HUMAN EVOLUTION:
What Makes Us Different
From Other Primates?
Name:__________________________ Pd.____
Evidence for what makes humans different, or possibly similar to primates, is based on
anthropologic strategies of observation and inference in order to illustrate the scientific
process of modifying a theory after new evidence has been obtained (discovered). This
week, you will examine the five major components of anthropologic evidence
demonstrating how primates evolved over 3.7 million years to today’s modern humans.
The scientific evidence is based on fossil evidence, either as extant or extinct hominid
skeletal evidence or as a trace fossil such as the Laeoti footprints found in E. Africa. You
must be prepared to answer all of the questions outlined in each category below.
EVIDENCE #1: HOMINIDS STAND UP
Video: Comparing How We Walk (Human vs. Chimp)
--Based on this video, what are the basic similarities vs. differences between
humans and chimps? Spinal curvature, pelvic differences, differences in the foramen
magnum, and in the upper limbs and toes.
--What characteristic distinguishes humans from all other primates?
The predominant form of human locomotion is bipedal.
--What kind of evidence did you observe in the Laetoli footprints?
Trace fossils.
--What two other types of evidence would anthropologists use?
Make comparisons between fossil bones and living primates. Fossil evidence evidence from reconstruction of the environments in which humans and their relatives
lived; molecular biology - compare sequences in DNA molecules and proteins between
living populations, and between living and fossil DNA; comparative anatomy - between
living populations and between living and fossil populations.
--What disadvantages would a chimpanzee have if its arms and fingers were
shorter, rather than as observed in “knuckle-walking”?
It would have uneven knuckles for knuckle walking. It would not be able to grasp
branches well for moving about in trees.
--Anthropologists agree that “Lucy” (A. afarensis), whose skeleton looked most
similar to that of a chimp, walked upright. What is a possible clue that anthropologists
may have had to indicate this? One of the clues to this is that Lucy's forelimbs were
fairly small compared to her hind limbs.
Video: Bipedalism Overview
--Based on this video, how did humans become bipedal (two-legged), habitually, in
the first place? There were definite advantages to being bipedal. A prime advantage
would have led to increased reproductive success, which would have promoted
survival of the species. Reproductive success included several factors -- surviving
until maturity, finding a mate and conceiving, surviving while reproducing,
producing viable offspring, and surviving while giving parental care. Being bipedal
allowed species to pursue each other as well as carrying food or babies, having
arms free to fight off predators, etc.
--What might have been the advantages to being bipedal? Transporting, threat
displays, tool use, heat stress, walk-a-lot, and care-giving.
Video: Evolution of Bipedalism: Different Views
--Based on this video, explain why Drs. Jablonski and Zihlman (from the video),
and Dr. Wheeler (from the Student Reader Article), had different hypotheses regarding
why hominids evolved to have bipedal locomotion. There isn't enough evidence to be
definitive, or it happened too long ago so evidence is not well preserved.
--What trends could possibly be observed in characteristics comparing apes to the
early hominids, to modern humans?
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The spine is more curved in bipeds and less curved in quadrupeds.
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The side-to-side and top-to-bottom dimensions of the pelvis change:
quadrupeds have a longer, narrower pelvis, while bipeds have a shorter,
wider pelvis. Also, quadrupeds have a flatter pelvis, while bipeds have a
bowl-shaped pelvis.
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The foramen magnum is under the skull and the skull sits more on top
of the spine in bipeds. In adult quadrupeds, the foramen magnum is
toward the back of the skull, and the skull is held in front of the animal.
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The upper/front limbs are similar in size or longer than the lower/back
limbs in quadrupeds; the upper limbs are shorter in proportion to the
lower limbs in bipeds.
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The big toe is opposed in quadrupeds and can be used for grasping; the
big toe is less opposed in bipeds.
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The toes become shorter in relation to the fingers in bipeds. Quadrupeds
have very long toes and fingers in relation to those of bipeds.
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The limb bones are more curved in quadrupeds and straighter in bipeds.
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The angle of the pelvis to the lower limb is more pronounced in
quadrupeds than in bipeds.
EVIDENCE #2: BIGGER BRAINS (HOMINIDS)
--Examining your own skull, can you identify the following?
