The'law of ancestral heredity'and the Mendelian-ancestrian controversy in England, 1889-1906.

36 Pages·2006·7.28 MB·English

Review Article
Journal ofMedical Genetics (1971). 8, 1.
The 'Law of Ancestral Heredity' and the
Mendelian-Ancestrian Controversy in England,
1889-1906
P. FROGGATT and N. C. NEVIN
From theDepartments ofSocial andPreventiveMedicine andMedical Statistics, andtheHuman Genetics Unit,
The Queen's University, Belfast
'I respect you as an honest man, and perhaps the ablest the three he was the most closely involved with
andhardestworkerIhavemet,andIamdeterminednot medical and statistical opinion and could-and
to take up a quarrel with you if I can help it. I have
thought for a long time that you are probably the only did-directly influence such opinion through his
Englishman I know at this moment whose first thought teaching, his writings including the publications he
istogetatthetruthinthese[inheritance]problems . . .'. edited, and his personal authority in the successive
(Letter from William Bateson to Karl Pearson of 13 posts he filled at University College, London. In
February 1902.)*
addition we deal with events in a defined period of
Itis frequently taughtthatafter Mendel's results time. Anydates selectedmustbecut-offpoints on
were 'rediscovered' (in 1900) the 'ancestrians',t led a continuum ofdebate; but our choice (1889-1906)
by KarlPearson, opposedtheiracceptance andthat is not arbitrary. Theyears 1889-1890 markatrue
this retardedthe development ofthesubjectlaterto beginning with the publication of Galton's book
be called human genetics. This generalization is Natural Inheritance-which made a profound im-
only partly true; and it is the purpose ofthis paper pression on all the principals-and Weldon's
to examine the facts and to explain the issues in- appointment to the Jodrell Chair of Zoology at
volved. UniversityCollege,London,wherehecameinclose
Thereweremanyprotagonists butweconcentrate contactwithPearson; whileWeldon's earlydeathin
on the three who led the rival schools in England: 1906 removed the most vibrant and committed of
William Batesonthe'Mendelian'; andKarlPearson theancestriansandthemainbuttfortheMendelians'
and Raphael Weldon the 'ancestrians'. (Francis attacks, and without him Pearson turned increas-
Galton, whose work influenced both schools, re- ingly to other applications ofthe methods theyhad
mained largely above the battle-he was 67 in developed together.
1889-enjoying throughout the respect and confi- This article is descriptive rather than interpreta-
dence of all. Sir Archibald Garrod, the pioneer tive: we describe the salient events and do not
human geneticist and Mendelian, was not directly attempt any wide-ranging critical discussion ofthe
involved to any extent.) Such was their pre- issues raised or their impact on the development of
eminence that restricting this article largely to their biological thinking. To reconcile this approach
work and mutual exchanges hardly reduces the with a reasonably concise and coherent narrative
scope of the controversy or the arena of battle. we have relegated some ofthe information to Notes
We deal inmost detail withthe work ofPearson: of which augment the customary bibliographical in-
formation. We have written for the reader ac-
quainted with human population genetics rather
aspR*eecPcteesairvosefodnh,,isOEcl.itfoeSb.aen(r1d953w61o)9r.7k0..KaBrilomPeetarriskoan,:2A8,n1a9p3p-r2e5c7i.atio(nPaogfes2o0m4e, dtihsacnuswsi,thhoawneivmearl,orwpolrakntognenentiocns-:hwuemahnavemahtaedriatol
ft.-note.) because Bateson and Weldon were field naturalists
wats'nAoitncienstdreipaen'nddeenstcroifbetdhetheexpvrieeswspiooinntofthtahteaspahmeenocthyapriacctcehrariancttehre not human biologists, and all biological data were
ancestry,i.e.inparents,grandparents,great-grandparents,etc. grist to Pearson's mill. Only Galton with his
1-J.M.G. I
2 Froggatt and Nevin
anthropometric interest and his habit of collecting ThirdWrangler inthe Tripos in 1879, Pearsonhad
data from the general public, and to a lesser extent written on a catholic range ofsubjects' encompass-
Pearson, dealtwithhumanmeasurements andtraits ing history, ethics, philosophy, art, mathematics,
to anyextent. andpoliticalthought2 butatthetimeofhisappoint-
Finally,manyoftheexchangeswereacrimonious, ment he had published only five original contribu-
some even grossly offensive, and read oddly today. tions inmathmatics and science,3 andthese were in
Apologists arguethat withthe issues andpersonali- strictly physical fields. During the rest of the
ties involved a vigorous and emotive style was eightiesthe development ofthis work,4 the comple-
inevitable and even necessary and that the ex- tion of Clifford's The Common Sense of the Exact
changes did not transgress the accepted canons of Sciences,5 his monumental editing of Todhunter's
contemporary expression and polemic. We pass History6 (muchofthefirstvolume4 andmost ofthe
nojudgementonthisview. 1300 pages ofthe second were written by Pearson
himself),7 his heavy teaching load and wide outside
PART I: 1889-1900 interests,8 absorbed Pearson's energy andtime; but
Development ofthe Ancestrians' Interest now there was developing that passion for seeking
knowledgeandtruthby thinking freed from dogma
InJune 1884,PearsonsucceededOlausHenricias
which was detectable in his earlier works9"10 and
Goldsmid Professor of Applied Mathematics and
whichwastobesoforciblyexpressedinhiscontem-
MechanicsatUniversityCollege,London. Hewas
porary books The Ethic of Freethought" and The
only 27. Two previous applications for chairs-
Grammar of Science'2 and consistently manifest
thatofMathematicsatQueen'sCollege,Manchester,
throughouthiswritings.
in 1881,andthatofPureMathematics at University
College, London, in 1883-had been unsuccessful. Though Pearson was at this time familiar with
AfterhehadcomedownfromKing's,wherehewas general concepts ofheredity and evolution he had
not developed any specific interest in them.13 All
this was changed bytwo events: the publication, in
1889, of Galton's Natural Inheritance;14 and the
appointment, in 1890, of Raphael Weldon to suc-
ceed Ray Lankester in the Jodrell ChairofZoology
at University College, London. These were to
have decisive and in a way complementary in-
fluences in shaping Pearson's scientific work and in
leading him into the then unborn subject ofbio-
metry.
