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.
