3. Gradualism (i.e. evolution proceeds slowly and WITHOUT jumps)
5. Natural Selection
*Darwin: Evolution is descent with modification.
FITNESS: ability to reproduce and act
ADAPTATION: useful feature, shaped by natural selection that PROMOTES SURVIVAL.
--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.
(1800s) Most people did not believe his Theory of Adaptation because they believed that adaptations were the result of divine creation.
Henslow = the professor who encouraged Darwin to travel aboard the HMS Beagle and map the nature found on the coast of South America.
Darwin’s 3 Postulates
The ability of a population to expand is infinite, but the ability of any environment to support populations is always finite.
Organisms within populations vary, and this variation affects the ability of individuals to survive and reproduce.
The variations are transmitted from parents to offspring.
*Darwin’s “Natural Selection”:Traits that confer advantages in survival and reproduction are retained in the population, and traits that are disadvantageous disappear.
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.
Evolutionary Theory: Phenotypes (i.e. finch beaks) will continue to deepen until the cost of larger-than-average beak size exceeds the benefits.
Even if phenotypes are not changing, natural selection is still occurring. In fact, populations do not remain static unless natural selection is operating!
Adaptation: comes from competition among individuals, and not between entire populations or species!!
Natural selection can help the individual but harm the overall species group.
Continuous variation(slow, steady, and constant with intermediate stages of characteristics) vs. Discontinuous variation (i.e. mutations)
Small, random variations of natural selection lead to complex adaptations.
Convergence: the evolution of similar adaptations in unrelated groups of animals.
*We don’t always have fossil records proving jumps in evolutionary patterns, but that’s probably because our fossil record is quite sparse!!
*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!)
HOWEVER, genetics account for much inheritance and NOT blending!!
CHAPTER II: Genetics
Genes are inherited from both the mother and father
Both the mother’s particles and the father’s particles are equally likely to be transmitted. Therefore, it’s an INDEPENDENT ASSORTMENT!
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).
Mitosis—normal cell division; Miosis—sexual cell division that produces gametes
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.
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.
CHAPTER III: The Modern Synthesis
Phenotypes vs. Genotypes
Population Genetics: What happens to genes in populations that are undergoing natural selection
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!!
Goal of Evolutionary Theory: HOW do genetic frequencies change over time?
4 processes that alter the frequencies of genes and genotypes:
Random mating among humans is similar to the random union of gametes!!
Weinberg equilibrium: The realization that sexual reproduction alone does not alter phenotypic and genotypic frequencies was the key to understanding how variation is maintained!!
**Although sexual reproduction and random mating alone cannot lead to evolution over time, natural selection can produce changes in the frequencies of alleles!!!** MODERN SYNTHESIS: using Mendelian genetics to explain continuous variation.
*There are no blending of genes during sexual reproduction. Even if offspring appear to be a blended/intermediate between their parents, sexual production actually produces NO blending in the genes themselves!
* “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.
Reading: Mayr 2001
--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.”
Even greater breaks in continuity occur where there are geographical boundaries limiting dispersal.
“A local population is sometimes called a deme, which may be defined as the community of potentially interbreeding individuals at a given locality.”
NATURAL SELECTION IS REALLY A PROCESS OF ELIMINATION.
everything leading up to the production of the new zygote.
EVERYTHING left up to chance.
Elimination: the “goodness” of the individual is continually tested.
“Survival of the fittest.” (Selection)
Reading: Marlowe, 2005
*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.”
Lecture: February 13, 2007
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.
PRIMATES as MAMMALS:
Linnaen Taxonomic System
(Complex to basic) Domain->Kingdom->Phylum->Class->Order->Family->Genus->Species
Hierarchical scheme of classification with species most basic unit
Classification based on function (biologically arbitrary)
Classification should reflect evolution
Evolution is change over time, therefore novelties (features that have changed) provide evolutionary information.
Closely-related organisms share novelties derived from a common ancestor (homologies)
Key distinction: Clade-share same common ancestor (better for evaluating evolutionary relationships) vs. Grade-similar level of organization
Very “primitive” primates.
