Anthropology 2.2

Nested hierarchies
1. Refers to the way taxonomic groups fit neatly and completely inside other taxonomic groups. For instance, all bats (order Chiroptera) are mammals. All mammals are vertebrates. Likewise, all whales (order Cetacea) are also mammals, and thus also vertebrates.
2. large box = inclusive
3. small box = relatedness
harder to define than to recognize
Biological species concept
*A group of organisms that interbreed in nature and are reproductively isolated
1. a depiction of species as groups of individuals capable of fertile interbreeding but reproductively isolated form other such groups
2. emphasis on gene flow and reproductive isolation
3. Recognition species concept: mate recognition
4. most used and preferred by zoologists
5. sometimes separate species mate but are infertile (e.g. mule)
6. According to this species concept, the way new species are first produced involves some form of isolation (geographical isolation)
7. Related to recognition species concept
Ecological species concept
1. The concept that a species is a group of organisms exploiting a single niche (ecological niche); this view emphasizes the role of natural selection in separating species from one another
2. Focuses on natural selection and emphasizes that speciation is a result of influences of varied habitats
Phylogenetic species concept
1. splitting many populations into separate species based on an identifiable parental pattern of ancestry
2. Species defined based on who is related to whom
3. Cannot know if interbreeding was/is occurring
4. Difficult to find/observe breeding in some cases – DNA
5. Fossils – morphology; ancient DNA
What is the most common and preferred species concept?
1. the process by which a new species evolves form an earlier species
2. the most basic process in macroevolution
Recognition species concept
*inability to recognize another as a mate prevents gene flow even when they are genetically compatible
1. A depiction of species in which the key aspect is the ability of individuals to identify members of their own species for purposes of mating (and to avoid mating with other species)
2. this type of selective mating is a component of a species concept emphasizing mating and is therefore compatible with the biological species concept
What species concept is compatible with the biological species concept?
Recognition species concept
Ecological niche
*the way a species makes a living
1. position of a species within its physical and biological environments
2. a species’ ecological niche is defined by such components as diet, terrain, vegetation, type of predators, relationships with other species, and activity patterns, and each niche is unique to a given species
3. together ecological niches come together to make ecosystems
*for each population the ecological niche will vary slightly, and different phenotypes will be slightly more advantageous in each. for example, one population might be more arboreal and another more terrestrial, but there would not be an intermediate population equally successful on the ground and in the trees
Ecological niches come together to make?
What does the biological species concept stress?
Gene flow and reproductive isolation
What does the ecological species concept stress?
Natural selection and ecological niches
Gene flow within a population helps maintain what? What happens without it?
1. Gene flow within a population helps maintain homogeneity
2. Lack of gene flow leads to differences
Even in the presence of gene flow, what can maintain differences between species?
Natural selection
3 Concepts as to how species form
1. Allopatric speciation
2. Parapatric speciation
3. Sympatric speciation
Allopatric speciation
1. Living in different areas; this pattern is important in the divergence of closely related species from each other and from their shared ancestral species because it leads to reproductive isolation
*this model requires complete reproductive isolation within a population, leading to the formation of an incipient species separated geographically form its ancestral population
2. difficult to observe, but it can be inferred from certain phenomena like ring species
3. Requires a physical barrier to gene flow
-Geographic isolation
4. Members of isolated populations diverge genetically from original population due to different selection pressures
What could be evidence for allopatric speciation?
Ring species
Ring species
Parent species -> barrier to gene flow and allopatric speciation -> two new species
Parapatric speciation
“weak” version
1.Partial geographic isolation, with selection against hybrids
2. reproduction isolation is required, so that the ranges of populations may be partially overlapping
3. a hybrid zone would form in an area between the two partially separated populations and more complete separation could then occur through enforcement of mate recognition and selective breeding
example: the fertile hybrids between savanna and hamadryas baboons
Sympatric speciation
“strong” version
1. No geographic isolation, natural selection alone may create or maintain species
2. occur completely within on population with no necessary reproductive isolation
3. in other words, two species result from the same geographical location
4. however this form of speciation, while possible, is not well supported by contemporary evidence and is thus considered the least significant of the three models
Adaptive radiation
1. The process in which a single species diversifies into a number of species in order to fill different ecological niches
2. the relatively rapid expansion and diversification of lifeforms into new ecological niches
3. a species or group of species will diverge into as many variations as two factors allow: 1) its adaptive potential 2) the adaptive opportunities of the available niches
A species will diverge into as many variations as two factors allow, what are they?
