Evolution theories

EVOLUTIONTheories on the Origin of Life

Extraterrestrial OriginThis theory states that life originated on

other Planets outside of our solar system, and was carried here on a meteorite or asteroid.

1. Intelligent life seeded the planet.2. Organic molecules (1st bacterial cells)

formed in space and were carried here by meteorites or asteroids.

Creationism

Life was put here, on Earth, by divine forces.• Because of the separation of church and state,

we are not allowed to teach this in school.• This is based on faith not fact.• Relies on stories that have been passed down

over the years.

Origin from Non-Living Matter

• Life arose from inanimate matter. Random events produced stable molecules that would reproduce themselves. Then Natural Selection favored changes that increased their rate of reproduction. This eventually lead to the first cell. Organic acids came together to form organisms.

Definition of Evolution

• Evolution is the process of change through time.

• It is the process by which modern organisms have descended from ancient organisms.

Evolutionary Theory

• Is the unifying principle for all the biological sciences.

• Provides an explanation for the differences in structure, function, and behavior among life forms.

• It includes the change in characteristics of populations through generations. Thus existing life forms have evolved from earlier life forms.

Supporting Evidence• Comparative Anatomy- this is the comparative

study of certain organisms showing similarities in anatomical features.

• Comparative Embryology- comparison of early embryonic development among groups of organisms reveals similarities which suggest common ancestry.

More Supporting Evidence• Comparative Cytology- Organelles are

structurally and functionally similar in most divergent organisms, suggesting that all living things are related to some degree.

• Comparative Biochemistry- Many different organisms have similar proteins and enzymes, therefore their DNA must be similar.

• Geologic Records- Fossils, the direct or indirect remains of organisms preserved in media, suggest links between modern and ancient forms, as well as, divergent pathways from common ancestors.

Origins of LifeEarly Theories on How Life Began:

Spontaneous Generation and

Scientific Experiments

Spontaneous GenerationABIOGENESIS- creation without life.Spontaneous Generation was the mistaken idea

that life can arise from non-living materials. We now believe the cell theory. The cell theory states that all cells come from pre-existing cells.

• Ancient Egyptians believed that eels and frogs came from the mud of the Nile.

• Aristotle “active principle” responsible for life:

fleas come from sweat mice come from garbage flies and maggots come from dead and

decaying meat

Scientists and Experiments

• Jan Baptista van Helmont- He was a supporter of the belief in Spontanous Generation. He experimented with wheat grains in a sweaty shirt. After 21 days wheat grains are gone and mice are present. The active ingredient was sweat.

• Francisco Redi- (mid 1600’s) discovered maggots came from flies not decaying meat. Questioning Spontaneous Generation.

• Anton Van Leeowenhoek- Was the first to use a microscope to see the first living cells. He called the small animals he observed “animacules”. Took pond water and boiled it. Then added hay. Organisms were found- hay was the active ingredient.

• John Needham- (1745) boiled flasks of broth, then sealed them. Days later microorganisms were found in the broth. Hypothesized that “animacules” came from the gravy.

• Lorenzo Spallenzini- challenged Needham. Boiled contents longer, and left one flask open and the others closed. Life was found in the open flask, and not in the closed flask. This experiment supported Redi’s in that it proved life can only come from existing life.

• Louis Pasteur- took microorganisms/spores in the air and used flask with long curved necks to demonstrate that it was exposure to the air that allowed for the microorganisms to get into the broth in the flask This experiment took place over one year. This finally, and conclusively, disproved Spontaneous generation.

Primitive Life Forms

• Raw Materials- primitive Earth was very hot, consisting of inorganic substances in liquid, solid, and gaseous states, having a rich supply of energy.

• Matter- water condensing and falling as rain, carried the dissolved and atmospheric gases and minerals into the seas, forming a hot, thin, soup.

• Energy sources- in addition to heat energy in the form of lightening, solar radiation, and radioactive materials in the rocks, provided an energy rich environment.

Synthesis

• Energy from the environment contributed to the formation of chemical bonds among the dissolved particles of the “hot, thin soup” of the seas.

• What was formed by the chemical bonds?

• This type of synthesis led to the formation of organic molecules such as simple sugars, amino acids, and nucleic acids.

EARLY THEORIES OF EVOLUTION

Theories of Evolution

Jean Baptiste Lamarck- 1809 French Biologist• Proposed that life evolves or changes.• Explained evolution as a process of adaptation.• Law of Use and disuse. -New organs arise

according to the needs of an organism, and their size is determined by the degree to which they are used.

• Inheritance of acquired characteristics.- Useful characteristics acquired by an individual during its lifetime can be passed on to its offspring.

• No evidence to support this theory.

Theories cont….

August Weissman-• Helped to disprove Lamarck’s theory

of Inheritance of Acquired Traits.• Conducted experiments involving the

removal of the tails of mice over several generations.

• Found that the offspring of the tail-less mice did not pass on that characteristic to their offspring.

