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Evolution Evolution

By Natural SelectionBy Natural Selection

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The Idea of ProgressThe Idea of Progress

• The spirit of the times in 19The spirit of the times in 19thth century, England especially.century, England especially.

• Derives from the Enlightenment and Derives from the Enlightenment and Rationalism and the Industrial Rationalism and the Industrial Revolution.Revolution.

• Steady upward direction to all life.Steady upward direction to all life.• Like a machine, but directed toward Like a machine, but directed toward

an end: perfection.an end: perfection.

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NaturphilosophieNaturphilosophie

• Nature is like an organism, alive and Nature is like an organism, alive and growinggrowing– Life follows a universal archetype.Life follows a universal archetype.

• The Problem of TeleologyThe Problem of Teleology– Goal directed activity.Goal directed activity.– How to reconcile with a blind How to reconcile with a blind

mechanism?mechanism?

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Science and ChanceScience and Chance

• AristotleAristotle– Accident vs. NecessityAccident vs. Necessity– Accidents don’t repeatAccidents don’t repeat

• E.g., Empedocles, the E.g., Empedocles, the “Man-faced ox progeny.”“Man-faced ox progeny.”

– Things that happen by Things that happen by chance don’t repeat, so chance don’t repeat, so ignore them.ignore them.

– Science concerns Science concerns regularities, not exceptions.regularities, not exceptions.

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The Effect of ChoiceThe Effect of Choice

• Newton on choiceNewton on choice– Evidence of God’s interventionEvidence of God’s intervention– Uniform direction of planetary revolution Uniform direction of planetary revolution

about the sunabout the sun– The nearly uniform plane of orbit of the The nearly uniform plane of orbit of the

planetsplanets– Gravitation – no mechanical cause evidentGravitation – no mechanical cause evident– ““Corrections” to the planetary orbitsCorrections” to the planetary orbits– The regularity of the parts of animals (cf. The regularity of the parts of animals (cf.

Query 31 of Query 31 of The OpticksThe Opticks))

• Compare this with Laplace’s conclusion Compare this with Laplace’s conclusion that he had no need for God.that he had no need for God.

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The Design ArgumentThe Design Argument• God is revealed by his design in God is revealed by his design in

nature.nature.• An inexplicable regularity is An inexplicable regularity is

evidence of God.evidence of God.• Nature is a second Scripture.Nature is a second Scripture.

– ““Natural Theology ”Natural Theology ”

• Many works published that Many works published that developed the Design developed the Design Argument, e.g., John Ray’s Argument, e.g., John Ray’s The The Wisdom of God Manifested in Wisdom of God Manifested in the Works of Creationthe Works of Creation, 1701., 1701.

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The Bridgewater The Bridgewater TreatisesTreatises

• The 8The 8thth Earl of Bridgewater left a Earl of Bridgewater left a bequest in 1829 for works “on the bequest in 1829 for works “on the power, wisdom and goodness of God as power, wisdom and goodness of God as manifested in the Creation.”manifested in the Creation.”

• 8 “Bridgewater Treatises” were 8 “Bridgewater Treatises” were published in the 1830s.published in the 1830s.

• One of them was: Charles Bell, One of them was: Charles Bell, The The Hand: Its Mechanism and Vital Hand: Its Mechanism and Vital Endowments as Evincing DesignEndowments as Evincing Design (1833).(1833).– An out and out attack on Lamarck’s theory.An out and out attack on Lamarck’s theory.

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Charles DarwinCharles Darwin

– 1809-18821809-1882

• Darwin came from Darwin came from wealthy middle-wealthy middle-class English class English family, prominent family, prominent in English in English intellectual life.intellectual life.

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Charles Darwin, 2Charles Darwin, 2• His paternal grandfather was His paternal grandfather was

Erasmus Darwin, a member of Erasmus Darwin, a member of the Lunar Society and an the Lunar Society and an early evolutionist, with a early evolutionist, with a theory something like theory something like Lamarck’s but not detailed.Lamarck’s but not detailed.

• His maternal grandfather was His maternal grandfather was Josiah Wedgwood, the Josiah Wedgwood, the famous potter, and also a famous potter, and also a member of the Lunar member of the Lunar Society.Society.

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Charles Darwin, 3Charles Darwin, 3

• Darwin’s father Darwin’s father was a prominent was a prominent physician and physician and expected young expected young Darwin to follow Darwin to follow him in the medical him in the medical profession.profession.

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Darwin’s EducationDarwin’s Education• Darwin went first to the University of Darwin went first to the University of

Edinburgh to study medicine. Edinburgh to study medicine. – But he did not like it and dropped out.But he did not like it and dropped out.

• Then he went to the University of Then he went to the University of Cambridge, ostensibly to study to Cambridge, ostensibly to study to become a clergyman.become a clergyman.

