Chapter 15-Darwin’s theory of Evolution

I. The Puzzle of Life’s Diversity• ___________________-variety of organisms• _________________-change over time• Voyage of the Beagle

– Charles Darwin-sailed____________________(1831) and collected many scientific observations –particularly of interest at the area around S.America and the Galapagos Islands

Biological Diversity

Evolution

H.M.S. Beagle

– Darwin collected ___________ remains-some resembled living organisms and some did not---

indicating species had disappeared.– Observed great diversity and saw so many

organisms were well suited to their environments and various patterns ----leaving him w/ many questions…

Fossilized

– Although the Galapagos Islands were very near S.America,their climates were different than S.America and each other.The _________________ and iguanas varied in predictable ways from island to island/also many observations on variations in birds-eg. Size or shape of beak.

– After returning to England , he began to wonder if the animals on different islands were once members of the same species.

tortoises

II. Ideas that shaped Darwin’s thinking

– Predominate thought was that the earth and inhabitants were only a couple thousand years old.

– __________________ published a detailed hypothesis about the geological forces that have shaped the earth-proposing layers of rocks formed slowly and the physical earth was shaped by a variety of forces..

– _____________________________________ wrote Principles of Geology .---stressed that scientists must explain past events based on processes they can actually observe---eg. By volcanoes that we still observe may we get an idea of how the earth has changed

1795-James Hutton

Charles Lyell in 1800’s

– _________________(1809)-realized organisms change over time but he felt that selective use or disuse of organs caused organisms to acquire or lose traits

• 1) _____________He said all organisms have a tendencies towards perfection ..thus continually acquiring characteristics to improve themselves----Thus he would say birds fly because they long ago tried to and their wings kept developing over the generations to fly.

Lamarck

Perfection

• 2) ________________if something is used it is transformed for that purpose while if it not used,it would eventually disappear

• 3)____________________.---If a giraffe stretched its neck to reach its food,it would pass that trait on…

• 4)Evaluating Lamarck- incorrect in many ways-– He did not know an organism’s

experiences or behavior have no effect on inheritance

USE AND DISUSE

INHERITANCE OF ACQUIRED CHARACTERISTICS

• Population Growth-_____________-reasoned that if the human population continued to grow unchecked,sooner or later there would be insufficient space & food---war,famine and disease work against this

• Darwin realized this applied less to humans than other animals and plants because _______________________________________

Thomas Malthus-1798

People do not reproduce as much young

III. Darwin presents his case

• A. publication

• 1858-Alfred Russel Wallace summarized the thoughts on evolutionary change Darwin had been looking @ for 25 years…This gave Darwin the incentive to publish his work

• 1859—Darwin Published “On the origin of Species…”proposed the mechanism for evolution to be ______________________________________

Natural selection

B. Inherited Variation and Artificial Selection

• Members of each species vary from one another• Some variation heritable-passed on• ______________________selective genetic variation

where nature provides the variation and humans select to breed for this characteristic

Artificial selection

C. Evolution by Natural Selection

– 1) Struggle for existence• Applying Malthus’ principles,He realized high

birth rate and shortage of resources produced _______________________-struggle for existence---faster,etc. avoid being caught

competition

2) Survival of the Fittest

• _____________________=ability of an individual to survive and reproduce

• ___________________=any inherited characteristic that increases an organism’s chance of survival

• Organisms w/ low levels of fitness are unlikely to survive and reproduce

• __________________________________=survival of the fittest….may inherited characteristics of a population

fitness adaptation

Natural selection

3) Descent with Modification

• Over long periods ,natural selection produces organisms that have different structures,establish different niches,or occupy different habitats---each species descends ______________________.

– Implies all living organisms are related to each other

– _____________________________-all species-living and extinct were derived from common ancestors

Modification/changes Common descent

D.Evidence of Evolution

– 1) Fossil Record-record of the history of life on earth-comparing fossils from different layers

– Felt the earth was millions of years old– Since Darwin,people have discovered many

transitional species in fossilized form– Gaps remain—providing some uncertainty

about how some species evolved

2)Geographic Distribution

• With reference to birds he observed,Darwin felt although they varied,they descended with modification from common mainland S.American ancestor

• Animals w/certain similarities between areas developed this way due to similar ecological conditions

3)Homologous Body Structures----structures that have different mature forms but develop from the same

embryonic tissue

• Example:The bones of a bird skeleton more closely resemble homologous bones of certain reptiles than that of bats

• ___________________________-traces of homologous organs….appear to have no function

Vestigial organs

4)Embryological Similarities-many embryos look esp. similar during certain stages of development…

producing homologous structures

E. Summary of Darwin’s Theory• Individuals differ and some can be

___________________________.• Organisms produce more offspring that can survive

and many do not _________________________.• Organisms ______________for limited resources.• Each unique organism has unique advantages and

disadvantages in struggling for existence---Those best suited will reproduce,passing on their traits.

