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CHAPTER 22
DESCENT WITH MODIFICATION:
A DARWINIAN VIEW OF LIFE
GENESIS 1
THE CREATION OF THE WORLD
1:1 IN THE BEGINNING1 GOD2 CREATED3 THE HEAVENS
AND THE EARTH.4
1:2 NOW5 THE EARTH6 WAS WITHOUT SHAPE AND
EMPTY,7 AND DARKNESS8 WAS OVER THE SURFACE OF
THE WATERY DEEP,9 BUT THE SPIRIT OF GOD10 WAS
MOVING11 OVER THE SURFACE12 OF THE WATER.13 1:3
GOD SAID,14 “LET THERE BE15 LIGHT.”16 AND THERE WAS
LIGHT! 1:4 GOD SAW17 THAT THE LIGHT WAS GOOD,18 SO
GOD SEPARATED19 THE LIGHT FROM THE DARKNESS. 1:5
GOD CALLED20 THE LIGHT “DAY” AND THE DARKNESS21
“NIGHT.” THERE WAS EVENING, AND THERE WAS
MORNING, MARKING THE FIRST DAY.22
I. HISTORICAL CONTEXT FOR EVOLUTIONARY THEORY
A.
WESTERN CULTURE RESISTED EVOLUTIONARY VIEWS OF
LIFE
DARWIN'S THEORY THAT NATURAL SELECTION IS RESPONSIBLE
FOR EVOLUTIONARY CHANGE WAS A RADICAL DEPARTURE
FROM THE DOMINANT RELIGIOUS AND PHILOSOPHICAL
CLIMATE OF THE NINETEENTH-CENTURY WESTERN
WORLDVIEW.
B. THEORIES OF GEOLOGICAL GRADUALISM HELPED CLEAR THE
PATH FOR EVOLUTIONARY BIOLOGISTS
GEOLOGISTS HUTTON AND LYELL PERCEIVED THAT CHANGES
IN EARTH’S SURFACE CAN RESULT FROM SLOW, CONTINUOUS
ACTIONS.
C. LAMARCK PLACED FOSSILS IN AN EVOLUTIONARY CONTEXT
LAMARCK HELPED PAVE THE WAY FOR DARWIN BY
EMPHASIZING THE INTERACTIONS BETWEEN ORGANISMS AND
THEIR ENVIRONMENT.
II. THE DARWINIAN REVOLUTION
A.
FIELD RESEARCH HELPED DARWIN FRAME HIS VIEW
OF LIFE: SCIENCE AS A PROCESS
DARWIN'S EXPERIENCES ON THE VOYAGE OF HMS
BEAGLE PROVIDED MUCH OF THE BACKGROUND FOR
HIS THEORY THAT NEW SPECIES ORIGINATE FROM
ANCESTRAL FORMS BY THE GRADUAL ACCUMULATION
OF ADAPTATIONS.
DARWIN AND ALFRED WALLACE INDEPENDENTLY
ARRIVED AT THE THEORY THAT NATURAL SELECTION IS
THE MECHANISM OF EVOLUTIONARY CHANGE.
B. THE ORIGIN OF SPECIES DEVELOPED 2 MAIN POINTS: EVOLUTION
AND NATURAL SELECTION AS ITS MECHANISM
NATURAL SELECTION IS BASED ON DIFFERENTIAL SUCCESS IN
REPRODUCTION, MADE POSSIBLE BECAUSE OF HERITABLE
VARIATION AMONG THE INDIVIDUALS OF ANY POPULATION
AND THE TENDENCY FOR A POPULATION TO PRODUCE MANY
MORE OFFSPRING THAN THE ENVIRONMENT CAN SUPPORT.
PRINCIPLES:
1.
2.
3.
4.
5.
6.
POPULATIONS PRODUCE MORE INDIVIDUALS THAT CAN POSSIBLY
SURVIVE
POPULATION SIZES REMAIN STABLE
RESOURCES ARE LIMITED
‘HERITABLE” VARIATION EXISTS AMONG ORGANISMS
INDIVIDUALS COMPETE FOR SURVIVAL
“SURVIVAL OF THE FITTEST”
FIGURE: 22.7 NATURAL SELECTION IN ACTION: BEAK EVOLUTION IN
ONE OF DARWIN’S FINCHES
III. EVIDENCE OF EVOLUTION
A.
EVIDENCE OF EVOLUTION PERVADES
BIOLOGY
EVOLUTION IS VALIDATED BY EVIDENCE FROM
THE FOSSIL RECORD AND FROM MANY FIELDS
OF BIOLOGY, INCLUDING BIOGEOGRAPHY,
COMPARATIVE ANATOMY, COMPARATIVE
EMBRYOLOGY, AND MOLECULAR BIOLOGY.
22.8 TRANSITIONAL FOSSILS LINKING PAST AND PRESENT
22.9 HOMOLOGOUS STRUCTURES
VESTIGIAL STRUCTURES
VESTIGIAL STRUCTURES: have no apparent function, but resemble
structures their presumed ancestors
Some Vestigial Traits in Humans
Ear-wiggling muscles Three small muscles around each ear that are
large and important in some mammals, such as dogs, turning the
ears toward a source of sound. Few people can wiggle their ears,
and none can turn them toward sound.
Tail Present in human and all vertebrate embryos. In humans, the
tail is reduced; most adults only have three to five tiny tail bones
and, occasionally, a trace of a tail-extending muscle.
Appendix Structure which presumably had a digestive function in
some of our ancestors, like the cecum of some herbivores. In
humans, it varies in length from 5–15 cm, and some people are
born without one.
Wisdom teeth Molars that are often useless and sometimes even
trapped in the jawbone. Some people never develop wisdom teeth.
Ontogeny Recapitulates Phylogeny
ONTOGENY: STAGES IN DEVELOPMENT
PHYLOGENY: EVOLUTIONARY
RELATIONSHIPS
22.11 MOLECULAR DATA AND THE EVOLUTIONARY
RELATIONSHIPS OF VERTEBRATES
B. WHAT IS THEORETICAL ABOUT THE DARWINIAN VIEW OF LIFE?
DARWIN'S THEORY OF NATURAL
SELECTION UNIFIED BIOLOGY AND
PLACED IT IN THE REALM OF
SCIENCE.