• While at Cambridge he came under While at Cambridge he came under the influence of the clergyman/the influence of the clergyman/naturalist J. S. Henslow and naturalist J. S. Henslow and became interested in becoming a became interested in becoming a naturalist himself.naturalist himself.

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The Voyage of the BeagleThe Voyage of the Beagle

• The British admiralty was planning a long, round-the-The British admiralty was planning a long, round-the-world surveying voyage and wished to take a world surveying voyage and wished to take a naturalist.naturalist.

• Henslow nominated Darwin, and he got the position.Henslow nominated Darwin, and he got the position.

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The Voyage of the The Voyage of the Beagle, 2Beagle, 2

• Darwin took the position; sailed on the Beagle for Darwin took the position; sailed on the Beagle for 5 years, from 1831 to 1836.5 years, from 1831 to 1836.

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Darwin and Lyell’s Darwin and Lyell’s Principles of GeologyPrinciples of Geology

• Lyell’s Lyell’s Principles of Principles of GeologyGeology was was published published during the during the years of the years of the voyage.voyage.

• Darwin took Darwin took volume 1volume 1 with with him. He had him. He had the others sent the others sent to him as they to him as they became became available.available.– Darwin read Darwin read

these all very these all very carefully.carefully.

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Darwin and Lyell’s Darwin and Lyell’s Principles of Geology, 2Principles of Geology, 2

• Lyell gave very good summaries of Lyell gave very good summaries of existing theories of flora and fauna existing theories of flora and fauna including Lamarck’s theory of evolution.including Lamarck’s theory of evolution.

• Lyell himself believed that there was Lyell himself believed that there was limited variation in plants and animals limited variation in plants and animals but no evolution into another life form but no evolution into another life form was possible.was possible.

• But Lyell believed that geological But Lyell believed that geological formations occurred naturally with small formations occurred naturally with small changes over vast periods of time (i.e., changes over vast periods of time (i.e., uniformitarianism).uniformitarianism).

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Darwin’s travels down the Darwin’s travels down the coast of South Americacoast of South America

• Darwin noted that life forms were similar Darwin noted that life forms were similar in all places, but had somewhat different in all places, but had somewhat different form in the different climates encountered. form in the different climates encountered. – This was true of both plants and animals.This was true of both plants and animals.– Plants became hardier as he moved away from Plants became hardier as he moved away from

the equator.the equator.– Animals had heavier fur, or thicker feathers, Animals had heavier fur, or thicker feathers,

etc.etc.– But changes were gradual as the climate But changes were gradual as the climate

changed.changed.

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Darwin’s in South Darwin’s in South America, 2America, 2

• They also appeared to They also appeared to vary over time.vary over time.

• Fossils and other Fossils and other remains of extinct remains of extinct creatures were found in creatures were found in the same locale as living the same locale as living creatures structurally creatures structurally similar to the extinct similar to the extinct ones, but perhaps ones, but perhaps varying enormously in varying enormously in size. size.

• E.g. the extinct E.g. the extinct edentatesedentates that were so much like that were so much like the living (and much the living (and much smaller) smaller) armadillos.armadillos.

Above: A giant, extinct, edentate, reconstructed from fossil remains. Below, a living armadillo.

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Darwin at the Galapagos Darwin at the Galapagos IslandsIslands

• After travelling down the east coast of South America, After travelling down the east coast of South America, the Beagle went up the west coast and then ventured out the Beagle went up the west coast and then ventured out to the Galapagos Islands, 600 miles west of Equador. to the Galapagos Islands, 600 miles west of Equador. These are volcanic (therefore recent) islands, isolated These are volcanic (therefore recent) islands, isolated from anywhere else. Both the climate and the terrain are from anywhere else. Both the climate and the terrain are similar from island to island.similar from island to island.

Galapagos Islands circled

The Galapagos Islands.

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Darwin at the Galapagos Darwin at the Galapagos IslandsIslands

• Darwin found that each Darwin found that each island had its own special island had its own special life forms.life forms.

• The giant tortoises had The giant tortoises had characteristic markings characteristic markings that could be used to that could be used to identify their home island. identify their home island.

• Fnches had anatomical Fnches had anatomical differences (e.g. shape of differences (e.g. shape of beak) that were suited to beak) that were suited to different diets. different diets.

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Darwin the naturalistDarwin the naturalist• When the five-year voyage was When the five-year voyage was

finally concluded, Darwin finally concluded, Darwin returned to England and wrote returned to England and wrote up his findings.up his findings.

• His book, His book, Journal of Journal of Researches into the Geology Researches into the Geology and Natural History of the and Natural History of the various countries visited by various countries visited by H.M.S. BeagleH.M.S. Beagle, became a , became a bestseller in 19bestseller in 19thth century century England, going through many England, going through many editions in Darwin’s lifetime editions in Darwin’s lifetime and establishing Darwin’s and establishing Darwin’s reputation as a naturalist.reputation as a naturalist.

