Kevin Elias History and Science 97b
From Without to Within
Kenji Ito
From Without to Within:
The Transition of
Evolutionary Mechanism
from Natural Selection to Genetics
Kevin
Elias
History of Science 97b
05/11/01
Kenji Ito
Wednesday
7-9
Introduction
When one opens any contemporary text on the working of evolution, scarcely
a minute’s worth of perusing is necessary before the term
“gene” hits the reader’s eye with unrelenting frequency.
Indeed, genetics has become the foundation of modern evolutionary thought. Yet,
when Charles Darwin was outlining his theory of evolution in the mid-nineteenth
century, he made no mention of genetics for the very simple fact that the field
did not exist. While that little insight might seem glaringly obvious in its
simplicity, it begins to unearth some very interesting questions in the history
of science. What were the circumstances wherein evolutionary theory became
intertwined with genetics? How did the nature of evolutionary work change when
genetics became involved? Much like genetics and evolution, these two questions
are inextricably spun around one another.
I contend that evolutionary
theory under Darwin was fundamentally different from evolutionary theory under
the geneticists. The transition was incremental. First, Darwin’s theory
of natural selection came under assault by August Weismann and William Bateson
in the late nineteenth century. They concluded that natural selection was true
as far as it went, but that this was probably not very far.[1]
Next, there
was the rediscovery of Mendel. Bateson and Hugo De Vries realized that heredity
and the Mendelian technique held promise for understanding how evolution really
worked. Finally, natural selection became subservient to the more important
evolutionary mechanism of mutation. De Vries and Thomas Hunt Morgan then defined
the experimental parameters of this phenomenon. After this last phase, a new
theory of evolution emerged. The mechanism of mutation replaced natural
selection as the primary wheel steering the workings of evolution.
I
believe that historians of genetics have not properly considered the
introduction of Mendelian genetics into the evolutionary arena. Peter J. Bowler
points out that the majority of works by professional historians of science
regarding turn of the twentieth century biology reflect "a certain
whiggishness."[2]
They focus almost entirely on the aspects of Darwinism
and Mendelism that would later bear fruit for the so-called evolutionary
synthesis,[3]
while little work has been done on evolutionary work at the
time that did not contribute directly to the modern stance on evolution. I
distinguish the present account from previous work on the subject by nature of
the fact that the traditional telling of the history of evolutionary science
takes for granted that the incorporation of genetics into evolutionary theory
was a simple modification of the preexisting evolutionary ideas. Indeed,
Michael T. Ghiselin suggests that any seeming gulf between genetics and natural
selection was never that great. He offers a history wherein genetics actually
served to hinder modern evolutionary theory by forcing a reconsideration of
alternative theories to natural selection that would later be dismissed.[4]
I disagree with Ghiselin's assessment as to the insignificance of this gap
between evolutionary theory under natural selection and what I see as a new
evolutionary theory put forth by the geneticists. Contrary to the Ghiselin
thesis, I propose that in the early twentieth century Darwin’s theoretical
account of evolution was not modified by the rediscovery of Mendelian
inheritance; rather, the entire natural selection theory was replaced with a
radically different approach to evolution created by William Bateson and the
other early geneticists.
I distinguish the geneticist theory from the
selectionist theory by two key characteristics. First, natural selection theory
was entirely based on observation in the field, while genetic theory was based
on experiment in the laboratory. While the former was overtly qualitative in
nature, the latter strove to be as quantitative as possible. Second, while
natural selection was seen as an external force that acted on populations of a
species, genetic variation was seen as an internal force that was an organic
part of an individual organism. The theory of natural selection was essentially
metaphysical in character in that it was a force of nature and not a principle
that could be shown to work by a rational mechanism. In contrast, the theory of
natural selection contained a spatial-temporal mechanism by which the workings
of evolution were understood to be a physical part of organisms and could be
followed over a period of generations. The result of these differences between
the theory of evolution before and after Mendel was that a completely new theory
of evolution emerged that could address not only the phenomena of the Darwinian
account, but also a whole host of new questions previously outside the bounds of
evolutionary science.
