Cecie Starr
Christine Evers
Lisa Starr
www.cengage.com/biology/starr
Chapter 24
Animals II: The Chordates
(Sections 24.9 - 24.11)
Albia Dugger • Miami Dade College
24.9 Primate Traits
and Evolutionary Trends
• Primates include humans and their closest mammalian
relatives
• They have hands and feet capable of grasping objects
• primate
• Mammal having grasping hands with nails
• Includes prosimians, monkeys, apes, and hominids such
as humans
A Primate
• A chimpanzee shows
off its grasping five-digit
hands and feet
• Primates have nails
rather than claws
Primate Lineages
• An early branching separated anthropoids (monkeys, apes,
and humans) from prosimians (lemurs and tarsiers)
• Hominoids include apes and humans
• Hominids are the most recent
• hominid
• Human or extinct humanlike species
Primate Classification
Primate Evolutionary Tree
Primate Evolutionary Tree
Lemurs
Tarsiers
New World Old World
monkeys
monkeys
Gibbons Orangutans Gorillas Chimpanzees Hominids
Tree shrewlike ancestor
Fig 24.23, p. 388
5 Key Trends in Primate Evolution
1. Structure of the face changed
• Early primates were shrewlike
• A flattened face, with eyes at the front of the skull,
improved depth perception
2. Teeth and jaw were modified for a mixed diet
Evolution of the Primate Skull
Evolution
of the
Primate
Skull
Tree shrew, a close relative of primates, has a pointy
face and its eyes are on either side of its head.
Early primate
(Plesiadapis)
Early anthropoid
(Aegyptopithecus)
Early hominid
(Proconsul)
Fig 24.24, p. 389
Evolution of the Primate Skull
Fig 24.24a, p. 389
5 Key Trends in Primate Evolution
3. Skeletal changes allowed upright standing and walking
(bipedalism)
• Backbone keeps body aligned over feet
• Skull sits over the backbone
• bipedalism
• Standing and walking on two legs
Posture of Gorilla and Human
• Gorillas are knucklewalkers
• Humans are bipedal
5 Key Trends in Primate Evolution
4. Hands developed increased dexterity
• Changes to bone and muscle in the hands allowed some
primates to manipulate objects and use them as tools:
5 Key Trends in Primate Evolution
5. Braincase and brain increased in size and complexity
• Social behavior, extended parental care, and culture evolved
in some hominid lineages
• culture
• Learned behavior patterns transmitted among members of
a group and between generations
ANIMATION: Primate evolutionary tree
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24.10 Emergence of Early Humans
• Fossils from central, eastern, and southern Africa show that
hominids evolved rapidly in the Miocene through the Pliocene
• We still do not know how they are related
Early Hominids
• Fossils that may be hominids (ahelanthropus tchadensis) are
about 6 million years old
• Ardipithecus ramidus was a hominid that lived 4.4 million
years ago
• An bipedal hominid, Australopithecus afarensis, was walking
in Africa about 3.9 million years ago
Lucy (Australopithecus afarensis)
Australopiths
• Australopiths (“southern apes”) include Australopithecus and
Paranthropus species
• Australopithecus species were petite, with a small face and
teeth
• australopiths
• Collection of now-extinct hominid lineages, some of which
may be ancestral to humans
Early Humans
• The human lineage (Homo) arose by 2 million years ago with
H. habilis as an early toolmaking species
• Most of the early known forms of Homo are from the East
African Rift Valley
• humans
• Members of the genus Homo
Homo habilis and Australopiths
Stone Tools from Africa
• A crude chopper, more refined chopper, hand ax, and cleaver
Homo erectus
• Homo erectus (“upright man”) traditionally refers to African
populations and to descendant populations who migrated into
Europe and Asia
• H. erectus was taller and had a larger brain than H. habilis
• H. erectus probably had improved hunting skills, built fires,
and cooked food
Hominid Skulls From Africa
ANIMATION: Primate skeletons
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24.11 Emergence of Modern Humans
• Judging from the fossil record, the earliest members of the
human lineage emerged about 2.5 million years ago, in the
great East African Rift Valley
• Neandertals (H. neanderthalensis) and modern humans are
relatives, but have distinct gene pools
Branchings of the Human Lineage
• Some populations of H. erectus differentiated into new
species: H. neanderthalensis (Neandertals), H. floresiensis,
and H. sapiens (modern humans)
• Compared to earlier hominids, H. sapiens had a higher,
rounder skull, larger brain, and capacity for spoken language
• Neandertals vanished when H. sapiens entered the same
regions
Recent Homo Species
• Whether H. floresiensis
belongs in this genus is
still debated
• Some think the fossils
belong to H. sapiens
individuals who had a
disease or disorder
Recent
Homo
Species
Homo
neanderthalensis
Homo
sapiens
Homo
floresiensis
Fig 24.30, p. 392
Where Did Modern Humans Originate?