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Darwin at DownDarwin at Down

• Darwin married his 1Darwin married his 1stst cousin Emma and settled down to a cousin Emma and settled down to a rural life in the village of Down, just outside of London, where rural life in the village of Down, just outside of London, where they remained for the rest of their lives. They had 10 children.they remained for the rest of their lives. They had 10 children.

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Darwin at DownDarwin at Down

• Darwin began a long and careful Darwin began a long and careful consideration of some of the problems that consideration of some of the problems that troubled him on the Voyage. He began to troubled him on the Voyage. He began to write these down in a series of notebooks in write these down in a series of notebooks in which he made observations. He continued which he made observations. He continued this for 20 years.this for 20 years.

• During those years, he made famous studies During those years, he made famous studies of barnacles – writing what is today still the of barnacles – writing what is today still the definitive text on barnacles. He wrote about definitive text on barnacles. He wrote about orchid breeding, cattle breeding, and orchid breeding, cattle breeding, and breeding pigeons for show.breeding pigeons for show.

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Darwin’s ProblemDarwin’s Problem

• Species vary systematically from Species vary systematically from place to place and over long periods place to place and over long periods of time. of time. – How could he explain the similarities? How could he explain the similarities? – How does inheritance work?How does inheritance work?

• Why were they not all identical? Why were they not all identical? – If there is evolution, how does it work?If there is evolution, how does it work?

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Lamarck’s viewLamarck’s view• Lamarck believed that species would adapt to Lamarck believed that species would adapt to

changes in their environment and pass those changes in their environment and pass those changes on to future generations.changes on to future generations.– That might explain the differences in species up That might explain the differences in species up

and down the coast of South America as the and down the coast of South America as the climate changed.climate changed.

– It might explain changes in species over vast It might explain changes in species over vast amounts of time.amounts of time.• E.g. the extinct giant edentates and the present smaller E.g. the extinct giant edentates and the present smaller

armadillos.armadillos.

– But how could it explain the differences from island But how could it explain the differences from island to island in the Galapagos, where the environment to island in the Galapagos, where the environment is virtually identical?is virtually identical?

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Darwin reads MalthusDarwin reads Malthus

• In 1798, the Reverend In 1798, the Reverend Thomas Malthus Thomas Malthus published his published his Essay Essay on Populationon Population, in , in which he predicted which he predicted that the human that the human population was population was growing at a rate at growing at a rate at which there would which there would soon not be enough soon not be enough food to go around.food to go around.

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Darwin reads Malthus, 2Darwin reads Malthus, 2• Malthus argued that Malthus argued that

populations will tend to populations will tend to grow exponentially if grow exponentially if there is ample food, there is ample food, doubling in about 25 doubling in about 25 years, as it had been doing years, as it had been doing in the United States in the United States according to a census in according to a census in his time.his time.

• Meanwhile any increase in Meanwhile any increase in the food supply depends the food supply depends on the amount of land on the amount of land under cultivation, which is under cultivation, which is necessarily limited.necessarily limited.

An illustration of Malthus’ projections for Britain in

the 19th century.

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Darwin reads Malthus, 3Darwin reads Malthus, 3• Malthus’ book caused a sensation in the early Malthus’ book caused a sensation in the early

1919thth century as people began to worry about century as people began to worry about the possible scarcity of resources.the possible scarcity of resources.– The book was recommended to Darwin as The book was recommended to Darwin as

interesting reading. He read it in 1838—two years interesting reading. He read it in 1838—two years after returning from the Beagle voyage.after returning from the Beagle voyage.

• Malthus’ thesis made Darwin began to wonder Malthus’ thesis made Darwin began to wonder whether the same causes could not be at work whether the same causes could not be at work in nature, with the effect of causing a in nature, with the effect of causing a competition at all times for available resourcescompetition at all times for available resources—across all species.—across all species.– In typical Darwin fashion, he pondered this very In typical Darwin fashion, he pondered this very

slowly.slowly.

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Alfred Russel WallaceAlfred Russel Wallace– 1823-19131823-1913

• Another 19Another 19thth century naturalist. century naturalist.• Wallace, 14 years younger than Wallace, 14 years younger than

Darwin, came from a poorer Darwin, came from a poorer family than Darwin and did not family than Darwin and did not have Darwin’s advantages.have Darwin’s advantages.

• But he shared many of Darwin’s But he shared many of Darwin’s interests.interests.

• Wallace trained and worked as Wallace trained and worked as a land surveyor, then took up a a land surveyor, then took up a career as a naturalist, career as a naturalist, collecting specimens from collecting specimens from exotic locations, writing about exotic locations, writing about them, and selling them to them, and selling them to museums back home.museums back home.