Natural Inheritance was a landmark and had a
profound effect on the development of human
biology. It created Galton's school and 'induced
Weldon, Edgeworth, and myself[Pearson] to study
correlation and in doing so to see its immense im-
portance for many fields ofenquiry':15 specifically,
it led Pearson to statistics especially as applied to
biological processes and phenomena. Pearson was
critical of some of Galton's methods'6 but he saw
clearly the epoch-making nature of the work and
was fired with enthusiasm by it. Forty-five years
laterherecalledhisfeelings:
'In 1889 [Galton]publishedhisNaturalInheritance. In
theIntroductiontothatbookhewrites: "Thispartofthe
enquirymay besaidtorunalonga roadonahighlevel,
that affords wide views in unexpected directions, and
from which easy descents may be made to totally dif-
ferentgoals tothosewehavenowinreach." "Roadon
FIG. 1. KarlPearsonin1890 aged 32. (Reproduced by courtesy a high level", "wide views in unexpected directions",
ofTheCambridgeUniversityPressandProfessorE. S.Pearsonon "easy descents to totally different goals",-here was a
behalfoftheBiometrikaTrusteesfromPearson,E.S.(1938). Karl
Pearson: AnAppreciationofAspectsofhisLifeand Work,PlateIII. field for an adventurous roamer! . .. I interpreted that
TheUniversityPress,Cambridge.) sentence of Galton to mean that there was a category
'LawofAncestralHeredity' andtheMendelian-Ancestrian Controversy inEngland, 1889-1906 3
FIG.2. FrancisGaltonin1902aged80. (Reproducedbycourtesy
ofTheCambridge UniversityPressandProfessorE. S.Pearsonon
behalfofthe Biometrika Trustees from Pearson, K. (1930). The r I
Life,LettersandLaboursofFrancisGalton,Vol. IIIA,PlateXXXI.
TheUniversityPress,Cambridge.)
broader than causation, namely correlation, of which
causation was only the limit, and that this new concep-
tion of correlation brought psychology, anthropology, FIG. 3. Raphael Weldon. (Reproduced by courtesy of The
medicine and sociology in large parts into the field of CambridgeUniversityPressandProfessorE.S.Pearsononbehalfof
mmaethfermoatmictahle tprreeajtumdeincte.thaIttwsaosunGdalmtaotnhwemhaotifcirsstcforueledd RthaephBaieolmeWterlidkoan,Tr1u8s6t0e-e1s90f6r.omBPieoamrestorni,ka,K.5,(11-95026.)). Walter Frank
only be applied to natural phenomena under the cate-
gory ofcausation. Here for the first time was a possi- Walter Frank Raphael Weldon, Pearson's associate and
bility, Iwillnotsayacertainty,ofreachingknowledge- close friend, was born in Highgate in 1860 to Walter
as valid as physical knowledge wasthen thoughtto be Weldon and Anne (nee Cotton). His father (d. 1885)
in the field ofliving forms and above all in the field of had been a journalist before making discoveries in in-
humanconduct.'"7 dustrialchemistrywhichledtoafortuneandhiselection
as F.R.S.;19 his mother, a stern disciplinarian, strongly
Exciting as these revelations were they alone influenced his early life and character. One sister died
would notnecessarily haveledPearson to the study in 1861 aged 6. and his younger brother Dante died of
ofinheritance; he couldas easilyhaveenteredother 'apoplexy' in 1881 duringhisfirstyearatPeterhouse, to
'fields ofliving forms and human conduct'. It was sbeudfdoelnlobweerdeawvietmheinntasfaenwdwtheeekcsombpyarhaitsivmeoltyheerar.lydTehaetshes
Weldon's enthusiasm and vigour, his eagerness to ofhis parents acted onhis deeply emotionalnatureand,
haveDarwinianevolutiondemonstratedbystatistical byseedingthedoubtwhetherhewouldlivetofinishhis
inquiry (Darwin's theories were hypothetical and work, generated some ofhis remorseless drive and rest-
less energy.
had never been put to test), and (from 1891) his Afterprivate tutoring and boarding-school at Cavers-
daily contact with Pearson, which tipped the scales. ham, Weldon entered University College, London, in
As Pearson himself wrote: 'Both [Weldon and 1876, where among other subjects he studied mathe-
Pearson] were drawn independently by Galton's matics (under Henrici) and zoology (under Lankester).