No wall (septum) behind orbit
Reduced upper incisors
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
New World Monkeys (Platyrrhines)
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
Old World Monkeys
-Both subfamilies very SPECIOSE
-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
Less Apes: Gibbons, Saimangs
Great Apes: rangutans, gorillas, chimpanzees, humans
KEY POINT: Primates are generalized arboreal, tropical mammals, and the niche: species context within an ecosystem
Primates are exclusively tropical, except some macaques
Habitat-Forest, Gallery Forest, Woodland, Savanna
Diet-As generalists, primates tend to be omnivors
Body Mass/BMR: direct relationship
Diet-> Log Matt. Rate vs Log Body Mass-> Higher animal higher rate of metaboli rate
One possible explanation involves the notion that bigger body has a longer throughput time, and moer fermentation.
Varied Diet requires generalized teeth
Small, nutritious, hard to get, binocular vision, manual dexterity Small, Nocturnal, tough exoskeleton
-Fruit Eaters: Long, small intestine, broad incisors
-Leaf Eaters: Enlarged long intestine
Flesh, eggs, etc.
Another key adaptation for diet: vision,
Enclosed forward facing orbits
Olfaction thought to be less important.
But, how do we smell?
In test, humans performed just as well as dogs tracking down chocolate and duck
Humans have good sense of smell
Nails instead of claws, sensitive tactile pads
Divergent big toes/thumbs, long, curved fingers, long palms
gibbon, chimp, gorilla
Different habitats pose different locomotor challengers
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.
Most primates are quadrupeds (arboreal/terrestrial)
Have dorsal scapular, narrow thorax, mobile hips, powerful elbow, bowed radius, mobile shoulder, plantigrade feet, bowed radius
Some are suspensory
High shoulder, flexible hip, long arm and wide forearm, long, curved fingers, flexible wrist (Gibbon and orangutan)
How to be terrestrial and suspensory arboreal and BIPEDALISM
Has traces of quadrupedal adaptation, suspensory adaptations, and knuckle-walking adaptations
Size (and its consequences)
Body size has other consequences/effects
Specifically, life history
Larger BMR, body mass, metabolic rate: More open, long lived , slow matures K-Selected
Smaller BMR, body mass, metabolic rate: Cryptic, short-lived, fast maturers, r-selected
Sociality & Cognition
Primate brains-highest on graph of Log Body Mass versus Log Brain Mass
Chimp(50 kg animal): 350-400 cc
Human (70 kg animal) :1300-1400 cc
Expansion is primarily in neocortoex (occibital lobe, gyri, sulci)
Primates are smart as a result of namely COMPLEX SOCIAL GROUPS rather than diet, predation
Larger groups: Mostly diurnal anthropoids
Most prosimians: Small, nocturnal, solitary
Monkeys, apes, etc.: Larger diurnal groups
Individuals live in groups because:
Potential fitness costs:
Increased visibility to predators, Intragroup competition for food
Potential fitness benefits:
Protection from predators, improved access to food (intragroup competition), access to mates, assistance in caring for offspring
But, intragroup competition for food and improved access to food (intragroup competition) are VERY habitat specific
Habitats differ in resource distribution
High vs. Low Density
Small vs. Large Patches
Also, resource distribution matters most for females, and female distribution matters a lot for males
Keystone resources and fallback foods are also important to the existence of species and available resources
Consequences of group life Complex social hierarchy, interactions, intrasex competition
Brains are expensive; probably why more social animals don’t have big brains
Another consequence of group life:
Polygynous dimorphic canines
Monagamous monomorphic canines
Human specializations are largely contingent on being primates
Specifically, humans are:
Visual and tactile
Diet (high quality foods and omnivores)
Humans are often unique and specialized in that:
We are large bodied, but don’t eat low quality food
We have large social groups, but not large canines
Primates are territorial and defend high quality resources and monitor the environment
Lecture: February 15, 2007
Evolutionary relationships between humans and apes (ancestors)
Comparative methods (behavioral reconstruction of fossils)