremes and favors the more common intermediate forms ,
many extreme forms are weeded out this way
Stabilizing Selection
eliminates the numbers of extremes and favors the more common intermediate forms ,
many extreme forms are weeded out this way
What type of selection keeps birth weights for humans between 6-9 lbs?
Stabilizing Selection
for babies much smaller or larger than 6-9 Lbs
mortality is greater
Disruptive or Diversifying Selection
increases the numbers of extreme types in a population at the expense of intermediate forms
Ex. of Diversifying Selection
A single population of snails can contain animals with either striped or plain shells
this results in balanced polymorphism where 2 or more phenotypes coexist in a population
Over great lengths of time
disruptive selection may result in the formation of 2 entirely new species
Directional Selection
changing environmental conditions give rise to directional selection where one phenotype replaces another in the gene pool
Example of Directional Selection
peppered moths is an example
The sources of variation in a population are
mutation, genetic drift, and gene flow
Single point mutation can introduce a
a new allele into a population
Single point mutations were first identified by
botanist Hugo de Vries in early 1900s who was studying polyploidy in plants
Genetic Drift
change in gene pool due to chance, for example, the bottleneck effect and the found effect
The Bottleneck Effect
Natural disasters (fires, earthquakes, and floods) reduce the size of a population nonselectively resulting in a loss of genetic variation
2 Factors of the Bottleneck Effect
- Resulting population is much smaller and not representative of the original one
- Certain alleles may be under or overrepresented compared with the original population
The Founder Effect
When a small population breaks away from a large one to colonize a new area, it is most likely not genetically representative of the original larger population
Gene Flow
movement of alleles into or out of a population
The founder effect can occur as a
result of the migration of fertile individuals or gametes between populations
Example of the Founder Effect
Pollen from one valley can be carried by the wind across a mountain to another valley
Population Stability- Hardy-Weinberg Equilibrium
Hardy and Weinberg (2 scientists) developed a theorem that described a stable, non-evolving population, one in which allelic frequency does not change
Example of Hardy-Weinberg
If the frequency of an allele for a particular trait is 0.5 and the population is not evolving
then in 1,000 years, the frequency of that allele will still be 0.5→ called Hardy-Weinberg Equilibrium
According to Hardy-Weinberg, if the population is stable, the following must be true:
- The population must be very large
- The population must be isolated from other populations
- There must be no mutations in the population
- Mating must be random
- There must be no natural selection
- The population must be very large
In a small population:
the smallest change in the gene pool will have a major effect in allelic frequencies.
1.The population must be very large
In a large population:
a small change in the gene pool will be diluted by the sheer number of individuals and there will be no change in the frequency of alleles.
2.The population must be isolated from other populations.
There must be no
migration of organisms into or out of the gene pool bc that could alter allelic frequencies
- There must be no mutations in the population
A mutation in the gene pool could cause
a change in allelic frequency or introduce a new allele
- Mating must be random
If individuals select mates, then those individuals
who are better fit will have a reproductive advantage and the population will evolve
- There must be no natural selection
Natural selection causes changes
in relative frequencies of alleles in a gene pool
Hardy-Weinberg Equation enables us to
calculate frequencies of alleles in a population. Can be applied to complex situations of inheritance
Hardy Weinberg Equation
p + q =1 or p^2+2pq+q^2=1
P= Q= p^2 = q^2= 2pq
dominant allele recessive homozygous dominant homozygous recessive all hybrid
Species
a population whose members have the potential to interbreed in nature and produce viable, fertile offspring.
Anything that fragments a population and isolates small groups of individuals may
foster the formation of a new species
Isolated populations are subject to different
selective pressures in their respective environments
If enough time elapses, the 2 populations may become so different that, even if they were brought back together
interbreeding would not occur. At this point, a new species is said to have come into being
6 Different forms of isolation cause
a new species to form
6 forms of isolation are
geographic isolation, polyploidy, habitat isolation, behavioral isolation, temporal isolation, reproductive isolation
Geographic Isolation
occurs when species are separated. Mountain ranges, canyons, rivers, lakes, or glaciers may cause significant isolation between species
Polyploidy
instead of being haploid (n) or diploid(tn), polyploid organisms can be tetraploid (4n) or octoploid (8n)
Nearly ½ of all flowering plants + vast majority of ferns are
polyploid
Polyploid organisms cannot breed with organisms that
are not polyploid and therefore are isolated from them
Habitat Isolation
occurs when two organisms live in the same area but encounter each other rarely.
