• NCEA Level 3 Biology• Achievement Standard 3.5

• ‘Describe processes and patterns of evolution by;

Discussing ways in which speciation occurs (sympatric and allopatric)

Discussing reproductive isolating mechanisms that contribute to speciation (geographical, temporal, ecological, behavioural, structural barriers and polyploidy)

Patterns and Processes of

EvolutionCharles Darwin

“Father of Evolution”

• From early times, people have tried to explain the origins of human beings and other living things on earth. Cultures, groups of people and individuals have various ideas about how life, earth and humans came about and what it means.

• In Science we learn about the Scientific theory of Evolution

Have the story that Papa, the earth goddess and Rangi the god of the sky, where joined so tightly that no light could come into the world and their children could not escape from between them. Tane, managed to separate them, which allowed light into the world meaning plants could grow and animals survive.

This is a tribe in central Africa. They believed that in the beginning there was only darkness, water and the god Bumba. One day Bumba had a bad stomach ache and vomited up the sun, moon, stars, animals and finally man.

God made the world in 6 days and rested on the seventh. This comes from the old Testament

and has been passed on through generations.

1. Charles Darwin (1809-1882) 73yrs oldSailed around the world 1831-1836

2. What did Darwin’s Travels reveal

• The diversity of living species was far greater than anyone had previously known.

• These observations led him to develop the theory of evolution.

3.How did tortoises and birds differ among the islands of the Galapagos?

• Each island had its own type of tortoises and birds that were clearly different from other islands

Galapagos Turtles

4. Evolution is when organisms change over time. So, modern organisms descended from ancient ones

5. Evolution is a Theory – Just like Gravity!

• Evolution is a well supported explanation of phenomena that have occurred in the natural world

• A theory in science is a well tested hypothesis, not just a guess

5. Geologists: Hutton and Lyell

• Fundamentalists said that the earth was around 6000 years old

• Hutton and Lyell argued that the earth is many millions of years old because;– layers of rock take time to form– processes such as volcanoes and

earthquakes shaped the earth and still occur today

6. LamarkTheory of acquired characteristics

• Lamark said organisms acquired traits by using their bodies in new ways

• These new characteristics were passed to offspring

• Lamark was totally wrong!

• … but raised some good points

7. Darwin finally published his ideas in

1859

• Other naturalists were developing the same theory that Darwin did.

• Even though he was afraid of the Church’s reaction to his book he wanted to get credit for his work.

Descent with Modification • Each living

species has descended with changes from other species over time

Summary of Darwin’s Theory

1. Organisms differ; variation is inherited2. Organisms produce more offspring than survive3. Organisms compete for resources4. Organisms with advantages survive to pass those

advantages to their children5. Species alive today are descended with

modifications from common ancestors

Evidence of Evolution

1. Fossil Record

2. Geographic Distribution of Living Species

3. Homologous Body structures

4. Similarities in Embryology

Evidence of Evolution

Fossil Record provides evidence that living things have evolved

Fossils show the history of life on earth and how different groups of organisms have changed over time

Relative vs. Absolute Dating

Relative Dating

• Can determine a fossil’s relative age

• Performed by estimating fossil age compared with that of other fossils

• Drawbacks – provides no info about age in years

Absolute dating

• Can determine the absolute age in numbers

• Is performed by radioactive dating – based on the amount of remaining radioactive isotopes remain

• Drawbacks - part of the fossil is destroyed during the test

Carbon-14 Dating

Fossil Formation

Primate Fossils

Australopithecus Homo erectus Homo sapien

Primate Bone structure

Human Relatives

Evidence of Evolution

2. Geographic Distribution of Living Species

Similar animals in different locations were the product of different lines of descent

Geographic distribution- the distribution of related species, especially on isolated islands, provides evidence of how new species have evolved.

Evidence of Evolution

Homologous Body Structures

– Structures that have different mature forms but develop from the same embryonic tissues

e.g. Wing of bat, human arm, leg of turtle

Turtle

Alligator

Bird

Homologous Body Structures

Vestigial Organs

– traces of homologous organs in other species– Organ that serves no useful function

e.g. Appendix, horse chestnut, dog claw…

Evidenceof Evolution

Similarities in Embryology– In their early

stages of development, chickens, turtles and rats look similar, providing evidence that they shared a common ancestry.

