certainty and circularity in evolutionary taxonomy- by david l. hull. evolution, vol. 21, no. 1...

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Certainty and Circularity in Evolutionary TaxonomyAuthor(s): David L. HullSource: Evolution, Vol. 21, No. 1 (Mar., 1967), pp. 174-189Published by: Society for the Study of EvolutionStable URL: http://www.jstor.org/stable/2406751.

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2/17

CERTAINTY

AND CIRCULARITY

IN EVOLUTIONARY TAXONOMY

DAVID L. HULL

Department f Philosophy,

University f Wisconsin-Milwaukee,

Milwaukee, Wisconsin 3201

Received

October 11, 1965

After considerable eriod

of uncritical

acceptance,

he

principles

nd procedures

of evolutionary

axonomy

ave been

sub-

jected to

careful crutiny

nd, none too

surprisingly,

ave been

found not

com-

pletely dequateor totally

ree rom ague-

ness and ambiguity. ne of the more eri-

ous

criticisms

urrently

opular

s that

vo-

lutionary easoning

s

inherently

ircular.

For example, obertR.

Sokal and

P.

H.

A.

Sneath 1963) say:

"In recent

years

three comprehensive nalytic

studies

of

systematicprinciples

have

been

pub-

lished

in books

by

Hennig (1950),

Reinane

(1956),

and Simpson (1961)....

"All

three

authors

mentioned

above are

fully

aware of the

dilemma

of

circular reasoning

n-

herent in systematic procedure. They are not

satisfiedwith

solutionsbased on

'groping.'

Simp-

son

(1961)

thinks

that taxonomy

is an

evolu-

tionary

science,

and

he

attempts

to outline

a

series

of

phylogenetic rinciples

on the basis of

which taxonomic evidence

should be

examined

to

yield

evolutionary nterpretations

nd classifi-

cations.

We

shall examine

these

principles

n

de-

tail

in

Chapter

8.

However,

Simpson

nowhere

n

his book

is able to present a logical and

con-

sistentdefense

of

the

circularity

f

reasoning

n-

herent n such

procedures.By calling the process

of classification n art, ratherthan a science,he

definesthe

problem

out of

existence.

"Hennig (1950)

describesthe dilemma

n

even

greaterdetail.

He defendsthe circularity f

rea-

soning by the method

of reciprocal llumination.'

By

this

he means

that some

light

s thrown

from

one

source of

logical

illumination nto a natural

situation

kindling another, brighter ight

in the

latter,which

in turn will throw added illumina-

tion onto the first source. Thus, in a

self-

reinforcing,

ositive feedback

type of analysis,

the

relationships

nder

study are eventually

lari-

fied. Hennig feels that phylogenetic elationships

are

the entity

of

systematics

whose

parts

consist

of

morphological, ecological,

physiological, and

zoogeographic

similarities. Each of these

parts

mirrors

phylogenetic elationships,

which are

to

be investigated

by the method of reciprocal

il-

lumination.

But we cannot

see how the principle

of reciDrocal llumination iffers rom the much-

condemned vertical

construction

of

hypothesis

upon hypothesis.

"Remane (1956),

in

spite

of his

fundamentally

phylogenetic

orientation,has also realized that

phylogenetic easoning cannot serve

as the basis

for

erecting

natural

system.

He

similarly ejects

affinitybased

on

a

few

characters)

as

the

basis

of

a natural

classification.

He

considers

hat

while

both of these approaches enteron occasion into

the

techniques practiced by 'good systematists,'

the exclusive

application

of

only one of

them is

likely to lead to misclassification.

Affinity r re-

semblancewhen based on one or a

few characters

can

lead the systematist stray,

Remane claims,

as

he

would be

too easily deceived by

chance con-

vergences

resulting from poor sampling of the

characters.

Remane attempts escape from the

circulus

vitiosus by basing his taxonomyon non-

phylogenetic

riteria of homology."

The charge of vicious circularity as

been commonthroughout he

history f

taxonomy.

For example,Darwin (1859)

accused

his

predecessors nd

contempo-

raries of

arguing n a circle

when they

claimed

that mportant rgansnevervary

and

decided

whichorganswere

mportant

by which

did

not vary. Sachs

(1890) re-

peated the

charge nd directedt specifi-

cally at

Linnaeus. It was only

matter f

time ntil heevolutionistshemselves ere

accused of

reasoning

n

vicious

circles.

Thompson 1952) seemsto

have been the

first o do so. The charge,

however, as

been

made

mostoften

nd

most

forcefully

by

A.

J.

Cain.

Initially

t

was

directed

against Cuvier;

Darwin was

expressly

exempted

1959a).

Cuvier

lassified

iving

organisms

y

means

of

properties

rdered

according

o

their

presumed

hysiological

importance.Cain allegesthat Cuvierde-

cided

which

roperties

ere

physiologically

important

y observingwhich

characters

were constant

n a

classification

lready

constructed

ccording

o overall

imilarity,

making

phenetic lassification

undamen-

EVOLUTION 21: 174-189. March, 1967

174

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3/17

CERTAINTY

AND CIRCULARITY

IN TAXONOMY

175

tal.

Darwin,on

the

other

hand, proposed

that iving

rganisms

e classified

ymeans

ofproperties

rderedccording

o

their re-

sumedphyletic mportance. n principle

which

roperties

re

phyletically

mportant

and, hence, ndicative

f

evolutionary

e-

scent

can be

discovered

ndependently

f

the

constancy

f

characters

n

any pre-

established

classification.

Cain

(1962a)

summarizes

is views s

follows:

"By equating

taxonomic with

ancestral

rela-

tionship, arwin,

ike Cuvier, dopted

two criteria

of the importance

of

characters.

On the

one

hand, he said that those characterscommon

to

large groups

(i.e.

natural

groups,

although

he

did

not

say

so

explicitly)

are

more

important

than

those common

to groups

containing ittle

diversity.

This is

always

right

if

only

natural

groups

are to be

made. But

he also said

(a) that

those least likely to

have

been modified

n rela-

tion to

particular

modes of life will

be more im-

portant

in showing ancestral

affinity,

nd (b)

that they can be recognized

because

they

will be

the

most constant

ones within

a

natural

group.

But this

assumes that natural groups

are always

phyletic

or, in

other terms, that

convergence

s

never so great as to obscure or outweigh an-

cestral

resemblance ven

in

poorly

known

groups.

He did

not commit he earlier

error

of arguing

n

a circle. His

principles

f

evolutionary

mportance

were not derived

from

a

pre-existing

axonomy,

but from the results of

artificial selection

and

from

he

study

of

heredity, ariation

nd

ecology.

This is a

point

worth

emphasizing. In

many

elementary

extbooks of

biology,

classification s

treated

as one

of

the

lines

of

evidence

for

evolu-

tion.

Darwin

did not treat

it

thus;

he discussed

it quite

late in the

Origin'

as consonant

with

the

theoryof evolution,and explicable as a conse-

quence

of

it.

He

never regarded

it

as

primary

evidence

for

evolution,

and

his

caution

was cer-

tainlv

iustified."11

But

later Cain

brings

the

charge

of

vicious

circularity

ull circle.

