Do Now
What different ways do these animals use to move about?
What traits does each animal have that help it move about as it does?

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

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
 Friday “Dangerous Mind” Movie on
Darwin (complete worksheet)
Remember!!! Reward Friday

Home Work (Monday)
 Computer time required at home or library. One page required
Choose 1 to write about
 Compare Darwin’s and Wallace’s theories.
 Compare and contrast both Darwin’s and
Wallace’s careers and background.


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

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 environment.
 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