Week 1 Lectures: February 6-8, 2007 5 Major Questions

1. What happened?

2. How do we figure out what happened?

3. Why are we the way we are?

4. How does evolution work?

5. Why is human evolution important?

--Humans are a good model for studying overall evolution b/c “nothing in biology makes sense except in the light of evolution.”

*5 Theories of Evolution*

1. Evolution as such

2. Common Descent

3. Gradualism (i.e. evolution proceeds slowly and WITHOUT jumps)

4. Multiplication

5. Natural Selection

FITNESS: ability to reproduce and act

ADAPTATION: useful feature, shaped by natural selection that PROMOTES SURVIVAL.

HUNTER-GATHERERS:

--They hunted a lot more than they gathered, and inversely, chimpanzees gathered a lot more than they hunted.

--H-Gs are COMPLETELY dependent upon tools!

--Most food is cooked or processed by H-Gs.

-H-Gs and aggression: Lethal violence and non-lethal violence are VERY low, the latter particularly staggeringly low compared to similar rates for chimps.
Reading: B&S 1-3

CHAPTER I: Adaptation by Natural Selection

*adaptations: exquisitely constructed components that interact to help the organism survive and reproduce.

CONSTRUCTION serves FUNCTION.

1. 
   Darwin
   
   1. 
      (1800s) Most people did not believe his Theory of Adaptation because they believed that adaptations were the result of divine creation.
      
   2. 
      Henslow = the professor who encouraged Darwin to travel aboard the HMS Beagle and map the nature found on the coast of South America.
      
   3. 
      Darwin’s 3 Postulates
      
      1. 
         The ability of a population to expand is infinite, but the ability of any environment to support populations is always finite.
         
      2. 
         Organisms within populations vary, and this variation affects the ability of individuals to survive and reproduce.
         
      3. 
         The variations are transmitted from parents to offspring.
         

4. 
   Darwin’s finches
   
5. 
   Grants and the island of Daphne Major on which they were able to study how much the drought effected the finches’ beak depths; through Natural selection, the morphology changed so as to make the finches better adapted.
   
6. 
   Evolutionary Theory: Phenotypes (i.e. finch beaks) will continue to deepen until the cost of larger-than-average beak size exceeds the benefits.
   
   1. 
      Even if phenotypes are not changing, natural selection is still occurring. In fact, populations do not remain static unless natural selection is operating!
      
   2. 
      Adaptation: comes from competition among individuals, and not between entire populations or species!!
      
      1. 
         Natural selection can help the individual but harm the overall species group.
         
      2. 
         Continuous variation (slow, steady, and constant with intermediate stages of characteristics) vs. Discontinuous variation (i.e. mutations)
         
      3. 
         Small, random variations of natural selection lead to complex adaptations.
         
      4. 
         Convergence: the evolution of similar adaptations in unrelated groups of animals.
         

*Jenkin’s Argument: Blending inheritance there’s little or no variation available for selection to act on. (And as one of Darwin’s three necessary postulates, variation remains essential to natural selection!)

1. 
   Mendel!
   
   1. 
      Variants: forms of traits
      
   2. 
      Crosses: matings between plants
      
   3. 
      Fo generation, F1 generation, F2 generation, etc.
      
   4. 
      2 of Mendel’s conclusions:
      
      1. 
         Genes are inherited from both the mother and father
         
      2. 
         Both the mother’s particles and the father’s particles are equally likely to be transmitted. Therefore, it’s an INDEPENDENT ASSORTMENT!
         
2. 
   Mendel is no longer refuted when in 1900, after 40 years of being ignored, scientific understanding of the role of chromosomes in the formation of gametes reinvigorate the believability of Mendel’s theory (recall, Mendel only observed plants and therefore dealt with just phenotypes and no genes).
   
3. 
   Mitosis—normal cell division; Miosis—sexual cell division that produces gametes
   
4. 
   GENES are carried on chromosomes!!! (Refresh yourself on the splitting of chromosomes!) All the genes carried on all the chromosomes are referred to as the genome.
   
5. 
   There is a lot of detailed information in this section. I read it all, and it doesn’t seem to pertain much to the information covered in lectures. So feel free to skim it (if you haven’t already done so), but chapters I and III are more pertinent.
   