Evolution According to Natural Selection
Establishing that genetic theory was a replacement of selectionist theory
rather than a modification of it requires a somewhat descriptive account of
history to provide the proper context.[5]
We start with the theory of
evolution in the late nineteenth century. Darwin had created a fundamentally
new science. For the first time, a mechanism, natural selection, was employed to
explain the variation among and within species. Darwin understood selection as
individuals "having any advantage, however slight, over others, . . . have the
best chance of surviving and of procreating their kind."[6]
Over time,
these advantages, or “adaptations,” as Darwin called them, would
accumulate sufficiently enough for one to be able to distinguish a new species,
clearly different from the original form. By a close study of species
adaptation, Darwin expected that a rational system for explaining the origin of
all species would emerge. In his view natural selection was the primary
mechanism for creating new species. Later, this would become a key point of
dispute for the geneticists. I detect a sense of disagreement in William
Bateson's observation that in Darwin's view "specific diversity had no
physiological foundation or causation apart from fitness."[7]
Problems with Darwin's Theory of Natural
Selection
While Darwin was able to call natural selection the primary force dictating
the development of species, he still was not able to remove all vestiges of
previous theories on the origin of species. Most importantly he conceded that
the “heredity transmission of parental experience and its
consequences” [8]
had some role in the origin of species, but
“with his habitual caution refrained from specifying [how great a role],
for the sufficient reason that he did not know.”[9]
This omission,
however, prevented Darwin's theory from getting clear of the proposals of J.
Lamarck. At the beginning of the eighteenth century Lamarck had put forth a
theory that the origin of species was due entirely to the inheritance of
acquired characteristics. Darwin's openness to the ability of traits to be
transmitted by virtue of use or disuse exposed him to attacks from a biological
community that was reluctant to accept this postulate.
The Need for Experiment
A leading assailant of Darwin on the point of acquired characteristics
became August Weismann. Weismann was a German biologist and junior contemporary
of Darwin. While supporting evolution, he could not accept the inheritance of
acquired traits. In a famous experiment, he cut off the tails of five
generations of mice, 901 mice in all, and yet the progeny of every mouse grew
normal tails. He challenged the scientific community for evidence that acquired
traits have any transmitted effects at all, but none of any merit was ever
produced. Though it was only a minor point of Darwin’s theory, the
collapse of acquired traits had a lasting effect on future biologists. First,
it cleared the ground for the construction of a new theory of
heredity.[10]
,[11]
Most importantly, it began to illustrate the
weaknesses of a theory based solely on observation and not experimental
fact.
This lack of experimental evidence arose from the shift of evolutionary
work after Darwin from physical concerns to theoretical matters. While Darwin
had explained the role of variations in the struggle for life, he could not
account for the physical causes of the variations themselves. Consequently, the
vast majority of evolutionary work done in the latter half of the nineteenth
century focused on the historical problems of evolution, rather than the causal
ones. Evolutionists turned to compiling phylogenetic evidence to support the
theory. For example, much effort was put into fieldwork and the cataloguing of
examples of variation and adaptation. I suggest that the movement away from any
experimental work was due, at least in part, to the rash of popular issues
raised by evolution, as evidenced by popular evolutionary accounts more
interested with theoretical aspects and opinion than with method.[12] Lock
suggests that even the majority of specialists gave up the experimental method
in favor of the controversial one for the fifteen to twenty years following the
acceptance of the theory of natural selection.[13]
As the century wore
down, William Bateson led a movement to return evolutionary biology to the realm
of experimental investigations.[14]
Bateson was an English biologist
educated at Cambridge. He was especially bothered by a system wherein natural
selection acted like a disconnected, metaphysical force. In 1894 he published
his theory of discontinuous variation. A precursor to the mutation theory of De
Vries, Bateson used experimental breeding of plants and animals to show that
evolution did not take place via continuous variation through the generations as
Darwin had suggested. Instead variations sporadically appeared and disappeared.
The experiments made it apparent that Darwin’s mechanism of inheritance
would actually be fatal to his theory of evolution if one attempted to use it to
explain the breeding experiment data. Lewontin explains that if inheritance
were of the continuous or blending form, then sexual reproduction would result
in a reduction of the variance in the population by a factor of one-half with
each generation. When this fact is combined with Darwin’s theorem that
advance under selection is limited by variance in fitness, it immediately
becomes obvious that evolution would be impossible in sexually reproducing
organisms.[15]
The Movement for a Quantitative Analysis
I contend that the complications raised by the breeding experiments seemed
to highlight larger ambiguities associated with the qualitative nature of
natural selection. Bateson was highly critical of the fact that one could
“never make any quantitative estimate of the amount of benefit or the
reverse which any particular structure may afford its possessor.”[16]
There was no benefit in assuming that every variety was an adaptation of some
sort if there was no way of measuring how much of a benefit that trait
impressed. For example, how could one measure the benefit of a bird being
brightly colored for mating purposes against the benefit of it having drab
colors to escape predators? Furthermore, if every trait was an extension of
another trait, how could new organs develop?[17]
The math did not agree
with Darwin, either. Calculations as to the possibility of natural selection
alone bringing about a new race showed that it would never happen.[18]
Darwin’s views, while theoretically persuasive, upon technical analysis,
seemed weak.
