The Herd as a Means- by David L. Hull. PSA: Proceedings of the Biennial Meeting of the Philosophy of Science Association,Vol. 1980, Volume Two: Symposia and Invited Papers (1980),

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1/21

The Herd as a MeansAuthor(s): David L. Hull

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2/21

The Herd as a Means

David L.

Hull

University of

Wisconsin-Milwaukee

In 1886

Friedrich Nietzsche noted the

following

basic error

in

the

philosophies of his day,

.".

..to place the goal in the herd and not in

single

individuals The herd

is

a

means,

no

more

But now one

is

at-

tempting to

understand

the

herd as

an

individual

and to

ascribe

to it

a

higher rank than to

the

individual--profound

misunderstanding

Also

to

characterize

that

which makes

herdlike,

sympathy,

as

the

more

valu-

able

side to our

nature '

(Nietzsche

1901, p.

403).

The recent

flap

over sociobiology

has

stemmed argely from

the

fear

that

biology is

being used to

justify a Nietzschean

view of

human soci-

eties, as

if

the chief

good

in

human relations must

be

basically

selfish,

as

if

apparently

altruistic

behavior

is

fundamentally

hypocritical.

FromDarwin to the present, biologists have blithely attributed the

presence and

persistence

of all sorts of

traits, including behavioral

traits, to

the "good

of the species".

Wynne-Edwards

1962)

pushed

this

view to

such an

extreme that

finally

biologists were

roused to

inquire

whether the emperor

really was wearing

any clothes.

Beginning

with Wil-

liams

(1966), a whole

series of

biologists

have shown

exactly how

dif-

ficult

it is

for

anything

to

be

done

for

the good

of

the species

if

spe-

cies

evolve

the

way that we think

they do.

The

biological

issues are:

(a) the nature

of

organization,

(b)

the levels of

organization

which

actually exist

in

particular

sorts of

organisms,

and

(c)

the

evolution-

ary

processes

which can take

place at

each of these

levels.

These are

among

the questions

with

which the

following

papers by Sober

(1981)

and

Wimsatt (1981) deal. The purpose of this paper is to explain the cur-

rent

state

of biological

theory

on these

issues and

its

implications for

human

societies. I argue

that

the nature of

biological evolution

and

biological

organization

have important

implications for

human

societies,

butnot the ones

usually

claimed. In

the first

place, the

fundamentals

of

evolutionary

theory

are currently in

a

state of flux.

Now is not the

time

to take a

particular

interpretation

of

biological

evolution

and

apply

it

uncritically to

social

evolution.

However, our

understanding

PSA 1980, Volume 2, np. 73-92

Copyright (

1981 by the

Philosophy of

Science

Association

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3/21

74

of the

complexities,

problems

and

possible solutions

in biology

can

profitably

be

used to

help

us increase

our

understanding

of societies

and how

they can

change.

Conversely,

there

is

no reason

why

our knowl-

edge

of social

organization

cannot be

used

to help

understand

biologi-

cal evolution.

1. Group

Characteristics

and Group

Selection

One

fundamental

question

in theoretical

biology

today

is

the nature,

existence

and role

of

"group characteristics"

in the

evolutionary

pro-

cess. For

example,

Wynne-Edwards

notes

that in developing

his

ideas:

...

it soon

became

apparent

that

the greatest benefits

of

sociality

arise

from its

capacity

to override

the advantage

of

the

individual

members

in the

interests

of

the

survival

of the

group

as a

whole.

The kind of

adaptations

which

make this

possible,

as explained

more

fully here, belong to and characterize social groups as entities,

rather

than their

members individually.

This

in turn seems

to en-

tail that

natural selection

has

occurred between

social

groups

as

evolutionary

units in

their

own right,

favoring

the

more

efficient

variants among

social

systems

wherever

they have

appeared,

and

fur-

thering their

progressive

development

and

adaptation. (1963,

p.

623).

Wynne-Edwards

s

claiming

three

things

in the preceding

quotation:

(a)

that groups

themselves

can

have adaptations,

(b)

that selection

can

operate

on such

groups,

and

(c)

that

the

good

of

the group

can

override

the good

of its

members.

Most

discussions

of

group selection

have

dealt with the final claim. If something

is

a genuine

group, then

the

conditions

under which

it can be selected

over and above its individual

membersare

very rare.

If

group

selection

occurs

at

all, it is

hardly

a

major

feature

of evolution (but

see Wade

1978).

Much

less

attention

has

been paid

to

the other two

claims.

The crucial

distinction

for

our

purposes

is

between properties

of

single organisms

and

properties

of

more inclusive

entities.

A single

mammal an

possess

mammary

lands.

These glands

not

only do

not

aid

this organism

in

its own

survival,

but

are

actually

detrimental.

Hence,

one

might be

tempted

to

explain

the

possession

of

mammary lands

by

individual

mammals

n

terms

of the

good

of

some group--the

family,

the tribe

or

the species.

However, these are not the traits of greatest interest to Wynne-Ed-

wards.

Some

properties

seem

to characterize

groups

as such and

not

their members

severally.

For example,

most

species

have

a 50-50

sex

ratio.

Although

such

a characteristic

may

be

analyzable

entirely

in

terms

of

the

sex

of

the members

of a

species,

it is

a

property

of

the

species

and

not the

members

severally.

As Williams

(1966,

p.

108) puts

it,

the

contrast

is

"between

a

population

of

adapted

insects

and

an

adapted

population

of insects."

Other

examples

of

putative

group

char-

acteristics

are

balanced

polymorphisms

and

frequency

dependent

selec-

tion.

These

are

the

sorts

of

adaptations

which Wynne-Edwards

s

chief-

ly

concerned

to explain

in

terms

of

group

selection.

One

element

in

Wynne-Edwards' argument, however, tends to get overlooked. As Nietzsche

fears, Wynne-Edwards

s "attempting

to understand

the

herd

as

an

indi-



4/21

75

vidual." If

too many adaptations

"belong

to and

characterize

social

groups

as entities," these

groups

cease to be

"groups"

and become

indi-

viduals

in their own right. One might be

tempted

to

treat an

organism

as a

group

of

cells.

Typically

we do not because

of the numerous

or-

ganizational properties which serve to integrate these cells

into

a

single

system (Hull 1976,

1978).

The same line

of

reasoning

should

apply as

readily

to

entities

more

inclusive

than

single organisms.

Organization

is what

counts.

