7.2 Darwin's Theory Flashcards
What is the mechanism for evolution?
Natural selection
What is another term for evolution that was used in Darwin’s time?
Descent with modification
Where does evidence for evolution come from?
fossil record
geographic distribution of species
comparative anatomy
comparative development
molecular biology
Where does evidence from natural selection come from?
Artificial Selection
Molecular Biology
What were the 2 main ideas of Darwin’s book, “Origin of Species”?
All species of organisms living on Earth today are descended from ancestral species (i.e. species evolve over time)
The mechanism that causes species to change over time is Natural Selection
Describe the role of the environment in Natural Selection
-The environment selects from organisms with variations that are best suited for that environment (e.g. Lamarck’s giraffes - more long neck vs. short neck)
Describe variation in Natural Selection
-Refers to differences among members of the same species
-Heritable
-Certain variations that suited the environment were more likely to be passed onto offspring
Describe the struggle for existence in Natural Selection
-All species tend to produce excessive numbers of offspring
-BUT in nature resources are limited
-More individuals being produced than an environment can support leads to struggle
-Competition for limited resources
-In most cases, only a small percentage of offspring survive each generation
3 key sets of observations in Natural Selection
-the struggle for existence
-variation
-the role of the environment
Steps in the process of natural selection
1) struggle for existence
2) variation and adaptation
3) survival of the fittest
4) natural selection
Theory of Natural Selection
-Process by which individuals with inherited characteristics well suited for their environment leave more offspring on average than do individuals with adaptations less suited to the environment
-The survivors’ offspring will also have these useful traits
-Causes population to change over time
What is fitness in evolution?
ability of an individual to survive and reproduce in it’s environment
Describe survival of the fittest in natural selection
-Certain adaptations make some species better suited for an environment
-Survival of the Fittest is a synonym to Natural Selection
-N.S. could eventually cause isolated populations of the same species to become separate species as they adapt to their different environments
True or false: Natural Selection does NOT make organisms “better”, just it’s adaptation enables an organism to pass on its genes to the next generation
true
How is the fossil record evidence for evolution?
Position of fossils in rock strata can reveal relative age
Links the past with the present(species vary over time)
E.g. whales, which have no hind limbs, evolved from land-dwelling ancestors that had four limbs
Can provide evidence of extinction of species
E.g. dinosaurs disappeared from fossil record 65 mya
Why isn’t the fossil a complete record for evolution?
only organisms with bones, shells, or exoskeletons can become fossilized
How is geographic distribution evidence for evolution?
-Closely Related but Different
E.g. Darwin’s finches – beak shape adapted to eating specific food
-animals on the various islands were all
descendants of a single ancestral species from the
mainland (e.g. tortoises on the Galapagos Islands)
-Distantly Related but Similar
-sometimes similar habitats select from similar
adaptations
-selection pressures had caused these species to
develop similar adaptations to survive in these
environments
-distantly related species that live in similar
environments have developed similar body types
Why are older fossils generally in deeper rock layers than younger fossils?
-Younger rock layers, or strata, are deposited on
top of older ones
-The deeper the layer in which the fossil is found,
the older the age of the fossil
How can evolutionary theory explain why Australia is home to relatively few native placental mammals?
The most widely accepted hypothesis suggests
that Australia’s diverse marsupial species evolved from marsupial ancestors on an island continent that was isolated from placental mammals in the distant past.
How can two species that look similar to each other be more distantly related than two species that look very different from each other?
distantly related species that live in similar environments develop similar body types therefore look similar to each other but are not closely related
Homologous vs Analogous structures
H- Share a common evolutionary origin (ancestor)= SAME structure, DIFF. function
-E.g. forelimbs of terrestrial vertebrates; whale flipper and human forelimb
A-Share similar function but not origin or structure=
SAME function, DIFF. structure
-E.g. bird and bee wing
What are vestigial structures?
-Type of homologous structures that have importance in one species BUT are not important in a related species
-Remnants of structures that may have had important functions in an ancestral species, but have no clear function in modern descendants
-Often reduced in size
E.g. pelvis in whales, appendix in humans
How can comparative development be used as evidence for evolution?
-Embryos of closely related organisms have similar stages of development
-Similarity in development in the early stages is further evidence of evolution from a common ancestor
How can molecular biology be used as evidence for evolution?
-Provides more evidence of relatedness between species
-If 2 species have genes and proteins with sequence that match closely, biologists conclude that the sequences must have been inherited from a relatively common ancestor
What is artificial selection?
-Selective breeding of domesticated plants and animals to produce offspring with genetic traits that humans value
-e.g. plant breeder might want to improve protein content
-e.g. animal breeder might want to improve growth rate
-Artificial Selection is what humans do, which’s the exact same to what the environment does in Natural Selection
How are changes in beak shape evidence for natural selection?
-Avg. beak and body of Medium Ground Finch changes as El Ninos come and go
Wet years – small seeds are abundant that finch eats few large seeds
Dry years – all seeds are in short supply, and large seeds make up diet
-Birds with bigger beaks are favoured because they can eat larger seeds + survive in the dry years when birds with smaller beaks die = N.S
What is an example of Natural Selection in action?
-resurgence of Tuberculosis
-drug-resistant bacteria arose by means of natural selection
-bacteria, like other organisms, have many variations. –some can be destroyed by antibiotics and others are resistant
-some bacteria that are resistant to these antibiotics are then able to survive due to natural selection
How is drug-resistant bacteria able to reproduce and become more common?
-N.S. favours them and helps them to survive + reproduce
-bacteria, like other organisms, have many variations
-some can be destroyed by antibiotics and others are resistant
-some bacteria that are resistant to these antibiotics are then able to survive due to natural selection
How did antibiotic resistance occur in bacteria?