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Wallace reads MalthusWallace reads Malthus• Like Darwin, Wallace had travelled on Like Darwin, Wallace had travelled on

long expeditions to far-away places, long expeditions to far-away places, carrying Lyell’s carrying Lyell’s Principles of GeologyPrinciples of Geology with him as a basic reference text.with him as a basic reference text.– Wallace also was struck with the evidence Wallace also was struck with the evidence

for evolution, but, like Darwin, could not for evolution, but, like Darwin, could not find a mechanism to explain it.find a mechanism to explain it.

• In 1858, twenty years after Darwin In 1858, twenty years after Darwin had done the same, Wallace read the had done the same, Wallace read the book by Malthus, while he was out on book by Malthus, while he was out on an expedition in Borneo.an expedition in Borneo.

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Wallace reads Malthus, 2Wallace reads Malthus, 2• Like Darwin, Wallace was struck by the Like Darwin, Wallace was struck by the

applicability of Malthus’ analysis to species applicability of Malthus’ analysis to species in general.in general.

• UnlikeUnlike Darwin, who wanted mountains of Darwin, who wanted mountains of supporting evidence, Wallace leapt at this supporting evidence, Wallace leapt at this explanation and wished to announce it to explanation and wished to announce it to the world.the world.– In just a few days, he wrote up a quick draft In just a few days, he wrote up a quick draft

paper outlining his explanation and sent it to paper outlining his explanation and sent it to Darwin seeking his opinion of the paper and Darwin seeking his opinion of the paper and asking him to forward it on to a journal for asking him to forward it on to a journal for publication if he thought it worthy.publication if he thought it worthy.

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Darwin’s crisis of Darwin’s crisis of conscienceconscience

• Darwin was shocked at Wallace’s Darwin was shocked at Wallace’s paper. Not only did Wallace seize upon paper. Not only did Wallace seize upon the same main point from Malthus, the same main point from Malthus, Wallace sketched out its implications in Wallace sketched out its implications in much the same way that Darwin had much the same way that Darwin had been planning to do in the book he had been planning to do in the book he had been working on for 20 years.been working on for 20 years.– Darwin wished to do the honourable thing Darwin wished to do the honourable thing

by Wallace, but did not want to be by Wallace, but did not want to be upstaged by this much less thought-out upstaged by this much less thought-out hypothesis.hypothesis.

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Darwin’s crisis of Darwin’s crisis of conscience, 2conscience, 2

• Darwin sought the advice of two of his Darwin sought the advice of two of his closest friends, Charles Lyell and Joseph closest friends, Charles Lyell and Joseph Hooker, virtually the only people who Hooker, virtually the only people who knew what Darwin had been working on knew what Darwin had been working on all these years.all these years.– Lyell and Hooker advised Darwin to send Lyell and Hooker advised Darwin to send

Wallace’s paper to the Linnean Society in Wallace’s paper to the Linnean Society in London, along with an excerpt from one of London, along with an excerpt from one of Darwin’s notebooks and a copy of a letter Darwin’s notebooks and a copy of a letter Darwin had written to an American botanist Darwin had written to an American botanist the year before. the year before.

– These would establish that Darwin had been These would establish that Darwin had been at work on the same idea for much longer.at work on the same idea for much longer.

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Darwin forced into actionDarwin forced into action• In July 1858, the three papers were read In July 1858, the three papers were read

at the Linnean Society meeting and at the Linnean Society meeting and published shortly afterward.published shortly afterward.– They made very little impression on the They made very little impression on the

Linnean Society members, who did not Linnean Society members, who did not understand their significance.understand their significance.

• Though Darwin was not ready to go Though Darwin was not ready to go public with his ideas, Wallace’s paper public with his ideas, Wallace’s paper forced his hand. Darwin therefore began forced his hand. Darwin therefore began work on an “abstract” of his larger work on an “abstract” of his larger work, for publication the next year.work, for publication the next year.

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On the Origin of SpeciesOn the Origin of Species• The “abstract” was The “abstract” was

called called On the Origin On the Origin of Species by means of Species by means of Natural Selection, of Natural Selection, or the Preservation of or the Preservation of Favoured Races in Favoured Races in the Struggle for Life.the Struggle for Life.– It was published in It was published in

18591859 – – remember remember this date.this date. It is the 7 It is the 7thth date you need to date you need to remember in this remember in this course.course.

– The “abstract” ran for The “abstract” ran for about 500 pages.about 500 pages.

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““The Book that Shook The Book that Shook the World”the World”

• The 1st edition of The 1st edition of The OriginThe Origin sold out on sold out on the day of publication, Nov. 24, 1859the day of publication, Nov. 24, 1859– There were 27,000 copies sold in Britain in There were 27,000 copies sold in Britain in

Darwin’s lifetime.Darwin’s lifetime.– A total of 6 editions.A total of 6 editions.– The 6th edition finally dropped the word “On” The 6th edition finally dropped the word “On”

from the title.from the title.– There were editions in America and other There were editions in America and other

English-speaking countries and many English-speaking countries and many translations.translations.