In

principle

phyletic

development

an

be

discerned

without ecourseo the constancyf prop-

erties

n

a phenetic

lassification

ut

too

often

n

practice

t cannot.

Cain

(1962b)

concludes:

"If there

were any

method

of analysing

ani-

mals so that

the

construction

nd

behavior

of

each

could

be

shown

to follow

from a

few great

principles,

hen ideally

each form

could be ex-

pressed

n terms

of these

principles

n such

a way

as to define

it

and

its properties

completely.

Something

f this

sort

has

happened

n the classi-

ficationof the elementsby their atomic struc-

ture.

Such

a taxonomy

of analyzed

entities

has

been

attempted

many

times. In

Linnaeus's

period

and before, logical

analysis, plus

Aristotelian

physiology,

was

thought

to help

in this.

About

the

beginning

f

the nineteenth

entury,physio-

logical criteria

of what

must be

the

most

im-

portant

characters

were widely

used.

But in

both

periods

there

was

far too

little

information

or

such analytical

taxonomy

to

be attempted,

nd

workerswere in fact

arguing

n a circle

from the

observed constancy

of

certain

characters

n al-

ready recognizednatural groups'to theirphysio-

logical

importance.

Darwin

rightly

ejected

such

attempts,

but

he

tried to

recognize

which

char-

acterswere

more ikely

to remain

constant

during

evolution

and

to use them

as

the best

indicators

of ancestry-and

his criterion

gain,

n

the

bsence

of a

really good

fossil

record,

ould

only

be con-

stancy

within

natural

groups.'

2

1

Darwin

discussed the

hierarchical

arrange-

ment

of taxa quite early n the

Origin

1859: 128)

and

treated

t

as he treated

all evidence

for evo-

lution,

as consonant with his

theory. The group

subordinate to group

relation evident

in nature

was just

one more fact nexplicable

n the

special

creation view but

to be expected

on his view.

Cain is right, owever, hat he did not treat clas-

sification

as primary evidence

for evolution, as

say George J.

Romanes (1892)

was to do

later.

As he

did with

so

many

of the

arguments

put

forth to justify

evolutionary theory,

Fleeming

Jenkin

(1897)

found a

hole in this one.

Initial

success n a rough

hierarchical

lassificationmight

be evidence

for

evolution,

but

just

the

opposite

should be the case

under continued

efforts.

He

argues

cogently

and

in agreement

with

Darwin)

that

evolution

by

gradual

change

entails

diffi-

culty,

not

success,

n classification.

Hence,

if

any-

thing, ontinueddifficultyn classification

hould

be considered

vidence

for

evolution.

2

Cain's

distinction

between

classifications

of

analyzed

and

unanalyzed

entities

reflects

n

ac-

ceptance

of the

Aristotelian

iew

of the

relation

between

mathematics

nd

the empirical

sciences

which

relativity

heory

has

made untenable.

The

reason

that

essential

definitions

n

the

Aristotelian

manner

re

possible

n geometry

s that the

vari-

ous

geometries

re pure

deductive systems

with

no empirical

import.

Such "entities"

as pure

Euclidean

triangles

can

be

completely

analyzed

into

the species

scalene,

isosceles

and

equilateral

because

there

is nothing

to analyze

but

some

axioms

and

definitions.

uch

is not the case

with

any

of

the

entities

n

empirical

cience.

The

clas-

sification

of

the physical

elements

according

to

their

atomic

numbers

s not

in

the

least

like a

taxonomy

of analyzed

entities.

One

end

of the

periodic

table

is

open.

There are

about

a hundred

elements

table enough

to

exist

for

any length

of



4/17

176

DAVID

L.

HULL

Sokal

and

Sneath,

nd Cain

have

been

quoted

at some

length

to make

clear

exactly

which

ines

of

reasoning

ommon

in evolutionary

axonomy

re supposed

o

be

viciously

ircular.

According

o Sokal

and

Sneath

no logical

and

consistent

e-

fense

has

been

presented

orsuch

"circu-

larity

n

reasoning."

t

willbe the

purpose

of

this

paper

o provide

ust

such

defense.

By the

very

nature

f the

accusation,

he

defense

will

have

to

be

in terms

f

logic

and logical

distinctions.

n

the first

half

of

the

paper,

t

will

be

explained

what

con-

stitutes logicalfallacy nd why t is un-

desirable

to

reason

fallaciously

nd then

several

inesof

reasoning

hich

have

been

termed

iciously

ircular

willbe

examined

to

see

if

they

ctually

re circular.

t will

be

seen

that

these

ines of

reasoning

e-

generate

nto

vicious

circles

only

if cer-

tain

evolutionary

aws

and principles

re

ignored.

he

ustification

orgnoring

hese

laws

and

principles

s

that

they

are

not

warranted.The secondhalf of thepaper

will

deal

with

heproblem

f

what

n

gen-

eral

makes an

inductive

nference

war-

ranted

nd specifically

hether

hose

in-

ferences

sed

in

evolutionary

econstruc-

tions

re warranted.

LOGICAL

FALLACIES

Since evolutionary

rocedure

s

accused

of being

circular

nd

reasoning

n

vicious

circles s a logical fallacy, t is certainly

worthwhile

o explain

what ogical

fallacies

are

and

why

it

is undesirable

o

commit

them.

The

general

tatement

hat

logical

fallacy

s

any

erroneous

rocess

f

reason-

ing or

arguing

s not veryhelpful.

What

is important

re

thereasons or onsidering

arguments rroneous.

They are

of two

types.

Logicians re mainly

oncerned

ith

formalfallacies,those lines of reasoning

which

re erroneousolely

because

of the

form f

the

propositions

nd arguments,

regardless

of the subject

matter. For

example,

t is fallacious o arguethat

ince

Communists isapprove

of abstract

art,

anyonewho disapproves

f abstract rt is

a Communist.

person eed

knownothing

of

either

ommunismr

abstract rt

to de-

cide that this arguments invalid. The

fallacy f reasoning

n vicious

circlesdoes

not

belong

o this lass of

fallacies.

nstead

it is

an example

of what logicians

all a

materialfallacy.

In diagnosing

material

fallacies othcontentnd

the use to

which

the argument

s

being

put play

central

roles.

An

argument

an

fulfill ll the re-

quirements

f formal

alidity

nd

still

be

fallacious

f

t

fails o

perform

he

task

t is

intendedo perform. ne of the common-

est uses of

arguments

s

to prove

conclu-

sions

th'at

re

in

some way

unknown r

doubtful

or that have

been called

into

question.

A

prerequisite

or

fulfilling

his

purpose

s

that the argument

annot

as-

sume

n

the

premises

what

t proposes o

prove.

An

argument hich

fails to prove

anything

because it somehow

takes for

grantedwhat

it is supposed

to prove

is

calledbegginghe question rpetitio rin-

cipii.

More

subtleversions

f this fallacy

are

often

ingled

out

and

termed

icious

circles.

An

argument

an

presuppose

r

depend

upon

its

conclusion

n

two

ways.

In

the

simplest

ase

the dependence

s

straight-

forwardlyogical.

One of

the

premises

s

just

a

restatement

f

theconclusion

o

that

anyone

doubtful f

the truth f

the

con-

clusionwouldhave to be equallydoubtful

of

the truth f

the

premises.