Natural Inheritance . . . but of this the writer feels bTrhiedgen,exwtityheaarvhieewttroanesnfteerrriendgtmoedKiicnign'es,Cboultleigne,18C78amh-e
sure,thathisearliestcontributions tobiometrywere enrolled at St. John's and despite a period of illness
thedirectresultofWeldon's suggestions and would fromoverwork,tookafirstintheNaturalScienceTripos
never have been carried out without his inspiration in 1881. He was appointed demonstrator and, on
andenthusiasm.'18 election in 1884 as a fellow of St. John's, lecturer
in invertebrate morphology. In 1891 he went to
4 Froggatt and Nevin
University College, London, as Jodrell Professor of Professorship in Geometry33 and was appointed on
FtZhroeiodlLaoiyg,nya1cb9ru0et6,Cmhaoagviered.dontloHyOe4x6df.ioerddInfinr1o81m8930p0hneoenumamaroprnpiioeaidnoFtnlmoeGrneotnoctdeo 3thiMnakricngho1f8W91e,l3d4oannadntdheGaglrtoownicnagnibnefljuuedncgeedonfrhoims
Tebb who was his constant companion onhis frequent the Greshamsyllabuses.35'36 His first (March and
travels andwhohelpedwithmanylaborious calculations April 1891) and second (November 1891 to May
and breeding experiments. There were no children. 1892) lecture courses dealt little with biological
WmealndyosnciwenatsifeilcescotceidetFi.esR..S.Hiins1w8o9r0kawnadswcalsosheolynoluirnkeeddbtyo problems; in the third (November 1892 to May
that of Pearson and together as 'Galton's lieutenants' 1893) the application ofprobability theory was de-
theymainlyfashionedthebiometricschool.20 veloped; while by the fourth and last37 series
(November 1893 to May 1894) he had turned
During the eighties while Pearson laboured at strongly to the consideration of methods required
applied mathematics in London, Weldon embarked forthesolutionofevolutionaryproblems.38
on his life work: testing Darwinian views ofevolu- Pearson's first practical involvement was in late
tion. He divided his time between teaching at 1892, and was due entirely to Weldon. In the
Cambridge, field work in Europe, the Channel summerof1891 theWeldons studied thePlymouth
Islands,andtheCaribbean,and(from 1888) experi- Sound shore crab (Carcinus moenas), and at Easter
mentation at the Marine Biological Laboratory in 1892 the Naples race ofthe same species. Eleven
Plymouth. His early papers show an orthodox parameters of the carapace (shell) in 2000 crabs
approach towards elucidating Darwinian principles were measured and in only one instance (frontal
by strict morphological studies, but later in the breadth in the Naples race) was the distribution
decade he came to realize the limitations of these skew.39 This curve was bimodal-'double
methods-especially in that they largely neglected humped' was Weldon's term-and Weldon was
'differences between individual members ofa race able to show that it could be a composite of two
or species '-and increasingly 'his thoughts were normal distributions. He was exhuberant at this
distinctly turning from morphology to problems in evidenceofdimorphisminwhatwascataloguedasa
variation and correlation'.22 Natural Inheritance single 'type', and in a letter to Galton concluded
introduced Weldon to a method of measuring 'either Naples is the meeting point oftwo distinct
associationand'fromthisbookas sourcesprings ... racesofcrabs,ora"sport"isinprocessofestablish-
the whole of the biometric movement which so ment. You have so often spoken of this kind of
changed the course ofhis lifeandwork'.23 curveas certaintooccurthat I am glad to send you
Weldon saw immediately the importance of the first case which I have found.'40 The same
Galton's work on frequency distributions and cor- dayhewrotetoPearson: 'Inthelastfewevenings I
relation to the study of evolution-frequency of have wrestled with a double humped curve, and
deviations from the type could now be described have overthrown it. Enclosed is the diagram and
and organic associations measured-and he at once [numerical results].... If you scoff at this I shall
set to use these tools to fashion answers to those never forgive you.'4' Pearson did not scoff: in-
problems which seemed insoluble from morpho- stead he rose to the challenge. He confirmed the
logical or embryological inquiry. In Plymouth he validityofWeldon's inference oftwo normal popu-
started his monumental series ofmeasurements on lationscompoundingthe'doublehumped'curve,re-
the common shrimp (Crangon vulgaris) which were calculated the statistics for Weldon's paper,39 and
to confirm the findings Galton had at first antici- dealtforthefirsttimewiththedissectionofa distri-
pated,24 then developed,25-27 and finally more bution assumed to be a composite of two or more
fully stated'4 for man, viz. that many organic normal distributions.42 This paperwas thefirstof
measurements are normally distributed28 and (in a Pearson's great series 'Mathematical contributions
second paper) that the 'degree of correlation' be- to the theory ofevolution',43 and heralded the de-
tween two organs is approximately the same for velopment of that rigorous analytical approach
each local race of the species and the regressions which was to characterize the biometric school and
are linear.29 The first paper was refereed favour- allow them to challenge accepted principles and
ably by Galton30 with whom Weldon also corres- tenets. Weldon expressed this view exactly: 'It
ponded on the second before its publication.3' At cannot be too strongly urged that the problem of
this time Weldon did not know Pearson;32 they animal evolution is essentially a statistical problem.
first met when Weldon took up the Jodrell Chair ... These[problems]areallquestionsofarithmetic;
earlyin 1891. and when we know the numerical answers to these
On 18November 1890,beforeWeldon's arrivalat questionsforanumberofspecies weshallknowthe
UniversityCollege,PearsonappliedfortheGresham direction and the rate ofchange in these species at
'Law ofAncestralHeredity' and the Mendelian-Ancestrian Controversy in England, 1889-1906 5
the present day-a knowledge which is the only share decreasing step-by-step in a geometrical ratio
legitimate basis for speculations as to their past with great rapidity.' Despite its misstatement-
historyandfuturefate.'39 Galton refers, by an 'obvious oversight',48 to
This year-1893-marked a major turning point 'father', 'grandfather' etc., instead of to 'mid-
inPearson's career: hehadideasandheintendedto parent', 'mid-grandparent', etc.-these views on
work them out in practice. This required more ancestral contributions represent the first, though
than Weldon's mere 'arithmetic': it required an primitive, enunciation of the 'law of ancestral
advanced theory of statistics and this Pearson heredity'-termedbelow 'theancestrallaw'.