Thus, two different

sorts of

group

selection

must be

distinguished:

(i)

selection

of

groups

as

well-integrated wholes,

and

(ii) selection

of

groups because of

extrinsic constraints. Most discussions concern

the possibility and

relative frequency of the second sort

of

group

se-

lection, the selection

of

aggregates

of

organisms which are

selected

together

merely because

they all happen to

live in

the same pool

of

water or on the same host

(Wilson 1980). Much

less

attention

has been

paid to the selection of groups which are really not "groups". In this

second

sense, a group can

function as a

unit

of

selection

only

if

it is

characterized

by enough organizational properties.

The

trouble

is

that

such highly organized

groups

are no

longer

properly interpreted

as

groups, but

as

individuals.

Anything

which is

sufficiently well-organ-

ized to

be selected must

be sufficiently well organized to count

as an

individual.

Williams (1966) reasons

along much the same

lines as Wynne-Edwards

but

comes

to

somewhat different conclusions.

He

argues

that

the f

t-

ness of

a group can be

treated as a simple summation of the

fitnesses

of its constituent organisms. The organisms are the entities with the

adaptations.

For

example,

the fleetness of a herd of deer is

totally a

function

of

the fleetness

of

individual

deer in the

herd. Only

if

the

herd

were a well-organized whole could it

have adaptations of its

own.

"Such

individual

specialization in a collective function would

justify

recognizing the herd as an adaptively

organized entity. Unlike

indi-

vldual

fleetness, such

group-related adaptation would require

something

more

than the

natural selection

of

alternative

alleles as an

explana-

tion."

(Williams 1966, p.

17).

One

point on which

Williams and Wynne-Edwardsdisagree is the

actual

status of

such things as

herds

of

ungulates and schools of fish.

WTynne-Edwardshinks they are organized wholes; Williams thinks they

are

not.

Williams views himself as an

"individual selectionist"

be-

cause

he

believes that

"adaptation

need almost

never be recognized at

any

level

above that

of

a

pair

of

parents and associated

offspring."

(Williams

1966, p. 19). Thus, he would agree

with Wilson (1971)

that

certain

sorts of

colonies

can exhibit adaptations. For example,

the

organisms which

comprise a

hive in

certain

eusocial insects

exhibit di-

vision of

labor, functional and structural

differentiation,

character-

istic

distributions in the hive both

spatially at any one time

and tem-

porally

during the "life cycle" of the hive,

and so on. If such

hives

are not

supraorganismic individuals, nothing

is.

For

this reason, Wilson

(1971) thinks that selection can take

place



5/21

76

at

the

level

of

hives. Williams

(1966) might agree that such hives

are

individuals and

exhibit adaptations of their own, but

he would draw the

line at their functioning

as units

of selection. This conclusion

should come as

no surprise because Williams does not

think that even

organisms can

function as units of selection. "One

necessary condi-

tion" for an entity to be selected "is that the selected entity must

have a

high

degree of permanence

and a low rate of endogenous change,

relative to the

degree of bias (differences in selection

coefficients).?

(Williams 1966,

p. 23). Dawkins

(1976, 1978) has made himself extreme-

ly unpopular among

biologists, first, by stripping

the emperor of yet

another layer

of clothes and, second,

by doing so in a popular format.

Time and again,

population biologists can be found

saying such things

as

"evolution

is nothing but changes

in gene frequencies.?" Although

models in population biology need

not be limited to

the relative fre-

quencies of two

alleles at a single locus, most are.2

The claim is,

however,

that the fitness of an organism

can be treated as a simple

summation of the fitnesses of its separate loci. Although Dawkins has

taken the heat for emphasizing this

position, it can

be found explicit-

ly expressed in Williams. According

to Williams:

Obviously

it is unrealistic to believe that

a gene actually ex-

ists in

its

own world with no complications other

than abstract

selection coefficients and mutation

rates. The

unity of the geno-

type and the

functional subordination of the individual

genes

to

each other

and to their surroundings would seem,

at first sight,

to

invalidate

the one-locus model of natural selection.

Actually

these considerations do

not

bear

on

the basic postulates

of the

theory. No matter how functionally dependent a gene may be, and no

matter

how

complicated

its interactions

with other genes

and

en-

vironmental factors, it must

always be

true

that

a given gene

sub-

stitution

will have an arithmetic

mean effect

on fitness

in

any

population. One allele

can

always

be

regarded

as

having

a

certain

selection coefficient

relative to another at the

same

locus

at

any

given point in time. Such coefficients

are numbers

that

can

be

treated algebraically,

and conclusions inferred

for one

locus can

be iterated over all loci. Adaptation

can thus be

attributed

to

the effect of selection acting independently

at

each

locus.

(1966,

pp. 56-57).

The preceding conviction is at the heart of the levels of selection

controversy

and

from

it to

sociobiology.

Some

of

the

objections

raised

to

sociobiology

have concerned any attempt

to

explain

human

social

characteristics biologically,

but

others are raised

to the

attempt

to

do

so on the

"gene

selectionist"

model.

These

critics

argue

that

this

overly simple model

will

not do for

ordinary biological

traits. It

surely

will

prove

inadequate

for

social

traits.

Although

Williams acknowledges the existence

of

adaptations

at

lev-

els

more

inclusive

than

single genes

and even

organisms,

he

is a

gene

selectionist

because

he

thinks that

all these

adaptations

can be

ex-

plained entirely in terms of selection acting on particular genes. For

example,

the adaptations exhibited by

hives

are to

be

explained by



6/21

77

means

of kin

selection,

not selection

acting

on

kinship

groups. Even

though Williams

(1966, pp. 159,

96-97)

acknowledges

that the

"central

biological

problem is not

survival as

such,

but

design

for

survival,"

he

maintains that an

organic adaptation

is a

"mechanism

designed

to

promote the success of an individual organism, as measured by the ex-

tent to which it

contributes genes to

later

generations

of

the

popula-

tion of

which it

is

a

member." Once

again,

if

Williams

thinks that

se-

lection does not act

on

entities

composed

of

parts

which all have

the

same

genetic

makeup--such

as

organisms,

he

certainly

cannot

acknowledge

as units of

selection

entities

composed

of

parts

with different

ge-

netic makeups--such

as beehives.

2.

Replication

and Interaction

One

minor

source

of

confusion in

the

group selection

controversy

is

equivocation over

what

actually

counts as

"individual"

versus

"group"

selection. Gene selectionists term themselves "individual selection-

ists" because

genes are

individuals.

Organism

selectionists

also

feel

that

they

have

the

right to term themselves "individual selectionists"

because

organisms

are

also

individuals.

