influence of geological thinking on darwin by time of “the beagle” voyage idea that earth was...

Influence of geological thinking on Influence of geological thinking on DarwinDarwin

By time of “The Beagle” voyage idea that By time of “The Beagle” voyage idea that Earth was young was being challenged.Earth was young was being challenged.

Opposition based on principle of Opposition based on principle of Uniformitarianism. Uniformitarianism.

Idea that geological processes happening Idea that geological processes happening today are the same as have operated in today are the same as have operated in the past.the past.


Uniformitarianism contrasted with Uniformitarianism contrasted with CatastrophismCatastrophism which proposed that which proposed that current geological formations had resulted current geological formations had resulted from catastrophic events (such as biblical from catastrophic events (such as biblical flood) which occurred on scale unknown flood) which occurred on scale unknown today.today.

Uniformitarianism first proposed by James Uniformitarianism first proposed by James Hutton and championed by Charles Lyell.Hutton and championed by Charles Lyell.


Hutton and Lyell inferred Earth must be Hutton and Lyell inferred Earth must be very old based on measurements of rate very old based on measurements of rate of ongoing rock forming processes (e.g. of ongoing rock forming processes (e.g. deposition of mud and sand).deposition of mud and sand).

These developments in geology focused These developments in geology focused Darwin on the potential importance of Darwin on the potential importance of gradual change in shaping structures.gradual change in shaping structures.

Darwinian Natural SelectionDarwinian Natural SelectionArtificial SelectionArtificial Selection

Artificial Selection. Humans have Artificial Selection. Humans have selectively bred for desirable traits in selectively bred for desirable traits in domestic animals and plants for millenia.domestic animals and plants for millenia.

Process has produced our crop plants, Process has produced our crop plants, garden plants, pets, and domestic garden plants, pets, and domestic animals.animals.

Darwin closely studied pigeon breeding.Darwin closely studied pigeon breeding.

Artificial SelectionArtificial Selection

Cauliflower, broccoli, kale, brussels Cauliflower, broccoli, kale, brussels sprouts all descended from wild cabbage. sprouts all descended from wild cabbage.

All these crops can be crossed and All these crops can be crossed and produce fertile offspring.produce fertile offspring.

Cauliflower: edible bit is the inflorescence Cauliflower: edible bit is the inflorescence or flower stalk.or flower stalk.


Cauliflower has large dense infloresence. Cauliflower has large dense infloresence. This results from mutant ‘loss of function’ This results from mutant ‘loss of function’ alleles of two genes that affect flower alleles of two genes that affect flower structure and infloresence density.structure and infloresence density.


Early farmers choosing among their crops Early farmers choosing among their crops selected those with largest infloresences. selected those with largest infloresences. Process has resulted in cauliflowers that Process has resulted in cauliflowers that are homozygous for both loss of function are homozygous for both loss of function alleles.alleles.

Evolution by Natural SelectionEvolution by Natural Selection

Darwin envisaged process similar to Darwin envisaged process similar to artificial selection that had produced artificial selection that had produced organisms we see today. He called it organisms we see today. He called it Natural SelectionNatural Selection..

Darwin proposed evolution the inevitable Darwin proposed evolution the inevitable outcome of 4 postulates:outcome of 4 postulates:

1. There is 1. There is variation in populationsvariation in populations. . Individuals within populations differ.Individuals within populations differ.

2. 2. Variation is heritable.Variation is heritable.



3. In every generation some organisms 3. In every generation some organisms are more successful at surviving and are more successful at surviving and reproducing than other. reproducing than other. Differential Differential reproductive success.reproductive success.

4. 4. Survival and reproduction are not Survival and reproduction are not randomrandom, but are related to variation among , but are related to variation among individuals. Organisms with best individuals. Organisms with best characteristics are ‘naturally selected.’characteristics are ‘naturally selected.’


If 4 postulates are true then the population If 4 postulates are true then the population will change from one generation to the will change from one generation to the next. next.

Evolution will occur.Evolution will occur.

Darwinian fitness: ability of an organism to Darwinian fitness: ability of an organism to survive and reproduce in its environment.survive and reproduce in its environment.

Fitness measured Fitness measured relativerelative to others of its to others of its speciesspecies


Adaptation is a characteristic or trait of an Adaptation is a characteristic or trait of an organism that increases its fitness relative organism that increases its fitness relative to individuals that do not possess it. to individuals that do not possess it.


