2. Evolution and Genetics
• What is evolution, and how does it occur?
• How does heredity work,
and how is it studied?
• What forces contribute
to genetic evolution?
3. Evolution
• Humans have uniquely varied
ways—cultural and biological—of
adapting to environmental stresses
• Many scholars became interested in
biological diversity and our position
within the classification of plants
and animals during the 18th century
4. Evolution
• Creationism: biological similarities and
differences originated at the Creation
• Linnaeus (1707–1778) developed
the first comprehensive and still
influential classification, or
taxonomy, of plants and animals
• He grouped life forms on the basis of
differences and similarities in physical
characteristics.
– Fossil discoveries during the 18th and 19th
centuries raised doubts about creationism
5. • If all life originated at the same
time, why aren’t ancient species
still around?
• Why weren’t contemporary plants
and animals found in fossil
records?
6. • Catastrophism: a modified
version of creationism that
accounts for the fossil record by
positing divinely authored
worldwide disasters that wiped
out creatures represented in the
fossil record.
7. Theory and Fact
• Evolution (descent with modification): an
alternative to creationism and
catastrophism was transformism
• Species arise from others through a long
and gradual process of transformation.
• Charles Darwin is the
best known of evolutionists
8. • Darwin influenced by 2 people:
– Grandfather, Erasmus Darwin, who
proclaimed a common ancestry of all animal
species
– Lyell’s principle of Uniformitarianism:
The present is the key to the past;
explanations for past events should be sought
in the long-term action of ordinary forces that
still operate today.
9. • Natural forces (rain, earthquakes, volcanic
eruptions) have gradually built and modified
geological features (such as mountain ranges).
• Cappadocia
10. – Uniformitarianism cast doubt on the
belief that the world was only 6000
years old. It would take much longer
for ordinary forces such as rain and
wind to produce major geological
changes.
– Theory of evolution
• Theory: a set of ideas formulated to
explain something
Darwin applied uniformitarianism and
long-term transformation to living
things and argued that all life forms are
related and the number of species
have increased over time.
11. • Natural selection: the process by which
the forms most suited to survive and
reproduce in a given environment do so in
greater numbers.
• More than survival of the fittest, natural
selection is differential reproductive
succes.
12. • When there’s a food shortage,
those with longer necks have
an advantage
• If this feeding
advantagepermits longer-necked
giraffes to survive and
reproduce more effectively,
then they will transmit more of
their genetic material to future
generations than will those with
shorter necks.
13. Evolution
• Physical development of the individual, not
species. (babies of weight lifters)
• Evolution works as the process of
natural selectiontakes advantage
of the variety that is already
present in a population.
14. Genetics
• Genetic science helps us understand the
causes of biological variation
– Mendelian genetics: studies the
ways in which chromosomes
transmit genes across generations
– Biochemical genetics: examines structure,
function, and changes in DNA
– Population genetics: investigates
natural selection and the causes of genetic
variation, stability, and change
15. Mendel’s experiments
• Austrian monk Gregor Mendel
began a series of experiments that
revealed the basic principle of
genetics in 1856
– Studied inheritance of seven
contrasting traits in pea plants
– Discovered that heredity is determined
by discrete particles or units
16. Mendel’s experiments
• Concluded that a dominant form
could mask another form in hybrid
individuals, without destroying the
recessive trait
• Basic genetic units Mendel described were
factors (now called genes or alleles) that
are located on chromosomes
17. Mendel’s experiments
• Chromosome: a paired length
of DNA, composed of multiple genes
• Gene: a place (locus) on a
chromosome that determines a
particular trait
• Allele: a variant to a particular gene
18. Mendel’s experiments
• Independent Assortment and Recombination
– Independent Assortment: chromosomes
are inherited independently of one another
– Recombination: the combination of genetic
traits in an offspring; this process creates new
types on which natural selection can operate
19. Biochemical, or Molecular,
Genetics
• Mutation: changes in the DNA
molecules of which genes and
chromosomes are built
• Gametes: sex cells that
make new generations
20. Biochemical, or Molecular,
Genetics
• DNA: initiates
and guides the construction of
hundreds of proteins necessary for
bodily growth, maintenance, and
repair.