Finally,

even such classic

group

selectionists as

Wynne-Edwardshave some

right

to be

termed "in-

dividual

selectionists" because

they argue

that

many so-called

"groups"

are

really

individuals

A

more

serious

source

of

confusion

has been a

systematic

equivocation

over two

different senses

of

"selection"

and

"unit

of

selection."

Williams (1966, p.

25)

proposes

to

redefine "gend'

in

evolutionary contexts

as "any

hereditary

information for

which there

is a

favorable or

unfavorable

selection

bias equal to

several or

many

times its rate of endogenous change." Dawkins (1978, p. 67) suggests

replacing

the term "gene"

in such

contexts with the

more

general term

"replicator",

which

he

defines as "any

entity in

the universe which

in-

teracts with its

world,

including other

replicators, in such

a way

that

copies

of

itself are made.

A

corollary

of

the

definition is

that at

least

some

of

these

copies, in

their turn, serve as

replicators...

.'"

I

find Dawkins'

notion

of a replicator

an

important Improvement

in

the

conceptual foundations

of

evolutionary theory,

but in

his defini-

tion he runs

two sorts of

interaction together, the

sort

of

interaction

necessary

for

a

replicator to

replicate

itself and the sort

which pro-

duces differential replication. That these are two different processes

can be

seen in the

fact that

they

are

usually carried on

by

different

entities

at

different levels of

organization. Not

only

that, but

be-

cause

these

functions are

so

different, the entities

which

perform them

tend to be

characterized

by different sorts of

general properties. The

only "adaptations"

which a

replicator needs

are

those to promote

repli-

cation.

All that

an entity need

be able to

do to function

as a

repli-

cator

is to

replicate

itself, the more

directly the

better. If all

that

goes on

is

replication,

evolution of sorts

might

result, but not

evolution

through

selection. In order for

selection to occur, an ad-

ditional

process is

necessary. Either the

replicator itself or else

some more

inclusive

entity produced

by the

replicator must

interact

with its environment in such a way that replication is differential.

These

latter entities are

the

entities which have

"adaptations" in the



7/21

78

usual

biological sense of this

term.

Elsewhere

I (Hull 1980,

p. 318) have

termed the entities

which

function in this

second process

"interactors" and

defined

these two

technical terms as

follows:

replicator:

an entity that passes

on its structure

directly in

replication.

interactor:

an entity

that directly

interacts as a cohesive

whole

with its environment

in such a way that

replication

is

dif ferential.

With the aid

of

these two technical

terms, the

selection process

it-

self can be defined as follows:

selection: a process in which the differential extinction and pro-

liferation

of interactors

cause the differential

per-

petuation

of the replicators

which produced

them.

In selection

processes,

replicators replicate

themselves.

In the

beginning,

the first replicators

probably

also functioned

as the only

interactors

as well.

However, as evolution

proceeded,

these two func-

tions

became differentiated.

Replicators

began to produce

evermore

in-

clusive

interactors

to cope with evermore

inclusive

and complex envi-

ronments. The result

is the

part-whole hierarchies

which

are so char-

acteristic

of the

living world. Some

entities

are extremely simple.

As organisms they are hardly more than encapsulated replicators. They

reproduce themselves

asexually

and that is that.

No

higher

levels

of

organization

are present.

Some organisms

are themselves

highly

complex,

highly

stratified

hierarchical systems.

Some

organisms

form colonies

and other sorts of kinship

groups.

Sexual organisms,

at least,

form

species.

(Contrary

to

common

sage,

just

as not

all

organisms

form

kinship

groups,

not all organisms form

species.)

The question now

be-

comes,

for

any particular

sort of organism,

at what

level or levels

is

replication

taking

place, at what level

or levels

is interaction

taking

place?

Typically replication

occurs

at the

lowest

levels

of

organiza-

tion,

primarily

at the level

of

the

hereditary

material,

while

inter-

action occurs both

at these

levels and at increasingly

more inclusive

levels as well. The point I wish to stress is that not only are both

processes necessary

for

selection,

but also

both are

important.

Nei-

ther

can be

omitted,

and neither

takes

precedence

over the other.

With

this distinction

in

mind,

one

disagreement

between

gene

and or-

ganism

selectionists can

be shown

to be

only apparent.

When

gene

se-

lectionists argue

that

selection

occurs

only

at the

level

of

the

genet-

ic

material, they

have replication

in mind. Rates

of

endogenous

change

are

relevant

to

replication,

not

interaction.

When

organism

selection-

ists claim that selection

occurs primarily

at the

organismic

level,

they have interaction

in mind. Genes

may

be the

entities

which

repli-

cate themselves most directly, but they tend to interact with their

evermore

inclusive environments

evermore indirectly.

Although organ-



8/21

79

isms interact

directly

with their

environments,

they

tend to

replicate

themselves

only

indirectly via their

genes.

Regardless of how it

might

appear,

the distinction between

replication

and interaction is

not

"merely

semantic".

Entities more

inclusive than

single genes

can

func-

tion as

replicators.

They

do not

thereby become

genes.

A

general

term

like "replicator" is necessary if confusion is to be avoided. Similar-

ly,

entities

both less

inclusive and more

inclusive

than

organisms can

function

as

interactors.

If

populations can function as

interactors,

then

they

are

interactors,

not

"superorganisms".

3.

Linkage Disequilibrium

and the Unity

of

the

Genotype

Once

the preceding

disagreement

between the

gene

and

organism

selec-

tionists has

been shown

to be

apparent,

an important difference never-

theless

remains.

Organisms

are

well-integrated cohesive wholes.

That

is

why

they can

function so

well as

interactors.

Each organism is

pro-

duced by its genome in interaction with successive environments. An

extremely complex

system

of

feedback loops becomes established between

the

developing

organism, its

environments

and the

genome

which is pro-

ducing

it. But

all

of

this is

relevant only to

interaction. How

about

replication?

Biologists such as

Mayr

(1963, 1975)

have

emphasized the

role of

the

unity of the

genotype

in evolution.

Although there is

a

one-to-one

correspondence

between

genomes and

organisms, many organisms

can

possess the same

genotype, e.g.,

clones.

Conversely,

many differ-

ent

genotypes can

produce, for

all

intents and

purposes,

the

same

phe-

notype, i.e.,

phenocopies. The issue

of

the unity of the

genotype

re-

fers to

the role of

genotypes themselves

as

cohesive systems. Geno-

types are functionally and structurally organized systems. In selec-

tion

processes can

they be

treated as if

they

were not?

