7.2 Darwin's Theory

Question 1

What is the mechanism for evolution?

Answer 1

Natural selection

Question 2

What is another term for evolution that was used in Darwin’s time?

Answer 2

Descent with modification

Question 3

Where does evidence for evolution come from?

Answer 3

fossil record
geographic distribution of species
comparative anatomy
comparative development
molecular biology

Question 4

Where does evidence from natural selection come from?

Answer 4

Artificial Selection
Molecular Biology

Question 5

What were the 2 main ideas of Darwin’s book, “Origin of Species”?

Answer 5

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

Question 6

Describe the role of the environment in Natural Selection

Answer 6

-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)

Question 7

Describe variation in Natural Selection

Answer 7

-Refers to differences among members of the same species
-Heritable
-Certain variations that suited the environment were more likely to be passed onto offspring

Question 8

Describe the struggle for existence in Natural Selection

Answer 8

-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

Question 9

3 key sets of observations in Natural Selection

Answer 9

-the struggle for existence
-variation
-the role of the environment

Question 9

Steps in the process of natural selection

Answer 9

1) struggle for existence
2) variation and adaptation
3) survival of the fittest
4) natural selection

Question 10

Theory of Natural Selection

Answer 10

-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

Question 11

What is fitness in evolution?

Answer 11

ability of an individual to survive and reproduce in it’s environment

Question 12

Describe survival of the fittest in natural selection

Answer 12

-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

Question 13

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

Answer 13

true

Question 14

How is the fossil record evidence for evolution?

Answer 14

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

Question 15

Why isn’t the fossil a complete record for evolution?

Answer 15

only organisms with bones, shells, or exoskeletons can become fossilized

Question 16

How is geographic distribution evidence for evolution?

Answer 16

-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

Question 17

Why are older fossils generally in deeper rock layers than younger fossils?

Answer 17

-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

Question 18

How can evolutionary theory explain why Australia is home to relatively few native placental mammals?

Answer 18

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.

Question 19

How can two species that look similar to each other be more distantly related than two species that look very different from each other?

Answer 19

distantly related species that live in similar environments develop similar body types therefore look similar to each other but are not closely related

Question 20

Homologous vs Analogous structures

Answer 20

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

Question 21

What are vestigial structures?

Answer 21

-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

Question 22

How can comparative development be used as evidence for evolution?

Answer 22

-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

Question 23

How can molecular biology be used as evidence for evolution?

Answer 23

-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

Question 24

What is artificial selection?

Answer 24

-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

Question 25

How are changes in beak shape evidence for natural selection?

Answer 25

-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

Question 26

What is an example of Natural Selection in action?

Answer 26

-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

Question 27

How is drug-resistant bacteria able to reproduce and become more common?

Answer 27

-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

Question 28

How did antibiotic resistance occur in bacteria?

Answer 28

-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

Question 29

Explain what Darwin meant by “descent
with modification.”

Answer 29

Darwin defined evolution as “descent with modification,”
-the idea that species change over time, give rise to new species, and share a common ancestor.

Question 30

How did Darwin use Malthus’s work to
formulate his theory of natural selection?

Answer 30

-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”

Question 31

Explain “survival of the fittest”.

Answer 31

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

Question 32

What makes an organism more “fit”
than others?

Answer 32

individuals with adaptations increase their fitness, survive and reproduce most successfully, while other species without these adaptions don’t survive

Question 33

How does natural selection depend on variation?

Answer 33

-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

Question 34

Why do distantly related species in different
places share similar traits?

Answer 34

-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

Question 35

Between homologous and analogous structures, which one is more important for evolution?

Answer 35

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.”

Question 36

Hemoglobin is common to all animals with
backbones. What does this tell us about the
evolutionary history of animals with backbones?

Answer 36

-suggest that these animals are evolutionarily related
-animals with backbones share a common ancestor

Question 37

Give an example of the fossil record and state what the evidence reveals about evolution.

Answer 37

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

Question 38

Give an example of geographical distribution and state what the evidence reveals about evolution.

Answer 38

-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)

Question 39

Give an example of comparative anatomy and state what the evidence reveals about evolution

Answer 39

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

Question 40

Give an example of embryology and state what the evidence reveals about evolution

Answer 40

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.

Question 41

Give an example of molecular biology and state what the evidence reveals about evolution

Answer 41

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

Question 42

Explain in terms of natural selection why
vestigial structures have not disappeared
completely

Answer 42

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

Question 43

What type of animals do you think would be
most represented in the fossil record? Explain

Answer 43

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.)

Question 44

Is protecting endangered species interfering with natural selection?

Answer 44

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.

Question 45

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?

Answer 45

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

Question 46

Lamarck hypothesized that evolution moves
species toward perfection. According to Darwin’s
theory, why is this statement incorrect?

Answer 46

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.

Question 47

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.

Answer 47

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.