For

example,

any proposition

an be deduced

validly

from

tself,

ut we

have

not

thereby

roved

anything.

t

is

formally

orrect

o

con-

clude that

the Pope

is

infallible

when

he

speaks

ex cathedra

rom he

premises

hat

time

under ordinary conditions;

there

are three

and

only

three species

of

triangles

on the

dif-

ferentia

mplied.

Further,

he

superficial

eatness

of

the periodic

table

is

destroyed

y the

existence

of isotopes

and

isomers.

No

such borderline

ases

can

occur in

a

pure

deductive system

ike Eucli-

dean geometry.

The entities

classified

in the

periodic

table have

been more

thoroughly

na-

lyzed

than have

most

of the

entities

lassified

n

the

Linnaean hierarchy,

but there

is not

the

slightest

ope

of ever

completely

nalyzing

either

of them,

n the sense

in

which

the "entities"

of

pure

geometry

can be

completely

analyzed.



5/17

CERTAINTY

AND CIRCULARITY

IN TAXONOMY

177

he said so

ex cathedra nd

everythinghat

the

Pope

says ex cathedra s true, ut such

an

argument ould stillbe

fallacious.

The dependence eedn't e

logical,how-

ever. Often the circle s epistemological.

The only

way thatyou couldknow hat he

premises

re true would be

to know that

the

conclusions true. All cases of deduc-

tion from enuine

numerative eneraliza-

tions

(generalizationsrrived t by com-

plete enumeration) re

examples f argu-

ing in

vicious circles. For

example, t is

formally

orrect o argue hat

certain all

in a jar is redbecause ll oftheballs n the

jar are

red, but such an

argument ould

be

viciously ircular

f

the generalization

had been

established only through he

examinationf each of theballs n the ar.

The only

way thatyou couldknow hat ll

of

the

balls

werered wouldbe by knowing

that the

ball in questionwas red. How-

ever,

rguing hat

Tamias

striatus volved

because all species volved s

not an exam-

ple of a viciouscircle. The generalization

was not

arrived t

simply y

enumerative

induction.

ome specieswere

examined

o

establish he

truth

f

the

generalization

o

be

sure

and

many

have been examined

since,

but the

acceptance

f the

generaliza-

tion

rests

primarily

n the

explanatory

power

of

evolutionaryheory.

HOMOLOGY

AND

PHYLOGENY

Thereare three inesof reasoningom-

mon

in

evolutionaryaxonomy

which

are

often

ingled

ut

as circular:

a)

the de-

fining f

"homology"

n

termsfphylogeny

and then

using

characters

laimed

to be

homologous

o

infer

phylogeny, b)

the

basing

of an

evolutionary

lassificationn

a

phenetically

onstructed

lassification,

and

(c)

the

inferring

f

phyletic

escent

from verall

phenetic imilarity.

he

first

two inesofreasoningrederivative f the

third.

They

shall be discussed

n

order.

Sokal

and

Sneath

1963) say

with

respect

to the first:

tor, by

the

common definition

f the term), or

to

decide a priori

which

characters

re important

r

are reliable

guides

to phylogeny,

oon leads

to a

tangle

of circular

arguments

from

which

there s

no escape. Even Simpson (1961), who

strongly

supports a

phylogenetically

ased

taxonomy,

s

aware

of and points

out the circulus

vitiosus

of

this procedure."

Sokal and

Sneath's

eference

o thedefi-

nition f

"homology"

n

termsf

phylogeny

mightmake

t

soundas

if

theywere

rgu-

ing that

uch

a definition

s

circular,

hen

their ntent eems

o be

that

the definition

can lead to

circular

rguments.

s Ghiselin

(1966a and 1966b) has pointedout, the

definition

f "homology"

n terms f phy-

logeny

s not

circular

ecause

"phylogeny"

is notdefined

n terms

fhomology.

okal

and Sneath's

point

s that

one is often

n-

ferred ia

the other

nd that

this

can

lead

to

circular

rguments.3

n

another

place

they

make t

clear

thatthey

havean

argu-

mentn mind

ndthat

he rgument

s sup-

posed

to be epistemologically

ircular.

Theysay:

"We

do

not know

of

any

infallible riteria

for

overall phenetic

convergence

that

may

be

ob-

tained

from

study

of

living

formsof

organisms

alone.

To

detect

convergence,

we have

to

dis-

tinguish

those

features

which

do

accurately

re-

flect

the

phylogeny

romthose

featureswhich

do

not. This,

however,

s

a

question

which can

only

be

answered by

knowing

the

phylogeny

first.

The

problem

therefore

s

insoluble within

this

logical

framework,

nd

one

must have

ndependent

evidence

(not

derived

from

phenetic

relations)

in

order to attack it."

It

is tautological

o

say

that

homologous

resemblances

re

indicative f

common

ine

ofdescent,

ince

by

definition

omologous

resemblances

re those

esemblances

ue to

"Any attempt to decide the phylogeny

n one

set

of

characters, n particular those believed

to

be homologous (derived

from

a

common ances-

3The

difference

etween

the

two

assertions

s

worth

pointing

out, since

there

is

considerable

difference

etween

a definition

nd

an

argument.

The

reasons

for the undesirability

of

circular

definitions

nd circulararguments re, however,

the

same.

If you

don't

know

what

the

word

"ex-

planation"

means,

it

doesn't

help

to be

told

that

an explanation

s something

which

explains

some-

thing.

Similarly,

f you

are

in doubt

of

God's

existence,

he

argument

that

if

God

is

all-good

and

existent,

then

He

exists won't

prove

very

convincing.



6/17

178

DAVID

L.

HULL

common

ineof descent.

To be sure,

any

evidence

o the effect

hat a particular

e-

semblance s homologous

ould

necessarily

be evidence

o theeffect

hat

t was due to

common ine of descentand vice versa.

But,the evidence

rom

which hylogeny

s

inferred

s not limited

ust to homologous

resemblances.

or example, wo

axawhich

in

point

of fact are

very closelyrelated

cladistically ould exhibit

striking

is-

similarity.

ny

evidence e.g.,

genetic

vi-

dence)

to the

effect hat this

particular

type f

dissimilarityan

arise

uitequickly

wouldcontributeo thecorrect econstruc-

tion of the

phylogeny

ut would

not

de-

pend

on homologies

t

all.

Fossil

evidence

that

it

did

so

arise

would

be even

more

conclusive.On

the other

hand,

evidence

that the genetic

mechanism ecessary

or

such

dissimilarityo

arise

s

such

that

he

change

could arise

only

very gradually

would

disprove

he

hypothesis

hatthe

two

share

a recent ommon

ncestry ven

in

the absence of fossil evidence. But too

often

the

only evidence

that

is

readily

available

is

phenetic

imilarity,

nd the

first

ine

of reasoning

hich

as been

called

circular

merges

nto

the third.

VICIOUS

CIRCLES

AND SUCCESSIVE

APPROXIMATION

The

second

ine of reasoning

which

has

been

termed

ircular

s

spelled

out

in

some

detail by Sokal and Sneath (1963) as

fnl

MAxIc

fined

on

the basis

of

this charactercomplex, ay

X. It

is

assumed

that taxon A

is

monophyletic

r

a

'natural' taxon.