• Two major models agree that H. sapiens evolved from H.
erectus but differ in details of where and how fast these
events took place
• Both attempt to explain the distribution of H. erectus and H.
sapiens fossils, as well as genetic differences among modern
humans who live in different regions
Multiregional Model
• By the multiregional model, H. erectus populations in far-flung
regions evolved into H. sapiens
• multiregional model
• Model that postulates H. sapiens populations in different
regions evolved from H. erectus in those regions
Replacement Model
• The replacement model has modern humans evolving from H.
erectus in Africa, then dispersing into regions already
occupied by H. erectus and driving them to extinction
• replacement model
• Model for origin of H. sapiens; humans evolved in Africa,
then migrated to different regions and replaced the other
hominids that lived there
• Fossils support the replacement model
Two Models for Origin of H. sapiens
Two Models for Origin of H. sapiens
H. erectus
H. sapiens
Africa
Asia
Europe
A Multiregional model. H. sapiens slowly evolves from H. erectus in many regions.
H. erectus
H. sapiens
Africa
Asia
Europe
Time
B Replacement model. H. sapiens rapidly evolves from one H. erectus population in
Africa, then disperses and replaces H. erectus populations in all regions.
Fig 24.31, p. 392
Leaving Home
• Fossils and genetic evidence allow scientists to trace human
dispersal routes
• In their journey, humans overcame hardships, devised
cultural means to survive inhospitable environments,
modified habitats, and developed languages
• Cultural evolution is ongoing
Dispersal Routes for Homo sapiens
• Ice sheets and deserts prevailed about 60,000 years ago
• Fossil evidence for appearance of modern humans:
• Africa by 195,000 years ago
• Israel 100,000 years ago
• Australia 60,000 years ago
• China 50,000 years ago
• Europe 40,000 years ago
• North America 14,000 years ago
Dispersal Routes for Homo sapiens
Origins and Extinctions
of Hominid Genera
Origins and Extinctions of Hominid Genera
Homo floresiensis
Homo rudolfensis
Australopithecus
anamensis
Homo
sapiens
Homo habilis
Australopithecus africanus
Australopithecus afarensis
Homo erectus
Australopithecus
garhi
Paranthropus
aethiopicus
Homo
neanderthalensis
Paranthropus robustus
Paranthropus boisei
4
3
2
Time (millions of years ago)
1
present
Fig 24.33, p. 394
Key Concepts
• Early Primates to Humans
• Primates have grasping hands with nails instead of claws
• Within the group, there is a trend toward increased brain
size and manual dexterity, a flatter face, and upright
posture
• Fossils provide information about lineages related to our
species, which most likely evolved in Africa
Windows on the Past (revisited)
• Scientists often disagree over fossils
• When Homo floresiensis was found, some other scientists
suggested that the fossils were remains of H. erectus or H.
sapiens with a genetic or nutritional disorder
• Further study of existing fossils, a search for more fossils, and
possibly DNA studies will help test competing hypotheses
ANIMATION: Genetic distance between
human groups
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