21. Cell Division
• Mitosis: ordinary cell division, wherein
one cell splits to form two identical cells
• Meiosis: the special process by which sex
cells are produced
– Four cells
produced from one
– Each cell carries
half the genetic
material of the original
cell
– Fertilization allows the
products of meiosis
from one parent to
recombine with those
from the other parent
– Chromosomes
sort independently
22. Crossing Over
• Crossing over: the process wherein
homologous chromosomes exchange
segments by breakage and
recombination
– Can occur with any chromosome pair
– An important source of variety
23. Mutation
• Base substitution mutation: substitution of
one base in a triplet by another
– If mutation occurs in a sex cell, the new
organism will carry mutation in every cell
• Chromosomal rearrangement: pieces
of a chromosome break off and reattach
someplace else on that chromosome
24. Mutation
• Approximately three mutations will occur in
every sex cell
– Most mutations are neutral
– Evolution depends on mutations
– Variants produced through mutation
can be especially significant if there
is a change in environment
25. Population Genetics and
Mechanisms of Genetic Evolution
• Population genetics studies
stable and changing populations
– Gene pool: alleles and genotypes
within breeding population
– Genetic evolution: the change in allele
frequency in a breeding population
26. Natural Selection
• Genotype: the genetic makeup of an
organism
• Phenotype: an organism’s evident
biological traits
– Natural selection acts only on phenotypes
– Human biology has considerable plasticity
– The environment works on
a genotype to build a phenotype
27. 3 Different Ways of Natural
Selection
1.Directional Selection
2.Sexual Selection
3.Stabilizing Selection
28. Directional Selection
• After several generations of
selection, gene frequencies change
– Adaptive: favored by natural selection
– Directional selection continues as long
as environmental sources stay the same
– Humans do not have to delay adaptation until
a favorable mutation occurs
29. Sexual Selection
• Selection also operates
through competition for mates
• Sexual selection: based on
differential success in mating; a selection
of traits that enhances mating success
30. Stabilizing Selection
• Balanced
polymorphism: the
frequencies of two or
more alleles of a gene
remain constant from
generation to generation
31. Random Genetic Drift
• Random genetic drift: loss
of alleles from a population’s
gene pool through chance
– Lost alleles can reappear in the
gene pool only through mutation
– Fixation, the replacement, for example,
of blue eyes by brown eyes,
is more rapid in small populations
32. Gene Flow
• Gene flow: exchange of genetic material
between populations of the same species
– Alleles spread through gene flow even when
selection not operating on the allele
– Species: group of related organisms whose
members can interbreed to produce offspring
that live and reproduce
– Gene flow tends to prevent
speciation: the formation of new species
33. RECAP OF LAST CLASS
• In the 18th century, Carolus Linnaeus developed
biological taxonomy. He viewed similarities and
differences among organisms as part of God’s
orderly plan rather than as evidence for
evolution.
• Charles Darwin proposed that natural selection
could explain the origin of species, biological
diversity and similarities among related life
forms. Natural selection requires variety in the
population undergoing selection.
34. RECAP OF LAST CLASS
• Through breeding experiments with peas in 1856,
Gregor Mendel discovered that genetic traits
pass on as units which are known as
chromosomes. He also formulated the law of
independent assortment. Each of seven traits he
studied in peas was inherited independently of all
others. Independent assortment of chromosomes
and their recombination provide some of the
variety needed for natural selection. But the
major source for such variety is mutation, an
alteration in the DNA molecules of which genes
are made.
35. RECAP OF LAST CLASS
• Genetics studies structure, function and changes in
genetic material-DNA.
• Genetic changes that provide variety within a
population include base substitution mutations,
chromosomal rearrangements and genetic
recombination.
• Natural selection is the most important mechanism of
evolutionary change. Others include random genetic
drift and gene flow.
• Natural selection work for characteristics already
present in a population. If variety is insufficient for
adaptation to environmental change, extinction
happens.
36. The Modern Synthesis
• Currently accepted view of evolution:
– Microevolution: small-scale changes in
allele frequencies over just a few
generations
– Macroevolution: large-scale changes in
allele frequencies in a population
over a longer time period that result in the
formation of new species.
37. The Modern Synthesis
• Punctuated equilibrium: long
periods of stasis may be
interrupted by evolutionary leaps
– Sudden environmental change
offers possibility for the pace of
evolutions to speed up
– Although species can survive
radical environmental shifts,
extinction is more common
38. Extinctions of Earth
• The earth has witnessed several mass
extinctions.
• The biggest one Palezoic Period to
Masezoic Period
245 million years ago
5 million species on earth 4.5 m. species died
39. Extinctions of Earth
• The second biggest extinction
– 65 million years ago
– Extinction of dinasours
– One explanation: long-lasting cloud of gas and
dust arose from the impact of a giant meteorite at
the end of the mesozoic period. The cloud blocked
solar radiation and photosynthesis, ultimately
destroying more plants and the chain of animals
that fed on them.
