Chapter 10 Flashcards
Nariokotome Boy
A nine year old fossil found in Kenya
most completed early homo erectus fossil
Named after the nearby lake village
Homo habilis and Homo erectus
Part of the homo genus
What criteria do scientists generally agree upon when it comes to grouping species into a genus?
When grouping species into a common genus, biologists will consider criteria such as physical characteristics
morphology), evidence of recent common ancestry, and adaptive strategy use of the environment). However, there is
disagreement about which of those criteria should be prioritized, as well as how specific fossils should be interpreted in
light of the criteria.
What characteristics do scientists believe species defined as Homo should have?
a relatively large brain size, indicating a high degree of intelligence;
* a smaller and flatter face;
* smaller jaws and teeth; and
* increased reliance on culture, particularly the use of stone tools, to exploit a greater diversity of environments
adaptive zone).
While most researchers agree on these characteristics, why is there debate about whether some species and/or particular fossils can be considered Homo?
First, many fossil specimens dating to this time period
are incomplete and poorly preserved, making them difficult to evaluate. Second, early Homo fossils appear quite variable
in brain size, facial features, and teeth and body size, and there is not yet a consensus about how to best make sense of
this diversity. Finally, there is growing evidence that the evolution of the genus Homo proceeded in a mosaic pattern: in
other words, these characteristics did not appear all at once in a single species; rather, they were patchily distributed
in different species from different regions and time periods. Consequently, different researchers have come up with
conflicting classification schemes depending on which criteria they think are most important.
The last paragraph of this section lists the goals for this chapter. Name those goals below.
In this chapter, we will take several pathways toward examining the origin and evolution of the genus Homo. First, we will
explore the environmental conditions of the Pleistocene epoch in which the genus Homo evolved. Next we will examine
the fossil evidence for the two principal species traditionally identified as early Homo: Homo habilis and Homo erectus.
Then we will use data from fossils and archaeological sites to reconstruct the behavior of early members of Homo,
including tool manufacture, subsistence practices, migratory patterns, and social structure. Finally, we will consider
these together in an attempt to characterize the key adaptive strategies of early Homo and how they put our early
ancestors on the trajectory that led to our own species, Homo sapiens.
Pliocene
The Pliocene (5.3 million to 2.6 million years ago) was marked by cooler and drier
conditions, with ice caps forming permanently at the poles. Still, Earth’s climate during the Pliocene was considerably
warmer and wetter than at present.
Ardipithecus ramidus and Australopithecus afarensis
Pleistocene
subsequent Pleistocene epoch 2.6 million years to 11,000 years ago) ushered in major environmental change. Instead, climate became much more variable, cycling abruptly between warm/wet interglacial) and cold/dry glacial) cycles. The climate pattern was likely influenced by changes in Earth’s elliptical orbit
around the sun. As is shown in Figure 10.2, each cycle averaged about 41,000 years during the early Pleistocene; the cycles then lengthened to about 100,000 years starting around 1.25 million years ago. Since mountain ranges, wind
patterns, ocean currents, and volcanic activity can all influence climate pattern, climate change had extreme effects on the environment in some regions but less effects on others.
Read the caption below the graphic. How do scientists determine what the weather was like millions of years ago?
Describe what happened to landmasses during glacial periods and give examples.
During glacial periods, the large Indonesian islands of Sumatra, Java, and Borneo were connected to the
Southeast Asian mainland, while New Guinea was part of the southern landmass known as greater Australia. There was a
land bridge connection between Britain and continental Europe, and an icy, treeless plain known as Beringia connected
Northern Asia and Alaska. At the same time, glaciation made some northern areas inaccessible to human habitation. For
example, there is evidence that hominin species were in Britain 950,000 years ago, but it does not appear that Britain
was continuously occupied during this period. These early humans may have died out or been forced to abandon the
region during glacial periods.
Explain what happened in Africa during the Pleistocene epoch.
grasslands expanded and shrank multiple
times during this period, even as they expanded over the long term. Among the African animal populations, the number of grazing animal species such as antelope
increased. Since our early ancestors were also part of this animal community, it is informative to consider how climate
change caused changes in the home ranges and migration patterns of animals.
How did variable climates affect hominin species?
Faced with the
unstable African climate and shifting landscape, they evolved bigger
brains that enabled them to rely on cultural solutions such as crafting stone tools that opened up new foraging opportunities. This
strategy of behavioral flexibility served them well during this unpredictable time and led to new innovations such as
increased meat-eating, cooperative hunting, and the exploitation of new environments outside Africa.
