The Theory of Evolution

Chapter 17

Evolution

• A process of change through time

Human Evolution

• MEMBERS OF THE SAME GENUS• Homo sapiens • Homo erectus• Homo habilius

• Homo neandertalensis• The oldest form of Homo sapien was found

to be about 100,000 years old. It was also found in Africa.

HUMAN EVOLUTION• The current belief is that between 8 and 14

million years ago the common ancestor to the ape and human evolved.

• Mitochondrial DNA has proven that this occurred in Africa. These early "Humans" are called HOMINIDS. The Australopithecus were one the earliest hominids to be bipedal. (Walk on 2 feet) Again the fossil record is proof of human evolution.

• The recent discovery of 6 million year old Australopithicus in Africa is the oldest to date.

Brain Size????

• One of the most important advancements was the increase in the size of the human brain. Although this is not the only factor in our advancement as a species it was crucial.

• Brain size is not alone the most important factor. If this were the only factor the blue whale would be the most advanced technological species on Earth.

• It has been proven that Neanderthal and Cro Magnon both had similar sized brains. Yet Cro Maganon is considered more advanced or modern due to it's much more sophisticated use of tools.(technology)

Theory of Evolution1. Suggests that existing forms of life

on earth have evolved from earlier forms over long periods of time

2. Evolution accounts for the differences in structures, function, and behavior among life forms as well as changes that occur in populations over many generations

• What Five observations are used to support the theory of organic evolution??

(I) Evidence of Evolution• Five observations supporting the theory of

organic evolution can be made through the study of:1. Geologic record2. Comparative Cytology 3. Comparative Biochemistry 4. Comparative Anatomy5. Comparative Embryology

(1) Geologic Record1. Earth is between 4.5 to 5 billion

years old (age was determined by radioactive dating of rocks)

2. Fossils- are the remains of traces of organisms that no longer exist.

Fossils have been preserved in ice, sedimentary rock, amber, and tar

3. Other fossils have been formed from petrification, a process by which the tissues are gradually replaced by minerals that produce a stone replica of the original material

4. Imprints, casts, and molds of organisms or parts of organisms are frequently found in sedimentary rock

5. In undisturbed layers (strata) of sedimentary rock, the lower strata contain old fossils while the upper strata contain younger fossils

Archaeopteryx: a remarkable fossil that has

provided paleontologists with insight to the origin of

birds.

          

(2) Comparative Anatomy1. Evidence supports that

similarities of basic structures exist between different organisms

2. Homologous structures are anatomical parts found in different organisms in origin and structure

3. The presence of such homologous structures suggest that these organisms have evolved from a common ancestor

(3) Comparative Embryology

• Although certain adult organisms may be different from each other, a comparison of the earl stages of their embryonic development may show similarities that suggest a common ancestor

(3) Comparative Embryology

(4) Comparative Cytology

1. All living things are made up of cells.

2. Cell organelles including the cell membrane, ribosomes, and mitochondria are structurally and functionally similar in most organisms.

(5) Comparative Biochemistry• All living things contain similar

biochemical compounds• Examples would include:

structure and function of DNA, RNA, and proteins (including enzymes) are similar in all organisms

Evidence of Evolution

1. Geologic record

2. Comparative Cytology

3. Comparative Biochemistry

4. Comparative Anatomy

5. Comparative

Embryology

(II) Theories of Evolution1. Attempts to explain the similarities

and differences among species2. Adaptations- are a major component

to these theories. Adaptations are features which make a species better suited to live and reproduce in its environment

(A) Lamark

• The evolutionary theory of Jean-Baptiste Lamark was based on the principle of:

1. Use and Disuse

2. Inheritance of acquired traits

Principle of Use and DisusePrinciple of Use and Disuse• For an organism, new structures appeared

in the course of evolution because they were they were needed. needed.

