Chapter 9 Flashcards
Bipedalism
walking upright on two feet
Hominin
humans and all of our extinct bipedal ancestors
and relatives since our divergence from the last common ancestor (LCA) with chimpanzees
Last common ancestor (LCA)
last common ancestor (LCA) with chimpanzees
The hypothetical final ancestor or ancestral population) of two or more taxa before their divergence.
Fossils
The remains or impression of an organism from the past
Paleoanthropologists
people who study human evolution
Encephalization
evolution of a big brain
Morphologically
the study of the form or size and shape of things; in this case, skeletal parts
East African Rift System
Ethiopia, Kenya, Tanzania, and Malawi
Site
A place in which evidence of past societies/species/activities may be observed through archaeological or paleontological practice
Use the terms “bipedal,” “hominin” and “last common ancestor” to explain what happened when our ancestors diverged from chimpanzees.
It’s when we started walking upright is when we deviated from chimpanzees
What do we know for sure about human evolution?
Yet there is still so much to understand. Modern debates now look at the relatedness of these species to us and to one another. New scientific techniques provide us with insight into the diets, environments, and lifestyles of these ancient relatives that was not available to researchers even ten years ago.
Phylogeny
The study of the evolutionary relationships between groups of organisms.
What ideas about human evolution were commonly held at one time but we now know are wrong? (use as many terms from the middle column as possible).
Increases in brain size do not necessarily correlate with an increase in intelligence in animals, especially if body size is not taken into consideration. However, the brain is an expensive tissue to build and maintain
Homo
human genus
Ardipithecus
Ardipithecus is an ancient hominin group that lived in Africa between 5.8 and 4.4 million years ago, before the emergence of Australopithecus and Homo
Paranthropus boisei
Paranthropus boisei is a species of australopithecine from the Early Pleistocene of East Africa about 2.5 to 1.15 million years ago. The holotype specimen, OH 5, was discovered by palaeoanthropologist Mary Leakey in 195
People often believe that brain size correlates with higher intelligence, but explain why this might not necessarily be the case.
Increases in brain size do not necessarily correlate with an increase in intelligence in animals, especially if body size is not taken into consideration
What do researchers basically believe about the brain?
Researchers therefore argue that the cost of maintenance must yield some evolutionary benefit
Taxa
Plural of taxon, a taxonomic group such as species, genus, or family
Taxonomies
The science of grouping and classifying organisms
Cladistics
Cladistics groups organisms according to their last common ancestors based on shared derived traits
The field of grouping organisms into those of shared ancestry
For example, if we use feathers as a trait, we can group pigeons and ostriches into the clade “birds.” Organisms that share the same traits.
Phylogenetics
The study of phylogeny (The study of the evolutionary relationships between groups of organisms).
Derived traits
Newly evolved traits that differ from those seen in the ancestor.
Clade
The field of grouping organisms into those of shared ancestry
Lumpers
large variability is expected among multiple populations in a given species over time
Splitters
species variability can be measured and that even subtle differences can imply differences in niche occupation that are extreme enough to mirror modern species differences
Polytypic
capable of interacting and breeding biologically but having morphological population differences
Chronospecies
Species that are said to evolve into another species, in a linear fashion, over time
What were taxonomies based on before DNA was discovered?
phylogeny (The study of the evolutionary relationships between groups of organisms)
How do researchers decide what organisms fit into a clade?
based on shared traits
What factors influence how researchers construct the hominin phylogenetic tree?
Constructed hominin phylogenetic trees are routinely variable, changing with new specimen discoveries, new techniques for evaluating and comparing species, and, some have argued, nationalist or biased interpretations of the record
Why do some researchers think a “braided stream” is a better metaphor than a tree?
More recently, some researchers have shifted away from “treelike” models of ancestry toward more nuanced metaphors such as the “braided stream,” where some levels of interbreeding among species and populations are seen as natural processes of evolution.