-Bacteria have many variations
-Some destroyed by antibiotics, others not
-Many people don’t take their full prescription
-Drug-resistant bacteria are able to survive due to N.S. and reproduce and become more common
Explain what Darwin meant by “descent
with modification.”
Darwin defined evolution as “descent with modification,”
-the idea that species change over time, give rise to new species, and share a common ancestor.
How did Darwin use Malthus’s work to
formulate his theory of natural selection?
-drawing from Malthus’s ideas about humans, Darwin recognized that all species tend to produce excessive numbers of offspring
-in nature, resources are limited
-the production of more individuals than the environment can support leads to a struggle for existence among the individuals of a population
-the struggle for existence is direct competition among individuals of a species for limited resources.
from this developed one part of his theory of natural selection- “struggle for existence”
Explain “survival of the fittest”.
The results of differences in rates of survival and reproduction is called survival of the fittest
-organisms with certain traits live longer and reproduce more= “fittest”
-organisms w/o these traits don’t survive as long or reproduce
What makes an organism more “fit”
than others?
individuals with adaptations increase their fitness, survive and reproduce most successfully, while other species without these adaptions don’t survive
How does natural selection depend on variation?
-Natural selection acts on existing heritable variation.
-it needs starting material, and that starting material is heritable variation
-for natural selection to act on a feature, there must already be variation, and that variation must be able to be passed on to offspring
Why do distantly related species in different
places share similar traits?
-similar selection pressures cause species to develop similar adaptations to survive in their environments
-so distantly related species that live in similar environments develop similar body types
Between homologous and analogous structures, which one is more important for evolution?
Homologous structures are more important for evolution
-Homologous structures support other evidence
that evolution is a remodelling process.
-Structures that originally functioned one way in ancestral species become modified as they take
on new functions.
-This idea is what Darwin meant by “descent with
modification.”
Hemoglobin is common to all animals with
backbones. What does this tell us about the
evolutionary history of animals with backbones?
-suggest that these animals are evolutionarily related
-animals with backbones share a common ancestor
Give an example of the fossil record and state what the evidence reveals about evolution.
Link the past with the present (species vary over time)
-e.g. whales, which have no hind limbs, evolved from land-dwelling ancestors that had four limbs
Can provide evidence of extinction of species
-e.g. dinosaurs disappeared from the fossil record 65 mya
Give an example of geographical distribution and state what the evidence reveals about evolution.
-Closely Related but Different
E.g. Darwin’s finches – beak shape adapted to eating specific food
revealed that the finches on the various islands were all descendants of a single ancestral species from the South American mainland
-Distantly Related but Similar
E.g. similar ground-dwelling birds in the grasslands of South America, Australia, and Africa
similar selection pressures had caused these species to develop similar adaptations to survive in these
environments (natural selection)
Give an example of comparative anatomy and state what the evidence reveals about evolution
Homologous structures - reveals that species with similar structures share a common ancestor
-e.g. forelimbs of terrestrial vertebrates; whale flipper
and human forelimb
Analogous structures - share similar function but not origin or structure
-e.g. bird and bee wing
Vestigial structures - remnants of structures that may have had important functions in an ancestral species, but have no clear function in modern descendants
-e.g. pelvis in whales, appendix in humans
Give an example of embryology and state what the evidence reveals about evolution
All vertebrates, for example, have an embryonic stage in which pharyngeal pouches appear on the sides of the throat. At this stage, the embryos of fishes, frogs, snakes, birds, and primates look relatively alike.
similarity of these structures at early stages reveals that all vertebrates evolved from a common ancestor.
Give an example of molecular biology and state what the evidence reveals about evolution
If 2 species have genes and proteins with sequence that match closely, biologists conclude that the sequences must have been inherited from a relatively common ancestor
-e.g. humans and gorillas are related because their amino acid sequence for hemoglobin is close in number
Explain in terms of natural selection why
vestigial structures have not disappeared
completely
Although many of these types of structures would disappear over many generations, some keep being passed down to offspring because they do no harm
-they aren’t a disadvantage for the species—or they have changed function over time
What type of animals do you think would be
most represented in the fossil record? Explain
organisms with bones, shells, or exoskeletons would be the most represented because they are the only organisms that can become fossilized
(e.g. vertebrates, echinoderms, brachiopods, and some groups of arthropods.)
Is protecting endangered species interfering with natural selection?
If a person tries to protect endangered species who are about to go into extinction due to irresponsible human activities, then it is not upsetting the process of natural selection but an act of conserving biodiversity.
Penguins and flying albatrosses might have
a common ancestor.
(a) How would Darwin use comparative
anatomy and the fossil record to establish
this evolutionary relationship?
comparative anatomy: if they have homologous structures (similar structures), that means they share a common ancestor.
fossil record: links the past with the present and can tell you how an organism evolved and what its ancestor was
Lamarck hypothesized that evolution moves
species toward perfection. According to Darwin’s
theory, why is this statement incorrect?
According to Darwin, all species of organisms arise and develop through the natural selection of inherited variations that increase the individual’s ability to compete, survive, and reproduce and not necessarily moving to perfection.
Figure 7.17 on page 198 summarizes natural
selection in a population of crickets. Suppose
the climate changed and the grasses in the
field tended to be a more golden brown
colour. Apply the theory of natural selection
to the population of crickets in these new
environmental conditions.
struggle for existence: competition among offspring
variation and adaptation: brown crickets blend better into grass
survival of the fittest: more brown crickets survive and
reproduce, they have greater reproductive success
natural selection: brown crickets become more common than green crickets in the population with each generation because
(1) more eggs are laid than can survive
(2) there is variation in colour, which is a heritable trait, (3) the environment favours brown crickets, so more survive and reproduce than green crickets.
