chapter 23 lecture outline - napa valley college · 5 origin of life ... – molecules combined to...

Chapter 23

Lecture Outline

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Human Evolution

Points to ponder

• What is chemical evolution?

• What is biological evolution?

• What is natural selection, and what three elements are vital for this?

• What was Darwin’s contribution to evolution?

• What have we learned from the fossil record?

• Explain the fossil, biogeographical, anatomical, and biochemical evidence that supports the theory of evolution by common descent.

• What are analogous, homologous, and vestigial structures? Give examples of each.

Points to ponder

• How are humans classified?

• What characteristics do primates have in common?

• Explain the evolution of hominids.

• Who was Lucy?

• Explain the evolution of humans.

• What is the most widely accepted hypothesis for the evolution of modern humans?

• Compare and contrast Cro-Magnons and Neandertals.

Origin of life through chemical evolution

• Steps of chemical evolution

– Gases of the primitive atmosphere formed

small organic molecules.

– Molecules combined to form

macromolecules.

– Only RNA might have been needed to form

the first cells; this is supported by the fact

that RNA can act as enzymes called

ribozymes (RNA-first hypothesis).

23.1 Origin of Life

– Protocells made of proteins and lipids could

metabolize by using oceanic organic

molecules, but could not reproduce.

– The true cell can reproduce and has DNA as

its genetic material.

23.1 Origin of Life

Figure 23.1 Chemical and biological evolution.

23.1 Origin of Life

ical E

protocell

early Earth

plasma

membrane

energy

capture abiotic synthesis

origin of

genetic code

DNA RNA

polymerisation

Stage 3

Stage 4

Stage 1

inorganic chemicals

small organic molecules

Stage 2 polymers

Biological evolution

• Biological evolution – change in population or species over time

• Two important points

1. Living things descended from a common ancestor and thus have common chemistry.

2. Livings things adapt to their environment.

• Adaptation – a characteristic that enables an organism to survive and reproduce in its environment

23.2 Biological Evolution

Natural selection

• Natural selection is a theory by Charles

Darwin that describes a mechanism by

which a species becomes adapted to its

environment.

Natural selection

• Three vital elements • Variation – there must be physical

variations that can be passed from generation to generation

• Competition – there must be competition for limited resources (food, mates, shelter), and those better adapted will survive and reproduce

• Adaptation – subsequent generations will see an increase in individuals with the same adaptations, as long as the environment remains unchanged

Originally, giraffes had

short necks.

Giraffes stretched their necks

in order to reach food.

Competition for resources

causes long-necked giraffes

to have the most offspring.

With continual stretching, most

giraffes now have long necks.

Originally, giraffe neck

length varied.

Due to natural selection, most

giraffes now have long necks.

Lamarck’s proposal Darwin’s proposal

Figure 23.3 The two major

mechanisms for evolutionary

change in the nineteenth century.

Evidence to support the theory

of evolution by common descent

1. Fossil record

2. Biogeographical evidence

3. Anatomical evidence

4. Biochemical evidence

1. What are fossils?

• Fossils are the traces of past life.

• Fossils allow us to trace the descent of a particular group.

• Charles Darwin, an English naturalist, relied on fossils to formulate the theory of evolution.

• Transitional fossils have characteristics of two different groups.

Transitional fossils

Figure 23.4 Transitional fossils.

Expanded ribs

Scales

Fish Rounded head,

eyes on sides

Tiktaalik

roseae

Neck Flat head,

eyes on top

amphibian

Amphibian

tetrapod

What have we learned from the

fossil record?

• The fossil record tells us that life progressed from simple to more complex.

• Prokaryotes are the first life forms seen in the fossil record, followed by unicellular eukaryotes, and then multicellular eukaryotes.

• Fishes evolved before terrestrial plants and animals.

• Nonflowering plants preceded flowering plants.

• Amphibians preceded reptiles.

• Dinosaurs are directly linked to birds.