1. 
   Phenotypes vs. Genotypes
   
   1. 
      Population Genetics: What happens to genes in populations that are undergoing natural selection
      
   2. 
      GENOTYPIC FREQUENCY: one should always track the frequencies of the genotypes rather than the number of individuals with each genotype because the former is independent of the local population size, whereas the latter is not!!
      
      1. 
         Goal of Evolutionary Theory: HOW do genetic frequencies change over time?
         
         1. 
            4 processes that alter the frequencies of genes and genotypes:
            
            1. 
               Sexual reproduction
               
            2. 
               Natural selection
               
            3. 
               Mutation
               
            4. 
               Genetic drift
               
         2. 
            Sexual Reproduction
            
            1. 
               Random mating among humans is similar to the random union of gametes!!
               
            2. 
               Weinberg equilibrium: The realization that sexual reproduction alone does not alter phenotypic and genotypic frequencies was the key to understanding how variation is maintained!!
               

* “Hidden Variation” = “hidden” genotypes are present even when phenotypes evolve to that which is of “higher fitness.” Therefore, variation and mutation are protected from selection. (And that’s good since Mutation add variation to a population by continuously introducing new alleles…thereby fulfilling one of Darwin’s three requirements for evolution.)

*Behavior plasticity vs. behavior canalization (i.e. showing the same phenotype in a wide range of environments)

*Genetic drift: particularly common among small sampling populations. More rapid change in small populations than in large ones. Also, because of genetic drift, isolated populations become genetically different from one another over time.

--Not until the 1930s did scientists finally agree that evolution based on essentialism was completely invalid.

*Darwin-Wallace Theory: Based on population rather than essentialism.

DARWIN’S EVOLUTIONARY MODEL OF NATURAL SELECTION:

1. Every population is so fertile that its size would increase exponentially if not constrained.

2. Size of populations remain stable over time.

3. The resources available to every species are limited. There is an intense struggle for survival among the members of that species.

4. No two individuals of a population are exactly the same; they differ in their probability for survival (i.e. natural selection)

5. Many of the differences among individuals of a population are heritable. Therefore, natural selection over many generations results in evolution.

• 
  “Owing to unequal survival and reproductive success of its individuals, there is a continuing genetic turnover in each population as a result of chance and natural selection.”
  
  1. 
     Even greater breaks in continuity occur where there are geographical boundaries limiting dispersal.
     
  2. 
     “A local population is sometimes called a deme, which may be defined as the community of potentially interbreeding individuals at a given locality.”
     
  3. 
     NATURAL SELECTION IS REALLY A PROCESS OF ELIMINATION.
     
     1. 
        2-step process:
        
        1. 
           everything leading up to the production of the new zygote.
           
           1. 
              EVERYTHING left up to chance.
              
        2. 
           Elimination: the “goodness” of the individual is continually tested.
           
           1. 
              “Survival of the fittest.” (Selection)
              

*Perhaps Hunter-gatherers (H-Gs) only appeared at the end of the last glaciaration.

*Our ancestors must have varied widely (and had varied technologies) in order to be able to survive in such varied climates.

*The fact that a habitat is good for farming does not make it equally good for foraging and vice versa.

*Women may use food from men merely to speed up their reproduction rate.

*Central place foraging is typical among most human foragers. = “central place provisioners”

*Highly variable species!

*Technological Advances: “The bow was such a technological leap forward that it could have led to an increase in meat consumption and population growth rates, eventually reducing game populations in certain areas and hastening the adoption of agriculture.”

As primates, our evolutionary history was contingent on what happened in earlier primate evolution. Primates provide key Comparative Data on relationships between aspects of behavior, ecology, and anatomy relevant to humans.

1. 
   Evolutionary Context
   
2. 
   Primate Diversity
   
3. 
   Primate Adaptations
   

1. 
   Evolutionary Context
   
   1. 
      Linnaen Taxonomic System
      
      1. 
         (Complex to basic) Domain->Kingdom->Phylum->Class->Order->Family->Genus->Species
         
      2. 
         Hierarchical scheme of classification with species most basic unit
         
      3. 
         Classification based on function (biologically arbitrary)
         
      4. 
         Classification should reflect evolution
         
   2. 
      Evolution is change over time, therefore novelties (features that have changed) provide evolutionary information.
      
