Presentation by Abdul Qadeer MBBS; DTM; BASc; CPHI-C, CIC
St. Clair College Continuing Education
ESSENTIALS
OF HUMAN
ANATOMY &
PHYSIOLOGY
Evolution
Evolution – Non Technical
Evolution is the accumulation of changes
through succeeding generations of organisms
that results in the emergence of new species
Since the origin of life , evolution has
transformed the first species (the common
ancestor of all living things) into a large
number of different species
Evolution – In Biology
Evolution is the change in the inherited traits
of a population from one generation to the
next
These traits are the expression of genes that
are copied and passed on to offspring during
reproduction
Mutations in these genes can produce new or
altered traits, resulting in heritable differances
between organisms
Evolution – In Biology
New traits can also come from transfer of
genes between populations, as in migration,
or between species, in horizontal gene
transfer
Evolution occurs when these heritable
differences become more common or rare in a
population, either non-randomly through
natural selection or randomly through
genetic drift
Evolution
Earth was created on
Sunday
October 23, 4004 BC
Archbishop James
Ussherof Armagh
(1581-1656)
Evolutionary Theories
The acceptance of theories of evolution has
never been universal
Many people hold cultural and religious
beliefs about the origin of life
May not be in harmony with scientifically
accepted reasoning and conclusions
Evolutionary Theories
A Irish scholar and
theologian published his
calculations for the age
of Earth based on
astronomy, history, and
biblical sources.
Declared that Earth was
created on Sunday,
October 23, 4004 BC. Archbishop James
Ussherof Armagh
(1581-1656)
Evolutionary Theories
Also calculate the dates of other significant
biblical events.
In 1701, his chronology was printed as
marginal notes in an authorized version of the
Bible.
About 150 years later, most Europeans
mistakenly thought his chronology was part
of the original scripture.
Evolutionary Theories
Today
Most people understand that the world is a
dynamic environment in which change is
both natural and unavoidable
Evolution
The process in which significant changes
in the inheritable traits (i.e. the genetic
makeup) of a species occur over time
Evolutionary Theory
500 years ago
Most people thought that their natural
surroundings changed very little
Immutable
Unchanged and unchanging, believed
(before evolutionary theory became
accepted) to be characteristic of life forms
Evidence From the Past
Fossil Record
Strong evidence for a changing Earth
began with a careful examination of
fossils.
Near the end of the 15th century, the
scientist were convinced that Earth's
surface had changed dramatically over
time.
Fossils offer evidence of environmental
change
Fossil Record
Fossils
Any preserved remains or traces of an
organism or its activity; many fossils are
of such hardened body parts as bone
Fossils
(a) Reconstructed
mammoth skeleton
(b) skull of a
young male
Homo erectus
(c) Pterodactylus
kochi from the
Jurassic period
Fossils
Permineralized fossil
A fossil formed when dissolved minerals
precipitate from a solution in the space
occupied by the organism's remains
Permineralized fossil
(a) dead organism
(b) organism is buried and compressed under many layers of sediment
Permineralized fossil
(c) under high pressure deposits harden to form sedimentary rock and the fossil remains become mineralized
(d) erosion or excavation of sedimentary rock exposes fossil remains on the surface
Fossilization
Fossilization
The process by which traces of past
organisms become part of sedimentary
rock layers or, more rarely, hardened tar
pits, volcanic ash, peat bogs, or amber
Microfossils
Microscopic remains of tiny organisms or
structures that have hard and resistant
outer coverings
Study of Fossils
Palaeontology
The scientific study of fossil remains
Catastrophism Theory
Baron Georges Cuvier (anatomist) in 18th centaury
Did not believe that species changed overtime
Numerous global catastrophes in the past had repeatedly caused the extinction of species that were then replaced by newly created forms
Catastrophism
Discrete rock layers
containing different
fossils reinforced the
idea that the Earth's
history could be divided
into ages marked by
catastrophic change
However, gradual
change, like that caused
by erosion, has also
played an important role
in the Earth's history
Fossil Record
Cuvier’s hypothesis
Relative age
An estimate of the age of a rock or fossil
specimen in relation to another specimen
Absolute age
An estimate of the actual age of a rock or
fossil specimen
Scientist of that time had no precise
method for calculating absolute age
Absolute Age of Earth
Estimate 4.6 billion years
Radioactive decay
The release of subatomic particles from
the nucleus of an atom, which results in
the change of a radioactive parent isotope
into a daughter isotope; when a number of
proton is altered, a new element is formed
Absolute Age of Earth
Radioisotopes
Atoms with an unstable nuclear
arrangement that undergo radioactive
decay
Parent isotopes
Daughter isotopes
Provide an accurate and reliable method of
determining the age of both rock and
fossil remains
Early Ideas About Evolution
Actualism Theory
James Hutton (1795- 1830)
The same geological processes occurring
in the present also occurred in the past
Uniformitarianism Theory
Sir Charles Lyell (1797-1875)
The Earth's surface has always changed
and continues to change through similar,
uniform, and very gradual processes
Early Ideas About Evolution
Lyell found evidence that valleys were formed
through the slow process of erosion, not by
catastrophic floods.
