Anthropology 151-Midterm 1

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Genus

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– Plural of genus = genera

– Includes one or more species

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Species

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– Singular of species = species

– A group of organisms capable of mating and
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producing fertile offspring (Biological definition)

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Why put people with primates?

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Because of shared characters:




- excellent vision



- grasping hands



- long gestation and


infant dependency

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Biological Evolution

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Defined as genetic transformations of populations through time

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1. Production

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of genetic variation via mutation and other genetic processes;

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2. Reduction

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of this variation primarily by natural selection;

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3. Species formation

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by reproductive isolation

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Production of genetic variation

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produced by chemical changes in the DNA (i.e. mutations) random with respect to the direction of evolution

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Reduction of genetic variation

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• Occurs primarily by natural selection

• It can also occur via genetic drift

• Natural selection shapes genotypic variation each
generation, but it operates on phenotypic variation

IMPORTANT: Natural selection is the guiding force in evolution but it has no foresight. It simply results from the fact that the best adapted variants
will tend to leave more offspring each generation.

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Darwin’s Four Postulates

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1. Individuals in populations differ from one another


2. Offspring resemble their parents: heritable traits


3. Tendency to overpopulate results in a “struggle for existence”


4. “Best fit” variants tend to leave more offspring

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1. Individuals in populations differ from one another

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from one another


• Both phenotype and genotype vary greatly

– Genotype - individual genetic make-up

– Phenotype - expressed genotype (i.e. behavior or morphology)


• 40% to 50% of coding loci exist in allelic form

– Allele - an alternate form of a gene


• Phenotypes are determined to some degree by genotype, but are also influenced by the environment


• All of the above mean a great deal of variability exists between individuals, but remember that only phenotypic variation is acted upon by natural selection

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3. Tendency to overpopulate

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• Darwin derived this from Malthus
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• Malthus wrote that with no obstacles opposed to them, the natural tendency of living things is to increase in number geometrically from generation to generation









• Available food, however, expands arithmetically, so population size is checked by lack of resources


• Obstacles that could limit population growth include:


– limited resources (i.e food and shelter)


– negative effects of predators and pathogens (such as parasites and disease)
More gametes are produced than can possibly survive


For example, the female cod lays two million eggs, but on average only two offspring
survive to reproduce

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4. Best fit variants tend to leave more
offspring

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Darwin proposed that in the “struggle for existence”, individuals possessing variations in phenotype “useful in the struggle” would leave more
descendants than others in the population


Differential success (and failure) at surviving and reproducing by individuals of a population as a function of their phenotypes, coupled with the strong tendency of offspring to resemble their parents, is
what Darwin called “Natural Selection”

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Natural Selection

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Natural selection operates on differences among individuals


Its evolutionary consequence is observed in the changing (or unchanging) proportions of genotypes and phenotypes in populations from generation to
generation

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Stabilizing Selection

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Most selection is stabilizing

It tends to prune off extremes, and favors
average and intermediat

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Directional selection

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Beak depth in finches changed after a drought – birds with deeper beaks were less likely to die because they could process large, hard seeds.


Average depth of finch beaks changed after a drought

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Reproductive Isolation

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• The last basic process of evolution– the formation of a new species by reproductive isolation.
All species have populations that live in different habitats
• If gene flow gets restricted somehow between any of these populations and the main species, then that population may begin evolving new adaptations to the different habitat.
Some of these isolated populations acquire reproductive isolating mechanisms.


If formerly isolated populations come to overlap in habitat but are reproductively isolated, they can be recognized as separate species.

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Reproductive Isolating Mechanisms:
• Mechanical

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– Reproduction may be physically impossible

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Reproductive Isolating Mechanisms:
• Temporal

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– Two populations might be capable of interbreeding but they
have developed different breeding seasons

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Reproductive Isolating Mechanisms:
• Behavioral

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– They might be capable of interbreeding but may have developed disparate mating behaviors

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Reproductive Isolating Mechanisms:
• Mate Recognition

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– They may have diverged phenotypically to the point that they
no longer recognize each other as mates

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Reproductive Isolating Mechanisms:
• Hybrid Inviability

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– Interbreeding may occur, but fail to produce viable offspring

