Immanuel Kant “It is absurd for human beings ... to hope that perhaps some day another Newton might arise who would explain to us, in terms of natural laws unordered by any intention, how even a mere blade of grass is produced.” Critique of Judgment, 1790
Daniel Dennett“I think Darwins idea of natural selection is the bestidea anybody ever had, ahead of Newton, ahead ofEinstein. What it does is it promises to unite the twomost disparate features of all of reality. On the oneside, purposeless matter and motion, jostlingparticles; on the other side, meaning, purpose, design.Before Darwin these were completely separaterealms. After Darwin we can see how they all ﬁttogether into a single big picture.” Evolution, 2001
ImplicationsMechanism Pathway Fact
Darwin’s Viewpoint Fact Pathway: Establishment of genealogical relationship (“tree thinking”) with common descent and multiplication of species via splitting or budding Mechanism: Natural selection and other mechanisms
T. Ryan Gregory (2008) “Natural selection is considered by many to be the prime component of evolutionary theory and is the only workable mechanism ever proposed that is capable of accounting for the adaptive features of organisms. At the molecular level, nonadaptive mechanisms are recognized as highly signiﬁcant.”
What is Evolution?
Evolution“Biological (or organic) evolution is change in theproperties of populations of organisms or groupsof such populations, over the course ofgenerations. The development, or ontogeny, of anindividual organism is not considered evolution:individual organisms do not evolve. The changes inpopulations that are considered evolutionary arethose that are ‘heritable via the genetic materialfrom one generation to the next. Biologicalevolution may be slight or substantial” Douglas J. Futuyma (1998) Evolutionary Biology
Natural Selection Economy of Tree Thinking Nature Gradual Genealogical Change Classification Darwin BiogeographicCoevolution Distribution Sexual Selective Selection Extinction Deep Time
1859 – First edition (1,250 copies)1860 – Minor changes (3,000 copies)1861 – Addition of the HistoricalSketch (2,000 copies)1866 – (1,500 copies)1869 – First use of Spencer’s term“Survival of the Fittest” (2,000 copies)1872 – Reset popular edition;Addition of “Miscellaneous Objectionsto the Theory of Natural Selection” inresponse to Mivart’s Genesis of Speciesand a Glossary (3,000 copies)
To Lyell, 1860 “I suppose ‘natural selection’ was a bad term; but to change it now, I think, would make confusion worse confounded. Nor can I think of better; ‘Natural preservation’ would not imply a preservation of particular varieties & would seem a truism; & would not bring mans & natures selection under one point of view. I can only hope by reiterated explanations ﬁnally to make matter clearer.”
“Survival of the Fittest” "This survival of the ﬁttest, which I have here sought to express in mechanical terms, is that which Mr. Darwin has called natural selection, or the preservation of favoured races in the struggle for life.“ Principles of Biology 1:444 (1864)
“Survival of the Fittest”Suggested by Wallace and ﬁrst used in 5thedition:“I have called this principle, by which each slightvariation, if useful, is preserved, by the term naturalselection, in order to mark its relation to manspower of selection. But the expression often used byMr. Herbert Spencer, of the Survival of the Fittest, ismore accurate, and is sometimes equallyconvenient.”
Darwin’s Big Idea Descent with modiﬁcation through natural selection
Fact #1Potential exponentialincrease of populations(“superfecundity”)Source: Thomas Malthus(1798), William Paley(1802), observation
Fact #2 Steady-state stability of most populations Source: observation
Fact #3Limitation of resourcesSource: observation
Inference #1Struggle for existence amongindividualsAuthor of inference: Malthus(1798)
Linear Growth Food ProductionExponential Growth Population Growth Malthusian Catastrophe
Thomas Malthus “The power of population is so superior to the power of the earth to produce subsistence for man, that premature death must in some shape or other visit the human race. The vices of mankind are active and able ministers of depopulation. They are the precursors in the great army of destruction; and often ﬁnish the dreadful work themselves. But should they fail in this war of extermination, sickly seasons, epidemics, pestilence, and plague, advance in terriﬁc array, and sweep off their thousands and tens of thousands. Should success be still incomplete, gigantic inevitable famine stalks in the rear, and with one mighty blow levels the population with the food of the world.“ Essay on the Principle of Population, 1798
Fact #4Variation between individualsSource: observation
Fact #5 Heritability of much of this variation Source: animal breeders
Inference #2Some of this variation is advantageous in certainenvironments therefore differential survival, i.e. naturalselection, will occur.Inference held by: Darwin, Alfred Russel Wallace, andothers
Inference #3Over many generations, provided selectionpressure is maintained, evolution will occurInference unique to Darwin & Wallace
AlternativelyIf there are variations in a replicating entity, andIf these are inherited, andIf one variant is more suited to some task than theothers, andIf that task directly affects survival and thereforereproduction of the entities,Then selection will result in evolutionary change inthe population of entities.