Biologists can be

found

arrayed on

both

sides of this

issue. As the

earlier

quotations

indicate,

Williams (1966)

maintains that

one-locus

models

should be

adequate

for

characterizing

the

evolutionary

process.

"iNo matter

how

functionally

dependent a gene

may be,

and no matter how

complicated its

interactions

with other

genes

and environmental

factors,

it

must

always

be true that

a given

gene

substitution

will have an

arithmetic mean

effect

on fitness

in any

population."

(Williams 1966,

p. 57).

The

issue is the

extent of

linkage

disequilibrium. The

coef-

ficient of

linkage

disequilibrium

is a measure

of the

statistical

de-

pendence between two loci. To some extent the term is misleading in

that

this

dependence

need

not have

anything to

do with

linkage of

loci

on

the same

chromosome.

(Roughgarden

1979, p. 113).

If

genotypes are as

unitary as Mayr

(1963,

1975) claims,

one

would

expect

to

discover

very high

linkage

disequilibrium

coefficients when

genes

in

the

same

functional

complex are

studied. So

far

the evidence

is not as

unequivocal

as one

might wish.

(See

Lewontin 1974

and

Rough-

garden

1979 for

reviews.) No

matter how

this issue is

decided, there

are

gains

and

losses on both

sides.

If genomes

are

highly

organized

functional

systems,

then

evolutionary

models which

take only

one or two

loci into account at once are liable to be inadequate. The recognition



9/21

80

of higher

levels

of organization in replicators is purchased at

the

price

of complicating studies

of evolutionary

processes

significantly,

possibly prohibitively.

If one-locus models

are good

enough, then the

task of

the evolutionary

biologists is

much

simpler, but he is left

with

explaining

why the highly complicated

internal organization

of

genomes can be ignored.

Both

Sober (1981)

and Wimsatt (1981)

argue

against reductionism

in

biology. Two sorts

of reductionism

are involved in the controversy

over the

unity of the genotype.

WhenWilliams (1966)

argues that

a

herd is nothing

but a collection

of organisms,

he is

claiming that

herds

are not sufficiently

well-organized

to

be counted entities

in

their own right.

Certainly

a herd of ungulates

is composed

of nothing

but individual

ungulates. Any relations

which

might justify viewing

a

herd as a higher-level

entity

would be relations

between these

individ-

ual organisms.

However,

when Williams (1966)

argues

that replication

can be treated as if only the genetic material can function as repli-

cators and that

individual genes can

be

treated

as if they were func-

tionally

independent

of each other,

he is presenting

an even

more re-

ductionist position.

Organisms

are not composed

just

of genes. They

are

made up of

numerous other parts

as well.

Only a small percentage

of

an

organism's mass consists

of

DNA.

On

the gene

selectionists'

view,

as far as

replication is concerned,

organisms

are nothing

but

collections

of genes.

4.

Genetic Diversity

and the Unity

of

the

Genotype

One of Mayr's main goals in his Systematics and the Origin of Spe-

cies (1942)

was to counter

the

typological

species

concept by

emphasiz-

ing the

amount of genetic

diversity

present in natural

populations

and

species

at large.

According

to the typological species

concept,

spe-

cies are

natural

kinds characterizable by

means

of fixed sets

of

essen-

tial traits.

All

members

of

a

particular

species

must

possess

all

the

essential traits

of

its

species, and

no other species

can be

character-

ized by precisely

this

same set of

traits.

All

variation,

whether at

any one

time

or

through

time, is purely

accidental.

Mayr (1942)

showed

that

if

one follows

a

species

through

its

range,

one discovers

consid-

erable geographic

variation.

An

allele which

is

common n

one

popula-

tion is

rare in

another,

and

so on.

Populations

at

the

termini

of

these clines may have little, if anything, in common. They may not

even be able

to mate

successfully.

According

to

current

best

estimates,

sexually reproducing

species

of

animals

are

polymorphic

for a third

of

their

genes,

and

at an

average polymorphic

locus,

a

quarter

of the in-

dividuals

in

a species

are heterozygous.

(Roughgarden

1979, p.

87).

This

means that at a third

of the

loci in

a

species

two or

more

alleles

can be

found,

and

that at

these loci,

a

quarter

of

the organisms

are

heterozygous, i.e., possess

different

alleles.

If

phyletic

evolution

is possible, one

should

expect to discover

that this

variability only

increases if one

follows

a species through

time.

Other

sorts

of

poly-

morphismalso

exist, e.g.,

trophic polymorphisms

(Turner

and

Grosse

1980).



10/21

81

Because of the

extensive

genetic diversity

which exists in

species,

Mayr (1969, p. 369) argues that the notion of a "typical" memberof a

species

makes

no sense. "Species

consist

of

variable

populations,

and

no single specimen can represent

this

variability.

No

single specimen

can be typical in the Aristotelian sense." Mayr, in his second synop-

tic work on the evolutionary process,

Animal

Species

and Evolution

(1963), emphasizes just

the

opposite characteristic

of

species.

As var-

iable as species are, each species possesses its own basic genotype:

The basic gene complex

of the

species (with

all the

species-specif-

ic canalizations and feedbacks) functions optimally

in the

area

for

which

it

had evolved by selection, usually somewhere near the cen-

ter. Here

it is

in

balance with the environment and here it can

afford much super-imposed genetic variation and experimentation in

niche invasion. Toward

the periphery

this

basic genotype

of

the

species

is

less and less appropriate

and

the leeway of genetic

var-

iation that it permits is increasingly narrowed down until much

uniformity

is

reached. (Mayr 1963, p. 527).

Because the "unity

of

the genotype places well-defined limits

on

the

potential for variation" (Mayr 1963, p. 176), a "genetic revolution" is

usually needed

for

new species

to

arise. Instead

of

speciation occur-

ring through numerous generations by the gradual accumulation

of minor

changes in gene frequencies,

it

usually occurs by means

of

the isola-

tion of a

small population

at

the

periphery

of

the species. Most

such

peripheral isolates go extinct, but every once in a while, one of them

becomes established

as

a

new

species

with

its

own

characteristic

geno-

type. (See also Eldredge and Gould (1972).)

