Mechanisms of EvolutionMechanisms of Evolution

Chapter 22Chapter 22

Descent with Modification A Darwinian View of Life

Chapter 22

History of Evolution Science

Ancient Beliefs

A. Plato (428-348 BC) idealism a. the "idea" is an eternal, unchanging essence b. variation has no meaning only essence matters

(VARIATION IS HUGE IN EVOLUTION!)

B. Aristotle (384-322 BC) 1. Scala Naturae or scale of nature 2. All things - from inanimate objects to plants to animals to man

a. fixed in place according to God's plan

b. permanent, unchanging

The views of these two early Greeks prevailed for almost 2000 years.

The Old Testament

C. Traditional Christian beliefs

state that all organisms resulted from the direct actions of a creator

1.Each organism has a specific role to play

2.Each was individually created by God

3.Each organism is such a perfect fit in its environment because it was “hand-crafted” for that environment.

4.The earth is about 6,000 years old

5.The universe is about 13,000 years old

Beginning of Modern Scientific Methods and Thoughts

D. Carolus Linnaeus (1707-1778)

1. father of taxonomy

2. defined fundamentals of biology in terms of nomenclature and classification

3. clustering groups into a hierarchy of increasingly general categories.

4. done for the greater glory of god - "God's Registrar"

Invented Binomial nomenclature

E. Cuvier (1769-1832)

1. founder of paleontology (studied fossils – anatomist)

2. observed that different strata of sedimentary layers contained different fossils.

3. catastrophism--explained changes in animal world in terms of catastrophes that had destroyed whole populations of living

things in prehistoric times (floods etc.)

Hutton (1726-1797) and Lyell (1797-1875) both were influential geologists

F. Hutton a. gradualism - same processes are responsible for both

past and present events b. one of first to imply great age of the earth (not what the

Bible says)

G. Lyell a. Theory of uniformitarianism small forces acting over long periods

of time can result in major changes e.g. destruction of mountains. b. great champion of Hutton's work c. historical and physical continuity of natured. Principles of Geology (1830)--greatly influenced Darwin even

though he himself did not admit biological evolution

A COMBINATION OF LYELL’S AND HUTTON’S

IDEAS IS EMPLOYED TODAY

Lamarck (1744-1829)

1. the first uncompromising advocate of evolution, attempted to provide a mechanism to explain evolution

2. argued that lowly forms of life arise continually from inanimate matter by spontaneous generation, and progress inevitably toward greater complexity and perfection -- an inherent tendency toward complexity

3. particular path of progression taken is guided by environment

4. changing environment alters the needs of the organisms 5. use and disuse alter morphology and is transmitted to

subsequent generations (inheritance of acquired characteristics)

7. emphasized great age of earth 8. Ideas were almost universally rejected, particularly by

Cuvier and Lyell

Charles Darwin (1809-1882)A. Early life

1. born in 1809 in Shrewsbury, England--the son of a physician 2. studied medicine in Edinburgh 3. studied theology in Cambridge--was very religious 4. at both places he pursued an interest in natural science

B. Voyage of the H. M. S. Beagle (1831-1836) 1. served as unpaid naturalist - paid his own way2. made stops along coasts and islands of the southern hemisphere 3. noted how plant and animal forms differed with geographical location 4. Observations in Galapagos Islands and South America. 5. Read Lyell's Principles of Geology on the voyage - true age of earth much

greater than 6000 years C. Return to England after voyage

1. did not accept notion of evolution until it was pointed out that his specimens of finches from Galapagos were so distinct as to represent different species. 2. this revelation led him to doubt the fixity of species 3. first published several volumes on geology and the voyage of the Beagle

Darwin's Evidence A. Hutton and Lyell's evidence supporting geological events. B. Observations

1. extinct species related to living (extant) organisms a. observations of the fossil record b. e. g. armadillos and glyptodont--found fossil species similar

to extant species c. both limited to one geographical area d. if both were created at the same time, and if they were so much

alike, why was only one of them alive in 1850? 2. characteristics of species varied from place to place

a. appearance of tortoises dependent on location b. slight changes in appearance after island isolation

3. great variety of organisms on young volcanic islands, e.g., finches 4. resembled forms on mainland, not distant places *organisms in forests of

S. America more similar to organisms of  grasslands of S. America than to organisms in forests of Europe *this would not be so if were created all at once to be perfectly adapted for  that environment.