Early Ideas About Evolution
The ideas of Hutton and Lyell led to an
understanding of "the rock cycle" as we know
it today
Early Ideas About Evolution
Spontaneous Generation Theory Chevalier de Lamarck (1744-1829)
Living organisms arise from nonliving matter
Acquired Traits Theory
Chevalier de Lamarck (1744-1829)
First scientist to recognize that the environment
plays a key role in the evolution of species
Changes in an individual resulting from
interaction with the environment (adaptation)
Early Ideas About Evolution
Charles Darwin Discovery
As a naturalist on a voyage to South America 1831.
Biogeography
The careful observation and analysis of the geographic distribution of organisms
Suggested that organisms evolve from common ancesters.
Darwin's Voyage of Discovery
HMS Beagle was a 10-gun brig, 27.5 m long, that offered little room or comfort for the 74 people onboard
What Darwin Observed?
Differences
between
closely
related
species human
whale
The forelimbs of these organisms are each adapted to carry out
very different functions, yet they all possess very similar bone
structure
Darwin’s Observations
Homologous features
Structures that share a common origin but
may serve different functions in modern
species
dolphin flippers and human hands
horse leg and wing of the bat
Darwin’s Observations
Analogous features
Structures similar in function but not in
origin or anatomical structure
wings of birds, bees and butterfly
eyes of lobster and fish
Vestigial Features and Anatomical Oddities
Vestigial features
Rudimentary and nonfunctioning structures that are homologous to fully functioning structures in closely related species
Dogs have a vestigial toe. Although the bones remain, this digit serves no
present purpose.
Pigs' feet have two well-developed digits; the others are vestigial.
Vestigial Features
Other examples in Humans
Humans have muscles for moving ears,
much as dogs and other mammals do
The appendix
Mechanism of Evolutionary Process
Artificial selection
A process to alter the appearance and
behavior of domesticated plants and
animals
Corn oil content dramatically increased in
only 60 generations
Evidence for an Evolutionary Mechanism
Darwin concluded that in the struggle for
survival
As species produce many more offspring
than can survive
there must be intense competition among
individuals in each species
the most favorable traits are inherited by
succeeding generations
Mechanism of Evolutionary Process
Natural Selection
Theory presented in 1858
Darwin postulated that natural processes
could act as agents of natural selection in
much the same way
Based on some basic observations and
inferences
Observations in Natural Selection Observation 1
Individuals within a species vary in many ways
Observation 2
Some of this variability can be inherited
Observation 3
Every generation produces far more offspring than can survive and pass on their variations
Observation 4
Populations of species tend to remain stable in size
Inferences in Natural Selection Inference 1
Members of the same species compete with each other for survival
Inference 2
Individuals with more favorable variations are more likely to survive and pass them on
Survival is not random
Inference 3
As these individuals contribute proportionately more offspring to succeeding generations, the favorable variations will become more common (This is natural selection)
Understanding Concept
Propose an evolutionary scenario in which a
species of ancient chameleons could evolve into a
species with an unusually long tongue
Understanding Concept
Keep in mind the two key elements
required for natural selection:
inherited variation
and
an environment that favors certain
traits over others
Summary of Natural Selection
All species exhibit inheritable variations that
are selected through the struggle by
individuals for survival in competition within
their population
Individuals with more favorable traits
produce more offspring that survive than
others and pass along those favorable traits
Summary of Natural Selection
Over many generations, this process results in
a change in the inheritable traits of the
population.