Embryological development

Define the terms species and population

• Species- A group of organisms that are sufficiently similar to each other to be capable of interbreeding to produce fertile offspring.

• Population – All the organisms of a particular species living in a defined area.

http://simonc.f2o.org/south/images/penguins_wallpaper.jpg

http://www.parks.tas.gov.au/threatened/graphics/seal.gif

NZ Fur Seal (Arctocephalus forsteri)

Example

• Dogs are within the species of Canines. they are similar enough to all other organisms in this group to reproduce and give rise to fertile offspring- wolves, foxes, poodles, husky…

• The population is all the Canines living in a certain area- African fighting Dogs in Southern Africa

• Population is localised, species is global

• So…• A species is a group of organisms whose

members can reproduce to give fertile offspring

• Genes can therefore be exchanged between gene pools of populations of the same species but not between populations of different species

Evolution is…

• A genetic change in a population• The genetic make up of a population is its

gene pool which is all the genes in the whole population

• When new offspring are born its genes contribute to the gene pool of the population

• When an organism dies, its genes are lost from the gene pool

Divergent Evolution

• This occurs when an ancestral species evolves into two or more species that become specialised to occupy different ecological niches.

http://www.sacs.ucsf.edu/home/johns/past/bc578/wk10/98-Exercise_10S09.gif

Adaptive radiation

• When an ancestral species diverges into a large number of species occupying separate niches.

• It is a relatively rapid process that involves the founder effect.

http://www.biology-online.org/images/darwin_finches.jpg

http://biology.leidenuniv.nl/ibl/S10/DesignS/lib/exe/fetch.php?w=&h=&cache=cache&media=terms:adaptive_radiation.jpg

Blue-black grassquit finch (seed eating ground finch)from South American mainland

The most famous example of adaptive radiation.

http://lshs.leesummit.k12.mo.us/kjones/Cameron's%20Website/EVOLUTION_files/slide0052_image098.jpg

http://www.rit.edu/~rhrsbi/GalapagosPages/Pictures/LandBirds/FinchTypes.jpeg

Parallel Evolution• Similar features may evolve in related species whose

common ancestral species did not have those features. This occurs through experiencing similar selection pressures.

• Many Biologists argue that this is really convergent evolution.

http://www.micro.utexas.edu/courses/levin/bio304/evolution/rabbitconverg.gif

Convergent Evolution

• When species that have a similar way of life evolve similar features, even though they have quite different ancestors.

• NZ example; divaricating habit of many unrelated shrubs (60 species belonging to 20 different plant families). This is thought to be linked to the presence of browsing Moas in the past.

http://www.bushmansfriend.co.nz/site/images/20525.jpg

http://home.earthlink.net/~snailstales/parallelism.JPG

In Summary

Which one’s which?!!

Punctuated equilibrium: evolutionary model in which there is long periods of little change in the species punctuated by short bursts of rapid change most often associated with speciation. Ancestor is still present.

Gradualism: evolutionary model for the rate of evolution where the accumulation of changes resulting in speciation occurs slowly and steadily over millions of years. Ancestor is extinct.

Natural selection

• We all have different genetic make ups (genomes)• These different genomes give rise to different

traits• Not all traits have the same chance of survival

therefore some are passed on through reproduction if they are selected FOR and some fail to survive and reproduce and therefore are eliminated from the gene pool of a population

• Natural selection uses phenotype which usually is determined by genotype

• Natural selection results in populations becoming more even and better adapted to survive in given locations

(Phenotype is the expression of the coding- genotype, that we usually see)

Natural Selection and Species Fitness

• Overtime, natural selection results in changes in the inherited characteristics of a population.

• These changes increase a species fitness (survival rate)

Natural Selection in a nut shell1. Present day species have evolved from ancestral forms.