Thus

every

member

f A

(both

known and

unknown

forms)

s

expected

o

possess

X; conversely, ossessionof the character com-

plex

X

defines

A.

"Henceforth roup A, as definedby X,

assumes

a

degree

of

permanence

nd

reality quite

out

of

keeping with the tentativebasis

on which

it

was

established.

Subsequently

studied

species

are

compared

with

A to

establish their

affinities;

they may be

within

A,

close to

it,

or

far

from t.

It

is

quite possible that a species

not

showing

X

would be

excluded

from

A, although

t

was closer

overall to most of

the

members

of

A than

some

were

to each other. It

may

be said

that

such

problemswould arise only when A was an 'arti-

ficial' group erected on the basis of 'unsuitable'

characters. However, except

in

long-established

taxa

or

those separated by very

wide

gaps from

theirclosest relatives, he effect f the last classi-

fication carried out with a limited number of

characters

s

quite pervasive. The circularreason-

ing arises from the fact that the new characters,

instead of being evaluated on their own merits,

are inevitablyprejudiced by the prior erectionof

taxon

A

on other characters X). Such prejudg-

ment

gnores

he

fact that the existence f A as a

natural

(or 'monophyletic') group defined by

charactercomplexX has been assunmed nd not

demonstrated."

In

all due respect, heprecedings not a

characterizationf thebest n evolutionary

taxonomy ut a parody f the worst. Per-

haps the practice of some evolutionists

sometimes egenerates o this evel,but it

need not and if the principles f evolu-

tionary axonomy re given proper con-

sideration,t shouldnot. Sokal and Sneath

are well awarethat ven themost arefully

formulated rocedures un the dangerof

unimaginativepplication

f

the principles

on

which

hey

re

based have

been

mper-

fectly nderstood.

he

principles f evolu-

tionary axonomyhouldnotbe judged ny

more

by

their

misapplication

han should

those

of

numerical axonomy.There

are

linesof

reasoning

n

evolutionaryaxonomy

which omeclosetobeing ircular. n the

preceding uotation okal

and Sneathhave

extracted

ne

of the

most

important

f

these ines of

reasoning,

ut their

descrip-

tion

tends

to

disguise

rather han reveal

the outlines

f this

potential

ircle.

For

example, ccording

o

their

ccount,

"It may

be advantageous

at this stage

to

out-

line an important

ogical

fallacy underlying

ur-

rent taxonomic

procedure.

It is the

self-reinforc-

ing circular

arguments

used to

establish

cate-

gories

[taxa],

which

on

repeated

application

in-

vest the

latter

with

the

appearance

of

possessing

objective

and

definable

reality.

This

type

of

rea-

soning s,

of course,

not restricted

o

taxonomy-

but it

is no less

fallacious

on that account.

Let

us illustratethis point. An investigators faced

with

a group

of similar species.

He

wishes to

show

relationships

mong

the

members of

the

group

and is looking

for characters

which

will

subdivide

t into

several

mutually

exclusive

taxa.

A search for

characters

eveals

that

within

sub-

group

A certain

characters

ppear

constant,

while

varying

n an uncorrelated

manner n

other sub-

groups.

Hence

a taxon

A is described

and de-



7/17

CERTAINTY

AND

CIRCULARITY

IN TAXONOMY

179

afterA

has been

defined

n

terms f

X,

any species

which

has

a

sufficient

umber

of the

properties

n X

is

automatically

placed

in

A

(although

t might

not be

similar n otherrespects o theother pe-

cies

already

n

A) and

any species

which

lacks a

sufficient

umber f these

proper-

ties

is

excluded

from

A

(although t

may

be

similar

n

other

respects

o the

other

species). The

classificationnd reclassifi-

cationwhich

goes

on all the

time

n

evolu-

tionary

axonomy

n

the light

of

the dis-

covery f

previously

nknownpecies

and

additional evidence belies this extreme

position.

However,

what

s

wrong

with

his

procedure,ven

f

evolutionary

axonomists

were

guilty

f

t,

s

not that

self-reinforc-

ing circle

s involved ut

that

no

reinforce-

ment s

involved.

f

anything,

healleged

procedure s

contradictory. n the

one

hand,

evolutionary

axonomists re

sup-

posed

to

reasonthat the

degree

f

covari-

ance

in

X

is

indicative

f phyletic imi-

larity. On the otherhand,they are sup-

posed

to maintain

hat

n

the

ight

f

more

evidence nd

a

slightly ifferentistribu-

tionof

characters, hat this

newcomplex

Y

is not

indicative f phyletic

imilarity.

The

wholepoint

of

evolutionary

rocedure

is that

f

X is

indicative f

phyletic

imi-

larity, henY is

more

ndicative.

Now

in

ordinary

discourse such

self-

reinforcing

roceduresare

often called

"vicious circles" f the consequences re

undesirable. or

example,

n

a

recent ssue

of a

popular

magazine

t

was

reported hat

doctorshad

"found that the

moreover-

weight

he

diabetic

gets, the

more nsulin

there s

in

his

blood.

And

the

morensulin,

the

more

he

tends

o eat and

thus

toreup

more fat in

an

ever-widening

icious cir-

cle."

The

situationmay be

vicious,

ut it

is not

circular

incethediabetic

gets

fatter

and fatter. imilarly,volutionaryaxono-

mists

lassify

nd reclassifyn

an attempt

to

represent

volutionary

escent

with an

ever

ncreasing

ccuracy.4

This

goal

may

be

undesirable.

n this

sense,

he

practice

is

vicious,

ut t

is not

circular

nd,

hence,

not

logically

fallaceous.

The

criticism

t

issue

s whether

r

not

evolutionary

axon-

omists re making logicalerror, ot an

error

n

tactics.

As Sokal

and

Sneath

say, the type

of

reasoning

hich

hey

have

indicated

s

not

restricted

o

taxonomy.

t is inherent

n

any

attempto

obtain

bjective

nowledge,

including

heefforts

f

the

numerical

ax-

onomists.

Abraham

Kaplan

(1964)

has

called

thisspecial

problem

he paradox

of

conceptualizationnd considerst an exis-

tential

ilemma:

"The

proper

concepts

are needed

to

formulate

a

good

theory,

ut we

need a

good

theory

o

ar-

rive at

the

proper

concepts.

Long

before

the

scientific

revolutions

of the twentieth

century,

Jevons

(1892)

remarked

hat almost

every

classi-

fication

which

is proposed

in

the early

stages

of

a science

will

be

found

to break

down

as the

deeper

similarities

f the objects

come

to

be de-

tected.'

Every

taxonomy

s

a

provisional

nd

im-

plicit

theory

or

family

of

theories).

As knowl-

edge of a particular subject-mattergrows, our

conception

of

the

subject-matter

hanges;

as

the

concepts

become

more

fitting,

e

learn

more

and

more.

Like all

existential

ilemmas

n

science,

of

which

this s

an instance,

he

paradox

is

resolved

by

a

process

of

approximation:

the

better

our

concepts,

he better

the

theory

we

can

formulate

with them,

and

in

turn,

the better

the

concepts

available

for

the next,

improved

theory.

V.

F.