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brain volume (space that the brain occupies)
brain case or cranium (protects the brain)
browridge (the area directly behind the eyebrows)
mandible (lower jaw) and teeth
zygomatic arch (cheek area where muscles that operate the lower jaw pass
up to the cranium for attachment)
occipital bone (back portion of cranium)
eye orbits (bony sockets that protect the eyes)
--Referring to the following, describe each in their proper chronological order:
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7--Teeth become smaller
1--Size of the skull (cranium) increases
6--Face protrudes (sticks out) less
3--Mandible, lower jaw, becomes smaller
4--Zygomatic arch becomes smaller
2--Browridge becomes less pronounced
5--Occipital bone enlarges
--What additional evidence would be useful in confirming the above sequence (or
deciding which sequence is correct? Radioactive dating, comparisons to skeletal
features, and actual measurements of cranial capacity.
--Over a period of about four million years, the hominid skull assumed its modern
appearance of today’s humans. Summarize those changes indicated above, over time.
The size of the cranium increased, the browridges and mandibles became smaller, and
the size of the brain increased relative to the size of the body. Body mass did not change
as much; while hominids did get taller, the mass of the body was redistributed.
--Which hominid is an exception in brain volume and body mass? The
Neanderthal fossil had an estimated brain volume and body mass that were both larger
than Homo sapiens, although its relative brain volume was slightly smaller.
EVIDENCE #3: MIGRATION AND VARIATION
--Define the term migration: To migrate means to move from one location to
another. Some birds migrate seasonally, for example, traveling south in the fall and
back north again in the spring. It is also called migration when a group of animals
permanently moves to another location, such as when a lot of people from one country
move to another for better job opportunities.
--What was the general trend of hominid migration? Hominids migrated out of
Africa and into Asia and Europe, then to North America.
--Did all the hominids leave Africa? No, some hominids stayed in Africa because
they were able to adapt to their immediate environment and did not need to seek
another location in order to survive.
--What species have been found outside of Africa? Homo erectus.
--How was H. erectus different from other hominids? H. erectus were taller and
had larger brains.
--What other changes were happening during this time period? There were
changes in tools, climate, and animals. As environmental changes occurred,
hominids either adapted staying in that location, relocated, or did not adapt and
therefore not survive.
--What might have prompted the taller and larger-brained Homo erectus to
expand beyond Africa? They may have been following food resources; they had
better tools for exploiting new environments; climate changes may have prompted
them to move; or they may have been more curious.
--The fossil evidence indicates that hominids first evolved in Africa, but as their
skeletons became more adept, their characteristics changed. What two characteristics
changed that made them able to move out of Africa and live in new environments?
Larger brains and a different form of skeleton which was more adept at bipedal
locomotion.
--The theorized split of the Australopithecines into two lines: one that led to the
genus Homo; and one that led to the robust Australopithecines (e.g., boisei) that stayed in
Africa, may have occurred as a result of diet. The latter appears to have depended on
plants for food, as evidenced by their heavier jaws and larger teeth. Homo; however,
probably added more meat to its diet. This enriched protein source would have been
necessary for what purpose? This enriched protein source would have been necessary
to support larger brains.
--People from different locations around the world vary in their degrees of skin
pigmentation. How is skin pigmentation inherited? Three genes are responsible for skin
pigmentation and each parent contributes one each of these three genes to each
offspring.
--How can two parents, both with medium skin pigmentation, have offspring with
skin pigmentation that varies from very light to very dark? The offspring inherit
different combinations of the genes for skin pigmentation.
most variations in offspring are due to genetic recombination, especially when
there are multiple genes for a trait, and that most traits are controlled by multiple genes
--Skin color is influenced by a variety of substances, the most important of which
is a molecule that is produced by specialized cells in the skin. What is the name of this
molecule? Melanin.
--Some individuals have the genetic ability to temporarily increase the production
of this molecule in their skin in response to a factor in the environment's sunlight or
ultraviolet light. Some individuals cannot increase production and their skin suffers
severe effects in the presence of sunlight. What is this adaptive process called, which is
only a temporary change in the amounts of skin pigmentation. Tanning is the temporary
change in the amount of skin pigmentation. Individuals that cannot increase melanin
production, burn rather than tan in the presence of sunlight!
