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Lecture 4

ASM 104 Lecture 4: ASM 104 - Module 4 - Primate and Human Beginnings


Department
Anthropology (Science and Mathematics)
Course Code
ASM 104
Professor
Christopher Stojanowski
Lecture
4

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Module 4: Primate and Human Beginnings
This module will cover the primate and human fossil record from approximately 53 to 2.5 million years ago!! There will be
information on primate origins, their evolution into the species that we know today, and of course the early hominins. The context
for the evolution of hominins, i.e., paleoecology, will be identified, and the morphological adaptations that identify bipedalism will
be explored. Finally, we will discuss the diet of the early members of our lineage.
This odule’s leaig outoes ilude:
1. Identify the temporal and geographic context of hominin evolution
2. Identify hominin synapomorphies
3. Identify the signatures of bipedalism in the skeleton
4. Identify the key synapomorphies for the most important species of fossil hominins
5. Place hominin species in a relative temporal order
6. Identify key technological, morphological, and social factors that are associated with the genus, Homo
Lectures 1-4/9
Primate Origins and Evolution
Modes of Evolution and Primate Origins
Why do all primates share the feature that they have?
2 reasons
o They had a common ancestor that was adapted to a particular way of life
o They originated in a particular habitat that promoted that way of life
Modules covers modes of evolution and 3 hypotheses about how primates originated
o The Arboreal Adaptation Hypothesis
o The Visual Predation Hypothesis
o The Angiosperm Hypothesis
The Phenomenon of Phylogeny
Darwin showed not only that organisms changed through time, but that one species could diverge into two or more descendants
o If speies did ot diege ito diffeet speies, e ould’t hae the hudeds of piate speies that eist toda
How does that happen and over how long of a time span?
Evolution
2 timings in evolutionary processes
o Modes
Cladogenesis
o Cladogenesis- the splitting of branches
o Ex. ancestral species splits into species A and B
Anagenesis
o Anagenesis- a transformation of an ancestral species into a descendant through gradual stages; ancestral
species can keep existing or not
o Ex. from A to B, from B to C
Morphospecies- changes in morphology
Chromospecies- small changes through time
o Tempo (or timings)
Gradual (phyletic gradualism)
o Gradual- occurs when morphological change accumulates gradually through time in evolving lineages
Fossil record often has gaps in these lineages
They become as a history of the world
Punctuated (punctuated equilibrium)
o Cladogenic event occurs rapidly as a response to a perturbation in the environment; speciation occurs
o Followed by a long period of equilibrium or stasis in which organisms are fine within their environments
Gradualism vs. Punctuated Equilibrium
Gradualism- is always a matter of character transformation
Cladogenetic punctuated equilibrium- is a splitting of branches
Through time, whether slow or rapid, there are eventually new species
Macroevolution
Evolution between species
Evolution of major phenotypic changes
Evolution is genetic change in a biological population over time
o Genetic is allele change
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Macroevolution is evolution on a grand scale what we see when we look at the over-arching history of life: stability, change, lineages
arising, and extinction
o Macroevolution- an accumulation of those genetic changes over a longer period of time that results in the myriad of species
Mutation, gene flow, genetic drift, natural selection + 3.8 billion years = macroevolution
Divergent Evolution
Names for the differences in relationships among organisms that occur through time
o First: divergent evolution
Divergent evolution- One ancestor evolves into two or more species, and they continue to evolve and become less and less alike over
time
o Common ancestor evolves
o A lot of time has passed before getting the species that we have today
Parallel Evolution
Second: parallel evolution
Parallel evolution- occurs when similar traits evolve independently from a similar ancestral condition
o Ex. vertical clinging and leaping in indris and tarsiers that descended from the same ancestor, but overtime are in different
groups, or clades
o Primate ancestor in common at some point in the past, but they do not share an immediate common ancestor
Both species are in a lineage that has evolved away from that common ancestor and they have independently
acquired the trait (vertical clinging and leaping)
o Ex. million years on Madagascar  common ancestor  millions of years in Asia
Different from divergent evolution because both species are in the same Order, in this case
Convergent Evolution
Third: convergent evolution
Convergent evolution- occurs when two or more groups that are not related resemble each other because of the utilization of similar
habitats and the adoption of similar ecological roles
o Different lineages and they share characteristics because of what they do rather than what group they belong to
o Analogous structures- traits arising through convergent evolution
Ex. bat, bird, and pterosaur wings
o They do not share a common ancestor, but have evolved wings for a specific function; flying
o Ex. ancestral bird  analogous groups  ancestral mammal
Different from parallel in that these groups do not have a common ancestor that can be identified
o Similar to, but distinguishable from parallel evolution
Theefoe…
The initial primate must have originated by splitting off and diverging from another mammalian species
Ex. shrew
o Mammals likely resembled a shrew, which is in the order Insectivora