2. Organisms produce more offspring than survive. The offspring compete for food and other essentials for survival.

3. Offspring produce by sexual reproduction will show variation; some characteristics that are more suited to their environment than others.

4. Those individuals of a species with favourable characteristics will survive longer and produce more offspring to pass their favourable characteristics on. Those with unfavourable characteristics will not survive as long or reproduce as frequently. This is called ‘survival of the fittest’.

5. Successive generations will become modified over time, particularly if their environment is changing. Gradually the species will change sufficiently to be recognised as a new species.

http://farm1.static.flickr.com/49/125046333_7123c38e73.jpg

Adaptation and natural selection

In all populations there is a large range of phenotypes that usually fall into the normal bell-shaped pattern of distribution.

Types of Natural Selection

Types of Natural Selection

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http://bio.research.ucsc.edu/~barrylab/classes/animal_behavior/IMAGES2.DIR/DIRECT.GIF

Disruptive Selection

http://www.micro.utexas.edu/courses/levin/bio304/popgen/disruptive.gif

http://img.sparknotes.com/figures/A/a3aa6bb95c7d70781cc0089d17f9160f/stable.gif

Artificial Selection • nature provides variation, humans select variations

that are useful. • Example - a farmer breeds only his best livestock

For evolution to occur there must be variation for natural selection to work against.

Variation is caused by• Meiosis and Sexual Reproduction• Crossing over during Meiosis• Mutations

http://staff.tuhsd.k12.az.us/gfoster/standard/3head.gifhttp://www.iespalomeras.net/allnatural/imagenes-web/dibujos/meiosis.gif

Speciation• Formation of 2 or more species from a single

species• Can happen slowly or quickly• Slowly- accumulation of small changes• Faster- polyploidy: mutation which causes

more than the usual haploid number of chromosomes to occur

Allopatric SpeciationThis is when a population becomes separated by

a geological barrier.This eventually leads to different species with

completely different gene pools.

Chatham Island Robin South Island Robin

Once the population has been separated by geological barriers, they become so different they are not able to interbreed if the physical barrier separating them were removed. There can be no exchange between their gene pools because of reproductive isolating mechanisms.

Sympatric Speciation• This occurs when a sub-population becomes

reproductively isolated in the midst of the parent population. These populations are said to be sympatric if their ranges overlap. These are species of the same genus living together in the same area.

• If there are no geological barriers separating populations then the isolating mechanism must be biological. There are two types of biological mechanisms Prezygotic which happens before fertilisation and Postzygotic which occur after fertilisation.

• Different species breed at different times on the year.

• Courtship and mating behaviour are different.• The reproductive structures of the species

may be incompatible.• The gametes of the species may not function

successfully together.

• Hybrid inviability: the sperm may fertilise the egg but full development does not occur.

• Hybrid sterility: the offspring may reach maturity but they are unable to have offspring of their own.

• Hybrid disadvantage: the offspring may be fertile but less fertile than normal or less likely to survive.

Describe the Key ideas that underpin the theory of evolution: genetic variation, competition, differential reproductive success (natural selection)

• Present day species have evolved from ancestral forms.• Organisms produce more offspring that will survive. These

offspring must compete for food, space etc to survive.• Sexual reproduction creates offspring with variation. Some

are born with characteristics that are more suited to their environment than others.

• Survival of the fittest allows some to survive long enough to pass on their genes through reproduction.

• Successive generations will become modified over time. Gradually the speices will change sufficiently to become a new species in many cases.

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Define gene and allelle frequency, speciation, gene flow and genetic equilibrium

• Gene frequency- The proportion of those individuals in a population with a particular allele.

• Allele frequency- The proportion of a given allele in the gene pool as a fraction of all forms of that gene, e.g frequency of 0.2 means that it accounts for 20% of all alleles of that gene in the population.

• Speciation- The process of forming a new species.• Gene flow- Exchange of alleles between populations by immigration and

emigration.• Genetic Equilibrium- A state in which a population is not evolving. The

species stays in its present form as there is no gene mutation, large population, isolated population, gene of interest has no effect on survival and reproduction and mating is random.