Compare Homo habilis with Australopithecus.
Homo habilis has a somewhat larger brain size–an average
of 650 cubic centimeters cc) compared to less than 500 cc for Australopithecus. Additionally, the skull is more
rounded and the face less prognathic. However, the postcranial remains show a body size and proportions similar to
Australopithecus.
Figure 10.3 A savanna grassland in East Africa. Habitats
such as this were becoming increasingly common
during the Pleistocene.
E
When and where did Homo habilis live?
East and South Africa. 2.5 million years ago to 1.7 million years ago, but a recent fossil was found that dates 2.8 million years ago.
What characteristics did Homo habilis have?
, the new fossils had smaller
molar teeth that were less “bulgy” than australopithecine teeth. Larger brained. The hand bones were similar to humans’ in that they were capable of a precision grip
Why did the Leakeys conclude that tools found nearby were likely made by Homo habilis?
The hand bones were similar to humans’ in that they were capable of a precision grip. This increased the likelihood that
stone tools found earlier at Olduvai Gorge were made by this group of hominins.
Homo rudolfensis
Larger brained than homo habilis
Developmental plasticity
The capability of an organism to modify its phenotype during development in response to
environmental cues.
Summarize the reasons why some scientists wanted to divide Homo habilis into two species.
The diversity of
the Homo habilis fossils prompted some scientists to question whether they displayed too much variation to all remain
as part of the same species.
Summarize the reasons why some scientists wanted to have just one Homo habilis species.
Researchers
who favored keeping all fossils in Homo habilis argued that sexual dimorphism, adaptation to local environments, or
developmental plasticity could be the cause of the differences. For example, modern human body size and body
proportions are influenced by variations in climates and nutritional circumstances.
Explain why some researchers think Homo habilis might actually be better classified as Australopithecus.
Analysis of the relative strength of limb bones suggested that the species, though bipedal, was much more adapted to arboreal
climbing than Homo erectus and Homo sapiens. This has prompted some scientists to question whether Homo habilis behaved more like an australopithecine—with a shorter gait and the ability to move around in the trees
Why do other researchers favor leaving Homo habilis in the Homo genus?
In particular, statistical
analysis performed indicates that the Homo habilis fossils differ significantly in average cranial capacity from the
australopithecines. They also note that some australopithecine species such as the recently discovered Australopithecus
sediba have relatively long legs, so body size may not have been as significant as brain- and tooth-size differences
Oldowan
named after the site of Olduvai Gorge where the tools were first
discovered. 2.5 mya to 1.6 mya. The tools
of this industry are described as “flake and chopper” tools—the choppers consisting of stone cobbles with a few flakes
struck off them
What do researchers hope to learn by studying how these early tools were used and made?
Studying the form of the tools,
the raw materials selected, and how they were made and used can provide insight into the thought processes of
early humans and how they modified their environment in order to survive.
What do Oldowan tools suggest about the hominins that made them?
This requires selecting rocks that will fracture predictably instead of chunking, as well as the ability to plan ahead and
envision the steps needed to create the finished product. The process leaves both the core and the flakes with sharp
cutting edges that can be used for a variety of purposes.
Ecological niche
Describe two important ways Homo habilis likely used tools.
Butchering animals and extracting marrow from the bone cavities.
What limitations did Homo habilis have that the tools helped them overcome?
increasing use of stone tools allowed hominins to expand their ecological niche and exert more control over their environment. consuming meat and plants or for making tools, shelters or clothing) represents a new and unique innovation, never seen before in the natural world
How was the Homo erectus species similar to modern humans? What innovations did they likely use to help ensure their survival?
These hominins were equipped with bigger brains and large bodies with
limb proportions similar to our own. Perhaps most importantly, their way of life is now one that is recognizably human,
with more advanced tools, hunting, use of fire, and colonizing new environments outside of Africa.
Occipital torus
A ridge on the occipital bone in the back of the skull.
Sagittal keel
A thickened area along the top of the skull.
Prognathism
Condition where the lower face and jaw protrude forward from a vertical plane.
Explain how Homo erectus compares to other early hominins and to modern humans.
Compared to Homo habilis, Homo erectus had a larger brain size average of about 900 cc
compared to 650 cc to 750 cc).
long head like a football
thicker cranial bones
slight thinkening
How did Homo erectus populations differ from region to region?