Fossils

Figure 23.5 Archaeopteryx. Figure 23.6 Evolution of the whales.

feathers

tail with vertebrae

artist depiction of Archaeopteryx

Archaeopteryx fossil

(fossil, left): © Jean-Claude Carton/PhotoShot; (drawing, right): © Joe Tucciarone

a. Ambulocetus

b. Basilosaurus

c. Right whale

modern

a (fossil Ambulocetus foot): © J.G.M. Thewissen, Northeastern Ohio Universities College of Medicine

2. Biogeographical evidence

• Biogeography is the study of the distribution of plants and animals throughout the world.

• It supports the hypothesis that organisms originate in one locale and then may spread out.

• Different life forms are expected whenever geography separates them.

• Islands have many unique life forms because of geographic isolation.

Biogeographical evidence

Figure 23.7 Biogeography.

Sugar glider, Petaurus breviceps,

is a tree-dweller and resembles the placental flying squirrel.

The Australian wombat, Vombatus, is nocturnal and lives in burrows. It

resembles the placental woodchuck.

Kangaroo, Macropus, is an herbivore that inhabits plains and forests. It

resembles the placental Patagonian

cavy of South America. (sugar glider): © ANT Photo Library/Photo Researchers; (wombat): © Photodisc

Blue/Getty RF; (kangaroo): © George Holton/Photo Researchers

• Common descent hypothesis offers plausible

explanation for anatomical similarities among

living organisms.

• Homologous structures – structures

anatomically similar that are inherited by a

common ancestor

• e.g., Vertebrate forelimbs

• Analogous structures – structures that serve the same function but they do not share a common ancestry, and thus are not constructed the same

• e.g., Wings of a bird and wings of an insect

• Vestigial structures – anatomical features fully developed in one group that are reduced and may have no function in another group

• e.g., Whales have a vestigial pelvic girdle and legs

whale human horse cat

humerous

radius

metacarpals

phalanges

Figure 23.8 Vertebrate

forelimbs are homologous

structures.

Homologous structures in

Pig embryo

pharyngeal

pouches

postanal

Chick embryo

(both): © Carolina Biological Supply/Phototake

Figure 23.9 Homologous

structures in vertebrate embryos.

4. Biochemical evidence

• Almost all living things use the same

biochemicals (e.g., DNA and ATP).

• Living things use the same triplet genetic code.

• Living things use the same 20 amino acids in

their proteins.

• Living things share many of the same genes.

Biochemical evidence describes

Cytochrome c is a small protein

that plays an important role in

the electron transport chain

within mitochondria of all cells.

Number of Amino Acid Differences Compared to

Human Cytochrome c

Species

monkey

turtle

Figure 23.10

Biochemical evidence

describes evolutionary

relationships.

The evolution of humans

22.3 Classification of Humans

common ancestor

animals

EUKARYA

protists protists

heterotrophic

bacteria

BACTERIA

ARCHAEA

plants

cyanobacteria

Figure 23.11 The three domains of life.

Primates

• Characteristics

• Opposable thumb

• Stereoscopic vision (depth perception)

• Well-developed brain

• Reduced number of offspring (usually a

single birth) with an increased period of

parental care

• Emphasis on learned behavior and social

interactions

• Two major groups (suborders)

• Prosimians – includes lemurs, tarsiers,

and lorises

• Anthropoids – includes monkeys, apes,

and humans

Primates

Asian and African apes

Figure 23.12 Asian and African apes.

white-handed gibbon,

Hylobates lar

Asian Apes

orangutan, Pongo pygmaeus chimpanzee, Pan troglodytes

western lowland gorilla,

Gorilla gorilla

African Apes

(gibbon): © Hans & Judy Beste/ Animals Animals; (orangutan, chimps, gorillas): © Creatas/PunchStock RF

Comparing the human skeleton

Human spine exits from the skull’s center;

ape spine exits from rear of skull.

Human spine is S-shaped; ape spine has a

slight curve.

Human pelvis is bowl-shaped; ape pelvis is

longer and more narrow.

Human femurs angle inward to the knees;

ape femurs angle out a bit.

Human knee can support more weight than

ape knee.

Human foot has an arch; ape foot has

no arch.

