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PHYSICAL ANTHROPOLOGY 2301 SECTIONS 1-3
TEST 1 SECTIONS
BIOLOGICAL ANTHROPOLOGY AND EVOLUTION? (SECTION 1)—What is?
(Biology and Culture, Variation, Evolution, Adaptation, subfields), Science
and
Evolution (Characteristics, theory, evidence for, science and religion
(almost 2
chapters in length)
HUMAN GENETICS (SECTION 2)—molecular genetics, Mendelian genetics,
Mutations
EVOLUTIONARY FORCES (SECTION 3)—Population genetics, evolutionary forces
THE ORIGIN AND EVOLUTION OF SPECIES (SECTION 4)—the birth and death
of species, misconceptions about evolution, a brief history of life
THE STUDY OF HUMAN VARIATION (SECTION 5)—measuring human variation,
the racial approach to variation, the evolutionary approach to variation
HUMAN ADAPTATION (SECTION 6)—types of adaptation, climate and human
adaptation, high-altitude adaptation, nutritional adaptation
THE HUMAN SPECIES (SECTION 7)—characteristics of living humans, the human
life cycle, is human behavior unique?
THE BIOLOGY AND BEHAVIOR OF LIVING PRIMATES (SECTION 8)—a
discussion on the biology of primates
HOMINID ORIGINS (SECTION 9)—the first hominids, evolutionary trends
THE EVOLUTION OF GENUS HOMO (SECTION 10)—the origin of genus homo,
homo erectus, archaic humans
THE ORIGIN OF MODERN HUMANS (SECTION 11)—anatomically modern homo
sapiens, recent biological and cultural evolution of homo sapiens
HUMAN BIOLOGY AND CULTURE CHANGE (SECTION 12)—The biological impact
of agriculture, the biological impact of civilization, recent changes
HCC Physical Anthropology (2301) Lecture
BIOLOGICAL ANTHROPOLOGY AND EVOLUTION--Section 1
I.
Definitions and Origins of Anthropology
A) Definitions
1. It comes from the Greek words Anthropos-human and logos-the study
of
2. Kottak (text) Anthropology is the study of the human species. It is the
exploration of human diversity in time and space. Also it is the study
of the human species and its immediate ancestors
3. Heider-Anthropology is the study of the cultural and biological
variations among human groups
a)
The term “culture” is defined by Kottak (5) as “traditions and
customs transmitted through learning, that govern the beliefs
and behavior of the people exposed to them.”
b)
It should be noted that this definition of culture does not
appear to be used extensively in Britain where the definition of
“culture” is generally used to denote elite practices generally
associated with the arts or music.
c)
Children learn their culture through interaction with members of
their society in a process that is called enculturation.
4. Webster’s Dictionary-Anthropology is the science which studies man
both as an animal and as living in society, his origins, development,
distribution, social habits, culture etc.
a)
This definition would be seen as a lesser definition because it is
not given by
someone of an academic background (lower in the hierarchy of
information)
b)
“hierarchy of information” refers to the quality of information
given through
various sources. Example: the internet (there are exceptions)
is usually not as good a source as a newspaper. The
newspaper is not as good a source as material in an academic
journal or academic text (due to “academic review”).
5. Relethford (5) expands upon these definitions when he suggests that
humans are biocultural constructs or the idea that humans are not
solely cultural or solely biological
a)
This biocultural idea is the main theme of his text
b)
It should be noted that even the idea of supposedly “pure”
cultural traits can be seen by some (sociobiologists) as
determined by biological conditions
1)
Unfortunately, this can lead to racial assumptions such
as the idea that one ethnic group has a higher I.Q. than
another (The Bell Curve)
2)
These racial ideas are dispelled through the designers of
the tests backgrounds, the testing material itself, the
idea that I.Q. can be different in different areas etc.
6. There are actually many definitions of anthropology with many
different shades of meaning
7. There is a tendency by anthropologists to define the term
“anthropology” in order to provoke new modes of thought and to fulfill
the “publish or perish” mentality when other issues cannot be
examined
II.
III.
8. In postmodernism, it is argued that a word can be defined in so many
different ways that it loses its meaning. Despite the multitude of
definitions this does not seem to be the case with Anthropology.
B) Origins of Anthropology--it’s all in the definition
1. It could be argued that if Anthropology is the “study of culture”
(whether one’s own or another’s) that as soon as “culture” developed
people began to think about it and were, therefore, “doing”
anthropology.
2. There are a few that might argue that Anthropology began with
Aristotle in the 4th century B.C. (or even earlier)
3. Some view the Enlightenment as the period of origin for anthropology
a)
The Enlightenment may have been rooted in the expansion of
European trade during the 1500s as Europeans (merchants,
seamen and the military) became exposed to new cultures.
The main increase in knowledge came when Europeans settled
in foreign lands and published their findings (popular reading in
the 1600s) prompting new inquiry into foreign “culture.”
b)
Revolutions in scientific thought began in the (earlier) Baroque
Age (1600-1715) an era of development referred to as the
Scientific Revolution. Many of the developments of this era
were in astronomy and physics
c)
Giambattista Vico a philosopher in cultural history and law
during the late 1600s and 1700s is seen as “the forerunner of
anthropology and ethnology.”
d)
The Enlightenment began in the 1700s in Europe. The
individuals of this period began to reject “superstition” and
“religion” and to view the world through a secular, human
centered perspective.
e)
The origins of anthropology lie in the areas of culture history
and philosophy both of which were examined during this period
f)
The development of Biological/Physical Anthropology will be
discussed later
The Nature of Anthropology
A) The fundamentals
1. Kottak and others suggest that the root of Anthropology is “holism”
which is defined as (Kottak pg. 3) “the study of the whole human
condition: past, present, and future; biology, society, language and
culture”
2. Heider notes that Anthropologists are “generalists” who despite doing
research on specialized problems end up studying a greater span of
subjects than those in “any other department”
3. It should be noted that these ideas are ideals and that as always
actual practice of these ideals can vary (Doug Holmes story)
General Anthropology and the 4 subfields
A)
Johnston and Selby offer an organizational chart for the field of
Anthropology
B)
General anthropology refers to all of anthropology taken together and
is inclusive of the four subfields.
1. In general it can be noted that the U.S. generally has 3 main subfields
of Anthropology, which are 1. Cultural or social, 2. Archaeology and 3.
Biological or physical. Some Universities add a fourth called linguistic.
2. This fourfold typology does not exist in Europe where the disciplines
exist separately.
3. Sometimes different names are given to the individual subfields and
your text notes a combination of social/cultural anthropology as
“sociocultural anthropology”
4. Kottak notes that the unity of the 4 fields in American anthropology is
based on the idea that “each subfield considers variation in time and
space (geography),” therefore, in order to pursue a holistic approach
these fields need to be studied together
C)
Cultural Anthropology
1. Cultural Anthropology according to Kottak (10) is “the study of human
society and culture…(it) it describes analyzes, interprets, and explains
social and cultural similarities and differences. Heider notes that it
studies peoples of the present i.e. living today.