foundedinseveral series ofpapers overthenextde- At this time Galton adduced no worthwhile
cade. His purpose was to develop statistical tools data for the law's validity; his articles contained
for studying, mainly though not exclusively, pro- simplylists ofdistinguished menwho had also able
blems of evolution and heredity: and we can relatives. On what evidence then did he shapehis
attribute to this pioneering his frequent concern ideas? There is no unequivocal answer. Un-
more with the technical aspects ofthe solutions he doubtedly his postulation of the geometric series
derived and their valid application than with the 2, T, 8 ... could have been reached from mathe-
interpretation and theoretical possibilities of the matical development of Darwin's 'provisional
results which flowed from them, or indeed even hypothesis of pangenesis'49 (the series would run
with the quality of the source data and the funda- r+or+sr..., with r= I and accepting-con-
mentals ofthe phenomena whichgenerated them- trary to the theory-that the individual whose
his main, evenifrelative, failings. characteristics were being predicted showed no
Two immediate objectives stand out: (i) the 'unexplained' variation ofhis own): but his papers
testingofthe adequacy ofGalton's 'lawofancestral were drafted four years before the promulgation of
heredity'44-whichledtoamoreaccuratestatement Darwin'spangenesistheory46andatleastsixmonths
of its assumptions; and (ii) the development of before Darwin's preparation ofthe relevant MS.50
methodsbywhichtomeasurevariabilityandcorrela- This suggests that Galton reached his theory inde-
tion and the influence on these ofvarious types of pendently:51 ifsoitcanbespeculatedthathedidso
selection, andtousethese ondatafrompopulations as a simple corollary of 'blending inheritance' (i.e.
under natural conditions rather than from experi- the hereditary mixing ofpaternal and maternal ele-
ments on individuals or species. Both of these ments so that characters in the offspring would be
struck at the heart ofthe evolutionary debate, viz. mid-way between those in the parents) which had
howingeneraldoanimals varyandwhatcauses and then been accepted as axiomatic for organic nature
maintains this variation, and in what way, under since the eighteenth century.52 In any event the
what 'laws',andbywhatmechanisms arecharacters guarded enthusiasm with which he first welcomed
inherited? The steps taken up to 1900 towards pangenesis,53 and which owed more to his esteem
achievingthesetwoobjectiveswillnowbedescribed. for Darwin than to the merits of the theory, was
short-lived,yethisbeliefinthewideapplicabilityof
The Law ofAncestral Heredity the ancestral law remained undiminished for the
Development by Galton. During the late rest of his life.54 A few years after his initial
eighteen-fifties Galton's interests turnedincreasing- papers47 Galtonwastopromulgatehisphysiological
ly from the study ofman's environment (he was a theory ofinheritance basedonhis concept of'stirp'
well-knownexplorerandgeographer)tothestudyof (stirpes=a root), and this offered a theoretical basis
man himself: 'About the time ofthe appearance of fortheancestrallawbyvalidatingthechoice,forthe
Darwin's Origin of Species [1859] I had begun to partitioningofthe'ancestralheritage',ofageometric
interest myself in the Human side of Geography series whichmust sumtounity.55 Itseems atleast
andwas inawaypreparedtoappreciatehis view.'45 possible that ideas whichwere to lead to 'stirp' as a
Late in 186446 he wrote two papers entitled physiological explanation for the phenomenon of
'Heredity talent and character',47 in which he 'blending' were germinating in his mind as early as
claimed that a wide range of'mental aptitudes' and the 1865 papers.47
components of'general intellectual power' could be The physiological theory of 'stirp' and his em-
inherited just as could physical characteristics. pirical acceptance of ancestral contribution to the
Inthe secondpaperhestated: 'Theshareamanre- phenotype led Galton to propound his 'law': what
tains in the constitution ofhis remote descendants was now neededwere data and techniques for their
is inconceivably small. The father transmits, on analysis, particularly a method for measuring de-
an average, one-half ofhis nature, the grandfather grees ofresemblance in quantitative characteristics.
one-fourth, the great-grandfather one-eighth; the He developed for this purpose regression, then
6 Froggatt and Nevin
correlation theory, and applied the principles first generation; and he reached, by grossly invalid
to size of parental and offspring sweet-pea seed,56 methods,51'66 values for the diminution at each
then,afteraperiodofeightyears ofdoubts astothe generation of4 on assumptions under (a) and 1- on
underlying assumptions, to such data from man as those under (b). He concluded: 'These values
stature,57 eye-colour,58 disease, the 'artistic faculty', differ but slightly from i-, and their mean is closely
good and bad temper, and others, most collected i,sowemayfairlyacceptthatresult[4].'26,68 Then,
fromhis 'Anthropometric Laboratory',59 'Recordof without comment he blandly chose the geometrical
Family Faculties' (R.F.F.),60 and 'Life History case (b) and concluded: 'Hence the influence, pure
Album'6' andmanyofwhichhebroughttogetherin and simple, ofthemid-parent may betakenas i, of
NaturalInheritance.14 The ancestral lawis set out the mid-grandparent 1, of the mid-greatgrand-
fully, though tentatively, for the first time in parent , and so on. That ofthe individual parent
1885;25 the results are summarized, the law re- would therefore be 1, oftheindividual grandparent
formulated'withhesitation',andaproofadducedin -j-6, ofanindividual inthenextgeneration 1-,andso
1889;14 and, as 'a statistical law of heredity that on26(Fig.5,seep. 13). He hadfinallyreachedthe
appears to be universally applicable to bisexual answerhehadfirst guessed, then theorized must be
descent', confidently presented in 1897.62 The true,twentyyearsbefore! Weshallseelaterthathis
validity ofthe assumptions has been studied in de- preference for the geometric series was wise even if
tail by Pearson63-though his treatment is very 'it was inspiration rather than correct reasoning
difficult to follow-and recently summarized by whichledhimtoit',69andthatbyitschoicehegave
Swinburne;5' wegiveonlyaresumehere. astartingpointforPearsonto develop thetheoryof
Galton's data on stature showed the meanheight multiple regression.
