So, Just Where Are We?

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So, Just Where Are We?

• Our course is concerned with US, where we came
  from, why we look and behave the way we do.
• In order to explore these issues, one of the
  first things that has to be done is to focus on
  us as humans, distinct from the rest of the
  animal world.
• Thus, over the past two weeks, we have looked at
  the pattern of human distinctiveness, in biology,
  behavior and language. It is necessary that we
  begin our investigations of ourselves with the
  examination of just what it is that makes us
• Homo sapiens

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Humans as Biologically Unique

• Two weeks ago, we explored the biological
  features that make us unique, including our erect
  posture, our large brains and our lack of
  projecting canine teeth.
• The chimpanzee film gives you an idea of just how
  different and similar we are to each other and
  sets in dramatic focus our evolutionary
  relationships with these African apes.
• Now, it is time to look at what we represent as a
  species.

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Humans as a variable species

• All modern humans are part of a single species
  Homo sapiens (we can all interbreed and produce
  fertile offspring). However, as we have already
  seen, we also differ in many biological features.
• Today, we begin our second section, dealing with
  variation what is the nature and causes of human
  biological, social and linguistic variation?

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Human Variation 1.

• There are all sorts of differences amongst
  humans, and we are all aware that people vary in
  facial and body features. We also know that
  these differences extend to the genetic materials
  themselves.
• Indeed, there are parts of the human genome
  that are so hypervariable that examination of
  these specific locales can identify specific
  individuals with a 1 in 88,000 chance of
  mistaking one person with another.

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Human variation I
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Human Variation II
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Human Population Variation

• All humans vary (except for identical twins, but
  that is a specific case, and usually by
  adulthood, there are differences resulting from
  environmental influences).
• This variation is the result of the complex
  interaction of genetic and environmental
  influences, but also random forces.
• It is clear that biological features are NOT
  randomly distributed across the human landscape
  but have specific geographic distributions. This
  is the basis for the simplistic notions of race
  that are used in social interactions.
• It is equally clear that most of the human
  variation that we observe is the result of human
  evolution to meet the needs of specific
  environmental demands, like climate, food,
  altitude and many other variables.

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Genetics The source of variability for evolution

• The basis for much of the variability we see in
  modern humans originates in our genetic material.
• Like all living things, humans possess a
  genetic structure based on DNA and its ability
  tocode for a huge class of functioning molecules
  Proteins.
• Our genetic structure has been formed over
  millions of years of evolutionary change.
• Our focus today how population survival
  strategies determine human biology and provide
  the basic background for human variation

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What does the genetic material do, anyway?

• The genetic material has a number of crucial
  functions
• 1. Transmit genetic information from one
  generation to the next (humans produce human
  infants and not rats or elephants).
• 2. Since every cell in the body (with several
  exceptions) has more or less the same genetic
  material as the original cell (the fertilized
  egg), the genetic material must be able to
  reproduce itself when new cells are produced
  during growth and development as well as normal
  body maintenance.
• 3. The genetic materials are organized around
  a sequence of chemical bases that encode for
  the synthesis of proteins, a huge class of
  chemicals that perform a wide range of functions
  in the body.

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What determines cell structure and function?

• Proteins that are expressed
• Unique expression by cell type
• How is this controlled?
• Look to the cell nucleus

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Chromosomes

• Carries information as part of their structure
• Namecolored bodies when stained and seen
  microscopically
• Species-specific number in each cell nucleus,
  with the chromosome number usually expressed in
  pairs (the complexity of the living thing is not
  reflected in the chromosome number (chimps, for
  example, have more chromosomes than humans).

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Human chromosomes

• Species specific number46
• 23 pairs of chromosomes
• Specifially
• 22 pairs of autosomes
• or, homologous chromosomes
• 1 pair of sex chromosomes
• XX female
• XY male
• Question Why are there pairs of chromosomes?

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Where do the chromosomes come from?

• We are originally one cell
• 23 of maternal origin
• ova carry these
• 23 of paternal origin
• sperm carry these
• If every cell has 46, how do these end up with
  only 23 and why?

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Meiosis
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Mitosis

• Cell Division
• Chromosomal Replication

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What does the genetic material do?