2. Some subfields of Cultural Anthropology are:
a) Urban Anthropology that usually deals with inner cities
b) Economic Anthropology—factors that affect the distribution of goods
within and between cities
c) Medical Anthropology—the relations between cultural attributes and
health and disease
d) Social Anthropology—usually associated with British scholars—
refers to studies that examine social organization especially in areas
that are that are heavily influenced by kinship relations.
3. 2 types of examination
a) Ethnography—provides an examination of a “particular community,
society, or culture” (Kottak 10) and usually involves fieldwork
involving a firsthand immersion into the culture of examination.
1 Many ethnographers use the ethnographic present which places
subjects at an imaginary moment in time when the community
is presumably in isolation from outside contact. However, few if
any cultures are ever in isolation. {Anasazi and Aztec or
Mississippian story if time}. Cultures also change over time
{discuss popular music and do belt buckles}
b) Ethnology—its goal is to compare and contrast or “make
generalizations about society and culture.” (Kottak 10) This
comparison and contrast is usually referred to as cross-cultural
studies.
D)
Archaeological Anthropology
1. Modern Archaeology has its origins in 19th century Europe
2. Archaeology according to Kottak (10) reconstructs, describes, and
interprets past human behavior and cultural patterns through material
remains.
3. 3 Goals of Archaelogy (in terms of prehistory—before written history)
are:
a) establishing chronology
b) reconstructing and describing ancient lifeways
c) explaining culture change
4. Early archaeologists often damaged sites where they were working and
filled museums with artifacts
a) One of the largest Egyptian Museums in the world is in Turin, Italy
(not Egypt).
b) Some nations are now speaking to Western museums about
recovering their heritage.
5. One of the first individuals to have a controlled dig was Thomas
Jefferson.
a) He opened a native American burial mound and tried to learn how
and why the mound was constructed
6. Even today, as an archaeological site is “dug” it is destroyed and some
archaeologists now leave sections of sites “undug” to allow for
improvements in technology (i.e. better digging techniques. {discuss
pick-ax archaeology}
7. The main raw data for archaeology involves material culture or artifacts
a) These are items that are made by people such as tools, houses,
pottery etc. that are excavated, described and analyzed in order to
learn about the past.
b) Early archaeologists generally focused on tools, buildings and other
artifacts.
c) Today, artifacts are used to reconstruct the culture and lives of the
people who designed and used them.
8. Archaeologists can join with other professionals such as geologists, soil
scientists and palynologists (study pollen) to determine the actual
environment during earlier periods of time.
9. In archaeology, what is often the richest areas in trying to explain how
people live is the midden or in plain English the trash heap.
a) The trash often yields potsherds, broken tools, food remnants and
animal bones.
b) William Rathje and his students examined trash cans in modern
Tucson, Arizona and found people were wasting “good food”
showing what people actually did as opposed to what they thought
they did or should have done. This examination of trash led to the
word “garbology” being coined.
10. Subfields of Archaeology
a) Archaeobotany—ancient plants
b) Archaeozoology—ancient animals
c) Experimental Archaeology—replicate ancient processes under
controlled conditions (flint knapping-film?)
d) Historical Archaeology—deals with the period after written records
are started
e) Classical Archaeology—deals with the literate old world
(exampleEgyptology)
f) Biblical Archaeology—deals with what happened in the Bible
g) Underwater Archaeology—deals with shipwrecks
h) Contract Archaeology—deals with the evaluation of sites that may
be damaged by construction
i) Some Archaeologists even blend with Paleontology (the study of
fossils) to look for early hominids forming a field known as
Paleoanthropology.
E)
Biological/Physical Anthropology
1. Biological/Physical Anthropology arose during the 19th century from 2
areas
a) increasing interest in the mechanisms for human origins (doubt of
the Biblical explanation)
b) observable physical differences or “race”
c) In the early 1900s the field was referred to as Physical
Anthropology, but after the 1950s it became increasingly thought
of in terms of biology, hence the phrase biological anthropology
d) Today, this subfield deals largely with human variation due to
adaptation to an environment
2.
3.
4.
5.
6.
7.
8.
Kottak (24) defines this field as “the study of human biological
variation in time and space; includes evolution, genetics, growth and
development and primatology.”
Heider offers a more simplistic definition for this field: “it focuses on
the human body including its physiology (especially its skeleton) its
diseases and other traumas” and can be used to study both the living
and deceased
Relethford (9) sees biological anthropology as focusing on the
evolution of humans and the relationships of humans to other
organisms and patterns of variation within and among human
populations
A key phrase in biological anthropology is descriptive morphology
which deals with the measuring of bones and noting of anomalies
Kottak notes 5 special interests within biological anthropology (14)
a) Human evolution as revealed by the fossil record
(Paleoanthropology can also be classified in this area as well).
b) Human genetics
c) Human growth and development
d) Human biological plasticity (the body’s ability to change as it copes
with stresses, such as heat cold and altitude).
e) The biology, evolution, behavior, and social life of monkeys, apes
and other nonhuman primates (primatology)
Relethford sees biological anthropology in terms of 4 main questions
a) What are humans? (how are we related to other creatures, who are
our closest relatives, what makes us similar to other creatures,
how are we unique)
b) What is the fossil record for human evolution? (where have we
come from, what does the history of our species look like
c) How are humans around the world like or unlike each other? (what
causes the patterns of human variation that we see)
d) How does culture affect biology, and vice versa? (what impact have
rapid cultural changes in our species recent past had on our
biology, do our biological and cultural changes mesh or are they
out of synch)
Concerns within biological/physical anthropology
a) Variations are differences among individuals or populations
(Relethford) measured in terms of both biology and culture
1) A comparative approach is used by anthropologists to
generalize about behaviors and biology that are similar or
different
b) Evolution involves changes in living organisms over time
(Relethford) [general changes]
1) Webster’s dictionary suggests that evolution is a movement
from simpler to more complex forms [directional] not always!
2) Turnbaugh and others suggest that evolution is “a change in
the genetic structure of a population from one generation to the
next” [genetics] (522)
3) Turnbaugh and others also suggest that the term “is also
frequently used to refer to the appearance of a new species”
(522) [creation of species—surpassing genetic changes]
c) Adaptation is seen by Relethford as “the process of successful
interaction between a population and an environment (involving)
9.
F)
1.
2.
3.
4.
5.
6.
7.
8.
G)
1.
2.
3.
H)
1.
2.
3.
4.
cultural or biological traits that offer an advantage in a given
environment” (473)
Subfields of Biological/Physical Anthropology (not previously
mentioned)
a) Primatepaleontology—examines primate fossil remains
b) Osteology—study of the skeleton
c) Forensic Anthropology—the use of anthropological techniques to
identify skeletal remains after a disaster or if a body is found (law
enforcement). These anthropologists identified the dead Branch
Davidians and Bosnians.
Linguistic Anthropology
Kottak (15) claims that “linguistic anthropology studies language in its
social and cultural context, across space and over time”
Heider’s definition is simpler and states that the subfield “analyzes
languages and the ways in which people use them.