The Species Problem
Bateson also had serious problems with Darwin’s antiquated
definitions of variation, species, and heredity. The ambiguity between species
and variety resulted from the system under which classification of species had
been conducted prior to Darwin's time. Naturalists classified organisms for
convenience of reference. The term species had no technical basis. As Bateson
points out, "if anyone had asked them what they meant by a species, it is
practically certain that they would have not the slightest idea what the
question might imply, or any suspicion that it raised a fundamental problem of
nature."[19] Naturalists were much more concerned with the descriptive work of
identifying organisms and much less concerned with the overarching order to any
system that was created.
The taxonomic system of Carolus Linnaeus, however,
sought exactly this rigidity that the naturalists had not. Debates broke out
with regards to what was a "good species" versus a "bad species." The whole
process lay entrenched in subjectivity. Any one feature of an organism, whether
its color, sex characteristics, or structural differences, could be enough to
merit a new species or to lump together a whole series of organisms as belonging
to one species. Rather than being a minor issue of particulars, the exact
denomination of every species formed the backbone of the entire systematist
philosophy. Because they claimed that every species could be found and named,
the Linnaen writings induced the conviction that the species of animals and
plants were immutably fixed.[20]
Linnaeus’s definition of a species
as that entity which owed its origin to a “separate act of creation”
helped further this idea.[21]
Even opponents to the immutability of
species failed to resolve the species-variety conflict. For example, Lamarck
incorporated the difficulty of distinguishing species from varieties as part of
his evidence for species transmutation.[22] Without an association with
physical phenomena, however, no one approached the species issue with the
mechanistic base that an explanation of the origin of life required.
Darwin
took on this task. He presented adaptation as the physical definition of
species. By seeing how two closely allied species had utilized different
adaptations to survive, he believed one could distinguish one species from the
other. This line of adaptations, then, would trace the paths of common descent
among species. By a close study of species adaptation, Darwin expected that a
more rational system for naming species would emerge.
While Darwin succeeded
in demonstrating variation among divers species, Bateson showed that he failed
to adequately address the species-variety dilemma. For Darwin, species had not
yet taken on theoretical importance in that the fundamental units of
classification had not yet become the fundamental units of evolutionary
theory.[23]
Bateson's criticisms of this omission can be seen as another
example of Bateson's desire to frame evolution in quantitative terms. First,
Bateson argued that variations were found to exist in a much greater abundance
than Darwin had anticipated. Second, species could still be distinguished by
any variety of features, many of which had no apparent role as adaptations.
Third, a single "species" might be subject to so much local differentiation, as
to make it impossible to state which variations connoted new species and which
were polymorphisms in the population.[24] Fourth, variations could be
compounded by hybridization of races, giving intermediates that had not
previously existed. Finally, the mechanism of selection could not explain how
two different strains of the same species could exist side by side.[25]
Surely, natural selection should have been seen eliminating the less adapted
strain in favor of the more adapted one. Taken together, these faults raised a
paradox: How could selection be such a loose process but speciation be so
precise? Evolutionary theory could not reject its emphasis on the fluid nature
of species; it had to find some new mechanism for explaining the transmission of
favorable traits.
The Effect of Mendel
In 1900 the rediscovery of Mendel’s breeding experiments dropped the
answer into the laps of the biologists. Gregor Mendel was an obscure Austrian
monk with a deep interest in botany. In 1865 he reported his findings on some
curious phenomena of plant hybridization. What made this work unique was the
meticulous precision with which Mendel carried out his experiments. Mendel was
convinced that among all the experiments performed by his predecessors, "not one
[had] been carried out to such an extent and in such a way as to make it
possible to determine the number of different forms under which the offspring of
hybrids appear, or to arrange these forms with certainty according to their
separate generations, or definitely to ascertain their statistical
relations."[26] In a footnote, Bateson points out that Mendel defined a
well-reasoned investigation of heredity by its examination of the number of
different offspring forms, their classification by generations, and their
statistical relationship.[27] The novel combination of these points of inquiry
marked the success of Mendel's work.
Despite what Bateson in 1900 realized
were significant advances for biology, Mendel's papers in their original
publications received no notice from the scientific community. The reasons for
this oversight have been much debated. Bateson points out that the Brünn
Society exchanged publications with most of the European Academies, so obscurity
of publication cannot be considered an overriding factor.[28]
I propose a
more likely explanation. At this time the biological community was still
overwhelmed by the writings of Darwin. Darwin's writings were markedly
observational and hypothetical in character, while Mendel's work was
fundamentally experimental and physical.[29]
Mendel's work was overlooked
because it did not follow the style of a contemporary species paper.
The
profound effect of Mendel's writings on Bateson and other biologists studying
heredity is difficult to understate. At the time, Mendel's ideas were
completely novel. While Mendel had not been writing in reference to evolution,
biologists like Bateson in 1900 were convinced that heredity and experiment
could be used to explain evolutionary concepts. Mendel made it abundantly clear
to Bateson that further progress was contingent on actual experiments in
breeding.[30]
Not only did this confirm Bateson’s notion that heredity
played a key role in understanding evolution, but Mendel's work also outlined a
new scientific process by which one could examine the inheritance of traits over
several generations. Mendel showed that statistical analysis could be used to
predict the appearance of "character" traits.
