Chapter 19: Change in Species

Chapter 19: Change in Species

What evidence exists to support evolution?

19.1 Fossil Evidence

Fossils – physical remains of ancient organisms

Fossils = largest piece of evidence for evolution


Paleontology – the study of fossils

How do fossils offer information about change?



They are a record of organisms that are not around today.

Ancestral relationships can be based on where they are found in relation to another fossil.



They can show us the rate of evolutionary change.

They are a clue to the physical structure of living things (clues to behavior).

19.2 Ecology & Homologies

Coevolution – the continuous adaptation of different species to each other

Example: predator-prey relationships

Galapagos tortoises & Cacti – the cacti have developed tall woody stems; tortoises have developed flared saddleback shells so their necks can stretch farther


Example: Flowers & pollinators

Bees have developed characteristics that make pollen stick to them (hairy abdomens) & flowers have developed characteristics to make them attractive to bees & other pollinators (colorful petals, smells)


Artificial Selection

Works in same way as “natural selection” except that someone controls the characteristics that are being chosen

Example: dog breeding


Homologies = similarities between species that suggest common ancestry (remember from last chapter)

Homologies help biologists understand the history of evolutionary changes

Example: Forelimbs of vertebrates

Shows evidence that these organisms have an ancestor in common.

Example: Mouse/Fruit fly eyes

Put the gene coding for eyes in mice into an eyeless fruit fly chromosome & the fly grew eyes

19.3 Genetic & Molecular Evidence

Darwin’s problem: explaining how variations are inherited

Study of genetics has provided more support for the theory of evolution


Sources of genetic variation:Mutation

Recombination of alleles – happens in sexually reproducing organisms; includes crossing over & fertilization to produce new combinations of genes


Genetic variation is the RAW MATERIAL OF EVOLUTION!!

We use molecular data (DNA information) to see the degree of relatedness between species – more DNA in common, more closely related.

Other Evidence for Evolution

Embryos

Early in embryonic development, it is very difficult to tell different organisms apart. The fact that we start off so similarly is evidence we all came from a common ancestor.

Other Evidence: Embryos

Other Evidence for EvolutionSkulls

Used often in human evolution – changes in skull shape/size show changes in humans over time

Other Evidence for Evolution

Vestigial StructuresStructures that are no longer useful in an organism (ex: appendix, goosebumps, body hair, etc. in humans)

Shows changes in organisms over time – our distant relatives needed them for something but over time they no longer are needed

19.4 Process of Speciation

Speciation – the appearance of a new species

Examples that have been observed: primarily in bacteria (because they reproduce – and so, evolve – so quickly); new species of grain – crossed wheat and rye


POPULATIONS EVOLVE, NOT INDIVIDUAL ORGANISMS WITHIN A POPULATION!!

Speciation occurs when 2 populations become so different in their genetic makeup, they can no longer interbreed.


Usually occurs as a result of isolation – a small population that gets isolated from the rest of the population develops into its own species.


3 Types of Isolation:

1. Geographic Isolation: most common; organisms cannot come into contact with one another so they can’t interbreed (get separated by body of water, mountain range, canyon, etc.)


3 types of isolation:

2. Ecological isolation: When two different populations adapt to different habitats


3 types of isolation:

3. Reproductive isolation (also behavioral): the mating patterns of a small group of organisms becomes so different from the main group that they become reproductively isolated

19.5 Patterns in Evolution

Adaptive radiation – the development of numerous species from a common ancestor in a diverse environment

When a population enters a habitat with few competing species, it will often divide into many smaller populations by adapting to different environments or using different resources


Stasis – the rate of large-scale change remains very slow for a long period of timeCauses of stasis: species is well adapted & the environment remains stableExample: the Australian lungfish – changed little in millions of years; the horseshoe crab


Two ideas on Progress of Evolution:

1. Gradualism – Speciation & evolutionary change occurred through the accumulation of many gradual & constant changes


Two ideas on Progress of Evolution:

2. Punctuated Equilibrium – Short period of rapid change just after a population becomes isolated and forms a new species, after which the process slows and approaches stasis

Population Genetics (from 16)

Microevolution – changes within species occurring over dozens – hundreds of generations

Changes in the frequencies of alleles in a population

Macroevolution – the larger changes of a species over time usually leading to the formation of new species (what we’ve been dealing with so far)

Population Genetics

Hardy-Weinberg model of Gene Pools

A mathematical model of gene pools that enables us to use the frequency of alleles in a population to calculate all the genotype frequencies in that population.

Population Genetics

Hardy-Weinbergp2 + 2pq + q2 = 1

p + q = 1p = dominant allele (A)q = recessive allele (a)p2 = homozygous dominant individuals (AA)q2 = homozygous recessive individuals (aa)2pq = heterozygous individuals (Aa)

Population Genetics

Hardy-Weinberg: 5 Conditions

1. Mutation rate is negligible.

2. Migration is negligible.

3. Population is large, diploid, & sexually reproducing.

4. Mating is random.

5. Natural selection does NOT occur.

Population Genetics

Hardy-Weinberg: 2 important results1. It enables you to use the allele

frequencies to calculate all of the genotype frequencies.

Example: If 50% of the alleles in a population are dominant (A) and 50% of the alleles in a population are recessive (a), what percentage of the population are heterozygous?

Population Genetics

Hardy-Weinberg: 2 important results

2. The allele frequencies are stable over time (under the assumptions of the model). This supports the idea that there will be variation in a species.

Chapter 19: Change in Species

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