Lenzen (1938)

has

spoken

explicitly

f successive

definition.'

It is only

through

such

successions

that

the

scientist

an

hope ultimately

o

achieve

success."

There

are

several

ossible

ways

to

avoid

the

dilemma

f which

Kaplan

speaks,

none

of which

have

engendered

ny

great

en-

thusiasm mong

cientists.

he

easy

way

s

to

introduce

ome

metaphysical

aculty

such

as

intuitionwhich

s capable

of

di-

rectly

nd

infallibly

pprehending

eality.

This

was

Aristotle's

ay.

At least

onecon-

temporaryaxonomisttill advocates uch

4 The claim

that

classification s to

represent

phylogeny s merely

he claim that there

must

be

some systematic

relationship

between phylogeny

and

some

system

of classification.

The

more

powerful

the

system

of

classification,

he more

extensive

and precise

this

relationship

can

be

made. Unfortunately,

he Linnaean

hierarchy s

not a very

powerfulmeans of classification.

See

Hull (1965) for further

etails.



8/17

180

DAVID

L.

HULL

a procedure

Sattler,

963).

Most philoso-

phersand

scientists,

owever,

ave long

since

come

to

the

conclusion

that

this

"solution"ustwon'tdo for cience

n

gen-

eral.

Cain

(1958)

and

Mayr (1959)

have

argued

quite

effectively

hat it

won't

do

for taxonomy

n particular.

(See also,

Hull,

1965.)

Another

lternative

s to deny

that a

classification

s

intended

o

approximate

anything

ut

thatany

classification

stab-

lishedon objective

riteria

s "true"

n its

ownright.

At times, umerical

axonomists

haveseemed obe arguing or hisposition.

At other

times,

however,

hey

maintain

that phenetic

lassification

s

to approxi-

mate something

alled

phenetic

imilarity.

On

this

view,

heevolutionists

nd

numeri-

cal taxonomists

hare

th'e

methodological

problem

f

justifying

he

process

of

ap-

proximation

y

successive

definition,

he

process

alled

"groping"

y

Cain and

"re-

ciprocal

illumination"

y

Hennig.

This

justifications no easy matter,but it

should

be kept

n mind that

theproblem

is one

shared

by

evolutionary

nd

numeri-

cal taxonomists

qually.5

To be

sure, ny

classification

ased upon

a

previous

tentative

lassification

s

in-

evitably

rejudiced

y

it. Any

error

n the

early

classification

might

well

infect

all

laterreclassifications,

utthe

effect

f

the

early

classification

ecreases

s

reclassifi-

cation akesplaceinthe ight fadditional

evidence.

A

gradual

decrease

in

error

might

not

sound

good

enough

for

some

taxonomists,

ut

there

s

no

other

lterna-

tive short

f complete

eclassification

ach

time

a

single

taxonomic

oundary

s

re-

evaluated.

Although

Sokal

and

Sneath

have advocated

some

rather

xtensive

e-

visions

n

taxonomic

rocedure,

venthey

have

notgone

o

far

s

tosuggest

he

com-

plete dissolution f all classificationnd

reclassification

e

novo

each time

single

taxon

is re-evaluated

n

the

basis of

a

single bit of additional

evidence.

Until

such a

drastic tep

s taken, arlyclassifi-

cationswill color

later classifications

e

theyphenetic

r phyletic.

VICIOUS CIRCLES

AND

EMPIRICAL

CERTAINTY

There

remains

he primary

ine

of rea-

soning,

whichhas been termed ircular,

o

defend. Once again

we turn o Sokal

and

Sneath

for

a

vigorous

tatement f

the

criticism:

"The

difficulty

ith the use

of

the

phylogenetic

approach in systematics mergedafter the first

wave

of

enthusiasm

for it

subsided

and

has

re-

mained apparent

to perceptive observors ever

since. We

cannot make

use of phylogeny for

classification, ince

in

the vast majority

of cases

phylogenies

re unknown.

This is one of the state-

ments

most commonlyheard at

meetings f tax-

onomists,yet it

is

most

consistently

gnored. Let

us

restate

t in other words for emphasis.

The

theoretical

principleof descent with

modification

-phylogenetics-is

clearly esponsible

or theexis-

tence and

structure f a natural classification;

we

may even agree with

Tschulok (1922) that the

natural systemcan be considered s proof of the

theory

of

evolution.

However, since

we have

only an

infinitesimal

portion of phylogenetic

history n the fossilrecord,

t is almost

mpossible

to establish

natural taxa

on a phylogenetic

asis.

Conversely, t

is

unsound

to derive a definitive

phylogeny rom a tentative

natural

classification.

We

have

described his fallacy of circularreason-

ing earlier."

[See also

Cain, 1962; Cain and

Harrison,

1960; and Bigelow, 1956

and 1958.]

This

quotation

ontains wo

distinct

riti-

cisms fevolutionaryaxonomy. hefirst,

which

has

already

been

discussed,

oncerns

the erection

f a

phyletic

lassification

n

the

basis

of

a

phenetic

lassification.

he

effect

of

the

original

classification

may

never

be eliminated

as reclassification

takes

place.

Since

reclassification

oes

take

place

and

the

aterclassifications

el-

dom

circleback on

the

original,

his

pro-

cedure

s not

circular.

Definition

y

suc-

cessive pproximationrovideseveralogi-

cal

difficulties,

ut none of

these

nvolves

vicious

ircularity.

he second riticism

s

that

inferringhyletic

elationships

or

a

group

n

the absence

f

a

reallygood

fossil

record

for

that

group

s

unwarranted.

n

most nstances,

o

fossil

ecord

s

available.

I

Sokal

and

Sneath

object

only

to

Hennig's

particular

use of the process

of

successive

defini-

tion,

the process

which

he

calls reciprocal

llumi-

nation,

not

to the process

tself.



9/17

CERTAINTY

AND CIRCULARITY

IN TAXONOMY

181

The only

observations hichevolutionists

have to go on are

pheneticproperties

(usually

morphological),nd phenetic

imi-

larity s

exactly hecriterion sed

by clas-

sificationistsnd numericalaxonomistso

construct

heir lassifications.

f an evolu-

tionary

axonomisteginswith

a phenetic

classification,eclassifies

xclusively

n the

basis of phenetic imilarity,

hen he will

end up with phenetic

lassification

nd,

perhaps,

lso a phyletic

lassification,e-

pending

n how goodphenetic

imilaritys

at indicating hyletic

imilarity. f phy-

leticrelationshipsannotbe inferred rom

phenetic similarity

with sufficient

er-

tainty,

then the

line

of reasoning ust

sketched

s unwarranted.

t

is

plainlynot

circular

These

two

criticisms, hough

distinct,

are related. They

are distinct,

ince

it is

one

thing

o arguethat a

line

of

reasoning

is circular; t is another

o arguethat t is

unwarranted.

n

fact,

the two errors re

mutuallyxclusive.No one argumentould

be

both circular nd

unwarranted.

The

two

criticisms re related,however,

ince

those

ines

of reasoningwhich

have been

termed ircular ecome ircular nly

f

cer-

tain other

ines

of reasoning an

be shown

to

be unwarranted. hus,

the

really

m-

portant

riticismf evolutionaryaxonomy

does not concern ircularity

n

classifica-

tion

t

all but the

ustification

f

inferring

phyletic evelopmentromphenetic imi-

larity n the basis

of certain

volutionary

principles

n

the absence

of a

fossil

ecord

for

the

group.