Example of Habitat Isolation
2 species of 1 genus of snake can be found in the same geographic area, but 1 inhabits that water and the other in mainly terrestrial
Behavioral Isolation
occurs when 2 animals become isolated from each other because of some change in behavior
Ex. of Behavioral Isolation
male fireflies of various species signal to females of their kind by blinking lights on their tails in a particular patter→ females only respond to characteristics of their own species, flashing back to attract males → if for any reason, the female doesn’t respond with the correct blinking pattern, no mating occurs
Temporal Isolation
temporal refers to time
Examples of Temporal Isolation
diff plants of 1 species living in the same area may become functionally separated into 2 populations via temporal isolation because some plants become sexually mature earlier and begin to flower in the cooler part of the season will other plants in the later, warmer part
Reproductive Isolation
closely related species may be unable to mate because of anatomical incompatibility.
Ex of Reproductive Isolation
For ex. A small male dog and a large female dog cannot matter because of the enormous size differences between the 2 animals
How species evolve are classified into 5 patterns
divergent, convergent, parallel, coevolution, and adaptive radiation
Divergent Evolution
occurs when a population becomes isolated (for any reason) from the rest of the species and becomes exposed to now selective pressures, causing it to evolve into a new species
Homologous structure are evidence
of divergent evolution
Covergent Evolution
when unrelated species occupy the same environment, they are subjected to similar selective pressures and show similar adaptations.
Ex. of Covergent Evolution
Ex. a whale (mammal) and a fish. Both have a streamlined appearance because that is advantageous in their environment. The underlying bond structure of a whale however, reveals ancestry common to mammals, not fish
Analogous structures are evidence of
covergent evolution
Parallel Evolution
describes 2 related species that have made similar evolutionary adaptations after their divergence from a common ancestor
Ex. of Parallel Evolution
many similarities between gray wolf of North America and Tasmanian wolf (marsupial) or Australia because they share a common ancestor and evolved in similar environments
Coevolution
mutual evolutionary set of adaptations of 2 interacting species
Ex. of Coevolution
pollinator-plant relationships are an example → When an insect, bird, or bat feeds on the nectar from a flower, it inadvertently ensures the reproductive success of the flower
Ex. of Coevolution
pollinator-plant relationships are an example → When an insect, bird, or bat feeds on the nectar from a flower, it inadvertently ensures the reproductive success of the flower
Adaptive Radiation
the emergence of numerous species from a single common ancestor introduced into an environment
When a honeybee that lives on the nectar of the scottish broom flower, the flower has a
tripping mechanism that arches the stamens (male part) over the bee and dusts it with pollen, some of which will rub off onto the pistils (female part) of the next flower that the bee visits
On the Galapagos Islands, Darwin discovered
14 species of finches each filling a different ecological niche, some lived on ground whale others adapted to live in trees
Biggest variation of finches is in
their beaks which are adapted for different diets
Thick, short beaks
pointy beak
eat seeds while longer
eat insects
Theories About Evolution
Gradualism
states that organisms descend from a common ancestor gradually, over a long period of time, in a linear or branching fashion
“Big changes occur by an accumulation of many small ones”
According to gradualism
fossils should exist as evidence of every stage in the evolution of every species with no missing links
Fossil record is at odds with gradualism because
scientists rarely find transitional forms or missing links
Scientists have abandoned gradualism for
punctuated equilibrium
Punctuated Equilibrium (theory favored today)
developed by Stephen J. Gould and Niles Eldridge and it states that new species appear suddenly after long periods of no change
Most likely, a new species arises in a different place and expands its range
competing with and replacing the ancestral species that becomes extinct
Spontaneous Generation
the theory that living things emerge from nonliving or inanimate objects
Spontaneous generation was disproved by
Franceso Redi (17th cen.)
Franceso Redi (17th cen.)
who put decaying meat into a group of wide-mouthed jars-some covered with lids, others with cheesecloth, and some open → demonstrated that maggots arose only where flies were able to lay eggs
Louis Pasteur
used a goosenecked flask to prove that microorganisms appeared only as contaminants from the air and not spontaneously
1860s
Organism alive today represent
3% of all organisms that ever lived meaning 97% of all life has gone extinct
After the big bang formed the planets, v
Earth’s outer surface cooled and solidified to form a crust.
The ancient environment most likely consisted of
CH4 (methane), NH3 (ammonia), H20 (vapor), and N2 but lacked free oxygen.
What created energy for many chemical reactions with produced?