Testing the postulatesTesting the postulates

Evolution of beak shape in Darwin’s Evolution of beak shape in Darwin’s Finches.Finches.

Peter and Rosemary Grant’s (and Peter and Rosemary Grant’s (and colleagues) work on Medium Ground colleagues) work on Medium Ground Finches Finches Geospiza fortisGeospiza fortis

On Daphne Major since 1973.On Daphne Major since 1973.


Postulate 1. Is the population variable?Postulate 1. Is the population variable?

Finches vary in beak length, beak depth, Finches vary in beak length, beak depth, beak width, wing length and tail length. beak width, wing length and tail length.


Postulate 2: Is variation among individuals Postulate 2: Is variation among individuals heritable?heritable?

Variation can be a result of environmental Variation can be a result of environmental effects.effects.

Heritability: proportion of the variation in a Heritability: proportion of the variation in a trait in a population that is due to variation trait in a population that is due to variation in genes.in genes.


Peter Boag compared average beak depth Peter Boag compared average beak depth of parents with that of their adult offspring. of parents with that of their adult offspring.

Strong relationship between offspring and Strong relationship between offspring and parent beak depths.parent beak depths.

FIG 3.7


Postulate 3: Do individuals differ in their Postulate 3: Do individuals differ in their success at survival and reproduction?success at survival and reproduction?

1977 drought 84% of 1977 drought 84% of G. fortisG. fortis individuals individuals died, most from starvation. In two other died, most from starvation. In two other droughts 19% and 25% of the population droughts 19% and 25% of the population died.died.


Seed densities declined rapidly during Seed densities declined rapidly during drought and the small soft seeds were drought and the small soft seeds were consumed first. consumed first.

Average size and hardness of remaining Average size and hardness of remaining seeds increased over the course of the seeds increased over the course of the drought.drought.

FIG 3.8b

FIG 3.8A

Fig 3.8c


Postulate 4: Are survival and reproduction Postulate 4: Are survival and reproduction nonrandom?nonrandom?

Do those who survive and reproduce have Do those who survive and reproduce have different characteristics than those that different characteristics than those that don’t?don’t?


As drought progressed small soft seeds As drought progressed small soft seeds disappeared and large, hard disappeared and large, hard TribulusTribulus seeds became a key food item.seeds became a key food item.

Only birds with deep, narrow beaks could Only birds with deep, narrow beaks could open them.open them.


At end of the 1977 drought the average At end of the 1977 drought the average survivor had a deeper beak than the survivor had a deeper beak than the average non-survivor and also a larger average non-survivor and also a larger body size.body size.

FIG 3.9

Did the population evolve?Did the population evolve?

Chicks hatched in 1978 had deeper beaks Chicks hatched in 1978 had deeper beaks on average than those hatched in 1976.on average than those hatched in 1976.

Population evolved.Population evolved.

Fig 3.10


Variation in weather from year to year on Variation in weather from year to year on Daphne Major over 30 years has led to Daphne Major over 30 years has led to variation in the traits that are favored by variation in the traits that are favored by selection.selection.

Population has evolved over time.Population has evolved over time.

Fig 3.11 A

Over the course of 30 years (1970 to 2000) beak size evolved. Rose sharply during drought (red line) thendeclined to pre-drought dimensions.

Fig 3.11 B

Over same 30-year period birds evolved more pointed beaks and (next slide) significantly smaller body size.

Fig 3.11 C

The nature of Natural SelectionThe nature of Natural Selection

Many misconceptions about how selection Many misconceptions about how selection operates and evolution occurs.operates and evolution occurs.

Points to remember about natural Points to remember about natural selectionselection

Natural selection acts on individuals, Natural selection acts on individuals, but its effects accumulate in but its effects accumulate in

populationspopulations

Individual finches live or die during a Individual finches live or die during a drought (the selection event). drought (the selection event).

But change occurs in the characteristics of But change occurs in the characteristics of the the populationpopulation, not in individuals., not in individuals.

Natural selection acts on Natural selection acts on individuals, but its effects individuals, but its effects accumulate in populationsaccumulate in populations

During drought individual finch’s beaks During drought individual finch’s beaks did not change, but average beak did not change, but average beak dimensions changed because more dimensions changed because more small-beaked birds died than large-small-beaked birds died than large-beaked birds.beaked birds.