In the 1800s and early 1900s anthropological linguists focused on
descriptive linguistics where many languages were recorded and
dictionaries were created
Comparative linguistics started in 1785 with the realization that the
Sanskrit language (an ancient “Indian” language) was related to both
Greek and Latin.
Comparative linguistics searches for the relationships between
languages and defines major language families such as Indo-European
An important aspect of language is that it both shapes and is shaped by
individual cultures
A second issue is that no language is completely homogeneous where
all people speak the same (dialects, accents, and the bilingual nature of
some ethnic groups.
Subfields of Linguistic Anthropology
a) Historical linguistics—examines changes in languages over time
b) Sociolinguistics—examines “the relationships between social and
linguistic variation.” (Kottak 15)
Applied Anthropology
Applied Anthropology can be considered the fifth subfield for
Anthropology despite the notion that it draws from the other 4 subfields
Applied Anthropology is a second dimension to Anthropology when
compared to academic anthropology.
Kottak (16) defines Applied Anthropology as referring “to the
application of anthropological data, perspectives, theory, and methods
to identify, assess, and solve contemporary social problems
Science basics
Kornblum (679) notes that science can be defined as “knowledge
obtained as a result of developing and testing hypotheses.
Hypotheses are suggested explanations of things and events
Relethford (13) argues that to be scientific a hypothesis must be
testable and that a potential rejection of the hypothesis is possible
Kornblum (679) defines the scientific method as “the process by which
theories and explanations are constructed through repeated
observation and careful description”
Kottak sees the key to science and understanding as “explaining” or
showing “how and why the thing to be understood is related to other
things in some known way.” (22)
5.
Kottak believes that explanations rely on theories and associations.
Associations are observed relationships between two or more
variables, while theories are more general and suggest or imply
associations and attempt to explain them
6. In the social sciences, associations are often stated in terms of
probabilities or the idea that 2 or more variables “tend to be related in
a predictable way” but exceptions do occur.
7. Science is often described in terms of cause and effect. In the social
sciences often what is being dealt with is a correlation. Correlation is
defined by Kottak as “an association between two or more variables
such that when one changes (varies) the other also changes (covaries)
8. The main way to evaluate theories is through falsification or showing a
theory to be wrong
9. Relethford also mentions “facts,” but his idea as expressed in the text
is a bit misleading
a) He claims that a fact is simply a verifiable truth
b) In a Cartesian (Rene Des Cartes) sense one could argue that
whenever we view an event we are trusting our senses and our
senses can be deceived
1) an example would be a mirage in a desert appearing to be
water
c) The resolution to this issue is that we should trust our senses
because they are the only tools (they can be modified, but at a
basic level) we have for viewing the world
1) it could be argued that an infinitely or almost infinitely
occurring deception of the senses is a “fact” in a subjective
sense (as opposed to an objective sense)
d) A “fact” then becomes something our senses perceive to be true
but, might not necessarily be true in an absolutist sense
e) A second issue is identity
1) The skull pictured on page 13 is perceived as a skull by those
with proper visual acuity (it may be described in other words in
other languages, but it is the same object). This is an identity
or naming of something perceived by the senses.
f) In terms of evolution, there is very strong almost irrefutable
evidence that changes have occurred in organisms through one
agency or another and can be accepted as a “fact” (alterations in
the next generation)
g) What is not a “fact” is the connection between the 5 toed horse, 3
toed horse and the modern one toed horse
h) There may be extremely strong evidence for this connection, but at
every stage of the evolutionary journey there is a potential for
error called “percent error.” (DNA and 99% accuracy…1 in 100
prisoners will be falsely convicted) Therefore, evolution in this
sense is a theory and not a fact.
I)
The Development of Evolutionary theory
1. Antecedents of Evolution
a) Ervin Laszlo, in his text Evolution the Grand Synthesis, suggests
that fundamentally similar ideas (evolution) have shaped thought
in human civilizations (11-13)
b) He sees Taoism in Asia and the Ionian (Greek) natural philosophers
as some of the antecedents of the paradigm of evolutionary theory
1) The Yin-Yang school of Chinese philosophy (in the Confucian
Universe) suggests that things are related to each other and
that reality is a process of constant transformation—a dynamic
worldview (W.-S. Chan 246)
a. Wing-Tsit Chan suggests that the origin of this idea
stretches back into “antiquity” and that obscurity surrounds
its origins (245)
2) In terms of Taoism, Chuang Tzu (btwn. 399-295 B.C.)suggests
that reality is ever changing and developing from the simple to
the complex (W.-S. Chan 204)
a. A partly paraphrased (some names of animals removed)
statement from Chuang Tzu: “All species have originative or
moving power (chi). When they obtain water, they become
small organisms like silk. In a place bordering water and
land they become lichens. Thriving on the bank they
become moss. On fertile soil they become weeds. The
roots of these weeds become worms, and their leaves
become butterflies. Suddenly the butterfly is transformed
into an insect…. After a thousand days…(the insect)
becomes a bird. The spittle of the bird becomes a different
kind of insect. This new insect becomes a wine fly that
produces still another kind of insect. (skipped section) The
plant yang-hsi paired with the bamboo which for a long time
has no shoot, produces an insect called ch’ing-ning
(different from the earlier ones). This new insect produces
a new insect called ch’eng, ch’eng produces the horse, and
the horse produces men. Man again goes back to the
regenerative process of nature. (W.-S. Chan 204
Sourcebook in Chinese philosophy)
3) In the 6th century (circa 580) B.C., Thales taught that all things
in the world originate from a common source, which he
identified as water
4) Heraclitus—the spelling of the name varies--(circa 540-480
B.C.) placed stress on eternal becoming and suggested that
“change is all” (one cannot step in the same river twice)
5) This dynamic model was subsumed during the Middle Ages
when the predominant component of the European world view
was stasis (Turnbaugh etc. 26)
a. Stasis refers to the idea that all aspects of nature inclusive
of all forms of life and their relationships to each other were
seen as fixed and unchanging (shaped by feudalism
b. Fixity of species rooted in the teachings of Christianity was
also present during this era and was a belief that God
created things and that they were immutable
A) Animals, humans etc. were also arranged hierarchically
(humans at the top) into The Great Chain of Being
6) Few if any changes occurred in the stasis paradigm until the
separation of science and church dogma began in the
Renaissance period in the 15th century (1400s) i.e. stress on
