Download Unit 5 Evolution

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 (overproduction)
Summary of Darwin’s Theory
 Because more organisms are produced
than can survive, they compete for
limited resources(competition)
 Individuals best suited to their environ.,
survive & reproduce most successfully
(natural selection)
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
Punctuated equilibrium
 : evolution that is characterized by long
periods of stability in the characteristics
of an organism and short periods of rapid
change during which new forms appear
especially from small subpopulations of
the ancestral form in restricted parts of its
geographic range
Gradualism
 the evolution of new species by gradual
accumulation of small genetic changes
over long periods of time;