5.4: Evolution5.4: EvolutionTopic 5: Ecology & EvolutionTopic 5: Ecology & Evolution

Miss FriedmanMiss Friedman

5.1: Definition5.1: Definition

Evolution is the cumulative change in the Evolution is the cumulative change in the heritable characteristics of a heritable characteristics of a populationpopulation

► Darwinian Evolution is not simply based on Darwinian Evolution is not simply based on natural selection but was in fact composed natural selection but was in fact composed of at least five different “sub theories”of at least five different “sub theories”

1.1. EvolutionEvolution2.2. Common descentCommon descent3.3. GradualismGradualism4.4. Multiplication of speciesMultiplication of species5.5. Natural selectionNatural selection

1. Evolution1. Evolution

►All life is and has been perpetually All life is and has been perpetually changing. This contrasts strongly with changing. This contrasts strongly with notions that all forms of life are notions that all forms of life are constant and unchangingconstant and unchanging

2. Common descent2. Common descent

►All living things share a common All living things share a common ancestor if traced back far enoughancestor if traced back far enough

3. Gradualism3. Gradualism

►Evolutionary change takes place Evolutionary change takes place slowly and gradually. This contrasts slowly and gradually. This contrasts with saltation in which changes are with saltation in which changes are sudden and extremesudden and extreme

4. Multiplication of species4. Multiplication of species

►Diversity of life is a consequence of Diversity of life is a consequence of speciation. Populations adapting to speciation. Populations adapting to locations and becoming reproductively locations and becoming reproductively isolated from other populationsisolated from other populations

5. Natural selection5. Natural selection

►A two stage process in which:A two stage process in which: Producing genetic variationProducing genetic variation selectionselection

5.4.2: Evidence of 5.4.2: Evidence of evolutionevolution

►Evolution, like any scientific theory, Evolution, like any scientific theory, requires evidence. requires evidence.

►Evidence shows that organisms change Evidence shows that organisms change over time and even result in the over time and even result in the production of new species of organismsproduction of new species of organisms

►Types of evidenceTypes of evidence1. Fossil record1. Fossil record

2. Homologous structures2. Homologous structures

1. Fossil Record1. Fossil Record

A fossil is the ancient preserved remains of an A fossil is the ancient preserved remains of an organism. The fossil can be dated from the age of organism. The fossil can be dated from the age of the rock formation.the rock formation.

► Sequences of fossil show the gradual change of an Sequences of fossil show the gradual change of an organism over geological timeorganism over geological time

► Although the planet Earth has extensive ocenas for Although the planet Earth has extensive ocenas for most of its existence, fish fossils have only been most of its existence, fish fossils have only been found in rocks for 500 million years (less than 15% found in rocks for 500 million years (less than 15% of the Earth’s age)of the Earth’s age)

► No top predators such as bears and orcas existed in No top predators such as bears and orcas existed in the time of dinosaursthe time of dinosaurs

► Very few organisms today have identical form today Very few organisms today have identical form today as hundreds of years agoas hundreds of years ago

2. Homologous structures2. Homologous structures

Similarities between anatomical Similarities between anatomical structure which are similar in form and structure which are similar in form and function but which are found in function but which are found in seeming dissimilar species.seeming dissimilar species.

The classic example is the pentadactyl The classic example is the pentadactyl (penta=five) and (dacytl=fingers) limb (penta=five) and (dacytl=fingers) limb of the vertebrateof the vertebrate

a)a) HumeruHumeruss

b)b) RadiusRadius

c)c) UlnaUlna

•In each example the bones are modified and adapted to the locomotion of the animal

•The fact that the basic shape and position of the bones is similar suggest that they have a common ancestor

•In the whale there is no real need for the fingers as they can still swim without them, this could suggest common ancestry with the other five-fingered organisms

DivergenceDivergence►The pentadactyl limb structure shows The pentadactyl limb structure shows

adaptation and modification from a adaptation and modification from a common limb (ancestor) structurecommon limb (ancestor) structure

ConvergenceConvergence►Two organisms with different ancestors Two organisms with different ancestors

have a limb structure that fulfills the have a limb structure that fulfills the same function but has evolved from same function but has evolved from different origins.different origins.

►Examples are wing of a bird and the wing Examples are wing of a bird and the wing of an insectof an insect

Selective BreedingSelective Breeding►Man has selectively bred animals and Man has selectively bred animals and

plants for thousands of years.plants for thousands of years.► If an animal posses a characteristic that If an animal posses a characteristic that

is considered useful or valuable then is considered useful or valuable then this animal is selected for breeding.this animal is selected for breeding.

►The hope then is that this characteristic The hope then is that this characteristic will be present in the next generation will be present in the next generation and at a higher frequency than before.and at a higher frequency than before.

► In subsequent generations it may even In subsequent generations it may even then be possible to select from an even then be possible to select from an even more advantageous characteristicmore advantageous characteristic

Selective breeding Selective breeding continuedcontinued

►The observations of artificial selection The observations of artificial selection (selective breeding) suggested that (selective breeding) suggested that natural populations would:natural populations would: Show phenotypic variationShow phenotypic variation Be subject to natural selection pressuresBe subject to natural selection pressures There would be selection of those There would be selection of those

individuals possessing the advantageous individuals possessing the advantageous characteristiccharacteristic

5.4.3: Population size & 5.4.3: Population size & evolutionevolution

► The population produces more offspring than the The population produces more offspring than the carrying capacity of the environment can support:carrying capacity of the environment can support: Offspring/population compete for limited resources Offspring/population compete for limited resources