Figure 23.13 Adaptations in the human skeleton allow upright locomotion.

Evolution of primates 23.4 Evolution of Hominins

Mammalian

ancestor

enters trees.

hominin

common

chimpanzee

western

lowland

gorilla

capuchin

monkey

New World Monkeys

ring-tailed

70 60 50 40 30 20 10 Million years Ago (MYA)

PRESENT

rhesus

monkey

Humans

Chimpanzees

Gorillas

Orangutans

Bornean

orangutan

Gibbons

white-handed

gibbon

Old World Monkeys

Tarsiers

Philippine

tarsier

Lemurs

Figure 23.14 The evolutionary

tree of the primates.

Evolution of hominins

• Hominins – All species of the genus

Homo and their close relatives

• Characteristics

• Bipedal

• Flatter face with more pronounced chin

• Brain size

23.4 Evolution of Hominins

Evolution of hominins

• Suggested fossils of the first hominins (6-7 MYA)

• Central African fossil 7 MYA (Sahelanthropus tchadensis)

• Eastern African fossil 6 MYA (Orrorin tugenensis)

• Eastern African fossil 5.8-5.2 MYA (Ardipithecus kadabba)

• Hominins split from the ape line of descent 7 MYA.

Australopithecines

• A group of hominins that evolved and

diversified in Africa ~3 MYA.

• Some had slight frames and others were

robust with massive jaws for feeding on

plant materials.

• They walked upright.

• Limbs proportions are apelike.

• They had a small brain.

Australopithecines

• Famous skeleton named “Lucy” is from

this group .

• Australopithecus africanus, with a large

brain, is the most likely ancestral

candidate for early Homo.

Australopithecines

Figure 23.15 Australopithecus afarensis.

Characteristics of Homo

1. Brain size is 600 cc or greater.

2. There is evidence of tool use.

3. Jaw and teeth of Homo resemble humans.

Early Homo representatives

• Homo habilis

• Homo erectus

Later Homo representatives

• Neandertals

• Cro-Magnons

23.5 Evolution of Humans

Human evolution 23.5 Evolution of Humans

Figure 23.16 Human evolution.

Early Homo: Homo habilis

• Lived 2.0-1.9 MYA

• Large brain with enlarged speech area

• Omnivorous (hunters and gatherers)

• Primitive tools

• May have had culture

Early Homo: Homo erectus

• Lived 1.9-0.3 MYA

• Larger brain than H. habilis

• Flat face with the nose projected

• Tall and stood erect

• Striding gait

• May have migrated from Africa to Europe

and Asia

• Advanced tools and fire (systematic hunters)

• May have had language

Homo ergaster

Figure 23.17 Homo ergaster.

Modern humans: Homo sapiens

• Replacement model, or out-of-Africa

hypothesis, is the most widely accepted

hypothesis.

– It proposes that modern humans evolved

from archaic humans only in Africa.

– Then, modern humans migrated to Asia

and Europe, where they replaced the

archaic species about 100,000 years BP.

Hypothesis for modern human evolution

Figure 23.18 Replacement model.

Migration of early Homo from

Africa

Neandertals

• Discovered in Germany 200,000 years ago

• Massive brow ridges

• Nose, jaws, and teeth protrude forward

• Low and sloping forehead, no chin

Cro-Magnons

• Lived about 40,000 to 100,000 years ago

• Oldest fossils to be designated Homo

sapiens

• Modern appearance

• Advanced culture including art, tools, and

maybe language

• Good cooperative hunters

47 Figure 23.19 The Cro-Magnons.

Cro-Magnons

Human variation

• Human variations between populations are

called ethnicities.

• Variations evolved as adaptation to local

environments.

– Skin color ranges from dark to light.

– Body shape

• Bergmann’s rule – colder regions mean

bulkier build

• Allen’s rule – colder regions mean shorter

limbs, digits, and ears

Human variation

Figure 23.20 Ethnic variations

in modern humans.

chapter 23 lecture outline - napa valley college · 5 origin of life ... – molecules combined to...

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