ofoffspringtobeclosertothegenerationmeanthan Galton then turned from the 'blended' charac-
wasthemeanparentalheighttoitsgenerationmean: teristic-stature-toconsidertheapplicabilityofthe
in his expressive language the (average) offspring ancestral law to traits considered to be transmitted
was 'more mediocre' or 'less exceptional' than the under 'alternative' inheritance, in the first instance
(average) mid-parent.63 He estimated this 'filial to eye-colour.70 Heamended theoriginal assump-
regression' as j-'thatistosay ... theproportionin tions andnowhypothesizedthattheancestrywould
which the Son is, on average, less exceptional [as contribute the postulated proportions not of the
regards height] than his Mid-Parent'64-and calcu- character, e.g. stature in the (average) individual
lated other regression coefficients of I for mid- descendant, butofthe character, viz. eye-colour, in
parent on offspring and for offspring onone parent, the pooled offspring of each generation, i.e. a
i for brother on brother,65 and, by multiplying ap- parent's eye-colour would completely determine on
propriate coefficients, reached 'implied' (but in- average that of 4 of his or her offspring, that of a
valid)66 values for the relationships between more grandparent -16 etc.-'reversion' rather than 're-
distant kin. gression'. He wrote: 'But ifone parent has a light
Galton then tried to deduce the separate contri- eye-colour and the other a dark eye-colour, the
butions of each ancestor to the deviation from the childrenwillbepartlylightandpartlydark,andnot
mean of the offspring's phenotype.67 By dubious medium.... The blending of stature is due to its
mathematics he reached an initial solution that the being the aggregate of the quasi-independent in-
'total bequeathable property' toanindividual is heritances ofmany separate parts while eye-colour
D 1+1+1+. ) 3D~ UapspienagrsthteoRb.eF.Fm.ucdhataleassndvairnigoeunsioiuns imtestohroidgisn.f'o5r8
'rateably assigning' intermediate tints, Galton
where D is the 'peculiarity' (deviation from the reached expected ratios of dark- and light-eyed
populationmean) ofthemid-parent and, as initially types to compare with those observed. Concor-
expressed,25'26theexpansionrepresents 'the sumof dance was good-inPearson's view 'remarkable . .
the deviates ofall the mid-generations that contri- consideringthecontradictoryassumptions onwhich.
butetotheheritageoftheoffspring'. Hethencon- they [the expected ratios] are based'7 -and Galton
sidered whether this 'bequeathable property' concluded: '.. . we may with some confidence ex-
diminishes in passage through generations, a pro- pect that the law by which these hereditary contri-
blemgermanetohisphysiological conceptof'stirp'. butions are governed will be widely and perhaps
He examined two extreme cases: (a) where there is universallyapplicable'.58
no diminution-in his nomenclature 'the bequests Confirmednowinhisfaithintheancestrallawfor
by the various generations [are] equally taxed',68 bothqualitativeandscalarcharacters Galtonturned
and (b) where it wanes geometrically through each to examine its universality. After abortive efforts
'Law ofAncestralHeredity' and the Mendelian-Ancestrian Controversy in England, 1889-1906 7
to obtain (with F. Merrifield) data from breeding series 'Mathematical contributions to the theory of
the Purple Thorn moth (Silenia illustraria)72 and evolution', Pearson gave inter alia the theory of
'taking some steps' to experiment with mice,73 he higher-order correlation8"-introducing the ex-
usedthecoat-colourofSirEverettMillais' pedigree pression 'coefficient ofdouble correlation' ('partial'
stock ofBasset Hounds.62'74 There were onlytwo and 'multiple' correlation were first developed by
phenotypes-'tricolour' and 'non-tricolour'-and Yule);82.83 evaluated, on Galton's R.F.F. data,
classification was known often for four complete partial regressions ofoffspring on each parent; and
generations. Accepting now the law as applicable, considerably extended his collateral studies of
i.e. thevalidityoftheregressioncoefficients, Galton heredity (see below) by considering types of selec-
again obtained close agreement of expected with tion, assortative mating, and 'panmixia'. He also
observed ratios and took this as indicative of the misinterpreted Galtoninaway84thatledhimtothe
universality ofthe law, at least in the animal king- paradoxical conclusion that 'a knowledge of the
dom. Pearsonwashardlylessenthusiastic.75 Not ancestry beyond the parents in no way alters our
all, however, echoed these two, particularly hybri- judgement as to the size ofthe organ or degree of
dists, but Galton was quick to point out that the characteristic probableintheoffspring'.85
ancestrallawappliedonlyto 'offspringofparents of After a further, preliminary article,86 Pearson
the same variety ... in short it has nothing to do consideredtheancestral law in a basic paper87 sub-
withhybridism'.76 This distinction was important headed 'A New Year's greeting to Francis Galton,
and the ancestrians made much of it after 1900: January 1, 1898'.88 In this Pearson propounded
Mendel's original paper after all was entitled whathe now christened 'Galton's Law ofAncestral
'Experiments in Plant Hybridisation'. Heredity', in the form of the multiple regression
Between 1897 and 1900 Galton wrote several equationofoffspring on 'mid-parental' ancestry
short papers germane to the ancestral law;76-78 but
thecentreofthestagewasnowtobesurrenderedto = 9(axl)+4- X2) + y-x)3...