--Explain how skin pigmentation is determined and how that affects offspring:
Skin pigmentation is determined by multiple genes and that recombination of the
alleles from two parents of intermediate skin pigmentation can result in wide variation
in the skin pigmentation of their offspring.
--What is the selective advantage of more darkly pigmented skin in areas where
ultraviolet intensity is higher and the selective advantage of more lightly pigmented skin
in areas where UV intensity is lower? Refer to the below chart. Lightly pigmented skin
reflects more light. Reflectance examples would be light colored clothing is often worn
in the summer because it reflects more light and is cooler; roofing material tends to be
light colored in regions where the summer sun is very intense.
Correlations Between Skin Reflectance (Pigmentation) and UV Intensity
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Mean Annual UV Intensity is greatest at the equator and decreases as latitude increases. (Greatest
amount of direct sunshine is at the equator, the least at the poles.)
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Skin Reflectance Rating of Indigenous People is least at the equator and decreases as latitude
increases. (The darkest skinned indigenous people live near the equator, the lightest skinned
indigenous people live near 60 degrees North.)
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Therefore, as UV intensity increases, so does pigmentation of indigenous people. Alternately, as
UV intensity decreases, so does pigmentation of indigenous people.
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There are people with medium levels of pigmentation in an area North of 60 degrees north
(Greenland) – an exception to the correlation
*Note: Indigenous people are people who are native to, or whose ancestors have
always lived in, a particular region, such as the Alaskan Eskimos.
--What conclusions can be drawn from the above correlations related to skin
reflectance and UV intensity? Basically, what is the relationship between UV light and
skin pigmentation? UV light is related to latitude; it is less intense as you move away
from the equator. The closer the population is to the equator, the darker the skin
pigmentation. Greenland presents an irregularity in that the region is above 60 degrees
latitude, yet has the same skin reflectance rating of populations at 30 degrees latitude.
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Cause and effect: one thing (or variable) causes another to change. In
cause and effect relationships, if all other things are held equal, a change
in one thing or variable will lead to a predictable change in the other thing
or variable.
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Correlation: two things or variables (sets of data or observations) that
change together. If one thing is causing the other to change, it would be a
cause and effect correlation. But two things can vary together and not be
related; this is called a false correlation. For example, both may increase
or decrease together, but neither would be causing the other to change.
--Explain why having darkly pigmented skin near the equator (high UV intensity)
is advantageous and why having lightly pigmented skin far from the equator (low UV
intensity) is advantageous: Having darkly pigmented skin near the equator (high UV
intensity) is advantageous and having lightly pigmented skin far from the equator (low
UV intensity) is advantageous. The words "melanin" and "folate" are key for the
advantages of darkly pigmented skin, and the word "vitamin D" is key for the
advantages of lightly pigmented skin. (Melanin is a skin molecule. Folate is the watersoluble form of Vitamin B-9, and is necessary for the production and maintenance of
new cells, which is especially important during periods of rapid cell division and
growth such as infancy and pregnancy. Folate is needed to replicate DNA.
--Based on the above understanding, why have people in the tropics developed
dark skin? Skin color is largely a matter of vitamins. To block out the sun and protect
their body's folate reserves.
--Why have people far from the Equator developed light skin? To absorb the sun
and produce adequate amounts of vitamin D during the long winter months.
EVIDENCE #4: TOOLS AND SPEECH
--Describe the changes in stone tools over time and how these relate to changes in
cranial capacity: The original stone tools were round rocks, which over time took
other shapes dependent upon what tasks they were used for. As hominids cranial
capacities advanced, so did their stone tools.
--Explain the selective advantages of varied tools and increased intelligence: They
would then be more likely to survive and reproduce,
passing on their intelligence and knowledge about
tools to their children.
--Our early ancestors used rocks of different shapes
and sizes as tools. What would the later, more varied
tools, suggest about how the lifestyles of the hominids
changed? They were able to obtain and use a wider
variety of foods and/or obtain and prepare them more
easily.
--What would the newer tools have suggested about the intelligence of the hominids
who used them? As hominids became smarter, they came up with new and more
refined tools.