Three issues are involved here: (a) the unity of particular geno-

types as discussed earlier, (b) the prevalence

of a

single

basic

geno-

type throughout a species in spite of considerable genetic heterogene-

ity, and (c) the role

of

the genotype in promoting the cohesion of the

gene pool. Mayr is concerned to argue that neither genomes

nor

species

are aggregates. Both are organized wholes. One explanation for the

cohesiveness

of the

gene pool is that all organisms belonging to the

same

gene pool have basically the same genetic makeup. However, this

is not the only explanation for or mechanism which can serve to enhance

the cohesiveness of the gene pool. Mayr (1963, p. 542) remarks that

throughout his book,

he has

"stressed

the

tremendously cohesive

effect

of

gene

flow.

Yet, when one

tries

to calculate the time it takes

for

genes

to

percolate

from

one end of the

range

of a

widespread species

to

the

other,

one arrives at rather astronomical

figures."

He

goes on,

however, "Without wanting to depreciate the importance

of

gene flow, I

advance the thesis that the cohesion

of

the species is also due to the

fact that

all

those of

its populations that

have

not undergone a genet-

ic

revolution share the same homeostatic systems and that these systems

give great stability." (See also Eldredge and Gould (1972) .) Thus, a

species is cohesive, both because gene flow promotes cohesiveness

and

because all organisms in the species possess the same basic genotype.

The problem is how to reconcile the unity of the genotype with the



11/21

82

simultaneous

existence of extensive

genetic heterogeneity.

One

possi-

ble solution is

that this

variability

is

limited to certain loci.

At

other loci,

no

variability

exists.

All organisms

within a single

spe-

cies possess

identically

the

same

genes at these

loci.

The question

then arises

if

these are also

the

genes which

distinguish

this species

fromall other species. If so, then species have an essence in an Ar-

istotelian

sense.

Or it may

be the

case that a

species

shares its

con-

stant

loci with several

other species and

is distinguished

from

them

only

by differences

at

its variable

loci.

If so,

then species

lack

essential genes

in the

Aristotelian

sense.

Or it may

be the

case that

the structure

of

the genotype

supplies

its unity.

Although

a variety

of

different

alleles

can exist

at any one

locus,

the overall

arrange-

ment

of loci

remains the

same.

This structure

is then

its

"essence."

Somehow

biological

species

seem

capable

of remaining

homeostatic

sys-

tems in spite

of

considerable

internal diversity.

Furthermore,

if

all

the organisms

which

belong to

the

same species

possess,

in some sense,

the same genotype, then there is some justification in using this com-

monality

in defining

particular

species.

If

so,

then asexual

organisms

form

species

as surely

as do

sexual organisms.3

As

Dawkins (1979)

documents,

the

recent revolution

in our thinking

about

the evolutionary

process has

its origin

in W.

D. Hamilton's

1964

papers

in the

Journal of Theoretical Biolog.

In these papers

Hamilton

introduces

his

notion

of inclusive

fitness--the

contribution

which

an

individual makes

to the

gene pool

of

the

next generation,

both directly

via

replicates

of its

own genes and

indirectly

via

duplicates

in relat-

ed organisms.

It is in this paper

that the

mathematics

or altruistic

behavior receives its first extensive treatment. Hamilton concludes

the first

of

these

papers

by

stating

that,

in order for altruistic

be-

havior to evolve:

...the

benefit

to a sib must average

at

least twice

the loss to

the

individual,

the benefit

to a half-sib

must be

at least

four

times

the

loss,

to

a

cousin

eight

times and

so on. To

express

the

matter

more

vividly,

in the world

of our model organisms,

whose

behavior

is determined

strictly

by genotype,

we expect

to

find

that no one

is

prepared

to

sacrifice

his

life

for

a

single person

but that

ev-

eryone

will

sacrifice

it

when he

can

thereby

save more than

two

brothers, or four half-brothers, or eight first cousins... . (1964,

p. 16).

As Nisbett

and Ross

(1980,

p. 45) note,

one

of the most

coammon

r-

rors

in

reasoning

made by

human beings,

scientists

included,

is

to be

unduly

affected

by

the

vividness

of information.

This

is

certainly

the

case with

Hamilton's

discussion

of

inclusive fitness

and

altruistic

be-

havior.

In

most

cases,

it is

his vivid

description

of the

consequences

of his

argument

which gets quoted

(e.g.,

Wilson 1975,

p. 415).

Although

the necessary

distinctionsare

made

in

the technical literature,

too

of-

ten

they

tend to

be

neglected

in

more

popular

expositions.

Time

and

a-

gain

we are told

that the

investment which

one organism

makes

to

anoth-

er should covary with the number of genes the two have in common. En-

ergy

flow

should

go

with gene

flow. For

example,

in the

commonest

orm



12/21

83

of

inheritance, siblings

should share

half

of their

genes, grandchil-

dren

a

quarter,

greatgrandchildren

an

eighth, and so

on.

Similar

cal-

culations can be made for

nieces

and

nephews, cousin, etc.

The

trouble with this way of

putting it is that it conflicts with

the actual facts of the

case. Even

though species are

genetically

quite

heterogeneous,

most alleles are present

in

very

low

frequencies.

Hence, any

two

organisms picked at random

are

likely

to

possess

exactly

the

same

alleles

at

the

vast

majority

of

their

loci, say,

90%. The

507,

25%, etc.

progression

concerns o

those loci at which the two

organ-

isms happen to differ.

Thus, any

two

organisms picked

at

random

are

liable to have the same

alleles at 90%

of

their

loci,

while

siblings

under

these same

circumstances should share 95%

of

their genes.

As

a

result, although nepotism

should

exist,

it should not be as difficult

to

overcome as

one

might

expect.

A second issue in which the preceding difficulty arises is the cost

of

meiosis. In many

cases, organisms

are

"outbreeders".

They

tend

to

mate with

organisms that are not

especially

closely

related

to

them.

They are

members of the

same species, but that is all. In

most

sorts

of

sexual reproduction, each

organism

loses

half

its

genes.

At

meiosis,

reduction

division occurs. Thus,

sexual reproduction has

a 50%

cost.

If

the name of the

evolutionary game

is to pass on one's genes,

sexual

reproduction must be extremely

advantageous

since

it has

to

make

up

a

50% loss.

Once

again, the fact

that

most

organisms

have

exactly

the

same

al-

leles at the vast majority of their loci is being overlooked. Two organ-

isms which

mate

are

likely

to

differ

at, say,

10% of

their loci.

Hence,

the

cost

of

meiosis

is

reduced

to

half

of

the

10%,

or

5%.

Although

a

5%

cost is not

negligible,

it

does

not

pose quite

the

problem

that

50%

does.