• While the functions of the genetic material
  located on the chromosomes are numerous and
  complicated, for our purposes, we can examine the
  major function that of the synthesis of
  proteins.
• Proteins are a very large class of molecules that
  perform a huge array of functions in living
  things. It has been estimated that there may be
  as many as 50,000 different proteins in the
  human body, only about 1500 of which have been
  identified.
• Proteins differ from one another, and thus
  perform differently, based on their organization
  and makeup.

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Proteins What are they?

• Basic You are what you eat!
• The ultimate source of
• your bodys protein is
• from your diet.
• Functions include
• Structure
• Transport
• Immune
• Function reflects their structure
• Proteins have 3 dimensional structure
• Folded chains

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Differentiation

• Unique proteins in different cell types
• Keep in mind that every cell receives a complete
  set of chromosomes and thus the genetic
  materials.
• Thus, although every cell has the ability to
  produce every single protein in the body,
  specific cells only turn on very small segments
  of the total genetic material and only synthesize
  a very few proteins.

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Proteins what distinguishes one from another?

• 1. Proteins are composed of chains of amino acids
  (Polypeptide chains).
• 2. Polypeptide chains have variable lengths.
• 3. The sequence of amino acids along the chains
  vary.
• 4. Proteins can be made up of one or, more
  usually, two or more chains of amino acids.
• 5. Proteins have a folded three dimensional
  structure

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Amino Acids What are they and where do they come
from?

• Chemical group based on their composition an
  amine and an acid
• Of the 20 common amino acids
• 12 the body can make
• 8 must be eaten be obtained from foods (these
  are the essential amino acids)

• Glycine (gly) Glutamic acid (glu)
• Alanine (ala) Aspartic acid (asp)
• Valine (val) Isoleucine (Ile)
• Leucine (leu) Serine (ser)
• Threonine (thr) Proline (pro)
• Lysine (lys) Arginine (arg)
• Glutamine (gln) Aspargine (asn)
• Methionine (met) Cysteine (cys)
• Tryptophan(trp) Tyrosine (tyr)
• Histidine (his) Phenylalanine (phe)

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Proteins How they are made amino acids

• Polypeptide chainsaa
• Sequence of aa crucial to structure, and thus
  function
• Sequence determined by series of nucleic acids
  and the genetic code
• Determined by a gene

met
val
his
leu
thr
asp
ala
glu
lys
ala
ala
val
ss
cys
leu
trp
gly
lys
val
asn
ser
asp
glu
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What is a gene?

• A recipe for a protein, or more accurately, for
  a single polypeptide chain.
• Located at a specific region (locus) on a
  specific chromosome.
• A gene can have many alternative versions of
  itself. These are known as alleles.
• Implications
• different chromosomes carry different information
• Alleles are one of the major sources of variation.

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Diversity of form and function

• The basis of evolution is variation
• This variability in biological form and function
  arises from genetic mutations, compounded by the
  random assorting of genetic materials during the
  production of eggs and sperm.
• There are two levels in evolution
• 1. Microevolution the generation by
  generation changes in a population.
• 2. Macroevolution the evolution of populations
  over long periods of time, usually resulting in
  the appearance of a new species.

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The origins of Variation I

• Random changes in the structure of the genetic
  material (DNA), which are called mutations,
  result in the appearance of new variations. This
  is one of the crucial pieces of information that
  Darwin lacked, and thus prevented him from
  actually directly addressing the name of his
  book The Origin of Species (1859).
• It was an ongoing criticism of Darwinian
  evolution until the discoveries of how genetic
  material can randomly change provided the missing
  data.

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The origins of Variation II

• The second major source of variation is the
  recombination of genetic traits that results from
  the transmission of genetic traits from male and
  female parents.
• During the process of producing sex cells, the
  genetic material carried in the chromosomes
  randomly assorts so that each offspring receives
  a random selection of parents genetic materials.
  
• Thus, each offspring confronts the environment
  with a slightly different set of genetic
  materials.

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Genetics and EvolutionA Darwinian View

• Thus, genetic mechanisms produce random changes
  (mutations) in the genes. The changes are not in
  any way dictated by the environment or the needs
  of the animal.
• These mutations are acted upon by natural
  selection via behavior.
• In time, the changes may come to characterize the
  entire population.