Pearsonwho,inhistreatmentofGalton'sideas,was
to develop multipleregressiontheoryandintroduce where xo is the predicted deviation ofan offspring
enormous mathematical complications into the fromthe generation mean, x, is a linear function of
primitivehypotheses. the deviation ofthe 'mid-parent' from that genera-
tion mean, x2 similarly for the 'mid-grandparent',
Modification by Pearson. Some ambiguities and so on, andora,al... . the standard deviations of
exist in Galton's writings as to whether he was the appropriate generations of the offspring, and
setting out exclusively a law of phenotypic resem- from this deduced theoretical values for various re-
blanceoroneestablishingaphysiologicalhypothesis gression and correlation coefficients between kin.
of inheritance.5' Probably he was doing both. He also generalized the geometric series of partial
There was no doubt, however, inPearson's mindas regression coefficients thus raising the parental
tohisowninterpretation. UnlikeGaltonhehadno correlations, tested observation (from Galton's
preconceived ideas about inheritance; to him stature data) against these expectations, evaluated
Galton's law was 'not a biological hypothesis, but fraternal correlations, and examined the effect on
themathematicalexpressionofstatisticalvariates... the constants of 'ancestral taxation' and ofchanges
[which] can be applied .., to many biological hy- in offspring variability through generations. He
potheses';79 andhenowsetouttoputthetheoryon sweepingly concluded: 'If Darwinian evolution be
a more rigorous footing and to establish the modi- natural selection combined with heredity, then the
fications necessary under conditions crucial to [ancestral law] must prove almost as epoch-making
various forms of 'selection'. He recognized the tothebiologistasthelawofgravitationtotheastro-
imperfections in Galton's derivation, but he was nomer'; andagain: 'Ifeitherthat [Galton's] law, or
unconcerned: his philosophy convincedhimthatall its suggested modification be substantially correct,
phenomena could be brought under statistically they embrace the whole theory ofheredity. They
expressed laws and he was certain that Galton's bring into one simple statement an immense range
geometric assumption was correct even though the offacts,thusfulfillingthefundamentalpurposeofa
regression constants (2, 4----) may not stand test. great law of nature.'87 Here was the demonstra-
He would fashion the absolute answers from tion ofthe truth ofhis rationalist philosophy-that
Galton's crudeblueprint. there existed great universal natural laws which
Pearson's direct involvement dates from 1896,80 couldbeexpressedmathematicallyandwhichcould
theyearbeforeGalton's definitiveenunciationofhis ultimatelybebroughtintoasinglesystem. Hehad
ancestral law.62 In this paper,80 the third in the written earlier: 'Many of our so-called laws are
8 Froggatt and Nevin
merelyempirical laws,theresultofobservation;but 'Till we know what class ofcharacters blend, and what
theprogress ofknowledge seems tometopointto a class of characters is mutually exclusive, we have not
within our cognizance the veriest outlines ofthepheno-
far distant time where all finite things of the uni- mena whichthe inventors ofplasmicmechanisms are in
verse shall be shown to be united by law, and that muchhastetoaccountfor.... Thenumericallawsforthe
lawitselfto be the onlypossible law which thought intensity of inheritance must first be discovered from
can conceive.'89 Small wonder he was later dis- wide observation before plasmic mechanics can be any-
thingbutthepuresthypotheticalspeculation.'97
inclined to abandon belief in these 'ancestrian
principles'. Thesewordswerewrittenin 1899.98 Ontheeve
Pearson saw clearly the line of inquiry he must ofthe 'rediscovery' they show that Pearson, and in
now follow. He knew that the ancestral formula factalsoWeldon,werenotweddedtoanyparticular
would need revision when selection, assortative biological theory of inheritance. This should be
mating, and differential fertility were taken into borne in mind when considering the basis of the
account, andheclearly signalledhis intentiontoin- Mendelian-ancestrian controversies which were
vestigate such effects further.90 Thus the road shortly toerupt.
ahead joined those from his other work on inheri-
tance (see below) to form a commonhighway along
whichhewas travellingin 1900. Beforethis,how- Selection and Variability
ever, there was one outstanding problem to be WeldonandtheEvolutionCommitteeofthe
tackled. Pearson had also been critical ofGalton's Royal Society. We have seen that Pearson was
handling of qualitative traits58'62 and he now first drawn to problems in evolution by analysing
settledtodevisemoreappropriatemethods.9' This Weldon's'doublehumped'curve42andthatWeldon
led him at first to the fourfold table and 'tetra- had grasped immediately the importance of being
choric r'92 which he used to measure kinship re- ableto demonstrate intraspecies sub-types as apre-
semblance on assumptions of alternative ('exclu- liminarytoidentifyingfactors inselection.39 Only
sive') inheritance,9' and then to a more general threeweeksafterthesepapers werepresented atthe
treatment of 'reversion', i.e. the phenomenon Royal Society (16 November 1893), Weldon
where, for the character in question, the offspring characteristically took the initiative in trying to
resembles completely one or other parent or 're- broaden the experimental scope: he arranged a
verts' to a more distant ancestor, but no inter- meeting with Galton and R. Meldola to discuss
mediate types occur.93 He was able to restate, for possible Royal Society sponsorship for a joint pro-
suchtraits, Galton's crudelawintheform ofa 'law ject into heredity.99 They petitioned the Royal
ofreversion', whichhe carefully distinguished from Society to establish a committee 'forthe purpose of
thetrueancestrallaw. conducting statistical inquiries into the variability
'Inbothcases [blendedandalternativeinheritance]94 we or organisms','00 and this committee-'The Com-
may speak of a law of ancestral heredity, but the first mittee for Conducting Statistical Enquiries into the
predicts the probable character of the individual pro- MeasurableCharacteristicsofPlantsandAnimals'-
duced by a given ancestry, while the second tells us the was constituted on 18 January 1894 with Galton as
percentages ofthe total offspring which, on the average,
revert to each ancestral type. I . . . term the first the chairman, Weldon as secretary, and a grant of150.