• The reaction to the book was strong and The reaction to the book was strong and immediate. There was a greater immediate. There was a greater immediate reaction to this book than to immediate reaction to this book than to any other scientific work ever published. any other scientific work ever published.

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Elements of Darwin’s Elements of Darwin’s Explanation of EvolutionExplanation of Evolution

• Continuous variationContinuous variation• Selective Breeding develops different traitsSelective Breeding develops different traits

– Plant, cattle breeders, etc. select traits Plant, cattle breeders, etc. select traits “artificially.”“artificially.”

– Nature selects the variations with the best Nature selects the variations with the best chance to survive in a given environment chance to survive in a given environment (“natural selection”).(“natural selection”).

• Sexual selectionSexual selection– Those who are most fit to survive are also most Those who are most fit to survive are also most

likely mate with each other and leave offspring.likely mate with each other and leave offspring.• Vast amount of time available (as evidenced Vast amount of time available (as evidenced

by geology).by geology).

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Different views on the Different views on the organization of species in organization of species in

naturenature• The Scala Naturæ or Great Chain of BeingThe Scala Naturæ or Great Chain of Being• Cuvier’s “bush” – an ordered branching Cuvier’s “bush” – an ordered branching

system with hierarchiessystem with hierarchies• Darwin’s undirected branching evolution Darwin’s undirected branching evolution

where lines continue so long as they fit where lines continue so long as they fit their environment, but may become their environment, but may become extinct if the environment changes or they extinct if the environment changes or they may branch off and evolve into some other may branch off and evolve into some other viable line. The result is a chaotic pattern viable line. The result is a chaotic pattern that, if sketched looks like that, if sketched looks like “a bush pruned “a bush pruned by a drunken gardener.”by a drunken gardener.”

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One generation in Darwin’s One generation in Darwin’s evolutionary processevolutionary process

1.1. Continuous variation: Continuous variation: • Many individuals born, exhibiting a variety of Many individuals born, exhibiting a variety of

characteristics.characteristics.

2.2. Natural Selection: Natural Selection: • Some are fit to survive, others are unfit or less fit, and Some are fit to survive, others are unfit or less fit, and

do not survive to mate.do not survive to mate.

3.3. Sexual Selection: Sexual Selection: • Of the remaining individuals, those with the most Of the remaining individuals, those with the most

attractive characteristics (in general, the healthiest attractive characteristics (in general, the healthiest individuals) will mate and produce offspring.individuals) will mate and produce offspring.

• Thus, the next generation are the offspring of Thus, the next generation are the offspring of the fittest of the previous generation, whatever the fittest of the previous generation, whatever the criteria of fitness may be at any time.the criteria of fitness may be at any time.

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VariationVariation• What is the cause of the variation What is the cause of the variation

assumed by Darwin?assumed by Darwin?– This is the main weak point in Darwin’s This is the main weak point in Darwin’s

explanation.explanation.– For Lamarck, variation is caused by an For Lamarck, variation is caused by an

organism responding to its environment, organism responding to its environment, and then passing on that adaptation to the and then passing on that adaptation to the next generation. next generation.

• For Darwin (and Wallace too), variation For Darwin (and Wallace too), variation was something observed as a fact.was something observed as a fact.– No mechanism was found that would cause No mechanism was found that would cause

the variations to occur.the variations to occur.

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PangenesisPangenesis• Darwin’s inheritance theoryDarwin’s inheritance theory• Faced with having to explain inheritance Faced with having to explain inheritance

somehow, Darwin adopted somehow, Darwin adopted pangenesispangenesis::– All parts (cells) of the body produce small bits All parts (cells) of the body produce small bits

“gemmules” that go through the blood system “gemmules” that go through the blood system and collect in the sex cells – the ova and sperm and collect in the sex cells – the ova and sperm cells in animals.cells in animals.

– These gemmules carry the imprint of the These gemmules carry the imprint of the structure of the cells they came from. structure of the cells they came from.

– Gemmules from each parent blend together to Gemmules from each parent blend together to form new cells that have characteristics drawn form new cells that have characteristics drawn from both parents.from both parents.

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Problems with the Problems with the pangenesis theorypangenesis theory

• How do these gemmules work? How do these gemmules work? • What is the mechanism through What is the mechanism through

which they direct growth?which they direct growth?• How do they blend together, taking How do they blend together, taking

aspects of both parents?aspects of both parents?

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Problems with Problems with pangenesis, 2pangenesis, 2

• If the gemmules If the gemmules emanate from the emanate from the actual cells of the actual cells of the bodies of the parents, bodies of the parents, what about the what about the offspring of offspring of amputees?amputees?– Such Such ad hocad hoc

explanations were less explanations were less acceptable in science in acceptable in science in Darwin’s day. Though Darwin’s day. Though not necessarily wrong, not necessarily wrong, they belonged in the they belonged in the realm of speculation, realm of speculation, not scientific theory.not scientific theory.