Barash (1976)

raised precisely this objection

to the

supposed

50% cost of meiosis,

only to have it

dismissed curtly by

Maynard Smith

and

Williams (1976) as

a total

misunderstanding of the problem. A

mis-

understanding it surely

is, but a misunderstanding

which is

perfectly

understandable given the

early

literature on

the

subject.

The

relevant distinction is

between the

percentage of genes which

two organisms share and the likelihood that a particular gene will be

passed on.

In most

sorts of sexual reproduction,

a particular

off-

spring

will

always

get 50%

of

each genes

from

one

parent and 50%

from

the

other.

Similarly, siblings will

share 50%

of

their genes. In the

case

of

the

next generation, the 25%

figure is an

average. On the av-

erage

a

grandchild will

receive

25% of

its genes

from

each

grandparent,

although it is possible

for it to

receive no genes from one

grandparent

(maternal or paternal)

and 50% from

the other. In all cases

these are

genes which

are identical

by descent. The second

set of

figures refers

to

likelihoods of

transmission. Given a

particular gene in a

parent,

what

is the

likelihood that

it will be passed on

to a

particular of f-

spring and

not its

allele? Given a particular

autosomal gene

in an

offspring, what is the likelihood that this gene was obtained from one

parent rather than the

other? The

answer in both cases is

50%. Be-



13/21

84

cause the numbers come out the same, it is easy to overlook the

fact

that we are dealing with percentages, average percentages, and likeli-

hoods.

A second important distinction is between genes with exactly

the

same structure and genes which have the same structure because they are

immediate replicates of the same ancestral gene. The latter

are genes

identical by descent. Whenwe say that each offspring receives

50% of

its genes from each of its parents, we are referring to genes

as mater-

ial entities. Nothing is implied necessarily about similarity

in

structure.

In

all natural populations, more than

50%

of the

offsprings'

genes

will be

similar

in

structure. How many depends on the percentage

of loci at which its parents possess alleles with the same structure.

Although these alleles will also be identical by descent, their

common

ancestral gene may have existed numerous generations in the

past. If

one counts only those genes which are similar because of iimmediate

de-

scent, 50% of the genes of each offspring will be identical by descent

to the genes of each of its parent. However, if more distant descent

is allowed, this figure begins to approach 100% as the percentage

of

loci at which the parents have alleles with the same structure ap-

proaches 100%.

As Stampe and Metcalf (1980, p. 613) point out, "Disagreement

be-

tween predictions of several theories can be traced to differences

in

the

interpretation

of

the meaning

of

coefficient

of

relationship (r).

Genetic models suggest that

r

is best defined as the probability

that

a

certain gene

is

shared

with

a

relative through

common

escent,

rath-

er than as the proportion of genes shared between relatives through

common escent." Both kin selection and the cost

of meiosis are

best

expressed

with

r

defined

in

the

first way.

The

fact

that

many

authors

define it

in

the second way (e.g.,

Wilson

1975) explains why

controver-

sies on these issues are

so

common. When the criterion

of

identity

through descent

is

ignored and

all

genes

with the same

structure are

considered genes

of

the

same sort, confusion

is

only

increased.

If

one

is not

concerned

with

selection processes, genes can be

considered

to

belong

to

the

same natural kind

solely

on

the

basis

of

structural iden-

tity

or

similarity,

just

as

organisms

can

be

considered

to

belong

to

the same species if they

have

sufficiently

similar

genomes (Caplan

1980). However,

if

genes

are the

things

which

are

being

selected and

species are the things which are evolving, descent takes priority to

similarity. Only entities which are identical (or similar) by

descent

belong

to

the same reference

class

(Hull 1976, 1978, 1980).

6. Implications for Human Societies

Present-day human societies are biologically peculiar

in

several

re-

spects. Throughout

most

of our

history,

human

societies

tended

to

be

of

the tribal sort--50 to 150 individuals,

most of whom

were relatives.

Present-day societies are much larger and much more heterogeneous

in

all

respects, including genetic heterogeneity.

Tribal wars

in

which

one tribe successively annihilated its neighboring tribes could affect

the

genetic makeup

of

the human gene pool

in

that area.

Wars

between



14/21

85

alliances

of

present-day

nation

states

are

not as

likely

to

have

such

an

effect.

Although

it

presents

precious

little

comfort,

the

effects

of

atomic warfare are

liable

to be

genetically

indiscriminate,

having

as

random an

effect

on

human

evolution as

mutations.

The major

problem

posed by

the size

and

genetic

heterogeneity of

human

societies,

however, concerns the

efficacy

of

possible

biological

mechanisms

for

promoting

cohesiveness of

these

societies.

If

one

looks

just

at the

number

of

loci at

which

any two

people picked at random

from

a

society are

likely

to

have

the

same

alleles,

one

should

expect

people to

cooperate

quite

extensively.

Although

human

societies

are

genetically quite

heterogeneous,

any

two

members

of a

society

are

like-

ly to be

genetically quite similar. The

problems which

have

been

raised

by

sociobiologists to

cooperation

among

human

beings

arise

only

if

one

concentrates

on

alternative alleles at a

single

locus.

If

loci

are

selectively

independent

of

one

another, then

genes at

different

lo-

ci neither cooperate nor compete with each other, only different al-

leles

at

the same

locus. In

this very

particularized

context,

it

is

difficult

to see how

an

"altruistic

allele" could come

to replace a

"selfish

allele".

However,

the

entities

referred

to

here

are

different

alleles,

not

different

genes,

and

certainly not

different

organisms.

The

inferences

from

selfish

alleles to

selfish

genes, and

from

selfish

genes

to

selfish

organisms

are

extremely problematic.

They

may

be

jus-

tified,

evolutionary

biologists

are

certainly

warranted

in

continued

attempts to

justify

them, but

they

currently

are less than

crystal

clear.

After all,

it

should be

remembered that, on

exactly this

same

line

of

reasoning, sexual

reproduction

should

be

rare,

and

according

to

most workers, it is extremely prevalent. (But see Hull 1980).

If

we limit

ourselves to

the

single

locus

interpretation,

it is hard

to

see how

behaviors

contributing

to social

cohesiveness in human

be-

ings can have much

of a

genetic basis. At

most, such

behavior can

be

"misfirings" of

previously

adaptive

behavior

which has

yet to be

elimi-

nated

(Dawkins

1976, p.

109).

For

example,

parental

investment

is

genetically quite

advantageous

as

long as it

is

directed

at biological

offspring.

Adoption of

unrelated

offspring

is not.