Evolution causes changes in Evolution causes changes in allele frequenciesallele frequencies

Evolution only occurs when traits have a Evolution only occurs when traits have a geneticgenetic basis. basis.

If beak dimensions were environmentally If beak dimensions were environmentally induced, no evolution could take place. induced, no evolution could take place. After drought, frequencies of phenotypes in After drought, frequencies of phenotypes in next generation might have been the same next generation might have been the same as before.as before.

Natural selection does not plan Natural selection does not plan ahead.ahead.

Each generation is result of selection by Each generation is result of selection by environmental conditions of the environmental conditions of the previousprevious generation.generation.

Evolution always one generation behind Evolution always one generation behind environmental changes.environmental changes.

New traits evolve even though New traits evolve even though selection acts on existing selection acts on existing

traits. traits. This occurs because: This occurs because:

1. mutation produces new alleles.1. mutation produces new alleles.

2. In sexually reproducing organisms 2. In sexually reproducing organisms meiosis and fertilization recombine meiosis and fertilization recombine existing alleles to produce new genotypes.existing alleles to produce new genotypes.

New traits evolve even though New traits evolve even though selection acts on existing traits.selection acts on existing traits.Artificial selection for oil content in corn.Artificial selection for oil content in corn.

After 60 generations oil levels were well After 60 generations oil levels were well above starting values.above starting values.

Fig 3.12

New traits evolve even though New traits evolve even though selection acts on existing traits.selection acts on existing traits.Natural selection can also modify existing Natural selection can also modify existing features over time for a new purpose e.g. features over time for a new purpose e.g. Panda’s thumb.Panda’s thumb.

Trait used in novel way and eventually Trait used in novel way and eventually developed into a new structure referred to developed into a new structure referred to as a as a preadaptationpreadaptation. This does NOT . This does NOT mean there is pre-planning by natural mean there is pre-planning by natural selection.selection.

Natural selection does not Natural selection does not produce ‘perfect’ solutionsproduce ‘perfect’ solutions

Panda’s thumb not a perfect solution.Panda’s thumb not a perfect solution.


On Daphne Major during drought finches with On Daphne Major during drought finches with narrow beaks survived better than those with wider narrow beaks survived better than those with wider bills.bills.

At end of drought, however, selection for deeper At end of drought, however, selection for deeper bills and bigger body size resulted in wider beaks bills and bigger body size resulted in wider beaks even through deeper narrower beaks would have even through deeper narrower beaks would have been a better solution.been a better solution. Presumably same genes control all three traits. Presumably same genes control all three traits. And solution is not perfect.And solution is not perfect.


Similarly, many characteristics of Similarly, many characteristics of organisms are the result of compromises organisms are the result of compromises between different selection pressures.between different selection pressures.

The wings of various species of auk The wings of various species of auk (seabirds that dive and swim) are a (seabirds that dive and swim) are a compromise between the need to “fly” (i.e. compromise between the need to “fly” (i.e. swim) underwater and in the air, two very swim) underwater and in the air, two very different media.different media.

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Razorbill polar.alaskapacific.edu/aharding/images/Littl...

Little Auk

Natural selection is nonrandom, Natural selection is nonrandom, but not progressivebut not progressive

There is no “goal” of natural selection.There is no “goal” of natural selection.

Evolution makes organisms better adapted Evolution makes organisms better adapted to their environments, but there is no trend to their environments, but there is no trend towards being more advanced.towards being more advanced.

E.g. Tapeworms have no digestive tract. E.g. Tapeworms have no digestive tract. They are simpler than their ancestors.They are simpler than their ancestors.

Selection does not act for the Selection does not act for the “good of the species”“good of the species”

Apparently altruistic acts (e.g. giving an Apparently altruistic acts (e.g. giving an alarm call) are favored because they alarm call) are favored because they enhance relatives’ survival.enhance relatives’ survival.

Infanticide in lions benefits individual male Infanticide in lions benefits individual male lions not the species as a whole.lions not the species as a whole.

influence of geological thinking on darwin by time of “the beagle” voyage idea that earth was...

Documents

darwin uniformitarianism

darwin hutton

species evolution

geological processes

geology focused darwin

darwinian fitness

fitness relative

current geological formations