(Intraspecific competition)(Intraspecific competition) Some individuals have characteristic (or combination) Some individuals have characteristic (or combination)

that gives them a competitve advantagethat gives them a competitve advantage These individuals are more likely to successfully These individuals are more likely to successfully

reproduce (offspring survive)reproduce (offspring survive) Through inheritance the frequency of these Through inheritance the frequency of these

characteristics become greater in the next generationcharacteristics become greater in the next generation By definition these characteristics have a genetic basisBy definition these characteristics have a genetic basis

5.4.4: Population size & 5.4.4: Population size & survivalsurvival

►Plant and animals produce far more Plant and animals produce far more offspring then could ever surviveoffspring then could ever survive Fish will lay hundreds of eggs yet only a Fish will lay hundreds of eggs yet only a

handful survivehandful survive

►Why are animal’s valuable resources Why are animal’s valuable resources wasted if they are never going to give wasted if they are never going to give offspring?offspring?

►Competition is set up for resources so only Competition is set up for resources so only the best adapted organism will survivethe best adapted organism will survive

5.4.4 5.4.4 continuedcontinued► It should be noted that the “struggle for It should be noted that the “struggle for

survival” in this model is a consequence survival” in this model is a consequence of over-populationof over-population

►The struggle takes the form of The struggle takes the form of individuals in the population being individuals in the population being “selected for” or “selected against” “selected for” or “selected against”

►Survivors form the new breeding Survivors form the new breeding populationpopulation

►The frequency of advantageous alleles The frequency of advantageous alleles has increasedhas increased

►The change in the heritable The change in the heritable characteristics is by definition evolutioncharacteristics is by definition evolution

5.4.5: Variation in a 5.4.5: Variation in a speciesspecies

►Populations of a species show Populations of a species show variationvariation

►Variation means differences in Variation means differences in phenotypesphenotypes

►Notice that no two humans are alike Notice that no two humans are alike (or other animals)(or other animals)

5.4.6: Sexual reproduction & 5.4.6: Sexual reproduction & variationvariation

► Asexual (bacteria) and sexual populations Asexual (bacteria) and sexual populations both experience mutation which increases the both experience mutation which increases the variation within the members of a populationvariation within the members of a population

► Sexual reproduction increases variation by Sexual reproduction increases variation by the selection of mate or mutationthe selection of mate or mutation A fish with a better shaped mouth might be able to A fish with a better shaped mouth might be able to

feed on coral that cannot be accessed by other feed on coral that cannot be accessed by other fish, he will have a better chance of survival into fish, he will have a better chance of survival into adulthoodadulthood

A fish mouth could be inadequately adapted and as A fish mouth could be inadequately adapted and as a result die of starvationa result die of starvation

5.4.6 continued5.4.6 continued

►Sexually reproducing populations also Sexually reproducing populations also experience significant additional experience significant additional sources of variationsources of variation

►There are two sources of genetic There are two sources of genetic variation in populations:variation in populations:

1. Meiosis1. Meiosis

2. Fertilization2. Fertilization

1. Meiosis1. Meiosis

►When is an egg is made during When is an egg is made during meiosis, only 50% of the mother’s meiosis, only 50% of the mother’s information is needed.information is needed.

►Due to random distribution of the Due to random distribution of the chromosomes during meiosis, each chromosomes during meiosis, each egg has a different combination and egg has a different combination and therefore two eggs are never aliketherefore two eggs are never alike

2. Random fertilization2. Random fertilization

► Increases the variation in the Increases the variation in the population a second timepopulation a second time

►Of the many sperm cells that exist, Of the many sperm cells that exist, only one will fertilize the eggonly one will fertilize the egg

ConclusionConclusion

►Genes get mixed up as a double Genes get mixed up as a double lottery once in meiosis and a second lottery once in meiosis and a second time in fertilizationtime in fertilization

“… “… can we doubt (remembering that can we doubt (remembering that many more individuals are born than many more individuals are born than can possible survive) that individuals can possible survive) that individuals having any advantage, however slight, having any advantage, however slight, over others, would have the best over others, would have the best chance of surviving and procreating chance of surviving and procreating their kind? On the other hand, we may their kind? On the other hand, we may feel sure that any variation in the least feel sure that any variation in the least injurious would be rigidly destroyed. injurious would be rigidly destroyed. This preservation of favourable This preservation of favourable variations and the rejection of variations and the rejection of injurious varations, I call Natural injurious varations, I call Natural Selection”Selection” Darwin C. (1859)Darwin C. (1859) The The Origin of SpeciesOrigin of Species

5.4.7: Natural selection5.4.7: Natural selection

Natural selection is a two stage process:Natural selection is a two stage process:

1. Production of variation1. Production of variation

2. Selection2. Selection

5.4.7 5.4.7 continuedcontinued►When a population evolves there is a When a population evolves there is a

cumulative change in the heritable cumulative change in the heritable characteristics of the populationcharacteristics of the population

►Natural selection can act on a Natural selection can act on a population without speciation occurringpopulation without speciation occurring

► In effect the genetic profile of the In effect the genetic profile of the population is adapting to changes in population is adapting to changes in local conditionslocal conditions

►Ever phase in the process of evolution is Ever phase in the process of evolution is affected by variation and by selectionaffected by variation and by selection

Factors in Factors in a Model of a Model of

Natural Natural SelectionSelection

5.4.8: Examples of 5.4.8: Examples of evolutionevolution

1, Antibiotic resistance in bacteria1, Antibiotic resistance in bacteria

2. Peppered Moth2. Peppered Moth

3. New Zealand Kaka3. New Zealand Kaka

1. Antibiotic resistance in 1. Antibiotic resistance in bacteriabacteria