The

desire by

hu-

man beings

to

adopt

children

can be

explained either

as

such a

misfir-

ing

or

as

an

extremely

cynical form

of

exploitation.

Arguments

gainst

the

efficacy of

the simple application of kin selection models to human

beings

cannot rest

solely on

unusually high

rates

of

adoptions in

cer-

tain

societies,

such as

Eskimos. It

must

also be

shown

that

adopted

children

are

not

by and

large

turned

into

reproductive

neuters.

The

pleasing side of

this same

coin is

that the

effects of

genes

being i-

dentical

by

descent drop

off

very

rapidly

as

genealogical

relationship

becomes

more

distant.

Either very

low

differences

in

inclusive

fitness

can

make

a

difference

or

else

distant

relatives

should treat

each

other

no

differently

from how

they

treat

non-relatives

(West

Eberhard

1975).

However,

it

should be

kept

in mind

that

considerable

disagreement

exists

among biologists

about the

precise nature

of

the

strictly

bio-

logical mechanisms which promote the cohesiveness of gene pools as such,

and

that some

biologists

doubt the

very

existence of such

cohesiveness.



15/21

86

One should

be both

very careful and

very

tentative

in

reasoning

from

such

problematic

biological principles. I

do

think, however, that

ex-

amining such issues

as

the

unity

of the

genotype

and the

cohesiveness

of

gene

pools can

be helpful in

understanding

humansocieties. By

this

I do

not mean that one

should

reason from the nature

of the

human

genotype and structure of the humangene pool to the nature of human

societies,

although such

inferences

might well be

warranted.

Rather,

I

think

that all

three might profitably

be

viewed as instances of

the

same sort of

phenomenon--highly organized

systems which,

nevertheless,

can undergo

change.

How much

can a

genome

be modified and

still

remain functional? Can

a

genome be modified

successively in time, one

or two loci

at a time,

until it forms

a distinctly new

genotype;

or are

genetic

revolutions

necessary? Currently the

answers

to

these

questions

remain elusive,

but

surely biologists have

investigated them in

greater

detail and have

discovered a greater variety of problems and suggested solutions for

genotypes

and

gene pools

than sociologists

have for

societies. Human

societies,

like gene pools,

are quite

heterogeneous. They

are also

co-

hesive, so it seems.

How can

such cohesiveness

be

maintained in the

face

of

such

heterogeneity?

Calls

for

human

freedom

if

answered pro-

duce

more

heterogeneous

societies. How "free"

can the

people in a so-

ciety become without

the

society ceasing to be a

society?

Too much ho-

mogeneity

also has its costs. If

the

analogy is

appropriate, one

is

justified

in

claiming that

neither

heterogeneity nor

homogeneity is

an

unalloyed

good. It all depends

on the

intensity and

nature of the

se-

lection

pressures.

Permitting

conscientious

objection in peacetime

or

during limited wars might well be a beneficial escape valve. During

all-out

wars,

it

might prove

detrimental.

Societies appear

to

be entities

in

their own

right,

with

their

o.m

characteristics.

From

a

biological point

of

view,

it

is

difficult

to

treat

societies

in

this

wray.

Organisms, kinship

groups

and human

so-

cieties differ

from

each

other

in

being

increasingly

genetically

heter-

ogeneous. The more

heterogeneous

they are, the

less

likely they

are

to

be

able to

function

as

replicators. From this it

does not follow that

they

cannot

function

as

interactors. Just as

cells

do not interact

with their

environments in isolation,

people do

not interact with

their

environments

in

isolation. Human

societies pose

problems

for

a

purely

biological theory of evolution, not because of any peculiarly human

characteristics

but

because

of

their

strictly

biological characteris-

tics. It is

important

to

distinguish those

problems

which

arise

from

human

societies

being

systems

from

those

which

arise because of

any

pe-

culiarities

of

human

social systems. Too

often

critics

of

the

"biolo-

gizing" of the

social

sciences leap over

substantial

biological pro-

blems

to dwell

exclusively

on the

sociological problems.

No one mentions

social evolution

without

emphasizing

its

partial

in-

dependence

of

biological

evolution.

Culture

flow

does

not

always

coin-

cide with gene

flow.

In

human

beings,

cross-lineage borrowing

is

pos-

sible (Campbell 1972, p. 33). One can teach one's own offspring, but

one

can also

teach the

offspring

of

others. The

ease with which



16/21

87

human beings can teach non-relatives must, on the gene selectionist

model, be interpreted either as another "misfiring"

or

as an instance

of "reciprocal altruism" (Trivers 1971, p. 46).

Whenever one

teaches

or "indoctrinates"

the

offspring

of

others,

social and

biological evo-

lution can come

into conflict.

Teaching

one's own

offspring

the

virtue

of patriotic self-sacrifice is genetically quite altruistic; teaching

others such

a

virtue is genetically

selfish.

Organisms

which

must

co-

operate

with

their sexual competitors

should be ambivalent

in

their

relationships. Add to this situation,

the

ability

to indoctrinate

a-

cross lineages,

and

the ambivalence

only

increases.

As

Campbell (1972,

p. 23) emphasizes,

a

self-sacrificial disposition

in

human

beings

is a

"product of social indoctrination, which

is counter

to rather than

sup-

ported by genetically transmitted behavioral dispositions."

A

second point which needs emphasizing is that currently

we have

no

detailed, well-developed theory of social evolution (Alexander 1979,

Blute 1979). It is all well and good to mention possible differences

between biological and social evolution, but until someone actually

produces a theory of social evolution comparable to current theories

of

biological evolution,

such

discussions must

remain

highly

tentative.

Recall all the really excellent arguments against the possibility

of a

genetic code (Commoner 961). Time

and

again the

Philistines

do what

their

intellectual superiors

know is

impossible.

Human societies

may

represent just another level of organization, presenting no new pro-

blems, or it may represent an insurmountable barrier to the literal

extension of a

strictly biological theory of evolution.

Conceptual evolution represents yet another level in the levels of

selection controversy. In order for biological theories of evolution

to be adequate for conceptual evolution, scientific ideas would have

to

be transmitted by the genetic material. It is plausible that certain

general

features of

human societies are

to

some extent influenced

by

our

genes. It is also plausible that the curiosity so necessary

for

science

is in human

beings genetically based. But it is very

unlikely

that calculus or

quantummechanics

is in

any sense "programmed

nto our

genes". However, one feature

of

this controversy which

I

find curious

is that the very same scientists who argue for biological influences

on

social

evolution draw back at

a

parallel argument one level up--social

influences on conceptual evolution.

