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CHAPTER 29: THE MODERN THEORY OF EVOLUTION

29-1: EARLY THEORIES OF EVOLUTION

Lamarck vs. Darwin: Both believed that _____________________ _________________; they changed over time.

Darwin à In 1831, sailed on the Beagle to South American islands and through the Pacific Ocean à collected specimens and made observations.

On the Galapagos Islands, he studied finches.

·       Each island had _________________________________________ _______________________ à developed special ______________

·       Thomas Malthus’ essay influenced Darwin’s theory of evolution

·       Darwin’s book on evolution: “On the Origin of Species by Means of Natural Selection”

6 Main Points of Darwin’s Theory:

1.         Overproduction – Most species ___________________________ ______________to maintain population à only a small fraction of offspring live to reproduce à ____________________________

2.         Competition –

3.         Variations – Slight differences in individuals’ characteristics within a species that ____________________________________ ___________________________________________________

4.         Adaptations – An ___________________ or variation that _____________________________________________________

5.         Natural Selection – Individuals with variations that make them ____________________________________________________ in greater numbers than those without such adaptations à ____________________________________________

6.         Speciation – ____________________________ brought about by the accumulation of numerous changes over a long period of time.

Weaknesses of Darwin’s Theory

·       It __________________________________________________ and are __________________ to the next generation

·       It does ____________________ between variations caused by ____________ differences and variations caused by ____________

The Rate of Evolution: 2 Theories

Ø   Gradualism – Evolution occurs ____________________________ over thousands and millions of years (Darwin)

Ø   Punctuated Equilibrium – ________________________________ _________________________________ à then, in a relatively short period of time, new species appear (Gould & Eldridge)

-        __________________________ à ____________________

-        ______________________________________

29-2: GENETICS AND EVOLUTION

Modern Theory of Evolution

·       ___________________ + ___________ + ____________________

·       Evolution happens to ________________, not individuals

·       “Evolution” –

(new definition)

·       Individuals are the “units” of Natural Selection

Population Genetics

_________________ – A group of organisms of the same species living together in a given region, capable of interbreeding.

_______________________________ – The study of changes in the genetic makeup of populations

·       As individuals reproduce & die, the genetic makeup of population as a whole may change

Gene Pool – The __________________________________________

·       Allele frequency ranges from 100% to 1/ 1,000,000

·       Allele frequencies _________________________ in a population

Genetic Sources of Variation

1.         Mutations – _______________________________________

·       DeVries discovered mutations in Evening Primrose plant à applied concept to Darwin’s Theory of Evolution

·       Explained _____________________________ (weakness of Darwin’s theory)

Gene Mutations:

·       Most mutations are _______________ (hidden by normal, dominant allele)

·       Mutations are __________

·       If environmental conditions change, harmful _______________ may become _____________ to species

·       Natural Selection will gradually _________________________ ______________________________________

·       Ex: Giraffe à mutation caused longer-than-normal necks à when grass became sparse, this was an advantage for getting food à these giraffes survived & reproduced

Chromosomal Mutations:

·       Result in _____________________________ in an organism à _________________ in later generations

2.         Genetic Recombination – Formation of _____________________ __________________________________ (egg + sperm = zygote)

·       Crossing over

·       Independent assortment

3.         Migration – Greatest effect on variations in small populations

___________: new individual joins population à bring new genes

___________: individual leaves population à genes removed

4.         Genetic Drift –

·       A few individuals have a certain allele that others in the population do not à individuals die before mating à ________ ________________________________

·       Gene pool is reduced, ____________________

·       ______________ to population

·       Not as common in large populations

Hardy-Weinberg Law

Genetic Equilibrium –

-        _______________ & _______________ of genes in sexual reproduction __________________________________ by itself

4 conditions must be met for H-W Law to hold true:

1.         ______________________ – in small populations, low frequency alleles are lost, genetic drift occurs

2.         _________________

3.         _________________________ **

4.         _________________________**

** 3 & 4 almost never exist in nature à

·       Because organisms with helpful adaptations are more likely to reproduce à changes allele frequency (____________________)

H-W Law allows us to discover whether or not ______________ is occurring in a population and _______________ it is occurring.