Theories cont…..

Hugo DeVries-• Discovered mutations and proposed that

it was these mutations that were the source of new traits that permitted evolution to occur.

• This was the one area, in Darwin’s theory, that was weak. Darwin’s theory did not account for the genetic basis for variations.

Charles Darwin- 19th century English Naturalist• Proposed that evolution occurred as the result of Natural

Selection.• Overproduction- within a population more offspring are

produced in each generation than can survive, because of limitations of space and food.

• Competition- individuals compete for the available food and opportunity to mate and reproduce.

• Variation- within each generation some individuals are better fitted to survive than others because of variations in characteristics.

• Survival of the Fittest- those individuals better fitted to survive are more likely to live long enough to reproduce.

• Transmission of Favorable Traits (Reproduction)- offspring of the fittest individuals will inherit the favorable variations that enabled their parents to survive and reproduce.

• Evolution of Species (Speciation)- accumulation of favorable variations will gradually lead to the appearance of new species better adapted to their environment.

• Weakness in Darwin’s Theory is that it does not account for genetic basis of variations. At the time, not much was known about the mechanisms of genetic inheritance.

Natural SelectionNatural Selection• Natural selection is the process where inheritable

traits that make it more likely for an organism to survive long enough to reproduce, become more common over successive generations of a population.

• It is a key mechanism of evolution.• The Galapagos finches provide an excellent example

of this process. Among the birds that ended up in arid environments, the ones with beaks better suited for eating cactus got more food. As a result, they were in better condition to mate. Similarly, those with beak shapes that were better suited to getting nectar from flowers or eating hard seeds in other environments were at an advantage there. In a very real sense, nature selected the best adapted varieties to survive and to reproduce. This process has come to be known as natural selection.

The Peppered Moth StudyAn Example of Natural Selection!

Write similarities and differences between these two

organisms!

Both have the Scientific Name:– Biston betulariaBoth are the same moth, commonly called

peppered moths. There is a story behind these two different color variations. Click to find out what happened!

• During the early 1800’s in Birmingham, England there were dark and cream colored moths. However, almost all peppered moths were cream colored because the tree trunks were light colored.

Can you find the moth on the tree trunk?

Would it be an advantage or disadvantage for the moth to be light?

Industrial Revolution•A greater number of factories were being created, which meant more pollution!

WRITE:

•What do you think was happening to the peppered moths as a result of industrialism?

Something was happening in the cities of England at this time,

What could that have been?

WHAT’S HAPPENING!• Around 1850, black-

colored peppered moths started to become more common than cream, usually in heavily industrialized areas.

Why did the frequency of black moths increase with the growing

industries?

Darwin’s Theory of evolution by natural selection suggests a

hypothesis.

White tree trunks were blackened by heavy pollution

from factories.

Which Moth is better adapted to its environment? Explain why?

•Perhaps dark moths sitting on soot-darkened bark escaped being eaten by birds because it was too hard for the birds to see the dark moths against the dark background.

•Light-colored moths would have stood out against a dark background and would have been easy prey for hungry birds. Therefore, more dark moths survived.

This is an example of Natural Selection!

• Natural Selection- is a gradual change in a species in response to the demands of its environment.

Do Now:• Write how the peppered moth

during the 1800’s was an example of natural selection in action!

Charles Darwin

Background and Observations

Background Info.• Darwin was born in England, Feb. 12, 1809.• Studied to become a physician, decided not to continue.• Studied to become a minister, decided not to continue.• Graduated college and at the age of 22, signed aboard

the HMS Beagle, as ship’s Naturalist. His job, as naturalist, was to collect and study plant, animal, and geologic specimens form the journey around the world.

• The voyage began in December of 1831 and lasted 5 years.

• Darwin kept extensive journals of his observations, studies, and thoughts.

• Darwin’s ideas on gradual change were influenced by the evidence presented by Charles Lyell. Lyell stated that gradual and observable geologic processes, such as erosion, could explain the physical features of the Earth today.

• Darwin was also influenced by James Hutton, who in 1785 proposed that the Earth was formed by geological changes that occurred over a very long period of time .

• Darwin’s most intriguing finds occurred on the Galapagos Islands.

• After returning home from his voyage, he continued to wonder about the things that he had seen.

• In 1838, he read an essay by Thomas Malthus, on human population. Malthus stated in his essay, that populations can grow much faster than the rate at which food supplies and other resources can be produced. Production of more individuals than the environment can support lead to a struggle for existence. This concept helped Darwin to propose a mechanism for evolutionary change.

• In 1844, Darwin outlined his ideas. In 1858, after another British naturalist, Alfred Wallace, came to the same conclusions about the basic mechanism for evolutionary change, Darwin published his book, The Origin of the Species by Means of Natural Selection.

Darwin’s Observations• There was an enormous number of species that

inhabited the Earth.• Patterns of Diversity- he asked why similar

ecosystems were inhabited by different types of species (why the grasslands of England had rabbits, why the grasslands of Australia had kangaroos?).

