Download Ch.15 - Jamestown Public Schools

Unit 5 Evolution
Ch. 15 Darwin’s Theory of Evolution
The Puzzle of Life’s Diversity
 Evolution - modern organisms have
descended from ancient organisms
(change over time)
 Theory - a well-supported, testable
explanation of phenomena that have
occurred in the natural world
Voyage of the Beagle
 Charles Darwin contributed most to our
understanding of evolution
 He made observations & collected
evidence that led him to propose a
hypothesis about the way life changes
over time
Voyage of the Beagle
 That hypothesis, now supported by a
large amount of evidence, has become the
theory of evolution
Darwin’s Observations
 Darwin collected the preserved remains
of ancient organisms - Fossils
 Some of these fossils resembled
organisms that were still alive
 Others looked unlike any creature ever
seen
Darwin’s Observations
 The Galapagos Islands influenced Darwin
the most
 He observed that the characteristics of
animals & plants
varied among
the different
Islands
An Ancient, Changing Earth
 Hutton & Lyell helped scientists
recognize that Earth is millions of years
old
 They also noted that the processes that
changed Earth in the past
are the same processes
that are changing Earth
now
Lamarck’s Evolution
Hypothesis
 The year that Darwin was born, Lamarck
published his hypothesis
 He proposed that by selective use or
disuse of organs, organisms acquired or
lost certain traits during their lifetime
 Over time, this process led to change in a
species
Lamarck’s
Explanation
Population Growth
 English economist, Malthus, published a
book, noting that babies were being born
faster than people were dying
 He stated that if the human population
continued to grow unchecked, sooner or
later there would be insufficient living
space & food for everyone
Darwin Presents His Case
 Darwin published the results of his work
in a book, On the Origin of Species
 In his book, he proposed a mechanism for
evolution called natural selection
 He stated that evolution has been taking
place for millions of years, & continues in
all living things
Inherited Variation &
Artificial Selection
 Artificial selection - nature provided the
variation, & humans selected those
variations that they found useful
 It has produced diverse
plants & animals by
selectively breeding for
different traits
Evolution by Natural Selection
 Struggle for existence - the members of
each species compete regularly to obtain
food, living space, & other necessities of
life
Predators that are faster & better at catching
prey are more
likely to
survive
Evolution by Natural Selection
 Fitness - the ability of the organism to
survive & reproduce in its specific
environ.
Fitness is the result of adaptations
Evolution by Natural Selection
 Adaptation - any inherited characteristic
that increases an organisms’ chance of
survival
Successful adaptations allow
organisms to become better
suited to their environ. & thus
better able to survive
Evolution by Natural Selection
 Individuals that are better suited to their
environ., with adaptations that enable
fitness, survive & reproduce most
successfully - Survival of the Fittest
Evolution by Natural Selection
 Since it is similar to artificial selection,
Darwin referred to survival of the fittest
as - Natural Selection
 In both AS & NS, only certain individuals
of a population produce new individuals
Evolution by Natural Selection
 However, in NS, the traits being selected,
& therefore, increasing over time,
contribute to an organism’s fitness
 NS takes place without human control or
direction
Evolution by Natural Selection
 NS results in changes in the inherited
characteristics of a population, that
increase a species’ fitness in its environ.
 Over time, NS produces organisms that
have different structures, & occupy
different habitats
Evolution by Natural Selection
 As a result, species today look different
from their ancestors
 Each living species has descended, with
changes, from other species over time Descent with Modification
Evolution by Natural Selection
 Descent with modification also implies
that all living organisms are related to
each other
 Common descent - all species (living &
extinct) were derived from common
ancestors
Evidence of Evolution
 Darwin argued that living things have
been evolving on Earth for millions of
years
 Evidence of this could be found: in the
fossil record, the geographical
distribution of living species, homologous
structures of living organisms, &
similarities in early development
Evidence of Evolution
 The Fossil Record:
Darwin noticed that the sizes, shapes, &
varieties of related organisms preserved in
the fossil record, changed over time
Evidence of Evolution
 Geographic Distribution of Living
Species:
Darwin realized that similar animals in
different locations were the product of
different lines of evolutionary descent
Evidence of Evolution
 Homologous Body Structures:
Homologous structures - structures that have
different mature forms but develop from the
same embryonic tissues
Not all homologous structures serve
important functions
Organs of many animals are so reduced in
size that they are just vestiges, or traces, of
homologous organs
Homologous Structures
Evidence of Evolution
 Homologous Body Structures:
Vestigial organs - may resemble miniature
legs, tails, or other structures, a trace of a
homologous structure
Evidence of Evolution
 Similarities in Early Development:
The early stages or embryos, of many
animals with backbones are very similar
Summary of Darwin’s Theory
 Individual organisms differ, & some of
this variation is heritable
 Organisms produce more offspring than
can survive, & many that do survive do
not reproduce
Summary of Darwin’s Theory
 Because more organisms are produced
than can survive, they compete for
limited resources
 Individuals best suited to their environ.,
survive & reproduce most successfully
Summary of Darwin’s Theory
 These organisms pass their heritable traits
to their offspring
 This process of NS causes species to
change over time
Summary of Darwin’s Theory
 Species alive today are descended with
modification from ancestral species that
lived in the distant past
 This process, where diverse species
evolved from common ancestors, unites
all organisms on Earth into a single tree
of life