experiment rather than dogma
2. Pre-Darwinian thought (European)
a) John Ray—(1627-1705) This Englishman was the first to note that
groups of plants and animals could be distinguished from other
b)
c)
d)
e)
groups “by their ability to reproduce with one another and produce
offspring” (Turnbaugh etc. 28)
1) Reproductively isolated organisms were placed into a single
category called a species
a. Relethford defines a species as a group of populations
whose members can interbreed naturally and produce fertile
offspring (482)
2) He also developed a second level of classification called genus
a. Relethford defines a genus as “groups of species with
similar adaptations” (476)
Karl von Linne or Carolus Linnaeus (1707-1778) This Swedish
naturalist is known for his development of a classification system
for plants and animals
1) He standardized Ray’s system into what is known today as
binomial nomenclature or “two names” referring to genus and
species ex. Homo Sapiens
2) Linnaeus added two more categories of class and order and this
fourfold system became the basis for taxonomy (branch of
science concerned with classifying organisms) or the system of
classification still used today
3) Marks (6) suggests that Linnaeus is usually known for his
classification system, but that his key contribution is that he
found a different structure than the one suggested by the Great
Chain of Being
a. Essentially his system disrupted the vertical idea of a
hierarchy of species by introducing a horizontal perspective
(species are under genus, but of equivalent value)
b. An example would be the idea that man’s species is no
different than that of the sea slug
Comte de Buffon or Georges Louis LeClerc (1707-1788) This
Frenchman believed that when groups migrated to new areas of
the world the group would be influenced by climatic conditions and
would gradually change through adaptation to the environment
(Turnbaugh etc. 29)
1) However, Comte de Buffon (Linnaeus’ opposition) did not
believe in categories higher than species and was a believer in
the Great Chain of Being
Erasmus Darwin (1731-1802) This was Charles Darwin’s
grandfather who had expressed similar ideas on natural selection
and had commented on evolution
1) It is known that Darwin read and was fond of his grandfather’s
writings, but the extent of influence on his own theories is
unknown
Jean-Baptiste Lamarck (1744-1829) was the first to organize his
beliefs into a system designed to explain the evolutionary process
1) Marks notes that Lamarck denied taxonomic categories
maintaining that they were artificial and denied that species
were actual groups (11)
2) However, Lamarck did recognize some branching (not fully
linear like the Great Chain of Being)
3) His main contribution is the idea that through the exercise of
will an animal might improve its physical characteristics during
its lifetime and then pass on these improvements to its
offspring (Jolly and Plog)
4) He ultimately saw evolution as synonymous with progress and
saw progress as linear
f) Georges Cuvier (1769-1832) He was a paleontologist and opponent
of Lamarck who postulated a series of creations and worldwide
cataclysmic extinctions
1) He explained the strata and strange fossils (remains of dead
organisms) being found during his era as reflecting God
wrought catastrophes such as the Biblical flood
a. fossils are the remains of creatures that lived and died and
were buried in sediment (these are bones and shells and
remains of plants entombed in solid rock) that later
solidified into rock
2) Cuvier’s idea of God wrought catastrophes is known as
Catastrophism i.e. the geological landscape is created through
violent cataclysmic events
3) In his view, God was seen as recreating life again that differed
or was similar to the destroyed forms
4) Sometimes only one region was destroyed and life forms
merely migrated there from other areas instead of being
created
g) Charles Lyell (1797-1875) is considered the father of modern
geology and developer of a theory initially proposed by James
Hutton in the late 1700s known as uniformitarianism
1) Uniformitarianism is the theory that the earth’s features are the
result of long-term processes that continue to operate in the
present as they did in the past (it opposed catastrophism)
(Turnbaugh etc. 31)
h) Thomas Malthus (1766-1834) Wrote the text An Essay on the
Principle of Population that inspired Charles Darwin and Alfred
Wallace to their separate discoveries of the idea of natural
selection
1) This essay suggested that without limited food supplies a
human population could double in 25 years
2) Malthus claims that life can be seen as a “struggle for
existence” (Johnston and Selby 78) or a competition for food
resources (adapt or fail)
3. Darwin & Wallace
a) Charles Darwin (1809-1882) clarified the theory of evolution or
more precisely the theory of “transmutation”
1) Transmutation is the change of one species into another and it
should be noted that the theory of evolution did not gain its
current meaning until the late 1800s
b) Darwin was initially a student of theology at Cambridge, but
became interested in natural science and geology.
c) After graduation he was recommended to accompany a scientific
expedition aboard the H.M.S. Beagle that began on December 17,
1831
d) The ship traveled down the Atlantic Coast of South America,
through the Straits of Magellan and up the Pacific Coast visiting to
the interior of the continent and exploring the fossil beds (Helena
Curtis Biology 6-7)
e) The most interesting stop was the Galapagos islands (Galapagos is
Spanish for tortoise) off the coast of Ecuador
1) Darwin discovered there a group of finchlike birds comprising
13 species in all that differed in the sizes and shapes of their
bodies and beaks
2) Darwin also collected finches from the mainland and these
groups seemed to represent one group or species
3) He did not make the connection that the finches on the
Galapagos Islands had descended from a common mainland
ancestor until he had returned to England (October 1836)
f) Darwin initially began to develop his views on what he termed
natural selection just after 1836 (Turnbaugh etc. 33-34)
1) Natural selection from his perspective refers to an idea
borrowed from animal breeders who “select” as breeding stock
those traits they hope to emphasize (
2) Animals deemed unworthy are selected against or not allowed
to breed
g) In 1838, Darwin read Thomas Malthus’ essay and realized how new
species could be created
1) This idea was that population size is checked by food resources
and Lyell’s idea of the survival of the fittest
2) Essentially, favorable variations in this struggle are preserved
while unfavorable ones would be destroyed eventually leading
to new species
3) Restated this theory suggests that environmental conditions are
the key forces operating on individuals in the creation of new
species (Curtis 9, 11)
h) The Origin of Species started in 1856 and published in 1859 was
the product of in Darwin’s own words “one long argument”
spanning a period of over 20 years (Curtis, Biology 11)
1) Some suggest that the 20 year lag was due to concerns about
public perception and its influence on his family (Turnbaugh
and others)
2) However, after 1836 Darwin had a chronic illness that troubled
him for the rest of his life characterized by vomiting, pain and
nausea (Johnston and Selby)
a. There have been different explanations for this malaise, but
one of the most interesting is advanced by psychiatrist Dr.