• Structures that were present and were used became better developed and increased in size; structures that were not used decreased in size and eventually disappeared

Ex: muscles of an athlete vs. appendix

Inheritance of Acquired Traits• Useful characteristics acquired by an

individual during its lifetime can be transmitted to its offspring

• These acquired traits results in species that are better adapted FOR their environment

• Ex: a giraffe’s neck became longer as a result of stretching to reach higher branches. This acquired trait was then passed down to the offspring

Lamark’s GiraffesLamark’s Giraffes

(B) Weisman1. August Weisman did not agree with Lamark’s

theory of acquired traits

2. In a series of experiments, Weisman removed the tails of mice.

3. The mating of these tailless mice produced offspring with tails of normal length.

4. Weisman removed the tails of these mice and allowed them to mate.

5. Again, offspring were produced with tails of normal length.

6. The acquired condition of “taillessness” was not inherited.

(C) Darwin•Charles Darwin devised a theory of evolution based on variation and natural selection

•Included in hid theory were five main ideas:

1. Overproduction

2. Competition

3. Survival of the Fittest

4. Reproduction

5. Speciation

Galapagos Islands

Galapagos Islands

                          

1. Overproduction

• Within a population, there are more offspring produced in each generation than can

possibly survive

                                  

         

2. Competition• Natural resources; like food, water, and space available to a

population is limited• Because there are many organisms

with similar nutritional requirements, there must be

competition between them for the resources needed to survive

3. Survival of the Fittest• Variations among

members of a population make some of them better adapted for the environment than others

• It is generally the best-adapted individuals that will survive

• The environment is the agent of natural selection determining which species will survive

4. Reproduction

• Individuals that survive and then reproduce transmit these

variations to their offspring

5. Speciation

• The development of a new species occurs as variations or adaptations

accumulate in a population over many generations

• Ex: caveman present man

This would be Darwin’s View of Lamark’s giraffes .

DARWIN'S REPRESENTATION OF EVOLUTION

Time line of Hominids

Beaks of Finches Lab

(III) Modern Theories of Evolution

• The modern theory of evolution includes both Darwin’s ideas of variation and natural selection

and the current knowledge of the sources of variations

(A) Sources of Variations

1. Genetic Shuffling:• Segregation (during Meiosis)

• Crossing Over (during Meiosis)

• Recombination of alleles (during sexual reproduction)

2. Gene mutation occurs spontaneously and at random

(B) Natural Selection1. Natural selection involves the struggle of organisms to

survive and reproduce in a given environment2. Traits which are beneficial to the survival of an

organism in a particular environment tend to be retained and passed on, and therefore, increase in frequency within a population

3. Traits which have low survival value to an organism tend to diminish in frequency from generation to generation leading towards extinction.

4. If environmental conditions change, traits that have low survival value may now have a greater survival value. Therefore, traits that prove to be favorable under new environmental conditions will increase in frequency

Ex: Insects resistant to insecticides1. Genetic make-up of some insects make them resistant

to the effects of insecticides

2. Before the widespread use of insecticides, this trait was of no particular survival value

3. With the increased use of insecticides, this trait developed a very high survival value

4. Therefore, insects with resistance to insecticides survived and reproduced much more successfully than those lacking the trait

5. As a result, the frequency of insecticide resistance has increased greatly in insect populations

1. Geographic isolationex: Pangea,

2. Reproductive isolation

•Gene frequency- the percentage of organisms in a population that carry an allele

1.Isolation of a population increases the chances for speciation (the development of a new species) by separating a small group of organisms from the main population with its large gene pool (inheritable traits)

2.Changes in gene frequency are more likely to occur in small populations than in large ones

3.Geographic isolation of a population is caused by natural barriers like mountains, large bodies of water, and deserts

(C) Geographic Isolation

Pangea and Continental Drifthttp://www.scotese.com/pangeanim.htm

Pangea and Continental Drifthttp://www.scotese.com/pangeanim.htm

Continental Drift

Geographic isolation leads to a genetic drift.

A classic example of genetic drift can be observed in the white-tailed deer population of Seneca Army Depot, an

11,000 acre reserve that was fenced off in the 1950s. Security is tight and hunting is not allowed at this ordnance depot. What is unusual is about this deer

population is that rare white-phased deer can be found in significant numbers within the fenced in area. In 1993, it

was estimated that there were 150 albino deer and 300 normal colored deer.

