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Chapter Three:
BIOLOGY AND EVOLUTION
Link to the Canadian Association for Physical Anthropology
What Forces Are Responsible For The
Diversity Of Primates In The World
Today?
What Is Evolution? How Does Evolution
Produce New Forms of Organisms?
What Are The Forces Responsible For
Evolution?
Our group of animals is so diverse because it is a
product of evolution
“Descent with modification”
(Charles Darwin)
Linnaeaus classified living things:


as a way of creating order and naming the
plants and animals to the glory of God’s
creation
on the basis of overall similarities in small
groups, or species
Modern classification



distinguishes superficial similarities
(analogies) from basic ones (homologies)
homologous structures are possessed by
organisms that share a common ancestry
analogous structures may look similar and may
serve the same purpose, but do not arise in
similar fashion from a common ancestor
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
Bird and bat wings are analogous — that is, they have
separate evolutionary origins, but are superficially
similar because they evolved to serve the same
function. Analogies are the result of convergent
evolution.
Interestingly, though bird and bat wings are analogous
as wings, as forelimbs they are homologous. Birds and
bats did not inherit wings from a common ancestor
with wings, but they did inherit forelimbs from a
common ancestor with forelimbs.
On the basis of homologies, as in Linnaeus’
system groups of like species are organized
into larger groups, genera (singular, genus)
Species

Population or group of populations capable of
interbreeding but that is reproductively
isolated from other such populations
Characteristics used
by
Linnaeus to classify:
1.
2.
3.
Body structure
Body function
Sequence of
bodily
growth
Characteristics used by Modern Taxonomy:
1.
2.
Body structure, function and growth
Chemical reactions of blood, protein
structure, genetic material, parasite
comparison
In Linnaeus’ time species were thought to be
unchangeable since the time of creation
Today creationism is supported by fundamentalist
Christian groups like the Creation Research
Society (CRS)
Creationism is based on a belief system rather than
on scientific evidence
Lamarck – species can change
Cuvier – different sedimentary layers held
different types of fossils, consistent with
existing 18th century view called
catastrophism (evidence of new acts of divine
creation)
Lyell – gradual process shaped the earth over a
long period of time and are no different
today, uniformitarianism



By the 19th century many naturalists had
come to accept the idea that life had
evolved
Charles Darwin and Alfred Russell
Wallace independently discovered how
evolution works
Their idea was natural selection
Darwin and Wallace based their idea on two
observations:
1.
All organisms display a range of variation
2. All organisms have the ability to expand
beyond their means of subsistence
The evolutionary process through
which factors in the environment
exert pressure that favours some
individuals over others to
produce the next generation

“I am, and shall ever remain in a hopeless
muddle,” Darwin wrote to Asa Gray (a friend)
in November of 1860. “I cannot think that the
world, as we see it, is the result of chance, and
yet I cannot look at each separate thing as the
result of design.”

…Chance…
…Design…
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First…genetic diversity. Thanks to the random sorting
out of traits inherited by offspring from their parents,
no two individuals (except identical twins) are alike.
Second…the ultimate source of variation is genetic
mutation. The genetic material, the DNA molecule, is
intrinsically vulnerable, due to its structure. Here,
spontaneous changes occur frequently. They are
random. Most are harmful.
Due to the fact that there is variation to select
from, an individual with a particular trait may
be better able to survive and pass on its genetic
heritage to its offspring.
The trait allows them to cope with change in their
environment better than others of their species.
So…
The environment has the power to design its
eventual occupants.
The size, shape, behavioral features, anatomical devices,
and even intelligence, of all animals, are dictated by the
interaction of the species with the environment.
V= Variation. All life forms vary genetically within a population. It is
the genetic variation upon which selection works.
I = Inheritance. Genetic traits are inherited from parents and are
passed on to offspring.
S = Selection. Organisms with traits that are favorable to their
survival have a chance to live and pass on their genes to the next
generation.
T = Time. Evolution takes time. Evolution can happen in a few
generations, but major change, such as speciation, often takes long
periods of time.
Gene
Portion of DNA
molecule containing
several base pairs that
directs the synthesis of
a protein, e.g. gene for
ABO blood type
Mendel
Law of Segregation