Intense heat + lightning + UV radiation
the 1st cell
A.I. Oparin and J.B.S. Haldane, 1920s
separately hypothesized that under the conditions of early Earth, organic molecules could form
A.I. Oparin and J.B.S. Haldane stated that
in the absence of corrosively reactive molecular oxygen that would react with + degrade them, organic molecules could form and persist
Stanley Miller and Harold Urey, 1950s
tested Oparin-Haldane hypothesis and proved that almost any energy source would have converted inorganic molecules in the early atmosphere into a variety of organic molecules, including amino acids
Stanley Miller and Harold Urey 1950s
Used electricity to
mimic lightning and U.V light that must have been present in great amounts in the early atmosphere
Sidney Fox
recent years, produced membrane-bound, cell-like structures he called proteinoid microspheres, which would last for several hours in a lab
The 1st organisms on Earth were
anaerobic heterotrophs
Heterotroph Hypothesis
states that 1st cells on Earth were anaerobic heterotrophic prokaryotes
Anaerobic heterotrophic prokaryotes
Simply absorbed organic molecules from the surrounding primordial soup to use as a nutrient source
Fossil record states that the 1st cell evolved about
3.5 billion years ago
Eukaryotic cells w/ a nucleus+other organelles evolved
- 5 billion years ago
- this occurred as tiny bacteria took up residence inside large prokaryotic cells and performed important functions for the host cell
Beneficial symbiotic relationships resulted in nuclei, chloroplasts, and mitochondria , this theory of endosymbiosis was
developed by Dr. Lynn Margulis
Fossil record states that the 1st multicellular animals appeared about
565 million years ago → over a span of 40 million years, every major phylum of animal appeared
Cambrian explosion
animals moved from oceans to the land filling every available niche as competition for limited resources increased in the oceans and as they evolved the traits necessary to lived in a dry environment
Several characteristics enabled animals to move to land:
lungs, skin to keep animals from drying out, limbs to move, mechanisms for internal fertilization, shell to protect their eggs and keep them from drying out
Several characteristics enabled plants to move to land:
Roots that anchor them into soil + absorb water, supporting cells to enable them to compete for light, vascular tissue to carry water upward, waxy molecule (cutin) to protect leaves frond dehydrating, seeds (protective package for the embryo + its food)
Mammal appeared about
210 million years ago, primates (including apes), appeared about 25 million years ago
Humans did NOT
evolve from apes; we both evolved from a common ancestor about 7 million years ago, human ancestors arose in Africa
Homosapiens (modern humans) arose about
150,000 years ago
A species may go extinct for many reasons
habitat destruction or drastic environmental change
Even if physical factors (temperature, humidity, CO2 levels) remain stable
because so many species are interdependent, the extinction of one species can result in the extinction of another
How many major extinction events have there been?
5 major extinction events in the past 500 million years
The two most important extinction events were
permian extinction
cretaceous mass extinction
The Permian extinction (250 million years ago)
- occurred during a period of enormous volcanic eruptions in what is now Siberia
- Lava, 100s of 1000s of meters thick, covered an area the size of Europe
The eruptions during the Permian extinction emitted enough CO2 into the atmosphere to
cause the global climate to increase 6 degrees C. Life on Earth was almost wiped out
The Cretaceous mass extinction (65 million years ago)
10km wide asteroid crashed into the Yucatan peninsula, Mexico , the scar can be seen from space
Theory about the Cretaceous mass extinction is that this collision caused a
huge cloud of debris to billow into the atmosphere blocking sunlight for months → resulted in the extinction of many marine and land animals including all the dinosaurs, excluding birds
Summary: Evolution is not always a slow process
a population of bacteria can develop resistance to a particular antibiotic after only a few months of exposure
Summary: Evolution does not occur at the same rate in all organisms
humans have changed a great deal in the last 100,000 years, whereas the horseshoe crab has hardly changed at all
Summary: Evolution does not always cause organisms to become more complex
instead it may cause complex forms to create simpler ones
Early embryo of the sea star is bilaterally symmetrical (similar to human development) considered to be advanced and complex
but the adult sea star, shows radial symmetry which is considered simple and primitive
Summary: Evolution occurs in populations not individuals
A single giraffe did not develop a long neck because it needed it, instead short-necked giraffes could not compete in a competitive environment and died out→ only long-necked giraffes survived
Summary: Evolution is directed by changes in the environment
animals that evolved int he ocean must be streamlined in order to move freely