Natural Selection“A non-random difference in reproductiveoutput among replicating entities, often dueindirectly to differences in survival in aparticular environment, leading to an increase inthe proportion of beneﬁcial, heritablecharacteristics within a population from onegeneration to the next.” (Gregory, 2009)
FitnessFitness is a measure of the reproductive outputof an organism with a particular genotype withrespect to that of other genotypes in aparticular environment.For a trait to be evolutionarily relevant, it mustaffect reproduction - it is not enough to affectsurvival.
Patrick Matthew Appendix to Naval Timber and Arboriculture (1831) Claims priority in 1860 letter to Gardeners Chronicle
Edward Blyth “An Attempt to Classify the ‘Varieties’ of Animals, with Observations on the Marked Seasonal and Other Changes Which Naturally Take Place in Various British Species, and Which Do Not Constitute Varieties“ Magazine of Natural History (1835) Natural selection working to preserve type and essence, i.e. selection as a negative force.
William WellsTwo essays: On Upon Single Vision with Two Eyes; The Other onDew…and An Account of a Female of the White Race…Part ofWhose Skin Resembles That of a Negro…By the Late W.C.Wells…with a Memoir of His Life,Written by Himself. (1818)Some inhabitants “would be better ﬁtted than the others tobear the diseases of the country. This race wouldconsequently multiply, while the others would decrease.”Darwin wrote “In this paper he [Wells] distinctly recognizesthe principle of natural selection, and this is the ﬁrstrecognition which has been indicated…” (4th edition, 1866)
Unique to Darwin Not in originating natural selection ... But in seeing what natural selection was capable of doing But where was the evidence for natural selection?
Analyzing SelectionIs the population variable?Is some of the variation among individualswithin the population heritable?Do individuals vary in their success assurviving or reproducing?Are survival and reproduction non-random?Did the population change over time?
Is the population variable?
Is some of the variation heritable?
Do individuals vary in their success at surviving or reproducing?
Are survival and reproduction non-random?
Did the population change over time?
Non- Random Random Variation SelectionNatural Selection is not a Random Process
LevelNatural selection acts onindividuals but its consequenceoccur in populations.It does not, however, work for“the good of the species.”
Predicting the Future No need to be able to predict long-term course of evolution. Evolution is analogous to a poker tournament.
Darwin“I have just been writing anaudacious little discussion, toshow that organic beings arenot perfect, only perfectenough to struggle with theircompetitors.”Letter to J.D. Hooker, 9/11/1857
Natural SelectionNature “cares not for mere externalappearances; she may be said to scrutinize with asevere eye, every nerve, vessel & muscle; everyhabit, instinct, shade of constitution, - the wholemachinery of the organization. There will be hereno caprice, no favoring: the good will bepreserve[d] & the bad rigidly destroyed.”“By nature, I mean the laws ordained by God togovern the Universe.”
Origin, 2nd ed. “A celebrated author and divine has written to me that ‘he has gradually learnt to see that it is just as noble a conception of the Deity to believe that He created a few original forms capable of self-development into other and needful forms, as to believe that He required a fresh act of creation to supply the voids caused by the action of His laws.’”
Letter to Asa Grey“There seems to me too much misery in the world. I cannotpersuade myself that a beneﬁcent and omnipotent God wouldhave designedly created the Ichneumonidae with the expressintention of their feeding within the living bodies of caterpillarsor that a cat should play with mice... On the other hand, I cannotanyhow be contented to view this wonderful universe, andespecially the nature of man, and to conclude that everything isthe result of brute force. I am inclined to look at everything asresulting from designed laws, with the details, whether good orbad, left to the working out of what we may call chance.” (1860)
Darwin“The old argument of design in nature, as given byPaley, which formerly seemed to me to me soconclusive, fails, now that the law of naturalselection has been discovered. We can no longerargue that, for instance, the beautiful hinge of abivalve shell must have been made by an intelligentbeing, like the hinge of a door by a man. Thereseems to be no more design in the variability oforganic beings and in the action of naturalselection, than in the course which the windblows. Everything in nature is the result of ﬁxedlaws.”