What challenges can fossils sometimes pose for researchers?
This could be because they do not easily preserve or are incomplete, making it difficult to compare and place within a specific species
Paleoenvironments
An environment from a period in the Earth’s geological past
Faunal Assemblages
Collections of fossils of other animals found at a site
Isotopes
Two or more forms of the same element that contain equal numbers of protons but different numbers of neutrons, giving them the same chemical properties but different atomic masses
Flora
The plants of a particular region, habitat, or geological period.
This chapter is about hominins, but paragraph two discusses the hippopotamus. What major point is the author making by including information about how the hippopotamus adapts to changes in climate?
It is an animal that thrives in environments that have abundant water to keep its skin cool and moist. If the environment for some reason becomes drier, it is expected that hippopotamus populations will reduce. If a drier environment becomes wetter, it is possible that hippopotamus populations may be attracted to the new environment and thrive.
What information can faunal assemblages provide us about what a site or region was like in the past?
comparing them to animals found in certain modern environments allow us to determine if the environments in the past mirror those seen today in the region. Changes in the faunal assemblages, as well as when they occur and how they occur, tell us about past environmental changes
What do isotopes tell us about diets?
if an animal ate more plants or meat
How can modern scientists tell what climate was like many millennia ago?
These can be studied by using marine core and terrestrial soil data and by comparing these lines of evidence across multiple localities/sites/regions
What aspects of early hominins were most likely affected by environmental change?
- the driving force behind the evolution of bipedalism terrestrial locomotion on two legs),
- the changing and diversifying of early hominin diets, and
- the diversification of multiple early hominin species.
Arboreal
one living in trees
Aridity Hypothesis
The hypothesis that long-term aridification and expansion of savannah biomes were drivers in diversification in early hominin evolution
Expansion of the savannah made hominins move from trees to the ground
Aridification
Becoming increasingly arid or dry, as related to the climate or environment.
Explain how this theory connects bipedalism and expansion of the savannah.
Because you need be to able to walk on the ground versus travelling in the trees
Sum up the evidence for the Aridity hypothesis.
Early hominims were associated with wetter climates and dust records increased over time
Ungulates
hoofed mammals of various kinds
Specialist vs. generalist eaters
Specialist eaters eat and rely primarily on specific food types
generalist are able to eat more varied and variable diets
Explain how ungulates who were specialist eaters compared with ungulates who were generalist eaters when the climate rapidly changed.
Specialist eaters eating and relying primarily on specific food types) faced extinction at greater rates than their generalist able to eat more varied and variable diets) counterparts because they were unable to adapt to new environments.
This meant that specialist eater species were often confined to isolated areas with dwindling resources, whereas generalist eaters were able to move out across the landscape in search of new food sources
Faunal turnover
the extinction
of many species and the speciation, diversification, and migration of many others to occupy various niches.
Quaternary Ice Age
The most recent geological time period, which includes the Pleistocene and Holocene Epochs and which is defined by the cyclicity of increasing and decreasing ice sheets at the poles
Interglacial
A period of milder climate in between two glacial periods.
Glacial
Colder, drier periods during an ice age when there is more ice trapped at the poles
What conclusion can we draw from faunal evidence in the Turkana basin?
Faunal evidence from the Turkana basin in East Africa indicates multiple instances of faunal turnover and extinction events, in which global climatic change resulted in changes from closed/forested to open/grassier habitats at single sites.
In the “interpretations” paragraph, the authors discuss whether the ungulate rapid turnover can be true for hominins. What conclusions do they draw?
Specialist hominin species do appear to exist for long periods of time during this time period, yet it is also true that Homo, a generalist genus with a varied and adaptable diet, ultimately survives the majority of these fluctuations, and the specialists appear to go extinct
Closed habitats
A phrase typically referring to a woodland, or tree-filled, environment.
Both the Savannah hypothesis and the Forest hypothesis provide an explanation for bipedalism. How are the theories different?