--What would have been the selective advantage for hominid groups that were able to
develop more refined or new tools? Reproduction and survival promoting continued
survival rather than extinction.
--Explain why some anthropologists have proposed that tool use and intelligence may
have stimulated each other's development in a kind of feedback loop in relation to
hominid evolution: Improving food sources improved reproductive success,
outweighing the cost of the energy for the big brain, and the cost of time and energy
for creating more complex stone tools.
--Relate the evolution of speech to its selective advantage and changes in the
structures required for speech: Speech enhanced communication. The tongue is crucial
to speech and verbal communication.
--Describe two types of indirect evidence and the ideas based on these that
anthropologists have used and proposed about the evolution of speech: Many of the
structures involved in speech do not fossilize, so anthropologists must use indirect
evidence to develop ideas about how speech evolved. Anthropologists used estimates of
cranial capacity as a measure of how large hominid brains were and a larger brain
would have contributed to more abstract thought and greater abilities such as
communication. Mutations in all of these structures would have been necessary in
order for natural selection to occur and articulate speech and abstract thought to
develop.
--How does cranial capacity correlate with tool use? Larger cranial capacities are
associated with more complex tools.
--What does this suggest about the thinking required to make and use more advanced
tools? More complex thought processes were required in order to develop ideas for
new tools and how to make them.
--Describe the relationship between stone tool use and intelligence. Specifically, what
would this suggest were the selective advantages? More complex tools make it possible
to obtain a broader range of foods or obtain foods more easily. Success in obtaining
food contributed to survival and reproductive success. Tool use and intelligence may
have stimulated each other's development.
--Speculate on what kinds of situations and events in the lives of early hominids
would have been very difficult without language: Communicating where to find food,
planning how a group of hunters would attack a large animal, how to care for a child,
the existence of a wildfire, how to handle an injury or illness, settling a dispute, etc.
--What characteristics and structures make articulate (clear) speech and abstract
thought possible? The larynx and vocal cords, tongue, teeth, lips, and control of
pushing air through the larynx. A larger brain contributed to abstract thought.
--Some body structures will fossilize and some will decay once a body expires.
Which body structures fossilize and which decay, and why? Teeth, bones, and skulls
will fossilize because they are made of calcium. Soft tissues, such as the tongue,
lips, vocal cords, brain, and nerves will decay. Soft tissue does not fossilize because
it does not go through the process of permineralization (fossilization).
--Lack of fossil evidence is why anthropologists must rely on indirect evidence to
determine when and how language evolved. Which of these body structures would be
most important in determining which hominid species had speech? The soft tissues,
including the brain and nerves would be most important in hominid speech.
--The brain controls our ability to speak. What body structure is essential to speaking,
and what physical structure do humans have that other primates do not, which
explains why we have the ability to speak and they cannot? Humans have a larger
tongue nerve canal - hypoglossal canal - than other primates, which explains why
humans can speak and other primates cannot.
--What other kinds of evidence have anthropologists investigated in examining the
question of how language evolved in hominids? Anthropologists investigate symbolic
artifacts, the skull, communication in other species.
--How is human language unlike the communication in other species? The larynx
and other structures make our speech clear, and that we can make references to
objects and use syntax.
--What is the role of the larynx in speech and how is it important in the evolution of
language? The larynx contains the vocal cords that produce sound energy. The
larynx is low in the human throat compared to the chimpanzee, making it easy to
swallow the wrong way, but also making it possible for humans to make clearer
sounds. Because of this significant disadvantage, the selective advantage of speech
must have outweighed it.
EVIDENCE #5: AGRICULTURE
--There are 10,000 species of grasses. Why are they essential to human survival?
Grasses are widespread; they are important to human survival; livestock eat them.
Most humans are carnivores, and therefore rely on livestock consumption, which
rely on eating grasses.