Scientists have long noted differences between the fossils from Africa and those from Indonesia and China. For
example, the Asian fossils tend to have a thicker skull and larger brow ridges than the African specimens, and the sagittal
keel described above is more pronounced
What evidence do scientists have to support the theory that Homo erectus lived fully on the ground?
This meant long, powerfully muscled legs that enabled these hominins to
cover more ground efficiently. Indeed, studies of the Homo erectus body form have linked several characteristics of the
species to long-distance running in the more open savanna environment. Many experts
think that hominins around this time had lost much of their body hair, were particularly efficient at sweating, and had
darker-pigmented skin—all traits that would support the active lifestyle of such a large-bodied hominin
How might differences in body size be accounted for?
One explanation for the range of body sizes could be
adaptation to a range of different local environments, just as humans today show reduced body size in poor nutritional
environments
What does diminishing sexual dimorphism likely mean about Homo erectus lifestyles?
However, if
Homo erectus was less sexually dimorphic, it may signify changes in social organization within the species.
Explain why losing body hair and being able to sweat may have given humans an advantage.
It would have allowed for survival.
What evidence helps to explain why and when humans lost body hair and acquired the ability to sweat. While larger brains and
long-legged bodies made it possible for humans to cover long distances while foraging, this new body form
had to cool itself effectively to handle a more active lifestyle
Many experts believe that the driving force behind our loss of body hair was the need to effectively cool
ourselves. Along with the lack of hair, humans are also distinguished by being exceptionally sweaty: we sweat
larger quantities and more efficiently than any other primate.
Where were Homo erectus fossils found?
the East
African site of Koobi Fora, around Lake Turkana in Kenya, and are dated to about 1.8 million years ago
Summarize what scientists discovered in Indonesia.
They found a fossil in 1800s, Java. Pithecanthropus erectus, upright ape man. While
the femur looked human, the top of the skull was smaller and thicker than a modern person’s.
What important discoveries were made in China?
Peking man. Dated to about
400,000–700,000 years ago, they were excavated from the site of Zhoukoudian, Bejing.
Why were some of those discoveries considered less important than the discoveries made in Africa?
Although Homo erectus fossils have been found at several sites in China, with dates
that make them comparable to those of Indonesian Homo erectus, none seemed to approximate the antiquity of African
sites. African ones are way older.
What problems surrounded some of the Chinese discoveries?
There were tools found that are older than any homo erectus fossil. But no fossil was found with the tool, we don’t know who made them. Fewer research projects on China.
As Japan advanced
into China during World War II, Chinese authorities, concerned for the security of the fossils, packed up the boxes
and arranged for them to be transported to the United States. But in the chaos of the war, they vanished and were
never heard about again.
Dmanisi
Compared to African Homo erectus, they have smaller
brains and bodies.
Where is Dmanisi?
Dmanisi is located in the Caucasus
mountains in Georgia.
What was surprising about the fossils found there?
However, despite the small brain size, they show clear signs of Homo erectus traits such as heavy brow
ridges and reduced facial prognathism. Second, although the fossils at this location are from the same geological context, they show a great deal of variation
in brain size and in facial features.
What are the possible theories that explain the variability in the fossils?
One explanation for these differences could be that the Dmanisi hominins represent a very early form of Homo erectus
that left Africa before increases in brain and body size evolved in the African population.
Sum up the discoveries in Europe.
What major question do researchers have about the fossils found in modern-day Spain and England?
Achulean Tool Industry
Acheulean tool industry–are more complex in form and
more consistent in their manufacture.
Name significant differences between the Oldowan and the Achulean Tools.
What are some reasons why Asian Home Erectus never developed Achulean tools?
One reason could be environmental differences
between the two regions. Perhaps the rocks available in Asia weren’t of the material suitable for making the Acheulean
handaxes. It has been suggested that Asian Homo erectus populations used perishable material such as bamboo to make
tools. Another possibility is that Homo erectus or even an earlier hominin) migrated to East Asia before the Acheulean
technology developed in Africa.
What do tools used by Homo erectus reveal about their cognitive abilities?
Apart from the actual shaping of the tool, other decisions made by toolmakers can reveal their use
of foresight and planning. Did they just pick the most convenient rocks to make their tools, or did they search out a
particular raw material that would be ideal for a particular tool?