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Darwin’s attack on the Darwin’s attack on the Design ArgumentDesign Argument

• The Design Argument asserts that The Design Argument asserts that “Design implies a designer.”“Design implies a designer.”

• Darwin tried to show that designs in Darwin tried to show that designs in nature can arise without purpose or nature can arise without purpose or intention, merely as the result of natural intention, merely as the result of natural selection. selection.

• To show that that assertion of the Design To show that that assertion of the Design Argument is invalid, Darwin only needs Argument is invalid, Darwin only needs to show that to show that it is possibleit is possible that a design that a design in nature could have arisen from natural in nature could have arisen from natural causes. causes.

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The Logical Structure of The Logical Structure of the Design Argumentthe Design Argument

• The power of the Design Argument The power of the Design Argument comes from its assertion that comes from its assertion that

1.1. The order and design is apparent in The order and design is apparent in nature – how individual organisms are nature – how individual organisms are purposely arranged for different purposely arranged for different functions, how species are functions, how species are interdependent, etc. interdependent, etc.

2.2. That order and design could only have That order and design could only have arisen by an intelligent creator: God. arisen by an intelligent creator: God.

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Logic of the Design Logic of the Design Argument, 2Argument, 2

• So long as the second point (that the So long as the second point (that the apparent order implies a designer) is apparent order implies a designer) is incontrovertible, the argument is incontrovertible, the argument is airtight.airtight.

• However, it completely loses its power However, it completely loses its power if it could be established that order if it could be established that order and purpose could have arisen some and purpose could have arisen some other way – such as by the process of other way – such as by the process of evolution by natural selection.evolution by natural selection.

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Logic of the Design Logic of the Design Argument, 3Argument, 3

• Darwin was totally unable to prove Darwin was totally unable to prove that nature arose from evolution by that nature arose from evolution by natural selection, but if he could natural selection, but if he could show that such a result (nature as show that such a result (nature as we know it) was a conceivable we know it) was a conceivable possibility, then the Design possibility, then the Design Argument loses its power.Argument loses its power.

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Logic of the Design Logic of the Design Argument, 4Argument, 4

• Charles Bell’s Bridgewater Treatise used Charles Bell’s Bridgewater Treatise used the example of the hand, with all its the example of the hand, with all its marvelous adaptations, to illustrate marvelous adaptations, to illustrate design in nature, and assert that it proved design in nature, and assert that it proved the intervention of God.the intervention of God.

• Darwin took this argument head-on with Darwin took this argument head-on with an even more complex organ, the eye.an even more complex organ, the eye.– He argued that a light-sensitive nerve could He argued that a light-sensitive nerve could

have survival value and over many have survival value and over many generations become more and more refined generations become more and more refined until it evolved into an eye.until it evolved into an eye.

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Weight of EvidenceWeight of Evidence• It was first in Darwin’s theory of It was first in Darwin’s theory of

evolution that the general public (and evolution that the general public (and even the scientific public) became even the scientific public) became aware that no scientific theories are aware that no scientific theories are ever “proven” in the sense of logically ever “proven” in the sense of logically certain, but are nevertheless accepted certain, but are nevertheless accepted because their explanations are so because their explanations are so much better than any alternatives.much better than any alternatives.

• Because living nature is so complex Because living nature is so complex and has so many forms, Darwin’s and has so many forms, Darwin’s presentation is notable for its presentation is notable for its emphasis on the weight of evidence emphasis on the weight of evidence presented in favour of his theory.presented in favour of his theory.

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Human EvolutionHuman Evolution

• In In The OriginThe Origin, Darwin hardly mentions , Darwin hardly mentions human evolution at all. Darwin knew human evolution at all. Darwin knew how controversial it would be, so he how controversial it would be, so he was willing to leave it alone.was willing to leave it alone.– His one hint in His one hint in The OriginThe Origin: “Light will be : “Light will be

thrown on the origin of man and his thrown on the origin of man and his history.”history.”

• However, the public immediately drew However, the public immediately drew the obvious conclusions and concluded the obvious conclusions and concluded that Darwin believed that humans that Darwin believed that humans descended from animals.descended from animals.

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Darwin’s BulldogDarwin’s Bulldog

• While Darwin preferred to While Darwin preferred to remain a recluse and not remain a recluse and not discuss his theories, one of discuss his theories, one of his disciples was more his disciples was more willing to engage in a good willing to engage in a good argument.argument.

• Thomas Henry Huxley was Thomas Henry Huxley was a prominent zoologist and a prominent zoologist and Darwin convert. He became Darwin convert. He became known as Darwin’s known as Darwin’s “Bulldog” because of his “Bulldog” because of his willingness to argue the willingness to argue the case for evolution.case for evolution.