lawofancestralheredity,itappliestoblendedinheritance; Ithelditsfirstmeetingon25January.'0'
the second I term the law ofreversion, it applies to ex- Weldon had already started work on selective
clusive inheritance.... In the former case every ances-
death-rates inPlymouth Sound shore crabs: testing
tor contributes, it may be a very small share of his
charactertoeachoffspring; inthelatter caseeachances- orthodoxDarwinianselectionbutbynon-Darwinian
tor contributes the full intensity ofhis character to his methods. Apart from measurements on herring
share, and it may be an indefinitely small share, ofthe and the ox-eyed daisy-which were never pub-
offspring. These two conceptions, summed up in the lished'02-these crab results were the first under-
termsregressionandreversion,oughttobekeptapart.'95
taken forthe committee and comprised its first two
Both these 'laws', despite heavy qualifications,96 Reports.'03"104 These Reports are important in
assume some mechanism of(geometrically waning) several ways: they formulated 'the whole range of
ancestral dilution; in fact the seeming antithesis of problems which must be dealt with biometrically
Mendelismasfirstpresented. Pearson,thoughnot before the principle ofselection can be raised from
Galton or Weldon, was not unduly concerned as to hypothesis to law';105 they raisedwhatwasthethen
what this mechanism might be: first establish the novel idea that Darwinian theory was amenable to
statistical relationships and then see what physio- statistical testing; they were the font from which
logical hypothesis ofinheritance accords with them sprangmostoftheworkontheinfluenceofselection
best. He concluded: on variability and, its corollary, the influence of
'Law ofAncestralHeredity' and the Mendelian-Ancestrian Controversy in England, 1889-1906 9
selection during growth; and they stimulated chairman of committee. They were not solely
Pearson: 'I realise also how much ofmy own work 'controversial', they were also highly disparaging of
floweddirectlyfromthesuggestiveness ofthispaper thecommitteeforendorsingtheworkandcarriedan
[the first Report]."06 implied criticism of Galton himself."9 Most,
These papers were generally unfavourably re- thoughnotall,'20werewrittenbyBatesonandthese
ceived by biologists, particularly by William alone'occupiedanentireboxinWeldon'spapers'.'2'
Bateson who was to prove the most influential and Galton had always respected Weldon and felt
outspoken critic of the biometric school and the intuitivelycompelledtoprotecthimagainst Bateson
ancestrian ideas. Weldon had suggested that (a) for whom he had little personal sympathy. Intel-
'sports' (recognizable mutations) only contributed lectually, however, hewasuncommittedastooneor
to evolution in exceptional circumstances, selection theother: thoughheagreedwithmanyofWeldon's
acting on continuous variation being the more ideas he did not care for the minor role in which
likelysource ofspecific modification, and (b) evolu- Weldon cast 'sports' inthe evolutionary process;'22
tion and selection were mass phenomena to be andhehadwelcomedBateson's book"0 for'bearing
studied by appropriate statistical methods.104 the happy phrase in its title of "discontinuous
(a) Represented more or less orthodox (and variation". . . it does not seem to me by any means
accepted) Darwin-Wallace views though they were socertainas is commonly supposed bythescientific
anathema to those who, like Bateson, held that any men at the present time [1894] that our evolution
advantage (or disadvantage) accompanying slight from a brute ancestry was through a series of
variations must be themselves slight and relatively severally imperceptible advances'.'23 Hetherefore
unimportantinevolutioncomparedtothemuchless fairly sought conciliation-first, by appointing (in
frequent but more variant 'sport'. However (b), if 1896) Pearson to the committee to add an authori-
not a revolutionary concept, introduced into the tativestatisticalvoice,'24 and second, bypersuading
evolutionary debateamethodology withwhichvery Weldon to agree to Bateson himself becoming a
fewbiologists werefamiliar andforwhichmanyfelt member.'25 This also furthered his own longer-
actualrepugnance. Onehas onlytoreadWeldon's term objective-to co-ordinate, then integrate, all
Report'03 with its substantial mathematics and sta- work on evolution (horticultural, zoological, and
tistics to realize this: even today's numerically human) through a widely-based committee, and
trained biologist would find parts he little under- this committee must in practice include Weldon,
stood. Many biologists accordingly used some Pearson,andBateson.'26 Consequently,inJanuary
imperfections inWeldon'sarguments andtreatment 1897, nine 'zoologists and breeders', including
to discredit his ill-understood approach, and ifthey Bateson,'27 'someofwhomhadsmalldesiretoassist
were followers of Bateson they also used them to quantitative methods of research','28 were elected,
discredit Weldon's ideas. A gulf now opened be- and laterthat yearthe committee was reconstituted
tween on the one hand the 'biologist'"07 and on the as the 'Evolution (Plants and Animals) Commit-
other the 'biometrician' and 'ancestrian', and this tee'.'29 Suchdevelopmentwasprobablyinevitable
was soon to be deepened by the personal animosity given the committee's need to encompass disparate
which, already seeded, rapidly developed between views; but the decision was coldly received by
Weldon and Bateson-formerly close friends, now Pearson and Weldon nonetheless. Harmony and
increasinglybitterenemies.'08 Thecourse ofthese the biometricians' dominance were sacrificed: 'the
controversies and enmities are examined later but old statistical object is dropped . .. and the whole
it is convenient to record here that in the previous scheme of breeding and enquiry by circulars to
year (1894) Weldon had annoyed Bateson by ad- breeders, comes into being'."30 Pearson promptly
versely reviewing'l09 the critical, though not the ceased to attend and later resigned"' along with
descriptive content, of Bateson's great book Weldon and others on 25 January 1900. Mostly
Materialsfor the StudyofVariation"0 (inwhichthe out ofduty Galton stayed on until later in the year.