      1. 
         Closely-related organisms share novelties derived from a common ancestor (homologies)
         
   3. 
      Key distinction: Clade-share same common ancestor (better for evaluating evolutionary relationships) vs. Grade-similar level of organization
      
2. 
   Primate diversity
   
   1. 
      Prosimians(Before Apes)
      
   2. 
      Strepsirhines
      
      1. 
         Very “primitive” primates.
         
      2. 
         No wall (septum) behind orbit
         
      3. 
         Reduced upper incisors
         
      4. 
         Grooming claw
         
      5. 
         Tooth Comb
         
      6. 
         Nails & Claws
         

• 
  Differences between Anthropoids (Monkeys) and Prosimians: Anthropoids have fused frontal lobe, fused manibular symphysis, postorbital closure, larger brain¸ lacrimal bone in orbit, nails
  

2. 
   Anthropoids (Monkeys)
   
   1. 
      New World Monkeys (Platyrrhines)
      
      1. 
         100 g-10 kg, Broad, flat external nose, Very diversive, 2 1 3 3, Underwent adaptive radiation, arrived in S. America 30 mil yrs ago
         
   2. 
      Old World Monkeys
      
      1. 
         Two subfamilies
         
         1. 
            Colobines-Leaf Eaters
            
         2. 
            Cercopithecines-omnivores
            

-Similarity between baboons and mandrills occurs namely because of CONVERGENCE- which is an expected outcome of natural selection

-Difference between Old World Monkeys and Apes (Hominoids)- Apes have narrow nose, narrow palete, while apes have a larger brain, single molars, long arms

1. 
   Apes
   
   1. 
      Less Apes: Gibbons, Saimangs
      
   2. 
      Great Apes: rangutans, gorillas, chimpanzees, humans
      
1. 
   Primate Adaptations
   
   1. 
      KEY POINT: Primates are generalized arboreal, tropical mammals, and the niche: species context within an ecosystem
      
   2. 
      Primates are exclusively tropical, except some macaques
      
      1. 
         Habitat-Forest, Gallery Forest, Woodland, Savanna
         
      2. 
         Diet-As generalists, primates tend to be omnivors
         
         1. 
            Body Mass/BMR: direct relationship
            
         2. 
            Diet-> Log Matt. Rate vs Log Body Mass-> Higher animal higher rate of metaboli rate
            
         3. 
            One possible explanation involves the notion that bigger body has a longer throughput time, and moer fermentation.
            
         4. 
            Varied Diet requires generalized teeth
            
         5. 
            Inventory
            
            1. 
               Small, nutritious, hard to get, binocular vision, manual dexterity Small, Nocturnal, tough exoskeleton
               
            2. 
               Frugivory
               
               • 
                 Seed dispersonrs, coevolution with angiosperms
                 
               • 
                 Selectivity- Color sensitivity, touch, manual dexterity
                 
            3. 
               Folivory
               
               • 
                 Problem=celluslose, foregut fermentators, hindgut germentat fermentators.
                 

-Fruit Eaters: Long, small intestine, broad incisors

1. 
   Flesh, eggs, etc.
   
2. 
   Another key adaptation for diet: vision,
   
   1. 
      Enclosed forward facing orbits
      
   2. 
      Stereoscopic vision
      
3. 
   Olfaction thought to be less important.
   
   1. 
      But, how do we smell?
      
      1. 
         In test, humans performed just as well as dogs tracking down chocolate and duck
         
      2. 
         Humans have good sense of smell
         

4. 
   Highly Tactile
   
   1. 
      Nails instead of claws, sensitive tactile pads
      
   2. 
      Good Climbers
      
      1. 
         Divergent big toes/thumbs, long, curved fingers, long palms
         
         1. 
            gibbon, chimp, gorilla
            
   3. 
      Locomotion
      
      1. 
         Different habitats pose different locomotor challengers
         
         1. 
            The higher metabolic rate, the more you tend to weigh, and the more you weight and have a higher metabolic weight, the more terrestrial you are, while on the other end, the less watts/grams the more arboreal you will be.
            