Genes, or the units controlling the
expression of visible traits, retain
their separate identities over
generations
Mendel
Law of Independent Assortment

Genes controlling different traits
are inherited independently of
one another
DNA -- A complex molecule
with information to direct the
synthesis of proteins and the
ability to produce an exact
copy of itself
RNA – carries instructions from
DNA to make amino acids
Genetic Code


Three-base sequence
(codon) of a gene that
specifies production of an
amino acid
Amino acids strung together
make a protein
Genome
The complete sequence of DNA for a species
Human Genome
3 billion chemical bases, with 30,000 functioning
genes
30,000 genes account for 1-1.5% of the human
genome
The rest is non-coding “junk DNA”
Two types of genes are responsible for what
organisms actually become:
Structural genes – contribute directly to actual
formation of the structure, e.g. eye colour
Regulatory genes – control expression or activity of
other genes, e.g. homeobox genes control
whether an organism has fins or legs
Chromosomes
Long strands of DNA in
a protein matrix
23 pairs in humans
Each chromosome in the
pair contains genes for
the same traits, e.g. gene
for A-B-O blood group
Variant forms of these
genes are called alleles,
e.g. A, B and O
Mitosis
Cell division that produces
new cells having exactly the
same number of chromosome pairs, and
hence, genes as the parent cells
Meiosis
Cell division that produces the sex cells, each of which has
half the number of chromosomes, and hence genes, as the
parent cell
Homozygous
Refers to a chromosome pair that bears identical
alleles for a single gene, e.g. each of the pair has an A
allele
Heterozygous
Refers to a chromosome pair that bears different
alleles for a single gene, e.g. one chromosome has A
allele, one has O allele
Genotype
actual genetic makeup of an organism, e.g. AA or AO
Law of dominance and recessiveness
Certain alleles are able to mask the presence of
others; one allele is dominant, the other is
recessive
Phenotype
The physical appearance of an organism; may or
may not include recessive alleles
Polygenetic inheritance
Two or more genes (as opposed to just two
or more alleles) work together to produce
one particular phenotype, e.g. skin colour,
stature
Concept of the population
A group of individuals within which breeding
takes place
It is within the population that natural
selection takes place, and at this level that
evolutionary change occurs
The stability of the population
In theory, the gene pool of a population
should remain the same generation after
generation, i.e. the alleles should occur in the
same frequency
Gene pool
The genetic variants available to a population
The percentage of individuals that are
homozygous dominant, homozygous recessive,
and heterozygous will remain the same from one
generation to the next provided certain
conditions are met:
Random mating
Large population
No new variants
Equal survival and reproductive success
Sources of change:
1.
Mutation – chance alteration that produces a new gene
2.
Genetic drift – chance fluctuations of allele
frequencies in the gene pool
3.
Gene flow – introduction of new alleles from nearby
populations
4.
Interspecies gene transfer – transfer of DNA between
species
5.
Natural selection – adaptation
Evolutionary process through which the
environment exerts pressure that selects some
individuals over others to reproduce
1.
2.
3.
Directional selection – a particular allele may
be favoured
Disruptive selection – individuals at both
extremes of the distribution are favoured
Stabilizing selection – populations are already
well adapted
Gradualism
if isolated over a long period of time, species
evolve from subspecies (or races) through
accumulation of genetic differences
races – in biology, populations within a species
that are capable of interbreeding but may not
regularly do so
**this concept has no biological validity in humans; races
are merely social categories
Punctuated Evolution


new species appear quickly, in geological
terms, and this dramatic change lasts for a
long time with little significant change
rapid appearance of novelty likely due to
involvement of homeobox genes
Factors that separate breeding populations,
leading to the appearance first of divergent
races and then divergent species
Isolating factors:
Geographical
Anatomical structure
Early miscarriage of offspring
Early death of offspring due to
weakness/maladaptation
Sterility of hybrid offspring
Genetic
Social
Isolation may cause a single
ancestral species to give rise to
two or more descendant species
This divergent evolution is
probably responsible for much
of the diversity of life today
Two distant forms develop greater similarities
because their structures serve similar functions,
e.g. birds and bats
Monkeys, Apes, and Humans:
The Modern Primates