Ralph Colp who suggests that it was a psychosomatic illness
brought on by stress
i) Alfred Russel Wallace (1823-1913) wrote a paper suggesting that
species came from other species and that the development of new
species was based on environmental factors in 1855 (1 year prior
to work being started on the Origin of Species)
1) This paper led to Lyell and others urging Darwin to publish his
ideas
2) In 1858 Wallace sent Darwin a paper titled “On the Tendency of
Varieties to Depart Indefinitely from the Original Type”
describing evolution as a process driven by competition and
natural selection
3) It is unclear whether there was a clear presentation of theory
competition occurring
J)
a. Curtis suggests a collegial spirit with Darwin’s friends Lyell
and Hooker taking the lead in presenting both papers (his
and Wallace’s) or
b. Turnbaugh and others offer the idea that that Darwin feared
that Wallace might be credited with his theory in and
became motivated to attempt to publish before Wallace
Evolutionary thought and evidence
1. Constraints on 19th century evolutionary theory
a) A major problem with the theory is that there was a lack of
understanding on how traits were inherited
b) A contemporary of Darwin, Gregor Mendel suggested a solution on
the problem of inheritance, but it was not until the 1900s that his
1866 theory was rediscovered
c) Richard Leakey suggests that since the 1920s population
geneticists (J.B.S. Haldane etc.) have synthesized Darwin’s work
on natural selection with Gregor Mendel’s work on genetics to
create a cohesive theory
d) This idea has been called the neo-Darwinian synthesis with the
“neo” being included because Mendel’s theory of heredity was
unknown to Darwin
2. Evidence for Evolution
a) The fossil record offers evidence of evolution in the sense of
change
1) Geffner (ed.—Earth Science) suggests that fossils are usually
found in sedementary (deposited sediments) rocks
2) Some are found in metamorphic rocks (rock changed by hear,
pressure or chemically active fluids after formation) (Leet and
Others Physical Geology)
3) However, Geffner claims that “virtually none are found in
igneous rocks” (formed from magma where the heat destroys
almost any animal entering it)
4) The layering effect of strata helps to create a chronology with
the oldest fossils at the bottom (this is the simplest view and
assumes that the sedimentary rocks have nor undergone
change)
5) Changes can occur in these rocks such as twisting, folding,
splitting or igneous intrusions (magma rises through the crust)
and erosion may remove layers of strata creating a bit of
confusion
6) William Smith (1769-1839) discovered that certain kinds of
strata contained distinctive kinds of plant and animal fossils no
matter what the positions of the strata were (similar fossils in
similar strata)
7) Smith through this finding was able to establish fossils that
were indicative of specific periods in earth’s history called guide
fossils
a. Guide fossils are defined as fossils that are highly
characteristic of certain strata (layers of solidified sediment)
b. These fossils are of rapidly evolving species that only lived a
shotr rime in geologic history, but were widely distributed
(Bill Matthews)
K)
1.
2.
3.
4.
5.
6.
8) Through the study of fossils in both disturbed and undisturbed
strata and the radioactivity present in rocks geologists can
arrange strata in the order that they were deposited
9) As a result of this scientists can show that simpler forms of life
developed before more complex forms of life
b) Comparison of living organisms is also evidence for evolution
1) Relethford uses the argument that African apes and humans
share the same type of dental pattern, have a similar shoulder
structure and have a DNA code that is over 98 percent identical
c) A third line of evidence for evolution is laboratory and field studies
of living organisms
1) One of the studies on evolutionary dynamics suggested by both
Relethford and Richard Leakey is that of the peppered moth
(pg. 18-19 in the text)
2) Originally black and white they blended in with tree trunks
having light colored lichen, later pollution (soot) from the
industrial revolution darkened tree trunks and caused the
lighter moths to be at a disadvantage (dark is selected for)
3) This pollution induced selection for darker varieties is known as
industrial melanism
Science and Religion
According to Johnston and Selby over 99.9 % of scientists accept
evolution as a proven theory
However, some believe that creation “science” or creation by a creator
should be taught in the classroom
My perspective on this issue is that the theory of evolution is the best
explanatory mechanism for human and other origins that science
(evidence based) can offer
This does not mean that creationism is incorrect, just that it does not
have anywhere near the supporting evidence (if any) of evolution
Several matters arise concerning creationism vs. evolution
a) Life has never been created under laboratory conditions
b) If matter can be neither created no destroyed (only change state)
then where did it come from?
Does this mean that I believe that creation should not be taught in the
classroom?
a) Science is probabilistic in nature outside of the simplistic/generalist
idea that organisms change there is a percent error every time an
experiment or examination is made
b) This suggests that the descent, for example, of humans from apes
can never be a full absolutist “fact” due to the time period involved,
but that evidence indicating this may increase (discuss limits)
c) In a sense, it is the idea of creationism that keeps evolution in the
scientific realm by suggesting that the theory is imperfect
d) Science is not religion in the sense that there are imperfections in
its explanations
e) I believe that religious classes of all types should be available as a
part of the educational system (an extra class) and that
creationism in the context of a religious perspective is a part of
being educated
f) I also believe that atheists or others who see evolution as
absolutist should as a part of their religious belief be entitled to
have it taught in the classroom as religion
g) The key issue is that both of these perspectives are “religious” and
not based on the nature of science which again is probabilistic and
based upon evidence
7. 2 main perspectives from Relethford
a) theistic evolution is the belief that God operates through the
natural process of evolution
b) Intelligent design creationism refers to the idea that the biological
world was created by an intelligent entity and did not arise from
natural processes
PHYSICAL ANTHROPOLOGY 2301Lecture
HUMAN GENETICS--Section 2
I.
Human Genetics
A) It should be noted that this chapter deals with some basic biology and
that biological topics outside of the framework of the text will not be
examined (Biology the short form)
B) Turnbaugh and others define genetics as “”the study of gene structure and
action and of the patterns of inheritance of traits from parent to offspring.
1. They further note that Genetic mechanisms are the underlying
foundation for evolutionary change
C) Some key initial definitions and ideas are provided by Relethford
1. Mendelian Genetics concerns the branch of genetics concerned with
patterns and processes of inheritance
a) This type of genetics was named for an Austrian monk named
Gregor Mendel (1822-1844) who was the first “known” scientist to
discover these principles
2. Microevolution refers to the changes that take place in the frequency
of genes within a population and deal with short term evolutionary
change
3. Macroevolution is the long term process of evolution that takes place
over long rime periods (to millions of years and includes the origins of
new species)
D) The study of genetics at a molecular level involves DNA or
deoxyribonucleic acid which provides coding for biological structures and
the means to translate this code
1. DNA was discovered as the material responsible for the transmission of
inherited traits in 1944
2. In 1953 Francis Crick and James Watson revolutionized the fields of
biology and medicine by publishing their structural and functional
model of DNA
3. The structure of DNA is a double helix (a picture is on the top of page
32) not a single helix as might be implied by the text
4. The National Human Genome Research institute suggests that DNA
looks like a ladder or coil and that the sides are formed by a backbone
of sugar and phosphate molecules and that the rungs are nucleotide
bases joined weakly in the middle by hydrogen bonds
5. A nucleotide is defined as one of the structural components of DNA
and RNA. It consists of a base plus a molecule of sugar and one of
phosphoric acid (National human genome research Institute)
6. The “rungs on the ladder” as Relethford suggests are composed of
chemical units called bases (note: the bases in the figure at the top of
the page are the individually colored strips in figure 2.1 or ½ a rung
each and not a full rung)
7. The four possible types of bases are A (adenine), T (thymine), G
(guanine) and C (cytosine)