      2. 
         Most primates are quadrupeds (arboreal/terrestrial)
         
         1. 
            Dog, Monkey
            
         2. 
            Have dorsal scapular, narrow thorax, mobile hips, powerful elbow, bowed radius, mobile shoulder, plantigrade feet, bowed radius
            
      3. 
         Some are suspensory
         
         1. 
            High shoulder, flexible hip, long arm and wide forearm, long, curved fingers, flexible wrist (Gibbon and orangutan)
            
      4. 
         Knuckle-walking
         
      5. 
         How to be terrestrial and suspensory arboreal and BIPEDALISM
         
         1. 
            Has traces of quadrupedal adaptation, suspensory adaptations, and knuckle-walking adaptations
            
   4. 
      Size (and its consequences)
      
      1. 
         Body size has other consequences/effects
         
         1. 
            Specifically, life history
            
         2. 
            Larger BMR, body mass, metabolic rate: More open, long lived , slow matures K-Selected
            
         3. 
            Smaller BMR, body mass, metabolic rate: Cryptic, short-lived, fast maturers, r-selected
            

5. 
   Sociality & Cognition
   
   1. 
      Primate brains-highest on graph of Log Body Mass versus Log Brain Mass
      
   2. 
      Chimp(50 kg animal): 350-400 cc
      
   3. 
      Human (70 kg animal) :1300-1400 cc
      
   4. 
      Expansion is primarily in neocortoex (occibital lobe, gyri, sulci)
      
   5. 
      Primates are smart as a result of namely COMPLEX SOCIAL GROUPS rather than diet, predation
      
   6. 
      Larger groups: Mostly diurnal anthropoids
      
      1. 
         Most prosimians: Small, nocturnal, solitary
         
      2. 
         Monkeys, apes, etc.: Larger diurnal groups
         
   7. 
      Individuals live in groups because:
      
      1. 
         Potential fitness costs:
         
         1. 
            Increased visibility to predators, Intragroup competition for food
            
      2. 
         Potential fitness benefits:
         
         1. 
            Protection from predators, improved access to food (intragroup competition), access to mates, assistance in caring for offspring
            
         2. 
            But, intragroup competition for food and improved access to food (intragroup competition) are VERY habitat specific
            
   8. 
      Habitats differ in resource distribution
      
      1. 
         High vs. Low Density
         
      2. 
         Small vs. Large Patches
         
      3. 
         Also, resource distribution matters most for females, and female distribution matters a lot for males
         
      4. 
         Keystone resources and fallback foods are also important to the existence of species and available resources
         
      5. 
         Consequences of group life Complex social hierarchy, interactions, intrasex competition
         
   9. 
      Social intelligence
      
      1. 
         Brains are expensive; probably why more social animals don’t have big brains
         
   10. 
       Another consequence of group life:
       
       1. 
          Intrasex competition
          
          1. 
             Polygynous dimorphic canines
             
          2. 
             Monagamous monomorphic canines
             

1. 
   Conclusion
   
   1. 
      Human specializations are largely contingent on being primates
      
      1. 
         Specifically, humans are:
         
         1. 
            Smart
            
         2. 
            Visual and tactile
            
         3. 
            Generalists
            
            1. 
               Diet (high quality foods and omnivores)
               
            2. 
               Specific locomotion
               
      2. 
         Humans are often unique and specialized in that:
         
         1. 
            We are large bodied, but don’t eat low quality food
            
         2. 
            We have large social groups, but not large canines
            

• 
  Primates are territorial and defend high quality resources and monitor the environment
  

1. 
   Evolutionary relationships between humans and apes (ancestors)
   

2. 
   Comparative methods (behavioral reconstruction of fossils)
   

3. 
   Contrast with humans ( last common ancestry)
   

1. 
   Evolutionary Relationships
   

1. 
   Monophyletic groups: descendants share a common ancestor
   

1. 
   Why important
   

2. 
   History: Darwin and Huxley believed humans more closely related to African apes: chimps and gorillas
   

3. 
   Realtionships very crude in early 20th century (purely paleontological view)
   

4. 
   1950s-1960s: surprising genetic data
   

1. 
   Quantitaive comparisons of proteins generated pairwise patterns of similarity/difference
   

2. 
   Genetic data can be arranged in many different ways to form matrices, and there is one matrix which is a 'best fit' where row entries are very similar
   

