Theory of Evolution

Chapter 15

The Old Testament

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

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

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. Believed that life appears from inanimate matter by spontaneous generation, and becomes more complex over time

2. changing environment alters the needs of the organisms

3. use and disuse alter morphology and is transmited to subsequent generations (inheritance of acquired characteristics)

4. Believed the earth was very old

Charles Darwin (1809-1882)

Voyage of the H. M. S. Beagle (1831-1836)

Made observations in Galapagos Islands and South America.

So What is Natural Selection?

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

Lamarck versus Darwin / Wallace

Artificial Selection

• Animal husbandry• Pet breeding

Human beings select desired traits

Sexual Selection

• A form of natural selection where individuals with certain inherited traits are more likely to finds mates.

• Sexual selection causes sexual dimorphism, where there are clear differences between the two sexes (Like in human males and females)

Intersexual Selection – Individual selects a mate based on certain physical characteristics such as showy feathers, muscles, etc. Females usually

follow this route.

Intrasexual Selection – Individuals of the same

sex compete actively and sometimes aggressively

for a mate from the opposite sex. Usually

males display this behavior.

Evidence of Evolution

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

Fossil Record

• Sedimentary rocks are the richest source of fossils

• As a result of these sedimentation periods, sedimentary rocks form strata

• The deeper the stratum, the older and simple the organisms

• The higher the stratum, the newer and more complex the organisms.

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

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

• When a population diverges from an original population and fills many parts of a new environment, it is called adaptive radiation.

• Coevolution – when one species evolves, the other species that depends on it must also evolve to survive.

Adaptive Radiation

Population Genetics and Speciation

Chapter 16

• A population is a group of individuals in a certain time and place that belong to the same species – that is: they can interbreed and produce viable offspring

• A Gene Pool is the total number of genes within a population at a particular time and place.

What causes variations?

• Mutations in an original gene will give rise to new alleles.

• Alleles will create the variations in a population that Darwin talked about

• Some alleles will help an organism, others will harm it

• The alleles that contribute to the survival of a species in a particular environment, will be passed on

Gene Pool

• All the alleles in a population are collectively called the gene pool of that population

Get Out! The Pool is Closed!

• The Amish for example – the only variations in the population arise from independent assortment and crossing over during meiosis and random fertilization within the community

• No external agents – immigration, for example

Gene Flow

• When alleles are introduced in or removed from a population it is called gene flow. This can happen due to:

• Immigration

• Emigration

Types of Natural Selection

Speciation

• Speciation – the formation of a new species

- Geographical isolation – when some members of a population become separated from the main population and eventually accumulated enough mutations to become a separate species.

-Reproductive isolation – when 2 individuals can no longer reproduce together, they become separate species.

Allopatric Speciation

 First geographic isolation...•Unless populations are geographically isolated they will continue to interbreed ...then genetic isolation•Populations diverge to the point where they no longer interbreed •This may be due to adaptation to different environments, or genetic drift

Allopatric speciation of squirrels in the Grand Canyon (see Campbell fig. 24.7, p. 451).The canyon is a barrier to dispersal by small mammals, and as a consequence the isolated populations can diverge.

Gradualism vs. Punctuated Equilibrium

THE END