If

a good

fossilrecordfor

the

group

n

question

s necessary efore

its evolutionaryevelopment

an be recon-

structedwith

sufficientertainty,

hen n

a vast

majority

f

the

cases

phylogeny

an-

not be reconstructed

nd

the evolutionary

program

n

taxonomy

ecomesuntenable.

It will be argued hatfossil ecords or ll

or evena

majority

f the

taxa to be classi-

fied re

not necessary.

All

that

s

required

is that

there be

some

reallygood

fossil

sequences

from

which

to derive

principles

concerning

he

trends nd

tendencies f

evolutionary

evelopment

nd

others

which

can be used

later to check

them. Further,

the evolutionary

rinciples

sed to

infer

phyletic

evelopment

eedn't

e completely

general

universal

tatements.

Much less

willhave to do. Nor do theyhave to be

eitherverified

r verifiable

n the early

positivistic

ense.

Partial

confirmation

ill

have

to do.

To demand

more f evolution-

ary

taxonomy

wouldbe to

demand more

than

any

science can

deliver-including

physics.

THE QUEST

FOR

ABSOLUTE

CERTAINTY

Philosophersnd scientists hroughhe

centuries

ave

demanded

more,but

these

demandshave

stemmed

rom failure

o

understand

he nature

f

empirical

cience.

Such "apriorists"

s

Aristotle warded

he

honorific

itle "science"

only

to deduction

from purely

universalgeneralizations

o

purely

universal

generalizations,

ecause

such nferencesecessarily

esulted

n

true

conclusions f

the

premises

were

true.

Aristotle ssured he truth fhis premises

by

claiming

hat

we

intuit

hem

nd

intui-

tion s alwaystrue

Largely

n

reaction

o

the excesses

of Aristotelianism,ome

phi-

losophers

nd

many scientists

doptedan

extremely

mpirical iew

of science

n the

18th and 19th

centuries.

These

extreme

empiricists

r "Baconians"

as

theycalled

themselvesooked uponscience

s an

"in-

ductiveprocess,"

but

they

too demanded

absolutecertaintynd attempted o get

it

by nevergoing

beyond

the evidence.

Scientificaws

were ust empirical

enerali-

zations, ust

summations

f the data.

Any-

thingelse was

mere speculation.

Even

though

Darwin

himself

laimed to have

proceeded

n

the true Baconian

manner,

the main

criticism eveled against

his

theory y

the

biologists

f

his

day

was

that

it was speculation.

He had

gone

beyond

his evidence n a manner nbecoming n

inductive

scientist and an

Englishman.

(See

Ellegard,1957.)

To a philosopher

t sounds

strange o

hear

a neo-Platonist

ike

Richard Owen

criticizing

arwin

for

dle

speculation,

all-

ing

himself

n inductive

cientist

nd

com-



10/17

182

DAVID

L.

HULL

plimenting uvier

fornot being

"the man

to draw conclusions eyond

his premises"

(Owen, 1860).

Inductive

nferences

re

just those nferences hichdo go beyond

the evidence t hand and which o

run the

risk of leading

to false conclusions

rom

truepremises.

As Peter Caws (1965)

put

it recently:

"One might

define

deduction

as a process of

inference n which one never goes beyond

the

given facts, nd

in which therefore here

s never

any loss of certainty. Induction, on

the other

hand, does go beyond the given facts,

nd there-

fore runs the risks that deduction does

not. We

shall find these risks at the root of scientific

theory."

Apriorists nd

extreme mpiricists ave

tried

o

obtain

bsolute ertaintylthough

by opposite

means. Neither

of these

ex-

treme positions

is appropriate for the

actual

practiceof any science,

ncluding

taxonomy.

During the

early years of this

century,

extreme

mpiricism

n

biology ecame

qui-

escentbut it burst forth n psychology

under the

name

of behaviorism. he be-

havioristsdemanded"operational

defini-

tions"

of

all the

termsnpsychology,efi-

nitionsof a type

which they

mistakenly

thoughtwere common

n

physics.

Under

careful nd repeated riticism y

philoso-

phersand theirfellow sychologists

e.g.,

Bergmann, 954

and 1956), and

afterbe-

ing abandoned

by the founder f opera-

tionism,. W. Bridgman1954), behavior-

istsbegantomodify heir xtreme

osition.

It has

now become

little more than an

emphasison a particular orm

f experi-

ment

nd a

cry for omeempiricalontent

in

psychological

aws.

The

history

f

oper-

ationism hould be an

object

lesson to

those

taxonomists

ho

are

attempting

o

introduce t

into

taxonomy. f

it is

in-

tended as a demandthat the basic con-

cepts

n

taxonomy

e

operationally

efined

in the

strict ense,

hen t is untenable.

f

on

the other

hand,

all

that

s

intended

s

that

the

definitionsnd

laws

in

taxonomy

be

operational

i.e.,

have some

empirical

consequences

hich

an be

checked),

hen

it is an

admirable

rogram

ut

one

that

s

neither

ew

norstartling.

THE

LANGUAGE

OF

LOGICAL

CRITICISM

In

his

early

critical

writings

. J.

Cain

exhibits

he

same

contradiction

hich

has

always

been

characteristic

f the

writings

of

extreme

mpiricists.

At

times

he

de-

mands

bsolute

ertainty

f

the

nferences

made

by

the evolutionists;

t

other

imes

he seems

to

be

arguing

more

reasonably

that

toomany

of these

nferences

re

not

sufficiently

arranted.

A

confusion

n the

language of logical criticism mphasizes

thisvacillation.

For example,

fter

rguing

against

the

use of

deduction

n

taxonomy

(Cain,

1958),

the only

kind

of

inference

which permits

categorical

demonstration

and

apodeictic

certainty,

ain (1959a)

complains

hat phyletic

nferences

re

not

"apodeictically

ertain"

or "categorically

demonstrated."

urthermore,

fter uoting

two

Aristotelian

hilosophers

n

the

im-

possibilityfapplyingAristotelianogicto

biological

lassification,

ain (1959)

says:

"The

relevance

of these quotations

from

ogi-

cians

for the

whole history

f

biological

taxonomy

from

Aristotle

o

the present

day can

hardly

be

over-estimated.

They epitomize

the

most

im-

portant

change

in taxonomic

theory

hat has

oc-

curred,

namely

the gradual

abandoning

of at-

tempts

to set up

classifications

n a

priori

prin-

ciples

agreeable

to the

rules

of

logic

and

some

particular

theory,

nd

the

partial

substitution

f

an empiricalattitude. This substitutionwas not

complete

when

the

theory

of evolution

arrived

to

provide

a

new

theoretical

approach

to the

problem

of classifying

rganisms,

he

full

impli-

cations

of

which

have

still not

been completely

thought

out.

[Taxonomists

should] proceed

em-

pirically,

imply

finding

out

what

subjects

exist

and what

are

theirattributes,

ot

deducing

them

from

known principles

nd

axioms."