Thomas Henry Huxley

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Wilberforce versus HuxleyWilberforce versus Huxley

• The most famous debate over evolution happened in The most famous debate over evolution happened in 1860, the year after the publication of 1860, the year after the publication of The OriginThe Origin..

• Samuel Wilberforce, Bishop of Oxford, taunted Huxley Samuel Wilberforce, Bishop of Oxford, taunted Huxley at a meeting of the British Association for the at a meeting of the British Association for the Advancement of Science, asking if Huxley was Advancement of Science, asking if Huxley was descended from an ape on his grandfather’s or his descended from an ape on his grandfather’s or his grandmother’s side.grandmother’s side.– Huxley took him on and made a fool of the Bishop.Huxley took him on and made a fool of the Bishop.

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Darwin on ManDarwin on Man

• Finally, in 1871, Darwin published his Finally, in 1871, Darwin published his work on human evolution, work on human evolution, The The Descent of Man.Descent of Man.– Darwin established the relationship Darwin established the relationship

between humans and primates (apes, between humans and primates (apes, monkeys)monkeys)

– As far as the human species itself was As far as the human species itself was concerned, Darwin asserted that all concerned, Darwin asserted that all humans were essentially alike. humans were essentially alike. • A common view in his time was that different A common view in his time was that different

races were actually different species.races were actually different species.

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Darwin on Man, 2Darwin on Man, 2

• Darwin showed the Darwin showed the similarity of similarity of humans to other humans to other animals at animals at different stages of different stages of development.development.

• At right is a human At right is a human embryo (top) and a embryo (top) and a dog embryo dog embryo (bottom).(bottom).

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Darwinians join inDarwinians join in

• Huxley obtained specimens of a human brain Huxley obtained specimens of a human brain and a chimpanzee brain and showed their and a chimpanzee brain and showed their similarity in construction.similarity in construction.

• Above: human brain on the left, chimp on the Above: human brain on the left, chimp on the right. This is not Huxley’s illustration, but it is right. This is not Huxley’s illustration, but it is similar.similar.

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Darwinians join inDarwinians join in

• Other Other Darwinians Darwinians followed followed Darwin’s lead Darwin’s lead with embryos with embryos and showed the and showed the striking striking similarity of similarity of many creatures many creatures at the early at the early stages of their stages of their fetal fetal development.development.

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Other views in circulation Other views in circulation in Darwin’s time:in Darwin’s time:

• The Great Chain of Being – humans were the The Great Chain of Being – humans were the top of the evolutionary chain, more “perfect” top of the evolutionary chain, more “perfect” than other speciesthan other species

• Europeans were the top of a pecking order Europeans were the top of a pecking order among humans.among humans.

• Microcephalic idiots were viewed as Microcephalic idiots were viewed as intermediate links between man and apeintermediate links between man and ape

• Anthropoid fossils – first discovered in 1836Anthropoid fossils – first discovered in 1836– Neanderthal Man (1886) – first thought to be Neanderthal Man (1886) – first thought to be

recentrecent– Java Ape Man (1891) had low cranial capacityJava Ape Man (1891) had low cranial capacity– These thought to be missing linksThese thought to be missing links

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General Criticisms of General Criticisms of Darwin’s TheoryDarwin’s Theory

• Evidence for Natural Selection is Evidence for Natural Selection is

lacking.lacking.

• There are no transitional species.There are no transitional species.

• The Design ArgumentThe Design Argument

• Orthogenetic TrendsOrthogenetic Trends– for example, sabre-tooth catsfor example, sabre-tooth cats

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General Criticisms of General Criticisms of Darwin’s Theory, 2Darwin’s Theory, 2

• The age of the earthThe age of the earth– Prominent physicist Lord Kelvin (William Prominent physicist Lord Kelvin (William

Thomson) in 1865 claimed that the sun (and Thomson) in 1865 claimed that the sun (and therefore the earth) could not possibly be old therefore the earth) could not possibly be old enough for evolution to have taken place.enough for evolution to have taken place.

• Inheritance unexplainedInheritance unexplained– Fleeming Jenkin (1867) argued that Darwin’s Fleeming Jenkin (1867) argued that Darwin’s

theory of blending inheritance could not possibly theory of blending inheritance could not possibly lead to the preservation of favourable lead to the preservation of favourable characteristicscharacteristics

• The Inheritance of Acquired CharacteristicsThe Inheritance of Acquired Characteristics– As opposed to Natural Selection.As opposed to Natural Selection.

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Social DarwinismSocial Darwinism

• The general application of Darwinian The general application of Darwinian principles to society and human principles to society and human endeavor, rather than just to species endeavor, rather than just to species evolution. evolution.