For

example, Wilson (1975) argues

for a biological basis for certain social features of human societies.

However, when his critics (Allen, et. al. 1976) argued for

a sociologi-

cal

basis for certain features

of

his conceptual system, Wilson ob-

jected.

These

issues, obviously, need

more

careful investigation.

However, the implication for human beings from evolution which I

find

most fascinating concerns the existence of "human nature". For

centuries

philosophers, scientists, theologians and the general public

have

argued

over

the particulars of human nature while assuming that

it

exists. Numerous traits have been suggested for the "essence" of

Homo

sapiens--rationality, language use, intensionality, the plantigrade

foot, etc. For some reason, this question has seemed extremely impor-

tant.

If

bees have a language or computers can think, then we are

in



17/21

88

danger of having to include

them

in our species. However understand-

able these inferences are, given our common-sense ways of

viewing bio-

logical species, they are not justified on the basis of at

least cer-

tain versions of evolutionary theory.

In the earlier discussion of inclusive fitness and the cost of meio-

sis, the importance of genes which are identical through descent

as

distinct from being just similar in structure was emphasized. If spe-

cies are the things which evolve as the result of

selection processes

occurring at lower levels, then organisms are included in

the same

species because of

gene

transmission, not similarity.

Being part of

the same genealogical nexus is what counts

(Ghiselin

1974). As biolo-

gists have emphasized, organisms which are phenotypically

quite dis-

parate can belong to the same species while organisms

which are all but

phenotypically indistinguishable can belong to different species. The

sort of variation which occurs in biological species is

such that the

notion of a "typical" organism makes no sense. Perhaps at any one lo-

cus, there will be one allele which is most prevalent, but

it is pos-

sible

that no one organism has ever possessed all the commonest

al-

leles. In

fact, they might

be

developmentally

incompatible.

What

does

this imply about

Homo

sapiens? It implies that

we are all

part

of

the same species in virtue of descent and mating. We are not

all members of the same species in virtue of possessing

its essential

traits,

or

even

enough

of

its

most important traits. Domesticated ani-

mals

may be part of human societies, but they are not part

of the

human

species. Humanreproductive neuters, regardless

of

the mechanism,

re-

main part of the human nexus, albeit at termini. The failure of human

neuters to contribute directly to human biological evolution

does not

mean that they cannot contribute indirectly through kin

selection

or

by

means of social influences. On this perspective, people

with mental

a-

bilities

no

higher than

those of

apes

nevertheless

remain

part

of

the

human

species.

The same

can

be

said

for all

other traits

which

have

been

suggested

as

"essential"

for

human

nature.

As

important

as the

emergence of the apposable thumbwas

in

the evolution

of

Homo

sapiens,

people born without thumbs remain no less human beings.

No fraudulent

references to "potentiality" is needed, as

if

people without

the

genet-

ic

instructions necessary to develop a

thumb

nevertheless potentially

possess a thumb. In this sense, pandas and porpoises also potentially

possess apposable

thumbs.

Although

individuals

lacking

one or

more

"essential" traits

may

be

less

than

"human" in a

variety

of senses

of

this

term, they

are no less

a

biological part

of

Homos

E

Al-

though

human homosexuals

may

be

immoral, sinful,

psychologically

ab-

normal

and even criminal,

at

least they need

not be considered

any

more

biologically abnormal than

worker

bees

or

soldier ants.

The

message

of

the

preceding

discussion

is

that

particular species

need have no essences

on

certain versions

of

evolutionary theory; they

cannot

have

them on other

versions. Even

so,

the

species category

it-

self

might

well be

a

natural

kind

with an

essence. All

species might

have some essential feature or features in common Hull 1980). Similar

observations hold for societies

if

societies evolve

in

anything

like



18/21

89

the same

way that species

do. If phyletic evolution

is

possible,

then

societies

can change indefinitely

through time until

later

stages of

the society

have none of the peculiarities

which

characterized

earlier

stages.

Hence, nothing

about

American society is essential

to

it,

the

Constitution notwithstanding. Even if societies

turn out

to be homeo-

static systems

which require

revolutions

to change,

they are likely to

be

marked

by

considerable internal

diversity. None

of

this

entails

that

societies as such

have nothing

in common. The class

of all

so-

cieties

might well form

a natural kind characterized

by certain essen-

tial

traits.

So the story goes,

Linnaeus

has been designated

the "type

specimen"

for Homo

sapiens.

The

peculiarity

of

claiming

that

an organism (as

distinct

from a character

state

or an allele) is

typical

of its species

can be seen by asking

in what sense

a Caucasion,

male, Swede

is a

"typical"

human being.

The point

is not that

Linnaeus

is the

wrong

person to choose as a type specimen but that no one organism could pos-

sibly

be

"typical"

of its species

in an

evolutionarily significant

sense.

Gould

(1980, p.

116)

remarks that human

history

"remains so

re-

calcitrantly ideographic

because it is

the story of single

species--it

represents the

vicissitudes

of an individual (Ghiselin

1974) of unpar-

alleled

flexibility.

W4hat eneral theory

could encompass

it?" It

would probably

be misleading to

say that

H

had

no nature,

but

species

do not have

"natures"

in the sense traditionally

ascribed

to natural kinds.

The

implications

of this feature

of

evolutionary

theory

for

scientific theories

which

are

limited

solely and

necessarily

to a

single species

such as Homo

si

are fundamental

and far-reach-

ing (Rosenberg 1980).

Notes

'The research for this paper was supported by a Guggenheim

Fellowship

for

1980-1981.

I

wish to thank Elliott Sober and William Wimsatt

for

commenting on an early draft of this paper.

2T,o-locus

models and models for multiple alleles remain

reasonably

tractable, but they rapidly become prohibitively complex as they are

extended and combined (Roughgarden 1979). As Wimsatt (1980)

argues,

no general solution is possible for multi-locus models.

3Mayr

is not

unaware of the conflicts and unresolved problems

con-

cerning issues on which he has worked for over forty years; see

for

example

the

introduction to the 1964 edition

of

Mayr (1942).



19/21

90

References

Alexander,

R. D. (1979).

Darwinismn

nd

HumanAffairs.

Seattle,

WA:

University

of

Washington

Press.

Allen, L., et.

Documents

The Herd as a Means- by David L. Hull. PSA: Proceedings of the Biennial Meeting of the Philosophy of Science Association,Vol. 1980, Volume Two: Symposia and Invited Papers (1980),