• Species alive today descended with modification from ancestral species…uniting us in a single tree of life

Inherited traits

reproducecompete

Strengths and Weaknesses

• Continues to change as new data and technology develop

• Argument about extinction

• Origin of life

Evolution cont’d-pieces of Chapter 16 & 17

• _____________________=all genes,inc. all the different alleles,that are present in a population

• ______________________of an allele= # times that the allele occurs in a gene pool,compared with the # of times other alleles for the same gene occur.(often a %)

• In genetic terms ,evolution is any change in the relative frequency of alleles in a population.

Gene pool Relative frequency

Sources of genetic Variation-

– 1)mutations– 2)gene shuffling– ----- Natural selection can affect the distribution of

phenotypes in any of the 3 following ways:• 1) Directional selection-Individuals @ one end

of curve have higher fitness than those @ middle or other end-Example-birds w/ large,wide beaks can crack large seeds….If the supply of small seeds decreases,they dominate

• 2) ___________________-individuals near center of curve have higher fitness—example-babies of average weight survive better than very low or high birth weights.

Stabilizing Selection

• 3)______________________________-individuals @ upper and lower end of curve have higher fitness than individuals near middle-example mid-sized seeds become less common and large beaked or small beaked birds both benefit.

Disruptive selection

_________________________________= random change in allele frequency

•

Genetic Drift

___________________________Principle-allele frequencies in a population will be constant unless one

or more factors change it.

• 5 conditions for it(GENETIC EQUILIBRIUM) to hold– 1)genetic equilibrium from generation to

generation– 2)random mating– 3)large pop.– 4)NO emigration or immigration– 5) no mutations or natural selection

Hardy Weinberg

• ___________________= formation of new species

• Due to-• Isolation-reproductive isolation due to

behavorial,geographic or ______________________isolation(reproduce @ different times)

speciation temporal

• ______________________________are scientists who study fossils

Paleontologists

How fossils form:

• sedimentary rock• sometimes an imprint and sometimes a preserved

remains• buried in resin-amber• tar pits

Dating-

– compare w/other sediments and fossils– radioactive dating using half lives-esp. C-14,since its half

life = 5730 years

• Geologic Time scale-see p.421

3 Eras

• Paleozoic,_______________________ and Cenozoic– 1) Paleozoic-diversity of marine life– 2) Mesozoic-increasing dominance of

Dinosaurs,flowering plants appear– 3) Cenozoic-mammals evolved adaptations to allow

them to live in various environments

_________________-are subdivisions of eras

periods

Mesozoic

• Earth’s early atmosphere probably contained H-cyanide,CO2,CO,N,H2S and H2O

• Miller & Urey’s experiments suggested how mixtures of the organic compounds necessary for life could have arisen from simpler compounds.This was not totally accurate –the experiment-but lead to similar experiments-even producing nitrogenous bases .

• ~ 200-300 million after earth cooled to carry water, cells similar to bacteria developed, beginning w/something similar to a cell membrane

coacervate

Amino acids produced

• Next eukaryotic cells developed by______________________________as a symbiosis formed between prokaryotes….eventually specializing into organelles like_________________

• Margulis supported this in the 1960’s w/the following evidence:– mitochondria and chloroplasts carry DNA similar

to bacterial DNA.– mitochondria and chloroplasts have ribosomes

similar to that of bacteria– mitochondria and chloroplasts reproduce by

binary fission a lot like bacteria

Endosymbiotic Theory

mitochondria

Patterns of Evolution-

• 1)extinction• 2) ___________________________-single species

evolve into several different forms in different ways

Adaptive radiation

3._______________________________-unrelated organisms come to resemble one another

• Convergent evolution

4._____________________________-2 species evolve in response to changes in each other over time

• Coevolution

• 5_____________________-long,stable periods,interrupted by brief periods of more rapid change

In spurts• 6. __________________--opposite of punctuated

equil.---slowly over a long period of time

Punctuated equilibrium

gradualism