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Microevolution

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involves studying the processes that produce genetic changes each generation (genetics and ecology)

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Macroevolution

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is the study of changes observed through geological time and deals with trans-specific evolution (paleontology and comparative biology)

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phyletic gradualism

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change occurred gradually through time
This implies that within a lineage, change occurs gradually along branches
(anagenesis)

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punctuated equilibrium

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the pattern seems to be one of long periods of little change (stasis) followed
by rapid change (punctuation)
Punctuated equilibrium postulates change occurs mostly at speciation events (cladogenesis)


Small populations isolated from the larger population undergo reproductive isolation


When the new species expands to overlap its parent, it becomes visible in the fossil record

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What evolution is not...

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The most common mistake is the belief that evolution produces a hierarchy of species, like a staircase with
humans at the top
Another common misconception is that evolution is goal directed - this is known as orthogenesis
Yet another very common misunderstanding is that apes and monkeys living today are
our ancestors

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How to become a fossil

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occurs when hard parts of the body (bones and teeth), are preserved by gradual replacement of their chemical compounds by minerals from the surrounding medium

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• Fossilization:

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– Possible only when animal's carcass is made inaccessible to predators and scavengers immediately after death


– Can take place in very dry conditions but may take much longer since moisture is necessary to the process


• In the absence of excessive microbial activity, hard parts of the body, such as the bones and teeth, are preserved by gradual replacement by minerals present in the surrounding medium.

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Steno’s Law = Law of Superposition

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– Strata deeper in the earth’s crust are older than shallower
strata in undisturbed areas


– Important that strata are undisturbed – fossils can be buried intrusively and re-deposited – this is not helpful for dating

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How do we know if a fossil is intrusive (i.e., not the same age as its strata)?

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• Bones that are buried and covered by soil take up the same proportion of Fluorine that is in the soil.


• We can measure the concentration of Fluorine in the fossil and compare it to concentrations in other fossils buried nearby.


• But it only works for fossils found at the same site.

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Absolute dating

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methods allow us to estimate the age of a fossil in a direct quantitative way
Most widely used absolute dating methods are radiometric methods: K/Ar,
C14, Uranium series, etc.

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Relative dating

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methods only allow us to say a fossil is older or younger than another, can give us a probable range of dates
Probably the most commonly used relative dating method is biostratigraphy
Flourine analysis mentioned earlier is an example of relative dating

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Key to determining climatic conditions of the past is oxygen isotope analysis of deep-sea cores


Oxygen occurs in 2 isotopes: 16O and 18O


Their ratio in deep sea cores tells us about what past climatic conditions were like.

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Oxygen Isotope Analysis

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• 16O weighs less, and so is high in water evaporating from the seas, and, therefore, in precipitation.


• In warm times, 16O returns quickly to the sea & 16O concentration is the same as before.


• During cold times, 16O is trapped in glacial ice. The ratio of 16O:18O declines.
• These patterns are detectable in cores of lake and sea floors.
Organisms called foraminifera live deep on the sea floor, where they take in oxygen from the ocean
When they die, they solidify but keep the same ratio of oxygen isotopes as when they were alive

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“superordinal” group called Archonta:

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– Primates, treeshrews, colugos, and bats

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Before phylogenomics

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primates were grouped in Archonta with bats, flying
lemurs, and tree shrews
Phylogenomics groups primates with flying lemurs and tree shrews in a group called Euarchonta


Euarchonta are closely related to rabbits & rodents in a group called Euarchontoglires

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Fossil primates are found

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as early as 65 mya if plesiadapiforms are considered primates
• But molecular evidence repeatedly suggests that the first primates may have appeared as early as 80-90 mya.

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What does an earlier origin mean?

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It means primates lived through the event that killed the dinosaurs.
K/T EXTINCTION

EVENT

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New models for the position of India ~65 Mya

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In time for primates to get from India to Asia and
Africa!
Primates could have dispersed from S. America to Indo- Madagascar via Antarctica, and then to Asia and Africa in time to leave their fossils behind.

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How to reconcile the fossil and molecular data?

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First, there are very few fossil mammals of any kind coming out of the Cretaceous.

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K/T Extinction and Primate Radiations

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The explosion of fossils afterward could have been a result of rapid expansion after the dinosaurs and others died off.