Darwin and Malthus

Malthus wrote Essay on the Principle of Population (1798) a. argued that unchecked growth of the human population must lead to famine  

– populations increase geometrically – food supplies increase arithmetically

b. nature acts to check population growth via death – in humans this is famine, war, and disease

Malthus’ ideas led Darwin to his idea of natural selection (competition for resources)

Alfred Russel Wallace

• A contemporary of Darwin, who also came up with the theory of Natural Selection independently.

• He sent his work to Darwin• Darwin’s work “THE ORIGIN OF SPECIES” was

published• Wallace insisted that Darwin get all the credit,

because Darwin had done more extensive work and research on it than Wallace. (what a decent guy!)

So What is Natural Selection?

5 observations Darwin made (does not apply to humans!)

1. If all members of a particular species survived to reproduce successfully, the population size would grow exponentially.

2. However, population sizes usually stay the same, except for some seasonal fluctuations.

3. In any environment, resources are limited4. Members of a populations vary in their

characteristics – no two are alike5. These variations are heritable

What Darwin inferred from his observations

1. Overproduction of offspring: When there are more organisms than an environment’s carrying capacity…

2. Struggle for existence: there will be a struggle for survival a.k.a COMPETITION

3. Genetic Variation: The organisms that possess a variation that will help them in this struggle, will survive to reproduce.

4. Differential survival and reproduction: These favorable traits will be passed on to their offspring, giving them the same benefit.

Summing it up

In the end, only those members of the population that are best adapted to their environment will be successful.

THIS WAS HIS THEORY OF NATURAL SELECTION

http://www.pbs.org/wgbh/evolution/library/11/2/e_s_4.html

Some of the 13 finches Darwin studied

Biogeography and Convergent Evolution

• The geographical distribution of species

• The same type of niche in 2 lands very far from each other my have different, but similar looking species

• This is because they share similar environmental conditions/niches, but independently, from different ancestors.

Biogeography and Convergent Evolution

The sugar glider is indigenous and endemic to Australia is a marsupial

mammal, related to the kangaroo

The flying squirrel is indigenous to North America is a eutherian

(placental) mammal

Indigenous – belonging naturally to a geographic area

Endemic – found nowhere else in the world

Lamarck versus Darwin / Wallace

Artificial Selection

• Animal husbandry• Pet breeding

Evidence of Evolution

• Anatomical Homologies• Embryological Homologies• Molecular Homologies • Vestigial Organs • Fossil Record

Anatomical HomologiesHomologous structures indicate evolutionary ties

Analogy vs. Homology

• Structures that are similar due to evolutionary origin, such as the forearm bones of humans, birds, porpoises, and elephants, are called homologous.

• Structures that evolve separately to perform a similar function are analogous. The wings of birds, bats, and insects, for example, have different embryological origins but are all designed for flight.

The bones in the three flying animals (not the insect) are homologous, but the wing structures of all 4 flying animals are analogous

Embryological Homologies

Molecular Homologies

• All life has DNA, RNA and the genetic code is universal

• So all animals could have descended from a common ancestor

• Even animals as dissimilar as bacteria and humans, share common genes inherited from a distant ancestor.

Vestigial Organs

Tonsils

Adenoids The adenoids are tonsil-like tissues that are located in the back of the nose, next to the opening of the

eustachian tube.

Coccyx (tail bone) Nictitating membrane of eye

Thymus Appendix

Little toe Wisdom teeth

Nipples on males Parathyroid

Nodes on ears "Darwin's points" Ear muscles for wiggling

Pineal gland The pineal gland is a tiny structure located at the base of the brain. Its principal hormone is melatonin, which regulates our day and night cycles

Body hair

Fossil Record (basically anatomical homology)

• Transitional fossils that link the past with the present

Approximately 50 million years ago, this wolf-size pakicetid—an ancestor of the whale—lived on land but

may have waded into streams to feed on fish.

Read article on origin of whales

END OF CHAPTER 22