BRAIN STORMING!
When natural selection was first proposed,
scientists had no understanding of the genetic
basis of inheritance and variation
70 YEARS AFTER?
Mechanisms of Evolution
DISTINDUISHING TRAITS: These individuals exhibit variations, but they also share inherited physical features
The genetic diversity
is readily apparent
Genetic Variation
The genetic
diversity of
many
populations,
such as this one
of long-nosed
bats, may not be
readily apparent
to human
observers
Genetic Variation - Traits
RRTT RRTt RrTT RrTt
RRTt RRtt RrTt Rrtt
RrTT RrTt rrTT rrTt
RrTt Rrtt rrTt rrtt
Rt RT rT rt
RT
Rt
rT
rt
Parent
RrTt
Parent
RrTt
Genetic Variation
Trait
Changes in the individuals resulting from
interaction with environment
Genotype
The set of alleles possessed by an individual
organism
Phenotype
Observable trait of an organism that result from
interaction between genes and the environment
Genetic Variation
Homozygous:
Descriptive of a gene for which the paired
allele differ are identical
Heterozygous:
Descriptive of a gene for which the paired
allele differ
Genetic Variation
The quantity of DNA and the number of
genes are highly variable among species
Variation within a species is a result of the
variety and combinations of alleles possessed
by individuals
Sexual reproduction results in the random
recombination of often thousands of different
alleles and results in a high degree of genetic
diversity within most populations
Genetic Variation
Genes
portions of the DNA molecule within a chromosome coding for particular polypeptide products
Alleles
particular forms of a gene; many genes have two or more alleles
Population
all members of the same species living in the same region
Random Change
Evolution occurs when the allele frequencies
of a population change over time
Genetic drift and gene flow produce changes
in allele frequencies and affect genetic
diversity
The source of all new genetic information is
mutation
Random Change
Gene duplications are the maim source of
new genetic material. They are free to mutate
without the likelihood of causing harm
Although rare in individual cells, mutations
are numerous in large populations over many
generations
Random Change
Genetic drift
A changes in the genetic makeup of a
population resulting from chance
Such changes are much more pronounced in
small populations
Gene flow
The movement of alleles from one population
to another through the movement of individuals
or gamete
Genetic Drift The remaining
populations of the
endangered
Blanchard's cricket
frog, Acris crepitans
blanchardi, once found
on Pelee Island in Lake
Erie, are very
vulnerable to the
effects of genetic drift
Genetic Drift - Scenario
Large Population Scenario
Assume l in 50 cricket frogs carries a allele,
C1
Population of 10,000 individuals - 200 allele
Random deaths of half the population
about 100 of the 5000 survivors to be
carrying the C1
The allele frequency would not be
expected to change
Genetic Drift
Small Population Scenario
Population were only 100 individuals
only two to possess the C1 allele.
Random death of half the population
What is the chance?
both the C1 carriers would die- extinction OR
both would survive - doubling the allele frequency of C1.
When populations are small, chance can play a significant role in altering allele frequencies
Genetic Drift - Bottleneck Effect
When a sever event
result in a dramatic
reduction in numbers, a
population may
experience a bottleneck
effect
Bottleneck effect
a dramatic, often
temporary, reduction in
population size usually
resulting in significant
genetic drift
Genetic Drift - Bottleneck Effect
The northern elephant
seal population was
reduced by overhunting
to 20 individuals in the
1890s. Although the
population had
rebounded to over
30 000 individuals by
1974, genetic testing of
24 loci exhibited total
homozygosity
Mutation
Unrepaired changes in DNA sequence or
chromosomes breakage or rejoining
Mutations are random changes to the genetic code
Rare in individual cells, mutations are numerous in
large populations over many generations
Types
Neutral mutation
Has no immediate effect on an individual's
fitness, or reproductive success
Mutation Harmful mutation
Reduces an individual's fitness
Occurs when a cell loses the ability to produce a properly functioning protein or when major chromosomal changes adversely affect meiosis and mitosis
Beneficial mutations
Occurs when a cell gains the ability to produce a new or improved protein, gives an individual a selective advantage
Increased reproductive success
Mutations and Genetic Variations What is the source of variation?