5. 
   3 surprises
   

1. 
   Humans closest to African apes = trichotomy
   

2. 
   Protein change = molecular clock
   

3. 
   Relationships can be calibrated and measured
   

6. 
   Perhaps most surprising result: genetic differences not equal to phenotypic differences
   

7. 
   Humans are behaviorally and morphologically different from African apes but genetically similar
   

• 
  Genetic and phenotypic change are "uncoupled"
  
• 
  b/c most DNA not under selective pressure, it acquires and maintains random mutations over time at a certain ratea and can be used judiciously as a "clock"
  
• 
  Phenotypic change is non-constant and cannot be used as a clock
  

2. 
   Comparative method
   

1. 
   Comparison of species in phylogenetic context to test/infer relationships between variables
   

1. 
   Relationship between diet and tooth size and structure
   

2. 
   Frugivores have larger brains and smaller guts than leaf-eaters
   

2. 
   Key point: such correlations are only 'patterns of association'
   

1. 
   A and B usually correlated in living species
   

2. 
   Therefore, if a fossil exhibits A, then we can expect B
   

3. 
   Correlation is not causation
   

3. 
   Key ape characteristics
   

1. 
   Tropical
   

2. 
   Forest
   

3. 
   Fruit-eaters
   

4. 
   Arboreal
   

5. 
   Variably social
   

6. 
   Smart
   

4. 
   What are critical factors necessary for survival and reproduction
   

1. 
   Food
   

1. 
   In patches, size has important effect in feeding strategy
   

2. 
   Safety
   

1. 
   How to avoid predators/aggression - interspecific: be social, choose resting place carefully
   

2. 
   Intraspecific:be social and use strategies for sex/age/rank
   

3. 
   Mates
   

1. 
   Reproduction requires investment of time/energy, sexes differ
   

1. 
   Females are ecological sex b/c limited by resources available
   

5. 
   Primate social groups: one sex tends to migrate
   

6. 
   2 species of chimp: common chimp (allopatric) and pygmy/bonobo (synpatric)
   

7. 
   Chimps live in tropical forest, prefer fruit
   

1. 
   Fallback foods very important b/c of effects on behavior and morphology
   

2. 
   Both arboreal and terrestrial
   

3. 
   Trees important for feeding, resting, avoiding predators
   

4. 
   Males and females dimorphic by about 30%
   

5. 
   Social groups or 'communities' vary in size: 20-100 malesl and females
   

1. 
   Males stay in natal group: more social, related, defend territory: more social, more related
   

2. 
   Females migrate when mature: less social, less related
   

6. 
   Hierarchical and status-seekers
   

1. 
   Male cominance based on aggression
   

2. 
   Males dominant over females - contest competition
   

1. 
   Scramble competition
   

7. 
   Little food sharing
   

1. 
   Occasionally tolerate scrounging
   

8. 
   Meat: minor but highly prized part of diet
   

1. 
   Dominant male usually determines distribution - unlike human meat sharing
   

9. 
   Tool-makers
   

10. 
    Reproduction and life history
    

1. 
   Matings are promiscuous, dominant male sires most of new offspring, consortships occasionally form, infanticide sometimes a problem
   

11. 
    Life history: summary of…
    

12. 
    Bonobos have more slender bones: legs longer relative to arms, smaller heads
    

8. 
   Gorillas: lowland western, mountainous eastern
   

1. 
   Big and dimorphic
   

2. 
   Preferred food: ripe fruit, fallback: pith and leaves
   

3. 
   Upright climbers, suspensors when young, mostly knuckle walkers like chimps
   

4. 
   Live in groups with single male or at most two adult males plus females and offspring, females leave natal groups to join male groups
   

1. 
   Surplus male adults - intermale fights, group take-overs, frequent infanticide
   

5. 
   Reproduction: gorillas reproduce faster than chimps, females first reproduce about 10 years vs 13-15 in chimps, interbirth interval is about 4 years vs. 5.5 in chimps, lifespan less
   

6. 
   Morphologically like chimps but bigger, how?
   

1. 
   African forests continually expanding and contracting creating isolated zones - areas where you can get allopatric speciation - fate of such isolation is to go extinct or evolve
   

2. 
   If forest isolate = fruit poor, one solution is to get bigger to cope with lower quality food
   

Many changes in shape scale with changes in size

African apes are larger and smaller versions of the same animal

Last common ancestor between gorillas and chimps must have been chimp-like, as well as between humans and chimps