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Evolutionary Mechanisms

• Evolutionary Mechanisms effect the frequency of
  genetic variations (alleles) in a population, and
  thus represent the way by which evolution
  operates.
• There are four evolutionary mechanisms
• 1. Mutation
• 2. Natural Selection
• 3. Gene Flow (Migration)
• 4. Stochastic Forces (random genetic drift).

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Evolutionary Mechanisms

• 1. Natural Selection
• reduces variation
• 2. Mutation
• increases variation
• 3. Gene Flow (Migration)
• can reduce or increase variation
• 4. Stochastic Forces (Genetic Drift)
• reduce variation

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Action of Evolutionary Forces

• These evolutionary forces do not work on
  individuals, but rather on populations.
• Individuals do not evolve, and in evolution, the
  only role played by individual animals is to
  receive genetic materials from parents and pass
  them on to offspring.
• Evolution is differential reproduction, and not
  necessarily survival .

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Human Variation and Adaptation

• Human variation is very often related to the
  evolutionary adaptation of a population to its
  environment.
• But, it is important to keep in mind that
  mutations are random events that do NOT appear as
  the result of some need that a population has to
  adapt.
• As a result, variations are NOT adaptive all of
  the time and in all places but are very much
  related to specific environmental conditions.
  When conditions change, it is often difficult for
  a species to modify to fit the new environmental
  conditions and they will often become extinct.

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The Basis for Human Variation

• Finally in this context, it should be kept in
  mind that there are variations that may not have
  an adaptive basis. It is possible that in small
  populations, variations have become part of the
  biology by random changes in the genetic
  material. This process, known as genetic drift,
  can result in the appearance of features that are
  not part of an adaptive system. These random, or
  stochastic (means random) processes add a measure
  of uncertainty and complexity to the study of
  human variation.
• For example, when a particular trait is examined
  (hair color), should we always assume that the
  variations are adaptive and look for an
  environmental cause?

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Human Variation

• There are all sorts of differences amongst
  humans, and we are all aware that people vary in
  facial and body features. We also know that
  these differences extend to the genetic materials
  themselves.
• We will see from our examination of the human
  fossil record that during our evolution, humans
  became established in environments with differing
  conditions.
• Thus, the origins of many of our biological
  variation appear to be directly related to our
  evolution as a geographically diverse species
  occupying a wide range of environments.

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The Nature of Variation

• Keep in mind the following
• The similarity of humans across all populations
  is very high, with numerous studies documenting
  that genetic variability within major geographic
  areas (i.e. Africa or Europe) is greater than the
  genetic variation between geographic areas.
• All modern humans share the unique attributes of
  the species, and thus are identical for this
  suite of features.
• What we can examine are those biological
  features, like skin color, which do vary amongst
  geographical populations, and which have often
  been used to characterize races.

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The study of human variabilityDescription and
process

• Populations vs individuals
• Nature vs nurture
• Stochastic vs adaptive

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Variability in form and function in adults is the
result of the interaction of biocultural
complexes and reflects evolutionary scenarios

• Genetic mechanisms
• mutation
• drift
• selection
• flow
• Development
• Environmental variables

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The Interaction of genes and environment

• In the development of an individual, a complex
  interplay of the genetic materials and
  environmental (which of course includes culture)
  factors is responsible for the outcome a
  functioning (and reproducing) adult
• GENES interaction with ENVIRONMENT
  ADULT Form
• (Genotype)
  (Phenotype)

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Adaptation The interplay of genotype and
phenotype

• Genotype is the underlying framework
• Environment molds and channels genotype into the
  final phenotype
• In humans, culture and the resultant complex
  behavior are a unique basis for the environment
  to influence and shape final phenotype.
• (This represents a complex interplay that few
  other animals have.)

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Adaptation

• Changes or modifications that enable a person or
  group to survive in a given environment
• This can be accomplished by means of
• Biological mechanisms
• Genetics
• Physiology
• Development
• Cultural, behavioral mechanisms

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Environmental challenges

• Human variation is related to environmental
  variation, with many biological complexes
  reacting to variations such as
• Disease
• Temperature
• Altitude
• Nutrition

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Adaptation The basis of body shape and size?
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Human variability populations vs individuals
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The variable human species Homo sapiens, The
product of evolution and adaptation