29-3: ADAPTATIONS AND NATURAL SELECTION

Types of Adaptations

·       Structural Adaptations – Involve the ________________________ _______________________ (wings of birds & insects)

·       Physiological Adaptations – Involves __________________ (poison venom made by snakes, protein web made by spiders)

Many adaptations provide protection:

·       _________________ – Organism blends in with environment à protection (shape, structure, coloration)

·       ______________________ – colors make animal easier to see à advantage for insects that birds don’t like to eat (Monarch butterfly) à birds remember to avoid that species (taste bad!)

·       _________________ – Organism resembles another species à protection (Viceroy butterfly avoids predators because it looks like Monarch)

Natural Selection

·       Disturbs genetic equilibrium à change allele frequencies in population

·       Determines which traits are favorable for a species

Types of Natural Selection

1.         Directional Selection –

·       When _______________________ or ___________________

·       New environment favors extreme phenotype à population evolves

·       Ex: Long neck in giraffes

2.         Stabilizing Selection –

·       __________________________________ (frequency of alleles for extreme phenotypes ¯)

·       Operates ___________________ in _____________________

·       ____________________ by keeping allele frequencies constant

·       Ex: small mice not strong enough to burrow underground in cold, large mice use too much E to keep warm à fewer small/ large mice survive to reproduce à selection favors medium/ average mice

3.         Disruptive Selection (rare) –

·       ___________________________________________________

·       Evolution of _______________________

·       2 populations can’t mate together à 2 new species

·       ex: species of crab shows continuous variation in color, light tan à dark brown. Environment changes to sandy beaches & brown mud (2 extremes) à these colors are camouflage against predators (favorable adaptation)

29-4: SPECIATION – Formation of new species

Speciation and Graphic Separation

Range –

·       Different regions have different environmental conditions à organisms of same species have ____________________________

·       Subspecies –

·       Organisms at _______________________________________ in characteristics & gene pools, and usually ________________ à still considered __________ because adjacent subspecies can mate.

·       If adjacent subspecies ____________________ à _____________!

·       Ex: Leopard frog

Types of Speciation

1.         Isolation – ___________________________________________ ___________________. Gene pool of group is separated from gene pool of the rest of the species

__________________ – through mutation, genetic recombination, natural selection à ___________________ evolves in each group

·       Geographic Isolation – _______________________________  (mountain, desert, river). ____________________ to it’s particular environment à ____________________________

·       Reproductive Isolation – ______________________________ _______________ by 2 isolated groups.

Ex: Kaibab & Abert squirrels, divided by the Grand Canyon

2.         Polyploidy –

-        offspring can interbreed only among themselves

3.         Adaptive Radiation – Process by which a species evolves into a number of different species, each occupying a new environment à adaptations occur.

·       Ancestral __________________ into several different environments à thru isolation, genetic variation, natural selection à _________________________ à __________ into ___________________

·       Ex: Darwin’s finches, Galapagos Islands

Convergent Evolution – Natural Selection causes _______________ _______________ to ________________ each other.

·       Produces _____________________________ (see ch. 28)

Coevolution –

Ex: BEES à active during day à Flowers adapted to bees for pollination are blue or yellow, sweet & minty, open during day.

BATS à active at night à Flowers adapted to bats easily seen at night, open at night

29-5:OBSERVED NATURAL SELECTION

Industrial Melanism –

Ex: The Peppered Moth

·       Before 1850’s à Most peppered moths were light in color. Black peppered moths with “melanin” pigment were rare

·       By 1900, there was heavy industrialization. Heavy smoke darkened trees à light colored moths killed by predators à 99% peppered moths were now black, light were rare.

In the 1950’s _______________& _______________ tested this with a controlled experiment: They placed peppered moths in industrial and non-industrial areas.

Industrial area = ­ black moths

Non-Industrial area = ­ light colored moths

·       ___________________________

·       ________________________________________________________________________________________________

Details of the evolutionary process:

·       Variability in gene pool (alleles for light & dark colors)

·       Trait that makes moth best adapted is preserved

Bacterial Resistance to Antibiotics

Hypothesis: In a large population of bacteria, __________________ __________________à exposed to _____________ à through ____________________, only the ___________________________ ______________& multiply à resistant strain becomes common type

Lederberg’s Experiment: (1950’s)

Because e.coli cells had never been exposed to Streptomycin, we conclude that ________________________________ that they had __________________________.

The ___________________________ (Streptomycin dish) ________ __________________________. It acted only as a ____________ for organisms already possessing the strep-resistant gene.