o Primitive mammals with many teeth are terrestrial
o Some time in the distant past, some of those insectivorous mammals became arboreal like this tree shrew
o Primitive mammal might resemble an ancestor to primates
Original Primate Features
First time we can identify a primate, it needs to have the features that make it a primate, including forward facing eyes, grasping hands
and feet, nails on at least the hallux, etc.
Look for hypothesis as to why primates became primates; we look at what those features represent
The Arboreal Theory of Primate Origins
Grafton Elliot Smith and Frederick Wood Jones: two paleontologists in 1913
o Came up with the arboreal theory for primate origins
o Suggesting that one only needed to look at the arboreal setting, and that primates were primates because they lived in the
trees; they were adapted to an arboreal life
Aoeal life, i ad of itself, as the ke otet i hih atual seletio ould fao piate attiutes
Fo eaple…
Grasping hands and feet could hold onto branches
And
Running and leaping in an arboreal environment required binocular vision for judging distances
o Bioula isio so the did’t fall out of tees
And
Sophisticated brains were needed to process complex three dimensional space
And
Sense of smell was of diminished value in the shifting air of tree tops
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o “ese of sell as edued eause it did’t atte hat ou selled i the tops of tees eause the id kept shifting,
which brought different smells all the time that were not important to survival
Any problems with the arboreal theory?
We know other mammals are arboreal and do NOT have primate features
Living in trees (having an arboreal existence) does not depend on primate features
o There are squirrels that have claws, sideways facing eyes, and no grasping hands and feet, and they do fine in trees
Other ideas about why a primate became a primate?
Visual Predation Hypothesis
Matt Cartmill (1972) proposed a new hypothesis for the origination of the primate order
Suggested that primates evolved from small mammals who lived in bushes at the forest floor
o They ate insects that also lived on the forest floor
o In order to catch an insect, these small mammals may have used their hands; therefore would have to be able to grasp objects
AND they would have to be able to see insects sitting in front of them in order to be able to grasp them (claws would not be
necessary)
Suggested that features for catching insects were then pre-adaptations for climbing on small, thin branches in trees (where one could
also look for insects)
Depth perception was needed to catch insects
It would serve well to be able to leap in trees after the insects
Thin branch access would have opened up new foods such as fruits
o There was no adaptation for getting at fruit on terminal or the ends of branches by climbing in the tree like birds or bats could
do since they had wings
Orbit Convergence and Hand Mobility
Animals that hunt and track prey items tend to have high degrees of optic convergence and prehension in their extremities
Cartmill determined this by looking at adaptations in other mammals
o Ex. carnivores
They have some degree of optic convergence caused by their eyes facing further forward
If you have a cat, you know it can kind of grasp and play with mice and birds (claws help with that)
Stereoscopy or Parallax View
Extreme convergence actually diminishes depth perception
Thus, this trait would be most useful in animals that needed a wide field of stereoscopic vision at close range
Parallax view- displacement of a relatively close object compared to a more distant background along two different lines of sight as the
location of the observer changes
Objects, such as insects, have a larger displacement than things that are further away
o Ex. close one eye and hold up a finger; align it with an edge of something vertical; then close that eye and open the other;
fige appeas to oe; fige is’t atuall displaed ut ou point of observation changed (this is parallax)
Stereoscopy vision would be important in hunting those insects close up because it prevents displacement of the bug
Cartmill Suggestions
Cartmill suggested that the ancestral primate was an insect hunting specialist that hunted in fine branches in the forest canopy or
undergrowth
Already arboreal mammals came to rely on visually directed predation to capture arthropods, insects, and other small prey
Of Course There is a Slight Problem
This suggests that the earliest primate did not depend on fruit, flowers, or other plant matter although primitive lemurs do just that
Strepsirrhines are the most primitive living primates
o They are not as derived as haplorrhines, and should therefore retain primitive characters
o Creates a problem with the visual predation hypothesis
Hoee…
Robert Sussman (biological anthropologist) noted that fruit bats have forward-facing eyes, just like primates
Fruit bats have a primate-like vision system, BUT eat exclusively from angiosperm products
o They eat fruit only from plants called angiosperms
Ete Agiospes…
Angiosperms are flowering plants (fruit-bearing plants) that evolved in the late Cretaceous geological period, about 90 million years ago
They had an adaptive radiation in the Paleocene, which was followed by the first appearance of Primates
The Hypothesis Was:
Sussman’s hpothesis
o Because angiosperms were a new species, and had a huge radiation across the planet, there would have been abundant fruit
resources in the terminal branches of trees that were likely utilized by the earliest primates
o New availability of rich AND abundant fruits and flowers in the terminal branches of tropical forests provided a windfall of
resources that were utilized by the earliest primate ancestors
This Fits ith All of the Piate Taits Beause it…
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