How are subtle differences passed from generation to generation?
Scientific understanding of genetics and mutations answered these questions
Mutations provide a continuous supply of new genetic variations, which may be inherited and expressed as different phenotypes.
Natural selection leads to a variety of outcomes when this genetic variation occurs within competitive populations living under diverse environmental conditions.
Mutations and Genetic Variations Sickle-cell anemia, a blood disorder, is a useful
example of how mutation, genetic variation, and the environment result in different patterns of natural selection
The allele for sickle-cell anemia differ from the normal hemoglobin gene by having a single base-pair mutation
Homozygous individuals for the sickle-cell allele are severely afflicted with this disorder
Heterozygous individuals are only mildly affected by sickle-cell anemia however, they are much more resistant to malaria than are people with normal hemoglobin
Mutations and Genetic Variations Of the 120 million new cases of malaria each year, about 1
million are fatal. The prevalence of malaria in Africa (a) closely
matches the distribution of the sickle-cell allele (b)
Malaria
P. falciparum in Africa
1-50% 5-10%
10-20%
Adapted from Biology 5/E. fig. 20.4 p. 407 Peter H. Raven and George B. Johnson, the McGraw-Hill Companies, Inc.
Mutations & Genetic Variations - Outcomes
In regions where malaria is uncommon
Individuals with the sickle-cell allele are at a
disadvantage
Their phenotypes are less likely to contribute
alleles to the gene pool
In regions where malaria is common
Heterozygous individuals are at an
advantage
They are much more likely to survive and
pass on their genes to the next generation
Mutation and Evolution The environment selects the best-adapted phenotype and
favors a particular set of alleles
The sickle-cell allele is only common
where it provides an overall advantage to the individual
where it has an overall harmful effect, it does not persist
This pattern establishes an important relationship between mutations and evolution:
Harmful mutations occur frequently
but they are selected against
these mutant alleles remain extremely rare
Beneficial mutations are rare
but they are selected for
these mutant alleles accumulate over time
Sexual Selection
Sexual selection
Differential reproductive success that
results from variation in the ability to
obtain mates; results in sexual dimorphism
and mating and courtship behaviors
Sexual dimorphism
Striking differences in the physical
appearance of males and females not
usually applied to behavioral differences
between sexes
Sexual Selection
Individuals that mate and reproduce
frequently make a substantial contribution to
the gene pool of later generations
Sexual selection favors the selection of any
trait that influences the mating success of the
individual
The most common forms of sexual selection
result from female mate choice and from
male-versus-male competition
Sexual Selection
In some species, females choose mates based on physical traits, such as bright coloration, or behavioral traits, such as courtship displays and song
In other species, males are equipped with physical features that assist them in establishing control of and defending their territory against other males
This territory provides an area to which they can attract, and sometimes forcibly detain, the females with which they mate
Sexual Dimorphism - Advantage
Sexual
dimorphism
may take the
form of a
physical
advantage,
such as a much
larger size in
males, or an
enlarged limb,
as in fiddler
crabs
Sexual Dimorphism - Disadvantage
In some species of
penguin males and
females look so similar
that even they have a hard
time telling each other
apart
A male picks up a stone
and drops it at the feet of
a would be mate. If the
other penguin happens to
be a male, the gift is
firmly rejected
Sexual Selection - Detrimental
(a)
The mating game is risky for male tungara frogs. When calling for a mate in the dark, they run the risk of giving away their location to the deadly frog-eating bat.
What might change this situation?
Sexual Selection - Detrimental Sexual selection favors inherited traits that enhance
mating success but may reduce an Individual's chances of survival
Figure (a)
Avoiding predators is not made easier, for instance, by brilliant plumage or a distinctive song
Figure (b)
A bizarre extreme-sometimes called runaway selection
Although males and females both have eye stalks, females have preferentially mated with males with the longest eye stalks to the point where the feature has become very exaggerated
Cumulative Selection Evolution of a complex structure is a cumulative
process
Cumulative Selection
The accumulation of many small evolutionary changes over long periods of time and many generations, resulting in a significant new adaptation relative to the ancestral species
Adaptation
Any trait that increases an individual's ability to survive or reproduce compared to organisms that do not have the trait
Evolution of Complex Structures
Figure 1
The skin of this poison-
arrow frog produces
substances that are very
toxic. How might the
bright skin coloration of
such frogs have evolved?