• Darwin wondered why so many organisms that were once alive, were now preserved as fossil remains. Why did these organisms cease to exist? How were the fossils related to the living organisms?

• The Galapagos Islands- a small group of 16 islands 1000km off the west coast of Equador. Darwin noticed that even though the islands were relatively close together, they still had very different climates.

The lowest were hot, dry, and barren The highest had more rainfall, vegetation, and more animal life.• Darwin noticed that the characteristics of many plants

and animals varied noticeably between the islands. Hood Island- tortoises had long necks, curved

shells open around the legs, allowing the animal to get more access to the sparse vegetation.

Isabella Island- tortoises had shorter necks, domed, curved shell, allowing for the animals to feed better on the more abundant vegetation that was close to the ground.

• Many specimens of finches were collected and differences were observed in the shapes and sizes of their beaks.

• After returning to England, Darwin began to wonder if the animals living on the islands were once members of the same species.

Supporting Observations For the Theory of Evolution

Geologic Records

• Earth has been estimated to be between 4.5-5 billion years old. (Determined through radioactive carbon dating).

• Fossil remains-the direct or indirect remains of organisms preserved in media such as tar, ice, rock, or amber.

• Fossils of prokaryotic life indicate that life existed over 3.4 billion years ago.

• Fossils can be found in the upper, and lower strata. These have been found to resemble each other, suggesting a connection between modern forms and older forms, as well as, divergent pathways from common ancestors.

Comparative Anatomy

• Comparative studies of certain organisms indicate similarities in anatomical features.

• Homologous structures- anatomical parts that are similar in structure and origin (development), but function differently. (Ex.- wing of bird, arm of man, foreleg of horse).

• Homologous bones exist in the forelimbs of many different vertebrates such as birds, horses, man, bats, whales.

• Analogous structures- are similar in appearance and function, but have developmental differences. (Ex.- wing of bird and wing of butterfly).

Comparative Embryology

The study of embryonic developments among groups of organisms reveals similarities that suggest common ancestry.

1. Early vertebrate embryos resemble each other.

2. As development proceeds, the distinctive features of each species becomes apparent.

3. All have gill slits, tail-bones (coccyx), segmented backbones, and are C-shaped.

Comparative Cytology

According to the cell theory, the cell is the unifying structure for living things. Organelles such as the cell membrane, ribosomes, and mitochondria, are structurally and functionally similar in most divergent organisms. This suggests that all living things are related to some degree. The fewer the differences in these cell structures, the closer the relationship appears.

• Nucleic acids, their structure and function, are similar in living organisms.

• Many different organisms have similar proteins and enzymes.

• In order for this similarity to occur, their DNA must be similar.

• The greater their biochemical similarity, the closer the relationship among organisms, thus suggesting evolutionary relationships.

Comparative Biochemistry

Vestigial Structures

• These are structures that do not have any use, but are the remains of structures that were once functional in ancestral organisms.

• Some examples of vestigial organs are: Humans- appendix, coccyx, 3rd molars Horses- splint bones Whales- pelvic (hip) bones

Modern Theory of Evolution

(continued) A Time Frame for Evolution

Geographic IsolationGeographic Isolation- favors speciation by

segregating a small group of organisms from the main population. Changes in gene frequency are more likely to occur in a small population. In time, this isolated population may evolve into a separate species due to:

• Different initial gene frequencies than the main population.

• Different mutations occur within the main population and the isolated population.

• Different environmental factors, thus having different selection pressures on each population

• An example of this would be Darwin’s Finches, and Australia’s marsupials, and the Albert Squirrel.

Reproductive Isolation

Reproductive Isolation- separated groups my become so divergent that even geographic barriers were removed, interbreeding could not take place. Thus the populations have become reproductively isolated and are now two separate species.

• These populations now have separate gene pools.

• Reproductive Isolation results from various isolating mechanisms that include: Geographic Isolation, Behavioral Isolation, or Temporal Isolation.

A Time Frame for Evolution

Gradualism- Gradualism proposes that evolution is slow , gradual, and continuous. This viewpoint is supported by geologic fossils, which show slight changes in organisms between adjacent layers of sedimentary rocks.

• Species originate through gradual change of adaptations. There is one line of descent.

Time Frame (cont.)Punctuated Equilibrium- Punctuated Equilibrium proposes that

species have long periods of stability, interrupted by geologically brief periods of significant change, during which a new species may evolve.

• This was proposed by Niles Eldredge, and Stephen Gould in 1972.• Speciation occurs in relatively quickly, in rapid bursts, followed by

long periods of genetic stability in between.• Environmental changes (higher temps., and introduction of

competitive species) lead to rapid changes in a small population’s gene pool that is reproductively isolated from the main population.

• Speciation happens relatively quickly- 10,000 years or less.• Punctuated Equilibrium involves many lines of descent, it is a

pattern of long, stable periods, interrupted by brief periods of more rapid change.