8. Biological structures are composed predominantly of proteins and
these proteins are composed of amino acids and these acids are coded
for by 3 of the 4 chemical bases (see table 2.1)
a) 64 codes are possible, but only 20 of these need to be specified by
the genetic code and in addition there are termination sequences
that can mean either “start” or “stop”
b) The sequence of bonding in DNA is A to T and G to C enabling DNA
to make copies of itself and direct the synthesis of proteins
9. Replication of DNA involves a separation of the two strands and each
strand attracts free floating bases (free basing?) when these free
bases unite with the DNA two identical strands are formed (Figure 2.2)
10. RNA or ribonucleic acid is the molecule that functions to carry out the
instructions (a messenger) for protein synthesis specified by the DNA
molecule
a) One of the main differences between DNA and RNA is that in RNA
base A (adenine) attracts base U (uracil)
b) The process involves DNA separating into two strands and an
inactive (does not attract RNA) and active strand (half DNA piece
that attracts RNA) being formed (pg. 36)
c) The active strand attracts free-floating bases to form a strand of
messenger RNA
d) This strand then moves to the site of protein synthesis and once
there the messenger RNA imparts its information via transfer RNA
(a free floating molecule)
e) Transfer RNA is defined by Relethford as a free floating molecule
that is attracted to a strand of messenger RNA resulting in the
synthesis of a protein chain
E) Chromosomes and Genes
1. In many types of organisms much of the DNA is contained in a
separate part of the cell (the nucleus)
2. The DNA sequences are tied together by proteins into long strands
called chromosomes and are found within the nucleus of each cell
3. Curtis says a chromosome is one of the bodies in the cell nucleus
along which the genes are located
a) with the exception of sex cells chromosomes normally occur in
pairs (humans have 23)—Downs syndrome has 1 “pair” with 3
chromosomes
b) The number of chromosomes have nothing to do with the
intelligence or biological complexity
4. Curtis defines a gene as a unit of heredity in the chromosome
composed of a sequence of nucleotides (a building block of nucleic
acid) in a DNA molecule that codes for a polypeptide (a compound
containing many amino acids joined by a peptide bond—RNA product)
5. Turnbaugh etc. claim that a gene may be composed of hundreds or
thousands of DNA bases
a) note: skip the hemoglobin section
6. However, not all DNA contains results in a polypeptide product and the
purpose of non-coded sequences is not known
7. The DNA sequence of a gene can contain both exons and introns
a) Exons are sections of a gene that encode for amino acids that
make up proteins
b) Introns are sections of DNA that do not code for the amino acids
that make up proteins (figure 2.4, note it is RNA not DNA)
8. Genes not only manufacture proteins, but they also regulate biological
processes
a) some issues such as sexual maturation at a given time
(adolescence and not infancy) are controlled by regulatory genes
b) These are genes that regulate other genes (turn them off and on)
c) These genes have great significance for evolution and can explain
phenotypical differences despite similar structural genes (apes and
humans 98% of our genes are similar yet there are large
differences)
d) Homeobox genes are regulatory genes that encode a sequence of
60 amino acids regulating embryonic development and divide the
embryo into different areas such as head and tail
9. Mitosis and Meiosis
a) mitosis is a process of cell division where chromosomes are
replicated in the body cells (in the film Blade Runner clones are
referred to as replicants) (top of page and 63)
1) The 5 phases of mitosis are given on page 63
b) Meiosis is the creation of sex cells by replication of chromosomes
followed by cell division
1) these cells first replicate and divide then divide again without
replication
c) Ultimately, when chromosomal information is transmitted from one
generation to the next sex cells contribute only one half the
chromosomes that are in one cell
1) in a human infant the male contributes 23 and the female
contributes 23 (46 total)
F) The Human Genome Project
1. Relethford suggests that The human genome project began in 1990 in
an effort to sequence the human genome and this is meant as an
update to his information (his latest information is from 2001)
a) a genome can be defined as all the DNA contained in an organism
or cell, which includes both the chromosomes within the nucleus
and the DNA in the mitochondria (chap. 5) (National Human
Genome Institute)
2. The National Human Genome Institute states that the Human Genome
Project (HGP)was “one of the great feats of exploration in history (sic)”
3. The HGP was completed in April 2003 and the project gives us the
ability to read nature’s complete genetic blueprint for building a human
being
G) Mendelian Genetics (Genotypes and Phenotypes)
1. Terminology
a) Locus—the specific location of a gene or DNA sequence on a
chromosome
b) Allele—the alternative form of a gene or DNA sequence that occurs
at a given locus
1) Alleles can be singular or many and occur in pairs on each
chromosome
2) The genetic basis of any trait is determined by an allele from
each parents
c) Mendel’s Law of Segregation also known as Mendel’s First Law
claims that sex cells contain one of each pair of alleles
d) Genotype refers to the genetic endowment latent or expressed, of
a cell or organism (from the 2 alleles present at a locus)
1) homozygous refers to having the same allele at the same locus
on both members of a chromosome pair
2) heterozygous refers to there being different alleles at the same
locus on members of a chromosome pair
e) As an explanatory mechanism a brief examination of Mendel’s
experiment with pea plants will be discussed
1) The upper case letters refer to dominant alleles or dominant
traits (example “T”)
2) The lower case letters refer to recessive alleles or recessive
traits (example “t”)
3) In his experiment “T” is the allele for tall ness and “t” is the
allele for shortness or “dwarfism”
4) “TT” would be a homozygous tall plant, “Tt” would be a
heterozygous tall plant and “tt” would be a homozygous short
plant
f) Phenotype refers to the observable or detectable physical
characteristics of an organism or the detectable expressions of
genotypes
1) If one looks at the Punnett square it is notable that ¾s of this
group will express the dominant phenotype and ¼ will show the
recessive phenotype
2) Relethford suggests that in a heterozygote the dominant allele
masks the other
3) He also suggests that a recessive allele in a heterozygote is one
that is masked by the other allele
4) It should be noted that whether dominant or recessive alleles
can be common or rare and harmful or helpful
5) Environment can also have an effect on phenotype (rainfall
amounts, soil and tree growth)
6) Some alleles are codominant and both traits are expressed so
neither allele is dominant or recessive
g) Mendel’s Law of independent Assortment or Mendel’s second law
involves the idea that the segregation of any pair of chromosomes
does not affect the probability of segregation for other pairs of
chromosomes
1) Simply if there are 3 pairs of chromosomes (6 total) numbered
1, 2, 3 with 2 chromosomes with each number then each
number 1, 2, 3 acts independently
2) Relethford claims that independent assortment is a powerful
mechanism for introducing great potential for genetic diversity
in humans
3) Curtis notes that this is an early idea and that linkages between
traits can occur (alleles on the same chromosome are inherited
together)
4) In the modern form of Mendel’s second law “unlinked” genes
assort independently
h) Recombination
1) Crossing over refers to the exchange of DNA between
chromosomes during meiosis (see figure 2.13)
2) The result of the crossing over is recombination or the
production of new combinations of DNA sequences caused by
exchanges of DNA during meiosis
3) Recombination can also occur through assortment of unlinked
genes during sexual reproduction or both methods combined
4) It should be noted that recombination does not change the
genetic material since the alleles stay the same, but they occur
in different combinations
i)
There are 2 basic types of chromosomes, autosomes and sex
chromosomes
1) Autosomes are all chromosomes except the sex chromosomes
2) Sex chromosomes are the X (larger) and Y (smaller)
chromosomes and are paired in a similar manner (XX for
women) and not in the other (XY for men)
H) The Genetics of Complex Physical Traits
1. The examination of genetics has focused on simple discrete genetic
traits (a single locus with a clear cut mode of inheritance
2. Traits can be more complex with one or more genes contributing to
the phenotype with the traits also potentially being affected by the
environment (natural Bonsai)
3. Many complex traits are polygenic or “continuous” and are the result
of 2 or more loci
a) this allows many different genotypes and phenotypes to arise (skin
color etc.)