Cain terms

he

principles

sedby

theo-

retically

riented

axonomists,

rom

Aris-

totle o theevolutionists,priori nd their

inferences

eductions,

hen

n

point

ffact

the

thrust f

his

objections

o evolutionary

taxonomy

s that the principles

re a

pos-

teriori

and the

nferences

nductions.

Cain

objects

to

evolutionary

rinciples

ecause

they

re

supposedly

priori

nd

then om-



11/17

CERTAINTY AND

CIRCULARITY IN

TAXONOMY

183

plains that theydo not have certain

rop-

ertieswhichonly

a

priori

tatements

an

have. He objects to evolutionary

nfer-

ences because they re supposedly educ-

tions nd then omplains hat theydo

not

exhibit type of certainty hat only

de-

ductions an

have. Cain findsAristotelian

logic inadequate for the

purposes of

science,but he turns roundand uses its

basic distinctionso criticize

volutionary

taxonomy.

f

Aristotelianogic won't

do

for he

working axonomist

n

his

everyday

pursuits,

hen t

won't

do for

the taxono-

mistwhenhe steps back to evaluatethe

structure f

his

science.

Terminological

confusions

ike

those

ust

mentioned

er-

vade the taxonomic

iterature,

nd a rea-

sonable decision s to

the ustification

f

evolutionaryeconstructionsependsupon

just those

distinctions

lurred by these

confusions.

The

principles

sed

by evolutionistso

reconstructhylogeny re

not

a

priori

n

the philosophical ense of this avowedly

philosophic xpression.According o ac-

cepted philosophicusage,

the

phrase

a

priori ppliesonlyto our knowledge f

the

truth f the

statement

lthough

t

is often

used

elliptically o refer o

the

statement

itself.

A

statement

s

a

priori rue

f

its

truth an be decided prior to experience.

For

example,

he

tatementhat ither

t is

raining omewhere n the plain

in

Spain

rightnow or it is not is a priori rue. Of

course,

ts

truth annotbe

known rior

o

all

experience,

ince

we

must

know what

the

words

n

the statementmean and

we

must

understand nglish syntax,but

its

truth

an be decidedwithout

eference

o

the

weather. f the truth f a statement

can be decided

priori,

erifications

ir-

relevant.

Empirical

considerations

ust

don'tmatter.

As

a

consequence,

uch

tate-

mentsare necessarily rue. We can be

apodeictically

ertain f

their ruth. The

scientific

rinciples as

distinct

rom

he

logical

and

mathematical

rinciples)

used

by

the evolutionists o reconstruct

hy-

logeny,

ike

all scientific

rinciples,

re not

a

priori

n

this ense.

Hence, they re

not

necessarily rue n

and of

themselves.At

best

they an be

onlyhighly onfirmedr

madehighly

robable.

In addition o thisphilosophic se of the

expression,here

s also a use in

everyday

discourse

ccording o

which a belief is

termed

a

priori

if

the person

who

holds

it refuses

o entertain

ounterevidence.

or

example, he

belief of

many people that

smoking

will

not

increase heir hance

of

contracting ung

cancer is

a

priori

in

this

sense.

The

belief

is

not

a

priori

in

the

philosophic ense,

since evidence s

rele-

vant. The problems thatthepersonre-

fuses

o

acknowledge

he

relevant vidence.

He

is certain hat

his belief s true, uthis

certainty

s

not

justified.

Perhaps

some

evolutionists

ave treated heir

principles

as

a

priori

in

this second

sense. If

they

have, t is

unfortunate. ut

sometimeshe

appearance

of

ignoring

counterevidence

stems

from

misconstrual f the

logical

nature f both

evolutionary

rinciplesnd

the nferences ade fromhem.The critics

of

evolutionary

econstructionsomplain

that even

though every

single

principle

used

by

the

evolutionistss

known ohave

exceptions,

he

volutionists

ontinue o use

them. It might

be noted

in

conjunction

withthis

claim that

every

ingleprinciple

in

Newtonianmechanicss

known o have

exceptions,

ut

physicists

ontinue

o

use

them. (See

Scriven, 1961

and Kaplan,

1964.)

The

misunderstanding

s

expressedmost

clearly

by

R. S.

Bigelow

1959)

when

he

argues

hat

a

hypothesis

o the effect

hat

all

the

balls

in

a

particular

ag

are

white

is

not probably

rueonce t is

known hat

one

ball

in

the

bag

is

red;

the

hypothesis

is

false.

Similarly,

he

hypothesis

hat

phenetic

imilarityorresponds

o

recency

of

common

ncestry

s

not

probably

rue

once it is known hatthere re numerous

exceptions

o

this

rule;

t s

false.

This

ine

of

reasoning

ollows, owever, nly

f

the

statement

elating

henetic

imilarity

nd

recency

f common

ncestrys

taken o be

categorical

n

form.

f

it is

intended

o be

a

tendency

tatement

as

it

certainly

s),



12/17

184

DAVID

L.

HULL

then

single

xception

oes

not

falsify

t.

Even

numerous

xceptions

re permissible.

Consequently,

f Bigelow

still wishes

to

registern objection o evolutionary

ea-

soning,

e is

left

n

the

unhappy

position

of

arguing

(as some

philosophers

ave

argued)

that

the

only

principles

roperly

admitted

nto the

pandects

of science

re

true

universal

eneralizations

nd

conclud-

ing

(as

some

philosophers

ave

concluded)

that

since

there

re

almost

no such

gen-

eralizations

nbiology,

iology

s almost

n-

tirely

evoid

of scientific

aws.

The logicbehind uch a lineof reason-

ing s

interesting.

f

scientific

aws

are re-

stricted

o

true universal

generalizations,

then

deduction

o

the particular

ase

is

possible

and

these particular

onclusions

follow

necessarily.

f the conclusion

urns

out

to be false

and

the argument

s

valid,

then t

follows

ecessarily

hat

t

least one

of the premises

s

false.

Hence,

universal

generalizations

re

in

principle

asily

falsi-

fiable.Such s notthecasewith nferences

from

generalizations

hich

are

less

than

universal

n

form.

nferences

o

particular

statements

re

only

more

or less

probable

and

falsification

s not so easy.

They are

falsifiable,ut

a

single

observation

on't

do

it. For

example,

rom

heuniversal

en-

eralization

hat

all parents

with

blue eyes

produce

nly

blue-eyed

hildren,

t can

be

deduced

with

podeictic

ertainty

hat f

a

certain hild s biologicallyheoffspringf

these

parents,

t

will

have

blue eyes.6

But

from

he

statements

hat

blue-eyed

arents

almost lwaysproduce

blue-eyed

hildren,

it cannot

e deduced

hat

fa certain

hild

is biologically

heirs,

t

will

have blue

eyes.

The

inference

s only

inductive

nd

the

conclusion

ollows

rom he premises

with

only

a degree

of certainty

r probability.

As G. G. Simpson 1961) has said:

"Scientists

themselves

frequently

eemed

con-

fused

as to the

degree

and indeed

also the

kinds

of 'certainty'

actually

always

probability)

that

are required

or

are possible

n

science."

The moral

f the

preceding

iscussion

s

that

f

such

empiricists

s Cain

are taken

at their

word,

thenthey

do not hold

an

empirical

view

of empirical

certainty.