Savannah: Humans moved from trees to the ground because of the expansion of the savannah.
Forest: There is a hypothesis that the last common ancestor used an arboreal form of bipedal locomotion like orangutans and wasn’t a knuckle walker
Sum up the evidence for the forest hypothesis.
Pollen evidence from the site of Makapansgat in South Africa indicated that around the time early hominins occupied the area, it was a closed, wooded environment.
Similarly, the earliest evidence for bipedalism occurs in specimens are found in sites with evidence of closed habitats
What are some cautions about this theory the authors pose in the “interpretations” paragraph?
However, it is worth noting that preservation and resulting fossilization might be better in these kinds of environments, biasing this interpretation of the fossil record. Evidence for knuckle-walking in our more distant ancestors is also highly contested.
The previous hypotheses suggest that people adapted in response to particular changes—i.e. temperature. What makes Variability Selection Hypothesis different?
Unlike previous notions, this hypothesis states that hominin evolution does not respond to habitat-specific changes or to specific aridity or moisture trends. Instead, long-term environmental unpredictability over time and space influenced morphological and behavioral adaptations that would help hominins survive, regardless of environmental context. This would allow certain groups to develop genetic combinations that would increase their ability to survive in shifting environments.
Sum up the Variability Selection Hypothesis’s evidence for this theory.
large climatic variability and higher survivability of generalists versus specialists. However, this hypothesis accommodates for larger time-scales of extinction and survival events.
The last sentence of the “interpretations” paragraph reads” In some ways, this Variability Selection Hypothesis accommodates both environmental data and our interpretation of evolution toward greater variability among species and the survivability of generalists.”
Explain what the authors mean by this sentence.
It’s not so black and white. It allows for discrepancies that the other hypotheses don’t account for.
Super Lakes
creation of large super lakes e.g., Lake Baringo and Lake Turkana) within East Africa.
Solar precessional cycles
cyclical changes in earth’s axis rotation- or wobble- that have global climatic effects
How do we know super lakes existed in East Africa?
This is documented by the increase of diatomaceous lake sediments during these times
How did super lakes lead to speciation?
These expanded lakes would act as geographic barriers to hominin populations, allowing for changes and diversification in diet and adaptive behavior to the variable regions, even resulting in allopatric) speciation
In the “interpretations” paragraph, sum up the evidence for this theory and the unknowns that call it into question.
High levels of species diversity during these time periods as well as environmental indications of these barriers may allow for an interpretation of allopatric-speciation i.e., speciation due to geographic barriers)events. However, the degree of interspecific variability and the extent to which these barriers acted as drivers of speciation are still debated
This section sums up similarities and differences in hypotheses about hominin development. In this space group theories together that are similar. Next, group together theories that oppose each other in some way.
Obligate bipedalism
Where the primary form of locomotion for an organism is bipedal
Extant
living
Thermoregulation
Maintaining body temperature through physiologically cooling or warming the body
What two main theories are there about why humans are bipedal?
- that early hominins descended from trees, and so we were a product of an arboreal last common ancestor LCA) or
- that our LCA was a terrestrial quadrupedal knuckle-walking species, more similar to extant chimpanzees.
What evidence supports the first theory?
based on skeletal morphology of early hominin genera that demonstrate adaptations for climbing but not for knuckle-walking
Describe how changing environment (from forest to savannah) may have created selective pressure for bipedalism.
As the environmental conditions changed and a savannah/grassland environment became more widespread, the tree cover would become less dense, scattered, and sparse and bipedalism therefore would become more important
Describe the selective pressures for bipedalism.
Energy conservation, Thermoregulation, and Bipedalism freed up our ancestors’ hands such that they could more easily gather food and carry tools or infants. This further enabled the use of hands for more specialized adaptations associated with the manufacturing and use
of tools.
Postcranium
the skeleton from below the head
Mosaic evolution
The concept that evolutionary change does not occur homogeneously throughout the body in
organisms