Mountains Form

The evolution of an isolated population into a new species may involve the following factors:

a) the gene frequency in the isolated population may have been different than the gene frequency in the main population to begin with

b) different mutations occur in the isolated population and in the main population

c) different environmental factors may also have exerted different selection pressures on each population (natural selection was different)

(D) Reproductive Isolation

• If the isolated population becomes so different from the main population that members of the two cannot interbreed and produce fertile offspring, then they have become two distinct species.

(E) Time Frame for Evolution• There are two different theories proposed

by scientists to address the rate of evolution:

1. Gradualism- proposes that evolutionary change is slow, gradual, and continuous

2. Punctuated Equilibrium- proposes that species have long periods of stability (several million years) interrupted by geologically brief periods of significant change during which a new species may evolve

Gradualism vs. Punctuated Equilibrium

Time

Var

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Time

Var

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Gradualism vs. Punctuated Equilibrium

Var

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Possible Explanations of howlife arose.

Heterotroph HypothesisHeterotroph Hypothesis

•Based on Scientific studiesBased on Scientific studies

CreationCreation

•Based on religious belief Based on religious belief systemsystem

Millers experiment• Stanley Miller, a graduate student in biochemistry, built the apparatus

shown here. He filled it with • water (H2O), methane (CH4) , ammonia (NH3) and

• hydrogen (H2) ) but no oxygenbut no oxygen• He hypothesized that this mixture resembled the atmosphere of the early

earth. (Some are not so sure.) The mixture was kept circulating by continuously boiling and then condensing the water.

• The gases passed through a chamber containing two electrodes with a spark passing between them

• . At the end of a week, Miller used paper chromatography to show that the flask now contained several amino acids as well as some other organic molecules

Millers experiment

(IV) Heterotroph Hypothesis

• Is one proposed explanation for how life arose and evolved on primitive earth

• According to this hypothesis, the first life forms were heterotrophic and had to obtain their nutrients from the environment

(A) Primitive Earth• Based on assumptionBased on assumption1. Earth was very hot consisting of inorganic

substances in all states: solid, liquid, and gas2. Many energy sources including heat, lightning,

solar radiation(x-rays and U.V. rays), and radiation from radioactive rocks

3. The atmosphere: water vapor, hydrogen, methane gas, and ammonia

4. As the earth cooled, water condensed in the atmosphere and rain fell forming seas described as “hot, thin soup”

Primitive Earth (cont)• Based on assumptionBased on assumption

As the earth cooled, water condensed in the atmosphere and rain fell forming seas described as “hot, thin soup”

(B) Synthesis of Organic Compounds

1. In the seas, chemical bonds formed between the dissolved substances

2. Eventually, various types of organic molecules formed in the seas, including amino acids and simple sugars

3. More complex organic compounds were then formed by the interactions between the simpler molecules

(C) Nutrition1. Some of the large. Complex molecules

formed groupings or clusters called aggregates

2. These aggregates developed a surrounding “membrane”

3. It is believed that aggregates absorbed simple organic molecules from the environment for food

4. Therefore, they carried on a form of heterotrophic nutrition

(D) Reproduction

1. In time, as these aggregates became more complex and highly organized, they developed the ability to reproduce

2. At the point where the ability to reproduce had evolved, the aggregates were considered to be living cells

(E) Heterotroph to Autotroph1. It is thought that these early heterotrophic life

forms carried on a form of anaerobic respiration known as fermentation

2. As a result of the extended periods of fermentation, carbon dioxide was added to the atmosphere

3. Eventually, as a result of evolution, some heterotrophic forms developed the capacity to use carbon dioxide from the atmosphere to form organic compounds (food)

4. These organisms were the first autotrophs

(F) Anaerobes to Aerobes 1. Autotrophic activity (photosynthesis) added

free oxygen to the atmosphere

2. Over time, the capacity to use oxygen in respiration (aerobic) evolved in both autotrophs and heterotrophs

3. Present day organisms may be heterotrophic or autotrophic; aerobic or anaerobic