How do they compare with the tools made and used by Homo sapiens?
. Such innovation and social signaling seem to have been absent
in Homo erectus, suggesting that they had a different relationship with their tools than did Homo sapiens
How did the diet of Homo erectus differ from the diet of australopithecines?
These include stone
tools used by Homo erectus, animal bones and occasionally plant remains from Homo erectus sites, and the bones and
teeth of the fossils themselves. These data sources suggest that compared to the australopithecines, Homo erectus
consumed more animal protein.
How do scientists know what Homo erectus ate?
From bones
What relationship might meat eating have to brain and gut size?
In order for large brains to evolve, there has to be a compelling benefit to having them
and a way to generate enough energy to fuel them.
What advantage would higher fat percentages give to early hominins?
Some researchers
also believe that body fat percentages increased in hominins particularly females) around this time, which would have
allowed them to be better buffered against environmental disruption such as food shortages
Describe what researchers know about the Homo erectus diet.
Meat of large animals and plants.
How do they know what they know?
For example, at sites such as Olorgesailie in Kenya Figure 10.14), there are numerous
associations of Acheulean tools with butchered remains of large animals. Studies of the tooth surfaces and microscopic wear patterns on hominin teeth
indicate that Homo erectus ate a variety of foods, including some hard, brittle plant
foods
What connections might there be between cooking, brain size, and gut size?
Cooking food and tools could also have contributed to the reduction in tooth and jaw size. Most importantly, it allowed for the
larger brain and body size and smaller gut size) seen in Homo erectus.
What challenges exist for researchers who wish to know exactly when humans began to use fire for deliberate purposes?
Unfortunately, such evidence is rare at ancient hominin sites,
which have been profoundly altered by humans, animals, and geological forces over millions of years.
What factors likely influenced Homo erectus’s decision to leave Africa?
The larger brain and body size of Homo erectus were fueled by a
diet consisting of more meat, and longer more powerful legs made it possible to walk and run longer distances to
acquire food. Since they were eating higher on the food chain, it was necessary for them to extend their home range
to find sufficient game. Cultural developments including better stone tools and new technology such as fire gave them
greater flexibility in adapting to different environments. Finally, the major Pleistocene climate shift discussed earlier
in the chapter certainly played a role. Changes in air temperature, precipitation, access to water sources, and other
habitat alteration had far-reaching effects on animal and plant communities
Life history
The broad pattern of a species’ life cycle including development, reproduction, and longevity
Human behavioral ecologists
study modern hunter-gatherer societies
Perikymata
Microscopic ridges on the surface of tooth enamel that serve as markers of tooth development.
What is unique about Homo sapiens life history compared to other animals and apes?
This suggests that the human life
history pattern of slow maturation and lengthy dependency was
a more recent development
How might a hunter-gatherer society and a long juvenile period be connected?
On the back end, a longer developmental period results in skilled, successful adults,
capable of living a long time
What advantages might a long developmental period have for a society?
Despite the time and energy demands, females could have offspring
at more closely spaced intervals if they could depend on help from fathers and grandmothers
What conclusions can be drawn about Homo life history from the Nariokotome skeleton?
We know that apes such as chimpanzees
reach maturity more quickly than humans, and there is some
evidence that the australopithecines had a growth rate more akin
to that of chimpanzees. Homo erectus had its own distinct growth
pattern—reaching maturity more slowly than chimpanzees but
faster than Homo sapiens.
Mosaic evolution
Different characteristics evolve at different rates and appear at different stages.
Describe the diversity in early Homo species. Why is there confusion about what fossils belong to what species?
Sum up theories about why hominin fossils show such diversity.
Characteristics we define as Homo
don’t appear as a unified package; they appear in the fossil record at different times. environmental instability. Multiple hominin forms could also evolve in the same region, as they diversified in order to occupy different ecological niches. However, even the presence of multiple species of hominin
does not preclude their interacting and interbreeding with one another. Diversity of brain and body sizes could also reflect developmental plasticity—short-term adaptations within a lifetime.
What old assumptions about hominins are now in question?
For example, one of the traditional dividing lines between Homo and Australopithecus was thought to be stone
tools: Homo made them; Australopithecus didn’t. Similarly, the belief that Homo erectus was the first species to settle
outside Africa may now come into question with the report of 2.1 million-year-old stone tools from China.
What overall trends in homo development can experts agree on?