Scientists ave a right o say thatthey re

certain f

the

truth f

a particular

tate-

ment ven

though

hey

mayfind

ut

later

that

the statement

as

false.

Any

use of

"certainty"

which

makes t

impossible

or

a scientist o be justifiably

ertain

f the

truth

of a statement

which

s later

dis-

covered

o

be false

s a view

of

certainty

inappropriate

o empirical

cience.

It

would eem

unlikely

hat he

founders

of numericalaxonomy, movement hich

relies

so heavily

on

the use of statistics,

should

hold

a view

of

inference

otally

t

variancewith

he

foundations

f statistics.

Yet,

at least

in

his

early

writings,

ain

seems

to do just

this.

In his later

works,

Cain clearly

eveals n

empirical

otion f

certainty,

or example,

n

Cain

and Har-

rison 1960).

But

in

thisvery

paper,

the

authors tate with

respect

o

the

recogni-

tionofconvergence,But wehaveno way

of estimating

hese probabilities;

ven

if

we

did,

we should obtain

only

probabili-

ties.

.

."

It

may

well

be

true that

pres-

ently

there

s no

way

to estimate

hese

probabilities,

ut

to

say

that

even

if

we

did,

we

shouldobtain

onlyprobabilities

s

to

label

oneself

an

extreme

empiricist.

Probabilities

re

all

that

scientists

ver

have

to go on, probabilities

hich'

ome-

times re so highthatthey an be termed

certainties.

Perhaps

statements

uch as

those cited

are

only

due

to careless

expression;

per-

haps

they

reveal a deep-seated

ntipathy

to

the

kind

nd

degree

f

certaintyossible

in

empirical

cience,

n antipathy

which

6

It should

be noted

that as

is

usually

the case,

this

universal

generalization

has exceptions

and,

hence,

s not

strictly

rue. One

way

to eliminate

the

obvious

exceptions

s

to add the phrase

"ex-

cept

in cases

of

mutations,"

but if

"mutation"

s

thendefined s it once was as any variationfrom

the regularities

f inheritance,

hen

the law de-

generates

o a

tautology

nd

is no

longer

an em-

pirical

aw.

In

order o retain

ts status

as an em-

pirical

aw, the

generalization

n question

must be

such

that

it is at least

logically possible

for there

to be

exceptions.

If

in point

of

fact, there

are

none,

then

t

is

true.



13/17

CERTAINTY

AND

CIRCULARITY IN TAXONOMY

185

has been traditionally

haracteristicf the

apriorists.Considering

he

mportant

on-

tribution hich ain has

madeto taxonomy

by pointing ut the dilatory ffect f the

a

priori utlook

n

taxonomy,ne hopes t

is the former. owever,whenthepoint

of

contentions

precisely

hose ssues which

the verbal confusion

lur, the results re

fatal.

EMPIRICAL CERTAINTY

AND EMPIRICAL

LAWS

With

such

distinctions

n

mind,

we are

now n a position oevaluate heevolution-

ary

laws and

principleswhich are at the

heart of the chargeof vicious circularity.

When

thecritics erm he aws and

princi-

ples of evolutionary

heory priori,

what

they usually

have

in

mind s

that evolu-

tionists ormulate

hemfrom he

study

of

certain

groups

of

organisms

n

less than

total evidence

for those

groups

nd then

extend hem o new

groups

or

which

on-

firmatorybservationsave notbeen made

and

may

notevenbe

possible.Hence,

with

respect o these attergroups, he applica-

tionof the

principless

prior

o

experience.

But

in

this sense all scientific rinciples

are

a

priori. They go

beyond

he

evidence

at hand.

They

wouldbe useless s

princi-

ples

if

theydidn't. This

is the sense of a

priori used when

weightings iven to a

character

efore he

taxon has

been

con-

structed re termed priori nd those s-

signed fter hetaxon

has been constructed

a

posteriori.

t is

also the

senseof

a

priori

used

by William

Coleman (1964)

in

his

book on

Cuvierwhenhesays, The natural

system

an be

prepared

n

two

ways:

1.

a

posteriori, y

direct

observation;

2. a

priori, y

the

principle

f the subordina-

tion of characters."

How inappropriate

his

particular sage

is in criticizingcience an be seenin the

followingxample for

the

sake

of

brevity

only

one

example

will be

given). Kepler

enunciated

his

laws

of

planetary

motion

whichwere

to

apply

to all

the

planets

n

the

solar

system

n

the

basis

of

ess than

handfulof

observationsmade

by Tycho

Brahe on a single planet,

Mars.

Later

astronomers

heckedhis laws for

other

planets n

the solar system nd for

other

positions f Mars, but they lso extended

them o cover

ll planetsrevolving

round

all stars.

We have little

hope of eververi-

fying r evenconfirming

hishypothesis

y

observation

ormore han an infinitesimal

portion

f the

star systems

n the

universe,

and

yet

no one wouldwant

to call

the

n-

ference unwarranted

r the hypothesis

meaningless.

Evolutionaryaws have

been devised

n

thebasis of innumerablebservationsut

observations

which have

been made pri-

marily

n

restrictedreasof the plant

and

animalkingdoms. ertain

ortions

f

phy-

logeny re

as inaccessible s

the farthest

corners f the universe.

These laws have

been formulated n

less than total

evi-

dence, but what is more

they have

been

found

o

be

not

completely

ccurate

ven

for hosegroups romwhich heywere

de-

rived. Even so, evolutionists xtrapolate

to other

groups

for

which

ittle

or

no evi-

dence s available.

Phenetic imilarity

as

been

found o

be a fairly ood

ndicator f

evolutionary

elationships

n

certain roups.

Cases

are

known, owever,

n

which

his

s

not true.

Even so, evolutionists

se phe-

netic similarity o infer hylogeny

or all

taxa.

We have ittlehope

of eververifying

or

even confirminghe

correspondencey

observation ormore han an infinitesimal

portion f

taxa thathave

evolved, nd yet

the

inference

s

not unwarranted,

or

the

assertion

meaningless.

volutionists

now

that

phyletic

imilarity

s not directly ro-

portional

o

phenetic

imilarity

n

all

cases,

but

it is

good enough

for their

purposes.

Astronomers

new hatKepler's aws

were

not completely ccurate,

but they

were

close

enough

or heir

urposes.

What us-

tifies evolutionarynferences s exactly

what

justifies

astronomical nferences-

theory.

The

inductiveeap which strono-

mers

made

concerning

lanetarymotion

s

much

reaterhan hose

volutionists

ould

ever

hink

f making-and for very

good

reason. Evolutionary

heory, ven com-



14/17

186

DAVID

L. HULL

binedwith

modern

enetic

heory,

oes

not

haveanything

ike the

power

f

Newtonian

theory.But

the ustification

n

both

cases

remains

he same.

The crux of

the

dispute

between

the

evolutionistsnd the

empiricists

s the

kind and

degree

f certainty

ecessary

o

justify

cientific

nferences.

Are

the

in-

ductive

nferences ade

by

evolutionists

n

reconstructing

hylog

certainty and circularity in evolutionary taxonomy- by david l. hull. evolution, vol. 21, no. 1...

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