4. a single allele may also have multiple effects upon an organism and
this is known as pleiotropy (sickle cells alleles affect both the structure
of hemoglobin and cause changes in body growth and health
5. Sometimes these effects are combined (polygenic traits and pleiotropy
(Figure 2.15 d)
6. It also should be noted that there are variations where not all alleles
have the same effect (dominant or not)
7. Heritability
a) Heritability is defined as the proportion of total variation of a trait
due to genetic variation in a specific population
b) Genetic variation refers to variation in human populations due to
genetic factors (height etc. Swedes)
c) Environmental variation can be due to differences in environment
due to issues such as diet (Japanese and height changes due to
diet changes)
d) Heritability is only a proportion of the total variation (explain
equation on pg. 52) and can range from 0 (no genetic Variation) to
1 (no environmental variation)
8. Major Genes have become important recently where a discernible
portion of genetic variation is due to a single locus
a) these genes have the primary effect on the phenotypic distribution
of a complex trait
I) Mutations are a mechanisms for evolutionary change resulting from a
random change in the genetic code; the ultimate source of all genetic
variation
1. Technically speaking mutation refers to changes in DNA bases as well
as changes in chromosome number and/or structure
2. They can arise due to background radiation or ingestion of certain
substances (caffeine)
3. Mutations are random and can be beneficial, deleterious (much of the
time) or neutral
4. Mutations may involve changes in a single DNA base, in larger sections
of DNA and in entire chromosomes
5. Although mutations are rare when estimated for a single locus it
should be remembered that human chromosomes have many loci
suggesting a higher mutation rate
J) Nature vs. Nurture
1. Genetic factors have been linked to human behaviors, but they merely
influence behavior and do not cause it
2. The reality is that both environment and genes influence some
behaviors
PHYSICAL ANTHROPOLOGY 2301 Lecture
EVOLUTIONARY FORCES—Section 3
I.
Population Genetics
A) The focus of this chapter is microevolution or changes in the frequency of
alleles in a population from one generation to the next
B) Population Genetics
1. A population can be defined as (Turnbaugh etc.) a group of inbreeding
individuals or the group within which one is most likely to find a mate
a) It should be noted that all members of a species are potentially
capable of mating, but the reality of their doing so is limited by 3
factors
1) The first limiting factor is geography, specifically, the idea that
people often tend to mate with those who live near them
a. It should be noted that there are small homogeneous
groups (towns), however, there are also heterogeneous
grouping such as New York City or even small towns (Texas
border—Hispanic-Anglo)
b. In the case of small isolated islands the probability of
finding a mate outside of the area is remote
c. This island group can be referred to as breeding isolates or
populations that are clearly isolated geographically and/or
socially from other groups
2) A second factor can be described as social/cultural
a. an example would be a desire to marry someone of the
same ethnicity
b. Some groups have an affinity for endogamy while others
lean toward exogamy and individuals with in the group may
go against their cultural values as well
A. endogamy refers to marrying or mating within the group
B. exogamy refers to mating or marrying outside of the
group
3) A third factor could be called individual preference such as a
preference for tall blondes among some men
2. A population shares a common gene pool
a) a gene pool is defined as the total complement of genes shared by
reproductive members of a population
C) Genotype and allele frequencies
1. Genotype computation involves taking a part of the population and
dividing it by the whole population
a) example: when taking genotype MM=98, MN=84 and NN=18
where n=200 (total pop)
b) MM=98/200=.49 (or 49%), MN=84/200=.42 (or 42%) and
NN=18/200=.09 (9%)
c) These are the percentage composition of each of these populations
2. For the computation of allele frequencies one must multiply by 2
because there are 2 alleles in each gene
a) Using the above example the total population becomes 400 (part
over whole again)
b) the frequency of the M allele can then be found thus
c) MM=98 (2 Ms are present, therefore 98x2=196) MN=84 (only 1 M
is present, therefore 84x1=84) and for NN=18 no Ms are present
or 18x0 or 0
d) 196+84+0=280 280/400=.7 or a 70% allele frequency, therefore,
NN has a frequency of .3 or 30%
D) Hardy-Weinberg Equilibrium
1. In 1908, the British mathematician G.H. Hardy and the German
Biologist W. Weinburg independently found a simple formula that
under certain conditions allowed the prediction of genotype
frequencies from the gene frequencies of a population
a) this Hardy-Weinburg equilibrium shows that with certain
assumptions genotype and allele frequencies will remain constant
from one generation to the next
b) It involves the simple model of one locus (specific position of a
gene on a chromosome) with 2 alleles “A” and “a”
c) p=frequency of “A” allele and q=frequency of “a” allele
d) Therefore the frequencies are thus: AA genotype=p squared,
Aa=2pq and aa=q squared
e) If p=.6, q=.4 then AA=.p squared=or.6 squared =.36 (36%),
Aa=2pq=2(.6)(.4)=.48 or 48% and aa=q squared or .4
squared=.16 or 16 percent
f) Given certain assumptions the allele frequencies (p=.6 or q=.4)
and the genotype frequencies (AA=.36, Aa=.48 and aa=.16) will
remain constant over time (one generation to the next
g) This does not suggest that there is no evolution since there are
other factors in volved
h) The 4 other factors or evolutionary forces are:
1) production of new variation or mutation
2) redistribute variation through gene flow
3) redistribute variation through genetic drift
4) select “advantageous” allele combinations that promote
reproductive success or natural selection
E) Evolutionary forces can be defined as those mechanisms that can lead to a
change in allele frequency over time
1. Although changes in allele frequencies alter genotype frequencies,
changes in genotype frequencies do not necessarily alter allele
frequencies
2. This can occur with a significant amount of nonrandom mating or mate
choice in a given population and the genetic consequences
3. 2 types of non-random mating are:
a) This can be due to inbreeding or mating between biologically
related individuals
b) It can also be due to assortative mating or mating by phenotypic
similarity or dissimilarity
4. Mutations
a) A mutation can be defined as a change in DNA that can occur
either as a change in the sequence of bases or at a larger
chromosomal level and can proceed in either direction
1) Example: A can change to a and then change back to A
(however, the changing back is less frequent than the initial
change)
b) Mutation is the only way that a totally new variation can be
produced
c) It occurs infrequently and when a single locus is involved it seldom
has any effect on allele frequencies
d) However, human beings have many loci (as many as 100,000)
they have many mutations they have accumulated over previous
generations (many of these are recessive and not expressed
e) As an example: In population of 100 people (200 alleles) an AA
genotype the frequency of the A allele is 1 or 100%, but if one
changes form during transmission to the next generation to “a”
then there are 199 A and 1 a or 199/200 or .995 for A and .005 for
a
5. Gene Flow can be defined as the movement of alleles between at least
2 populations
a) When gene flow occurs a mixing of genetic material between 2
populations takes place and they tend to become more alike
genetically
b) In an illustration of gene flow it can be assumed that all the alleles
in population 1 are A and population 2 are a (pg. 86)