author advocated the more or less exclusive im- After this 'capture' the committee, under F. D.
portance to evolution of discontinuity and variant Godman, became very largely a vehicle for the
forms)andwithothers"'"-14hadattackedBateson's work and views ofBateson and was stigmatized by
views'15"'16 on the origin of the cultivated Cine- Pearsonas'merelyabodyforrunningMendelism'."32
raria.1"7
While Galton was struggling to reconcile the
Galton was now placed in a difficult position. irreconcilable,Weldoncontinuedhisworkoncrabs;
The 'folios' of written criticism of Weldon's but his Report was never published.'33 Then a
Reports, 'purely controversial... [and] some even newforumpresented. In1898hebecamePresident
eighteen sheets long',"18 were addressed to him as ofthe Zoological Section oftheBritishAssociation,
10 Froggatt and Nevin
and in his Address'34 considered the question (a) Skew curves. Following his analysis of
of measurable natural selection. He showed that Weldon's'doublehumped'curvePearsonwasdrawn
compared to crabs with larger frontal breadth rela- to consider the general theory offrequency curves
ative to shell length, those with smaller breadth and not just as they related to problems in growth
survived longer in polluted Plymouth Sound water, and evolution. His first paper42 had dealt with
though not in fresh water, and he ascribed this to dissectionofa distributionassumedto bea mixture
theirmore efficient waterfiltrationthroughthegill- ofnormal curves, i.e. a composite ofseveral known
chambers.135 This delighted him since it seem- homogeneous populations-what he called 'com-
ingly demonstrated a basic Darwinian hypothesis, poundness'; his second paper'47 dealt with asym-
viz.specificmodificationbyagradualprocessresult- metrical distributions generated from homogeneous
ing from the 'accumulation of innumerable slight material-true'skewness'.'48 BothheandWeldon
variations, each good for the original possessor'.'36 recognized the importance of establishing true
Hewas disappointedthatitattracted onlymoderate skewness, and Weldon for one hoped that ifa dis-
support: the idea was too prevalent that Darwinian tribution followed a skew binomial, viz. (p+q)n
theorywasincapableofstatisticaltestingandtosug- with p#q, the degree of asymmetry would give a
gestotherwise excited suspicionandevenhostility. measure ofthe difference between p and q-in his
In February 1899 Weldon moved to Oxford: interpretation this would be the tendency of the
from thenapart from correspondence'37 his contact characteristictovaryinonedirectionratherthanthe
with Pearson was to be mainly through their joint other. He argued that in the event it would be
editorship of Biometrika and their mutual working possibletovisualizeafinitenumberofcauses acting
holidays, often with Galton,'38 which were to pro- collectively to produce the results, thus justifying
duce and nurture many ideas, three papers'39-14" his views ofsmall continuous variations controlling
and at least one joint review.'42 Their lives con- evolution. As early as April 1893 he was writing
tinued to the end in perfect harmony'43 and their toPearsononthispoint.'49
championing ofthebiometricmethodunitedandin Inthispaper'47andlatersupplements'50 Pearson
style complementary-'Weldon with his dashing developed his wonderfully flexible system of fre-
cavalry charges into the foe, Pearson with his quency curves (Types I-XI)-derived as solutions
heavier artillery'.'44 Such understanding and of a simple differential equation as limits either to
solidarity were to be important in the Mendelian the binomial orthehypergeometrical series-which
controversies ahead. have since proved so successful in graduating data
from widely disparate sources,'5' and which were
later shown (Pearson was unaware of this at the
Pearson's contribution. While Weldon was time) to represent, under limiting conditions, the
working with crabs, Pearson was following the sampling distributions of many common statistics
logical lines ofstatistical inquiry whichflowed from used in normal sampling theory.'52 To establish
his first involvement in Weldon's work:42 the their generality, Pearson tested these curves against
measurement of the factors that influence intra- a wide range ofbiological, medical, economic, and
racial selection and variability. Three streams, other data and was sanguine as to the results:
often confluent, canbeidentified: (a)theanalysis of whereasWeldonsawonlyevolution,Pearsonsought
frequency distributions and the development ofthe general obedience ofall phenomena to his models.
theory ofskew curves; (b) the study ofsuch funda- (Thispaper'47alsolaidthegroundworkformuchof
mental factors ofnatural selection as reproduction Pearson's appliedstatisticalworkinotherfields, but
andfertility,selectivedeath-ratesandlongevity;and these neednot concern us here.) Pearson also saw
(c) the use of the new correlation and regression another, more technical, result of skewness, viz.
techniques to study variability especially as it bore that if the distributions generating the correlation
on problems of selection and evolution. Each of coefficients were skew rather than normal, then the
theseflowedonafter 1900-thefirstuntiltheendof 'theory of correlation as developed by Galton and
Pearson's life. Nevertheless, 1900 is a realturning Dickson requires very considerable modifica-
point: it saw the 'rediscovery', the foundation of tions'.'53 He immediately pursued this line of
Biometrika (see later), the publication ofthe second inquiry80"154155 which he considered crucial to his
edition of The Grammar of Science'45-which con- evolutionary studies, because only by knowing the
tainstwoextrachaptersofthedistillationofPearson's sampling variation of the statistics obtained could
views on evolution-andgenerallyit 'marks aphase reliance be placed on conclusions drawn from re-
in the history of biometry'.146 These are now sults using correlational methods. If at times he
briefly discussed. allowed what then appeared as minor numerical