P6:Define the terms genetic drift, founder effect and bottle neck effect.

• Genetic drift- Random changes in allele frequency due to chance, only significant in small populations.

Figure 7.7 Concept of genetic drift. In a large population with random mating, large fluctuations of gene frequency are unlikely. In a small population, however, gene frequency can change dramatically from one generation to the next, if, for example, only the AA individuals participate in mating by chance.

www.blackwellpublishing.com/korfgenetics/

This is a change in the allele frequencies of a population as a result of chance processes. This has a big influence in small populations where chance alone may play a considerable role.

Two examples of these chance events are the genetic bottleneck and similarly the Founders effect.

Founder effect- Changes in allele frequency due to chance, as a result of small group of founders become isolated from the main

population.

1. Double disaster: The island fruit flies are now geographically isolated from their mainland relatives, but only a few larvae have survived the harrowing journey to end up colonizing the island.

2. Rare genes survive: These few survivors just by chance carry some genes that are rare in the mainland population. One of these rare genes happens to cause a slight variation in the mating dance. Another causes a slight difference in the shape of male genitalia. This is an example of the founder effect.

3. Gene frequencies drift: These small differences, which are rare on the mainland, drift to fixation in the small population on the island over the course of a few generations (i.e., the entire island population ends up having these genes).

Bottleneck effect- Period in which a population becomes temporarily reduced to very small numbers, as a result of which its genetic diversity

becomes reduced.

An example of a bottleneck:Northern elephant seals have reduced genetic variation probably because of a population bottleneck humans inflicted on them in the 1890s. Hunting reduced their population size to as few as 20 individuals at the end of the 19th century. Their population has since rebounded to over 30,000—but their genes still carry the marks of this bottleneck: they have much less genetic variation than a population of southern elephant seals that was not so intensely hunted.

http://evolution.berkeley.edu/evosite/evo101/IIID3Bottlenecks.sht

www.brooklyn.cuny.edu/.../C21_Bottleneck_2.GIF

www.brooklyn.cuny.edu/.../C21_Bottleneck_2.GIF

http://nationalzoo.si.edu/Animals/ZooAnimalWallpaper/images/cheetah.jpg

All of the following can lead to changes in the gene pool

•Immigration•Mutation•Natural Selection•Genetic Drift•Population size•Mate Selection

http://www.biology-online.org/images/darwin_finches.jpg

A change in the frequencies of certain alleles in a gene pool over successive generations is called microevolution. This term is often used to refer to small, reversible changes within a species.

Large, irreversible changes in a gene pool, such as those involved in the formation of a new species (speciation) or in adaptive radiation is called macroevolution.

The following agents change the frequency of genes in the gene pool of the population:

• Non-random mating• Mutation• Genetic drift• Gene flow • Natural selection.

This occurs when a certain phenotype is

preferred over others. This eventually leads to the decrease in the un-preferred phenotypes.

Mutation is the ultimate source of variation that can change the equilibrium within a

population.

This is caused by the immigration and emigration of individuals into a population.

This increases and decreased the genes within the population.

Some combinations of alleles are more likely to help survival and reproduction than others. This means that the frequency of these alleles in the population will increase. This is what is meant by the ‘survival of the fittest’.

Different forces such as predation, competition, disease, lack of food, water, climate etc. act on the different phenotypes causing the normal

distribution to change.

Stabilising selection: is when the average is favoured over the other extremes.

Directional selection- favours one extreme over the average or the other extremes.

Disruptive selection- favours both extremes over the average.

Industrial Melanism- An example of Natural Selection

Dark forms of the British peppered moth (Biston betularia), as well as many other species of moth, became common in the middle of the 19th century near centres of industrial pollution. Soot coated the trunks and branches of trees, and killed lichens. In the photos, a pale form (typica) and a dark form (carbonaria) rest side-by-side on an unpolluted lichen covered trunk in Dorset (above), and a soot-covered trunk near Birmingham. (From HBD Kettlewell, 1956, Heredity 10: 300).

www.ucl.ac.uk/.../courses/b242/OneGene/pep2.jpg