1) It is stated in the text that if 10% of the individuals in
population 1 move to 2 the population 1 is 90% A alleles and
10% a and population 2 is the opposite creating greater
similarity between the 2 populations
2) If it is assumed that this rate (10%) continues the populations
will become increasingly similar (after 20 generations the
populations will be almost identical)
3) Gene flow does not only occur through some form of mass
migration, but can involve transportation marriage patterns
4) In terms of determinants of gene flow it should be noted that
the closer one lives to someone the more likely it is for
intermarriage to take place (and less likely given a higher level
of distance)
5) The idea of near or far, however, has changed
a. When people were limited to horses or foot travel the
transport range was about a 10 mile radius
b. However, affordable rail transportation in rural England in
the 1800s allowed the average marital distance (distance
between husband’s and wife’s birthplace to increase to 2030 miles
c. Today, aircraft allow a worldwide marriage pool
d. However, actual patterns are more restrictive and the town
of Ann Arbor, Michigan has an average marital distance of
about 160 miles
6. Genetic Drift can be defined as evolutionary changes (changes in allele
frequencies) produced by random factors. Genetic drift results from
small population size
a) The term drift is used because it is a completely random process
where the allele flows can change in any direction
b) Genetic drift refers to, for example, a father and mother with an Aa
allele
1) The father may pass on the A or the a allele as can the mother
(AA, Aa, aA, aa genotypes i.e. 2 alleles together-Punnet
square)
2) Their children may have any of these 4 genotypes and the
distribution is random
3) In Relethford’s example, he flipped coins to determine the
inheritance from the parents of four children with the percent
chance of an A=.5 or 50% and a=.5 or 50%
4) The 4 children have a total of 8 alleles and his coin flips
produced 6 “As”=6/8=.75=75% and 2 “as”=2/8=.25 or 25%
5) The only time that drift will not produce a change in allele
frequency is when an allele is lost
6) As an example if an A allele is passed on to all four children in
Relethford’s example then the recessive a allele is lost
7) This potential for loss of an allele suggests that extremely small
populations will tend to be homozygous (same alleles) and
experience less variation
c) An example of genetic drift in modern populations is the founder
effect or Sewall-Wright effect
1) This effect is a special kind of genetic drift where the alteration
of allele frequencies occurs in a small population that is taken
from or is a remnant of a larger population
2) The only available genes are those of the founders and not the
genes of the population from which they came
7. Natural selection--Individuals with biological characteristics that allow
them to survive in a given environment pass on their genes and those
that are less likely to survive do not
a) Turnbaugh and others argue that the most important factor
influencing the direction of evolutionary change is natural selection
b) Natural selection does not create new genetic variation only
mutation does
c) Natural selection focuses on fitness or the probability that an
organism will survive
d) It should be noted that human beings neither quickly reproduce
nor should they be used in controlled laboratory manipulations
e) It is, therefore, difficult to find unambiguous examples of natural
selection in modern humans
f) The best documented case or example of natural selection is the
sickle cell allele, which if inherited in homozygous form causes
anemia and frequently death
1) it is interesting to note that the highest allele frequencies for
this disease are in West and central Africa (and somewhat high
in Greek and Asiatic Indian populations)
2) It is in these areas of the world that malaria is found caused by
a single celled parasite
3) In areas where malaria is endemic (continuously present) many
suffer from sharply lower reproductive success (high infant
mortality and lowered vitality of adults)
4) In a study based on highly questionable ethics British biologist
A. C. Allison (1950s) injected the malarial parasite into
volunteers from the Luo tribe of East Africa
a. His study showed that a short time after infection
heterozygous carriers of the sickle cell allele were much
more resistant to malarial infection than the homozygous
b. The blood cells provide a less conducive environment for the
parasite to reproduce itself and the parasite often dies
5) Turnbaugh etc. believe that a genetic trait such as sickle cell
anemia that provides a reproductive advantage is a clear
example of natural selection in action
6) The evolutionary mechanism in the sickle cell example is
balanced polymorphism and comprises the genetic load of a
population
a. The genetic load of a population refers to hidden,
deleterious recessive genes in a population
b. balanced polymorphism is the maintenance of 2 or more
alleles in a population due to the selective example of the
heterozygote
c. A genetic trait is called a polymorphism (many forms) by
Bodmer and Calli-Storza when two or more alleles at a
given genetic locus occur with appreciable frequencies in a
population
d. Turnbaugh etc. suggest that appreciable frequencies refers
to about (.01) 1%
e. Essentially, if a population is sampled for a particular trait,
and frequencies for more than one allele are higher than
1% then the locus that governs the trait is polymorphic
f. The use of 1% is to offset the effects of mutations that
occur at rates far below 1%
g. The term “balanced” in “balanced polymorphism also needs
to be explained
A. This term refers to pressures operating in the malarial
environment
B. Some individuals (mostly homozygous normals—no
sickle cell allele) will be removed due to the disease
C. Some homozygous recessives will also be removed due
to sickle cell anemia
D. Those with the highest rate of reproductive success will
be the heterozygous, therefore, both alleles will be
maintained at roughly the same frequency and balance
between the 2 is attained
E. However, it should be noted that in a non-malarial
environment homozygous normals would not die from
malaria
F. The sickle cell allele would, therefore, decrease if the
sickle cell individuals continue to die before reproduction
G. This gradual removal of the sickle cell allele is known as
directional selection
g) 5 Types of selection
1) Selection against recessive homozygotes
a. This refers to when the aa genotype is fatal in a population,
therefore, its frequency decreases
b. It should be noted that as the presence of “a” decreases the
rate of its decrease also declines (fewer people are
homozygous)
2) Selection for recessive homozygotes
a. If AA and Aa are removed due to complete selection against
A then only aa individuals remain after 1 generation
b. However, mutations can occur reintroducing A periodically
3) It should be noted that any dominant or recessive homozygotes
can be selected for or against
4) Selection for the heterozygote
a. When both homozygotes are selected against as in the case
of sickle cell anemia in areas with malaria
b. Then the heterozygote is selected for in a selection both for
and against both alleles
5) Complex selection
a. Stabilizing selection occurs when selection is against both
extremes of a trait’s range in values (extremes are unlikely
to survive)
b. Directional selection (mentioned earlier) is a selection
against one extreme and/or a selection for the other
extreme
8. Interaction of evolutionary forces
a) Even though the 4 evolutionary forces have been discussed
separately, they actually act together to produce allele frequency
change
b) They can act together or in opposition
c) Genetic drift and Gene flow have opposite effects on variation
between and within populations and can counteract each other
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