Transcript 5.54 MB - Human Evolution and Prehistory, Second Canadian Edition

Human Evolution
and PREHISTORY
Chapter Three:
BIOLOGY AND EVOLUTION
Link to the Canadian Association for Physical Anthropology
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Chapter Preview
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?
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PRIMATES
Our group of animals is so diverse because it
is a product of evolution
“Descent with modification”
(Charles Darwin)
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THE CLASSIFICATION OF
LIVING THINGS
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
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THE CLASSIFICATION OF
LIVING THINGS
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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THE CLASSIFICATION OF
LIVING THINGS
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
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THE CLASSIFICATION OF
LIVING THINGS
Characteristics used by
Linnaeus to classify:
1. Body structure
2. Body function
3. Sequence of bodily growth
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THE CLASSIFICATION OF
LIVING THINGS
Characteristics used by Modern Taxonomy:
1. Body structure, function and growth
2. Chemical reactions of blood, protein
structure, genetic material, parasite
comparison
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THE DISCOVERY OF EVOLUTION
Creationism
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
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THE DISCOVERY OF EVOLUTION
18th Century Influences
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
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THE DISCOVERY OF EVOLUTION
 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
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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
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Natural Selection
The evolutionary process through
which factors in the environment
exert pressure that favours some
individuals over others to produce
the next generation
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ORIGINAL STUDY
The Unsettling Nature of Variational Change
 Before Darwin evolution was seen as moving in predictable
fashion, and ultimately, to humans at the pinnacle
 Darwin introduced the idea of “undirected variation”, of
which only a selected portion was passed on to the next
generation
 The difficulty lies in seeing human evolution as
unpredictable and nonprogressive in nature
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HEREDITY
Gene
Portion of DNA
molecule containing
several base pairs that
directs the synthesis of
a protein, e.g. gene for
ABO blood type
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HEREDITY
Mendel
Law of Segregation
 Genes, or the units controlling
the expression of visible traits,
retain their separate identities
over generations
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HEREDITY
Mendel
Law of Independent Assortment
 Genes controlling different
traits are inherited
independently of one another
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HEREDITY
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
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HEREDITY
Genetic Code


Three-base sequence
(codon) of a gene that
specifies production of an
amino acid
Amino acids strung
together make a protein
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HEREDITY
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” (see Applied Box)
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HEREDITY
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
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HEREDITY
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
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HEREDITY
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
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HEREDITY
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
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HEREDITY
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
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HEREDITY
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
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POPULATION GENETICS
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
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POPULATION GENETICS
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
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The Hardy Weinberg Principle
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
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EVOLUTIONARY
FORCES
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
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NATURAL SELECTION
Evolutionary process through which the
environment exerts pressure that selects
some individuals over others to reproduce
1. Directional selection – a particular allele may be
favoured
2. Disruptive selection – individuals at both
extremes of the distribution are favoured
3. Stabilizing selection – populations are already
well adapted
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Adaptation and Sickle-cell Anemia
In malarial areas of the world selection favoured
heterozygous individuals (HbAHbS) because of an
increased ability to survive the effects of the malarial
parasite
Culture played an important role with respect to this
biological adaptation
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SPECIATION
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
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SPECIATION
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
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ISOLATING MECHANISMS
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
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Divergent or Branching Evolution
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
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Convergence
Two distant forms develop greater similarities
because their structures serve similar
functions, e.g. birds and bats
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NEXT TIME:
Monkeys, Apes, and Humans:
The Modern Primates
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