• In general, the chief new factor is In general, the chief new factor is the recognition of the importance of the recognition of the importance of processes that happen over long processes that happen over long periods of time.periods of time.

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Some examples of Social Some examples of Social DarwinismDarwinism

•TheologyTheology– The authority of the Bible, and the The authority of the Bible, and the

creation story in Genesis creation story in Genesis rethought.rethought.

– The issue of the uniqueness of man The issue of the uniqueness of man as opposed to other species, as as opposed to other species, as taught in many religious doctrines.taught in many religious doctrines.

– The Design argument, both The Design argument, both supported and argued against.supported and argued against.

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Examples of Social Examples of Social Darwinism, 2Darwinism, 2

• Racism and SlaveryRacism and Slavery– Darwin’s view: All races are equally Darwin’s view: All races are equally

human, therefore slavery is a human, therefore slavery is a historical accident of who happened historical accident of who happened to have power at a particular timeto have power at a particular time

– Another, opposed view, but which Another, opposed view, but which many people thought to be many people thought to be “Darwinian” was that Europeans “Darwinian” was that Europeans were “more evolved” and therefore were “more evolved” and therefore had a natural right to enslave other had a natural right to enslave other racesraces

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Examples of Social Examples of Social Darwinism, 3Darwinism, 3• PoliticsPolitics

– National Socialism (the Nazis) were based upon the National Socialism (the Nazis) were based upon the notion that keeping the race pure would be an aid to notion that keeping the race pure would be an aid to the evolution of a super race (Ernst Haeckel’s view)the evolution of a super race (Ernst Haeckel’s view)

– Capitalism and the Capitalism and the Laissez-faireLaissez-faire approach to approach to economics viewed market forces as a sort of natural economics viewed market forces as a sort of natural selection.selection.• Therefore the self-made millionaire was seen as the Therefore the self-made millionaire was seen as the

highest form of evolution (William Graham highest form of evolution (William Graham Sumner’s view).Sumner’s view).

• The “Invisible Hand” of Adam Smith was The “Invisible Hand” of Adam Smith was considered comparable to Natural Selectionconsidered comparable to Natural Selection

– CommunismCommunism• The group viewed as more important than the The group viewed as more important than the

individual in order to advance the cause of society.individual in order to advance the cause of society.• Karl Marx wished to dedicate Karl Marx wished to dedicate Das CapitalDas Capital to to

Darwin (who was horrified at the thought).Darwin (who was horrified at the thought).

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Examples of Social Examples of Social Darwinism, 4Darwinism, 4

• SociologySociology– Sociology, touted as the “Science of Society” Sociology, touted as the “Science of Society”

needed a theoretical structure. Natural needed a theoretical structure. Natural Selection provided a basis on which to explain Selection provided a basis on which to explain why societies have taken the forms they have.why societies have taken the forms they have.

– British popular philosopher Herbert Spencer British popular philosopher Herbert Spencer (1820-1903) wrote extensively on the bases of (1820-1903) wrote extensively on the bases of many social sciences. He is the person who many social sciences. He is the person who coined the term “Survival of the Fittest,” in coined the term “Survival of the Fittest,” in 1858 – the year 1858 – the year beforebefore the publication of the the publication of the Origin of SpeciesOrigin of Species. (Darwin later incorporated . (Darwin later incorporated the phrase in the subtitle of later editions of the phrase in the subtitle of later editions of the the OriginOrigin.).)

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Examples of Social Examples of Social Darwinism, 5Darwinism, 5

• EugenicsEugenics– A movement to help evolution along by sterilizing A movement to help evolution along by sterilizing

those who are seen as less likely to have ideal those who are seen as less likely to have ideal characteristics. In other words, using artificial characteristics. In other words, using artificial selection (like animal breeders) to help natural selection (like animal breeders) to help natural selection.selection.

– Darwin’s cousin, Francis Galton, was one of the Darwin’s cousin, Francis Galton, was one of the leaders of the movement.leaders of the movement.

– In Germany the National Socialist Party adopted In Germany the National Socialist Party adopted eugenics as a central part of their political eugenics as a central part of their political platform. After the Second World War, the platform. After the Second World War, the movement fell into complete disrepute.movement fell into complete disrepute.

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Examples of Social Examples of Social Darwinism, 6Darwinism, 6

• Intelligence testsIntelligence tests– Though Darwin viewed all humans as Though Darwin viewed all humans as

essentially the same, he did view them as essentially the same, he did view them as exhibiting a range of characteristics, which exhibiting a range of characteristics, which would be better or worse from the point of would be better or worse from the point of view of survival value. view of survival value.

– Such characteristics included mental Such characteristics included mental abilities. Around the turn of the century, abilities. Around the turn of the century, tests were developed to determine such tests were developed to determine such abilities and used evolutionary theory as abilities and used evolutionary theory as their justification.their justification.