PaleyA: X is intricate and well suited to a task TW1: X is a product of intelligent designW2: X is a product of random physical forcesPaley claims that the likelihood of W1 given Aexceeds that of W2, i.e. P(A|W1) >> P(A|W2)
DarwinA: X may or may not be intricate or well-suitedto a task T.W1: X is a product of intelligent designW2: X is a product of a non-random naturalmechanismDarwin claims that the likelihood of W2 given Aexceeds that of W1, i.e. P(A|W2) >> P(A|W1)
Part I – The Descent orOrigin of ManPart II – Sexual SelectionPart III – Sexual Selectionin Relation to Man andConclusion
1: Evidence for the Descent ofMan from Some Lower FormsHomologous structures in man and the loweranimalsDevelopment [Embryology]Rudimentary structures, muscles, sense-organs,hair, bones, reproductive organs, etc.
2: On the Manner of Development of Man from Some Lower FormsVariability of body and mind in manInheritanceLaws of variation the same in man as in thelower animalsNatural Selection
ManThe causes which have led to his becoming erectConsequent changes of structureDecrease in size of the canine teethIncreased size and altered shape of the skullNakednessAbsence of a tailDefenseless condition of man
Man the Biped“As soon as some ancient member in the great series of thePrimates came to be less arboreal, owing to a change in itsmanner of procuring subsistence, or to some change in thesurrounding conditions, its habitual manner of progressionwould have been modiﬁed: and thus it would have beenrendered more strictly quadrupedal or bipedal. … Man alonehas become a biped; and we can, I think, partly see how he hascome to assume his erect attitude, which forms one of hismost conspicuous characters. Man could not have attained hispresent dominant position in the world without the use of hishands, which are so admirably adapted to act in obedience tohis will.”
3 & 4: Comparison of the Mental Powers of Man and the Lower AnimalsInstinct ... Emotions ... Curiosity ... Imitation ...Memory ... Imagination ... ReasonTools and weapons used by animalsAbstraction, Self-consciousness, LanguageSense of beautyBelief in God, spiritual agencies, superstitions
The Moral SenseOrigin of sociabilityMan a social animalThe importance of the judgment of themembers of the same community on conductTransmission of moral tendencies
5: On the Development of the Intellectual and Moral Faculties During Primeval and Civilized TimesAdvancement of the intellectual powersthrough natural selectionImportance of imitationNatural selection as affecting civilised nationsEvidence that civilised nations were oncebarbarous
6: On the Afﬁnities and Genealogy of ManPosition of man in the animal seriesThe natural system genealogicalRank of man in the natural systemBirthplace and antiquity of manAbsence of fossil connecting-linksEarly androgynous condition of the Vertebrata
7: On the Races of ManArguments in favour of, and opposed to, ranking theso-called races of man as distinct speciesMonogenists and polygenistsNumerous points of resemblance in body and mindbetween the most distinct races of manEach race not descended from a single pairSlight or no inﬂuence of natural selectionSexual selection
Sexual SelectionInter-male competition Female choice
Female choice in Widowbirds
Is there clear sexual dimorphism?
Do long tails hinder males?
Do females prefer long tails?
19 & 20: SecondarySexual Characters of ManOn the inﬂuence of beauty in determining the marriages ofmankindTheir ideas of beauty in womenThe tendency to exaggerate each natural peculiarityOn the effects of the continued selection of women according to adifferent standard of beauty in each raceOn the manner of action of sexual selection with mankindOn the women in savage tribes having some power to choose theirhusbandsColour of the skin
21: General Summary & ConclusionMain conclusion that man is descended fromsome lower formManner of developmentGenealogy of manIntellectual and moral facultiesSexual selection
“Man may be excused for feeling some pride at having risen,though not through his own exertions, to the very summit ofthe organic scale; and the fact of his having thus risen, insteadof having been aboriginally placed there, may give him hopefor a still higher destiny in the distant future. But we are nothere concerned with hopes or fears, only with the truth asfar as our reason permits us to discover it; and I have giventhe evidence to the best of my ability. We must, however,acknowledge, as it seems to me, that man with all his noblequalities, with sympathy which feels for the most debased,with benevolence which extends not only to other men butto the humblest living creature, with his god-like intellectwhich has penetrated into the movements and constitutionof the solar system—with all these exalted powers—Man stillbears in his bodily frame the indelible stamp of his lowlyorigin.”
Expression of Emotions in Man and Animals (1872)
Darwin’s Legacy We have a professional discipline and a convincing naturalistic explanation of the design-like appearance of organisms.
Controversies• Is evolution always gradual? • Can complex features be regained if lost?• Balance between chance and non-random mechanisms • Does “junk” DNA have a function?• At what levels can selection work? • Did mammals diversify because of the extinction of• Are genomic duplications the dinosaurs? common and are they associated with major • What are the direct evolutionary changes? ancestors of Homo sapiens?