--Wild grasses, already in existence during the Ice Age, spread quickly after the
retreat of the glaciers. Wild grasses had adapted to the long winter and short growing
season. The seeds were quick to mature and self disperse, lying dormant until the next
growing season. The grasses were poised to exploit the new land exposed by the retreat
of the glaciers, and Homo sapiens in turn exploited the grasses. Between 12,000 and
9,000 years ago, on each of the major landmasses, people began to cultivate cereal grains
(as well as root crops which come from grasses). Speculate why an understanding of how
to cultivate grasses would be an important step for hominids: Adding the ability to grow
their own food (the use of agriculture) to a knowledge of hunting and gathering would
have increased hominids' chances of surviving and reproducing.
--Identify three different methods that humans have used, and continue to use, to
"make a living": Hunter-gatherers, herders, and agriculturalists.
--Describe two or three lifestyle characteristics for each.
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Hunter-gatherers: hunt wild animals and gather wild plants.
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Herders: raise herds of cattle, goats, and sheep.
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Agriculturalists: grow crops (grasses in particular).
--State two factors related to the predominance of agriculture as a method of
obtaining food. Modern humans are largely dependent on grasses/grains. When the
glaciers receded at the end of the last ice age, the grasses expanded their territories,
and therefore, agriculture became the predominant form of food source rather than
hunting.
--Explain the effect of innovations on human population size. As humans became
more advanced and better able to take care of themselves, the human population
grew in size and became a stronger population, able to reproduce and thrive.
--Modern humans are largely dependent on grasses/grains. When the glaciers receded
at the end of the last Ice Age, the grasses expanded their territories. How might such
expansion affected human populations? Increased migration into new territories;
possible cultivation of plants; larger populations of humans.
--What three ways might our earliest hominid ancestors obtained food? By hunting
animals and gathering plants, and cultivation of plants.
--What would be the three types of evidence to support these methods? From
anthropologists' observations that have been made in the field or in a laboratory from
field data. Some of the evidence, such as fossil finds, is direct, and some of the evidence
is inferred from the fossil finds, including cave/rock drawings, as well as food use
evidence and environmental evidence.
--Describe how these groups of people would differ in terms of health concerns,
leisure time, and amount of energy required to make a living: Hunter-gatherers had the
least leisure time, agriculturists were the healthiest, and herders just had to follow their
herds around.
--Which of the three types would have lived in one place, and which would have
traveled around (from place to place)? Hunter-gatherers would have moved around
looking for food sources, and herders may move around to find water or fresh grazing
for animals. Agriculturists would have stayed in one location to tend their crops.
--Which would have lived in big or small groups? Hunter-gatherers would have
lived in small groups.
--Would they depend on many or just a few food sources? They would depend on
many sources (plant or animal) — whatever they could find.
--What environmental resources would be important to the groups? Grasses for the
animals to eat, and water sources would be important.
--What type of physical evidence might exist to indicate which type of group each would
have been in? Provide an example with each piece of evidence. Skeletal and dental
evidence would have been indicative of problems of agriculturists. The bending over to
tend and reap crops led to the hunched skeletons and dirt, grit, and husks from
processing grains, as well as the switch to a starchy diet, led to cavities. Tools found
nearby which would have been unique to that group would also have indicated which
group they would have been in (eg. arrowheads for hunter-gatherers).
--What is the time span during which tool-making was the major technological
innovation? Tool making was the major technological innovation from 1,000,000 to
10,000 years ago.
--What is the time span during which agriculture was the major technological innovation?
Agriculture was the major technological innovation from 10,000 to 1,000 years ago.
--What is the time span during which science and industry were the major technological
innovations? Science and industry were the major technological innovations from
1,000 years ago until the present.
--What was the effect of each of these three innovations? Increased population size.
--Which innovation had the greatest effect on population growth? The innovation of
agriculture caused a much steeper rise in human population.
--Agriculture led to four major benefits for human society. What were those benefits,
which ironically, are not necessarily considered advantageous today? It produced extra
food that would feed more people; extra food could be used to trade for other goods;
and children could contribute to the work of growing food and raising animals, so
having more children was favored.
--What are two possible reasons why humans changed to an agriculturist type of society?
The climate became warmer and drier, which could have prompted innovations,
creating a need for different food sources. It is also possible that knowledge of plants
and animals improved, leading to new innovations, all of which resulted in larger
human populations, and subsequent innovations has further increased the size of the
human population to over 6 billion people worldwide today.