1. the species’ adaptive potential
2. adaptive opportunities of the available niches
is the term used to describe the manner or pattern of evolutionary change; dependent on environment
is the term used to describe the rate of evolutionary change; dependent on environment
two geographical areas come together
How does parapatric speciation select against hybrids? (baboon example)
Different baboons mate but hybrid doesn’t fit either environment well so natural selection selects against them
Lemurs and adaptive radiation
1. Lemurs are only on madagascar where there was huge biodiversity
2. most species weren’t there when madagascar originally broke off – not there when it became an island
3. Lemur ancestors went/floated to madagascar where there was wide biodiversity, no competition, and no predators
4. there were 120+ lemurs species but the large ones were killed now, now there are 30 species left
5. Each to their specialized ecological niche, examples:
cyanide bamboo eating lemur (no competition) and night lemur
2 Modes of evolutionary change
1. Cladogenesis
2. Andogenesis
1. mode speciation through branching patterns
2. two or more daughter species evolved from one parent species (allopatric speciation)
1. when one species (as a group) evolves into another over time
2. Entire species undergoes speciation in response to steady, directional environmental change
What mode of evolution change is produced by allopatric, parametric, and sympatric speciation?
1. Cladogenesis
Phyletic gradualism is a combination of what two modes?
Cladogenesis and Andogenesis
Phyletic gradualism
1. Speciation occurs through the slow and steady, constant accumulation of changes
2. both anagenesis and cladogenesis contribute to speciation
3. periods of change caused by geographical isolation
Punctuated equilibrium
1. long periods of stasis (no change) interrupted by episodes of rapid (in geological terms) cladogenetic speciation
2. concept that evolutionary change proceeds through long periods of stasis punctuated by rapid periods of change
3. Gould and Eldridge
4. Periods of rapid change could be caused by adaptive radiation
Who came up with punctuated equilibrium?
Gould and Eldridge
What are the 2 tempos?
1. Phyletic gradualism
2. Punctuated equilibrium
How are the 2 tempos considered in modern synthesis?
Evolutionary biologists have suggested that both modes and tempos occur; some groups of primates for instance, simply have slower or faster durations of speciation, which is why Old World monkeys typically speciate more slowly than the great apes
1. to reconstruct evolutionary relationships
2. family tree
3. based on similarity of characteristics
1. field of study that specializes in establishing the rules of classification (organization)
2. still uses Linneas’ scheme
3. classification
Linnean Hierarchy
nested (hierarchical) classification system that groups species based on shared similarities
Taxon (taxa)
1. any group in the hierarchy
Scientific binomial
unique name assigned to each species
1st part of scientific binomial/2nd part of scientific binomial
genus category/species name
Primata – primates includes prosimians, monkeys apes and our bipedal ancestors
Anthropoidea – monkeys apes and us
Hominoidea – apes and us
Hominidae – great apes and humans
Homininae – upright walking ancestors and us – only we are still around
Phylogeny can be based on similar characteristics but what is the issue?
1. Different structures can be used for similar functions – Bats and birds fly
2. Similar structures can be used for different functions – Human hand, bat wing and whale flipper
2 Different approaches to phylogeny
1. Evolutionary systematics – less rigorous definition of the kinds of traits that can be used to construct phylogenies
2. Cladistics – requires members of a group represent most recent shared ancestry
Evolutionary systematics
1. less rigorous definition of the kinds of traits that can be used to construct phylogenies
2. Goal is to build a classification that portrays general branching pattern of evolutionary history
3. Establishes grades (groups of species that share a close biological relationship and have a degree of overall similarity)
groups of species that share a close biological relationship and have a degree of overall similarity
1. Goal is to build a classification that accurately mirrors branching pattern of evolutionary history
2. Establishes clades (groups of species that share one last common ancestor)
1. (groups of species that share one last common ancestor)
2. lineage that share a common ancestor
1. evolutionary group that contains all members who share only one common ancestor
1. evolutionary grouping that includes members who may share more than one common ancestor
Analogous traits
1. similar characteristics that evolve independently b/c species inhabit similar environments = similar selective pressures = convergent evolution
2. These traits were not inherited from a common ancestor between the species – bat wing, bird wing, butterfly wing
exampe: Tasmanian Wolf: Australian Marsupial Mammal; Gray Wolf: North American Placental Mammal
1. similar characteristics that are based on genetic inheritance, reflect biological relatedness and common descent
2. Primitive or derived
Primitive (ancestral) traits
traits inherited from a distant ancestor, widespread among many descendant species
Example: upper limb
Derived traits
traits inherited from a recent ancestor; shared among a few closely related (sister) species
Example: bipedalism
Which traits are the only ones useful for reconstructing phylogenies ?
Shared derived traits
How to distinguish between ancestral and derived characters
1. Characters that appear early in development are ancestral – “ontogeny recapitulates phylogeny”
2. Characters that appear earlier in fossil record are ancestral
3. Characters that appear in outgroups are ancestral
What are genetic characters useful for?
Genetic characters, especially at neutral loci (not subject to natural selection) are especially useful and can even be used to date the time of branching between lineages
How use DNA to infer phylogeny
1. DNA of different species slowly diverges because members of different species do not mix genes
2. Genetic distance = a measure of overall genetic similarity (or dissimilarity) between two species
Genetic distance
1. a measure of overall genetic similarity (or dissimilarity) between two species
2. tells us how closely species are related – the more nucleotide differences, the bigger the genetic distance