Figure 3
The flamingo feeds on
tiny aquatic organisms
with its bill held in an
"Upside-down"
position. How might
this bill shape and
feeding pattern have
evolved?
Figure 2
Eyes positioned on the sides of
the head provide a wide field
of vision, more helpful for
detecting predators. This
primate has the trait of
forward-positioned eyes,
shared by humans, which
results in a very large blind
spot. How might forward
positioned eyes have evolved?
Evolution of Complex Structures
Rare beneficial mutations might have
occurred
Natural selection might have favored them
Adaptations produced accumulated one by
one
This slow process of cumulative selection
could have produced complex structures, such
as eyes, and continues to produce them
The Formation of New Species
Species
Members of groups or populations that
interbreed or have the ability to interbreed
with each other under natural conditions
Speciation
The formation of new species is a result of
the evolution of one or more reproductive
isolating mechanisms
The Formation of New Species
Reproductive Isolating Mechanisms
Any behavioral, structural, or biochemical
traits that prevent individuals of different
species from reproducing successfully
together
Geographic barriers are a cause of the
reproductive isolation of two populations
by allowing accumulation of differences in
mating systems
The Formation of New Species
Once two populations become reproductively
isolated, they no longer share mutations and
subsequent selection processes
Significant evolutionary changes that occur in
either population will result in differences
between the two gene pools, creating separate
species
Reproductive Isolating Mechanisms
Prezygotic mechanisms
Reproductive isolating mechanisms that
prevent interspecies mating and
fertilization
Ecological isolation,
Temporal isolation, and
Behavioral isolation
Prezygotic Mechanisms
Ecolological isolation Species that occupy separate habitats or separate niches of the same habitat do not encounter one another to reproduce (e.g. ground hogs in field & marmots in elevations)
Temporal isolation Similar plant species may bloom at different times of the day (e.g., day- and night-blooming cacti)
Behavioral isolation Each species may use different signals for attracting a mate. The mating behavior of male jumping spiders is an elaborate dance in which they shake their legs and wave their palps. Females of different species do not respond to the dance.
Reproductive Isolating Mechanisms
Postzygotic mechanisms
Reproductive isolating mechanisms that prevent maturation and reproduction in offspring from interspecies reproduction
Zygotic mortality
No fertilized zygotes or embryos develop to maturity
Hybrid inviability
Hybrid offspring are unlikely to live long
Hybrid infertility
Offspring of genetically dissimilar parents are likely to be strong but sterile. An example is ?
Modes of Speciation
Any series of events that results in the
reproductive isolation of two populations may
also lead to the formation of new species
Allopatric speciation
The evolution of populations into separate
species as a result of geographic isolation
Sympatric speciation
The evolution of populations within the
same geographic area into separate species
Allopatric Speciation
The Atlantic blue-
headed wrasse (a) and
the Pacific Cortez
rainbow wrasse (b) are
probably descendants of
a single species that
underwent allopatric
speciation after the
formation of the
Isthmus of Panama
separated the Atlantic
and Pacific oceans
(b)
Sympatric Speciation
Evidence strongly suggests that a number of species
of sticklebacks evolved by sympatric speciation
Question #1
Define speciation. Explain how the reproductive isolating mechanism affect speciation.
Speciation is the formation of new species as a result of the evolution of one or more reproductive isolating mechanisms
Reproductive Isolating Mechanisms
Any behavioral, structural, or biochemical traits that prevent individuals of different species from reproducing successfully together
Geographic barriers are a cause of the reproductive isolation of two populations by allowing accumulation of differences in mating systems
Once two populations become reproductively isolated, they no longer share mutations and subsequent selection processes
Significant evolutionary changes that occur in either population will result in differences between the two gene pools, creating separate species
Question #2 Define the following terms.
Genetic drift is a change in the genetic makeup of a population resulting from chance. Such changes are much more pronounced in small populations
Gene flow is the movement of alleles from one population to another through the movement of individuals or gamete
Genotype is the set of alleles possessed by an individual organism
Phenotype is the observable trait of an organism that result from interaction between genes and the environment