Evolution and the Gene
The most striking element of Mendel's work was this concept of "characters"
effecting the expression of physical traits. The "character" concept, later
called the gene, broke down heredity from the study of individuals to the study
of independent characters that those individuals possessed. Mendel proposed that
each organism contained a "pair of different characters in hybrid union," one of
each inherited from the parental stock.[31] These characters could be assigned
variables and mathematically assessed. This allowed Mendel to predict all the
possible combinations of characters that a plant with parents of a known
character-type (genotype) might possess. He was then able to show that the
ratios of traits predicted by this mathematical modeling were in fact the true
proportions of physical expressions in his plants.
Through careful collection
of data, Mendel was able to formulate the conclusions that became the foundation
for Bateson's work. First, he postulated a segregation of characters in the
male and female germ cells of hybrid plants. Each germ cell contains only one
member of the pair of differentiating characters present in each parent. Each
member of such a pair of characters is represented in an equal number of germ
cells of both sexes.[32] Second, he put forth the law of independent
assortment. This means that separate pairs of differentiating characters are
inherited independently of one another. In other words, the inheritance of one
trait does not preclude the inheritance of another.
A Physical Mechanism for Evolution
A key element of Mendelism was that it designated the actions of a
particulate entity as the mechanism for evolution. Natural selection had put
the origin of species in the hands of a supernatural force that had no physical
manifestation. For Bateson there was a simple beauty in Mendel’s ideas.
He preferred the “cosmic” Mendelism to the “chaotic”
natural selection.[33] The order of the system meant that “no matter how
low in the scale we go, never do we find the slightest hint of diminution in
that all-prevailing orderliness, nor can we conceive an organism existing for a
moment in any other state.”[34] The metaphysical natural selection was
replaced with the physical genetics.
Application of Mendelism
Mendel's ideas brought about a radical change in the way biologists
understood the mechanisms of heredity. The experimental evidence offered by
Mendel's techniques allowed them to escape the theoretical difficulties that had
begun to obscure their understanding of evolution.[35] First, Mendelism solved
De Vries's problem of a new trait being bred out of the population before it
could have any evolutionary effect. With the concept of heterozygous
characters, a recessive trait could continue to be passed on through the
generations even if it was not being expressed. Eventually, a homozygous
recessive individual would arise who would again express the new trait.[36]
Furthermore, Mendel's conclusions offered an explanation for the preponderance
of observable variations within species. Lewontin shows that the fewer
characters needed to control a trait, the more likely it is that a new trait can
develop. By suggesting that "the number of particles controlling a character is
the absolute minimum" Mendel was able to show that the possibility for evolution
is maximized.[37] Identifying these characters and following their inheritance
through several generations would be the great new pursuit for evolutionary
biology.
Mendel's Work Brings a Return to Experiment
The novelty of Mendel’s discoveries and analytical approach began a
rash of experimental work in genetics. Bateson introduced the term
“genetics” to describe the investigation of heredity through
Mendelian techniques. [38]
The field was characterized by an amalgam of
Bateson, Mendel, and Darwin. Bateson continued to employ his theory of
discontinuity to characterize the distribution of variations in a population.
From Darwin came the axiom that the specific form of organisms fit the places
where they lived. This proposition was important for explaining how one
variation might be selected over another. The quest then was to discover the
mechanisms by which variation happened and the conditions that caused these
mechanisms to occur. Geneticists knew that Mendel's characters provided the
physical mechanism whereby variations were inherited. Furthermore, geneticists
realized that his experiments provided the model for future progress in
understanding why these variations occurred.
Bateson's experimental approach
to answer these questions was a novel combination of four methods of study.
First, he continued to directly compare organisms. Second, he used statistical
examination to chart the distribution of genetic traits. Third, he did cultural
experiments. The idea was to raise as many of the organism as possible and to
watch for variations to occur. Finally, once variations were found, he
performed Mendelian crossbreeding experiments to see how the trait was
inherited. Bateson channeled his enthusiasm for genetic theory into creating
the first center for genetic research at Cambridge. He and his lab became the
recognized authority on genetic work.[39]
The rash of genetic research
that followed was linked to a growing movement by younger biologists to return
biology to the experimental sciences. Garland Allen suggests that prior to
1900, these biologists were painfully aware of how few of the accepted
generalizations in biology could be tested by experiment.[40]
The movement
to ground evolutionary theory in experiment was part of a larger movement by the
generation of post-Darwin biologists to have biology follow the example of
chemistry and physics and to put these generalizations to a clear experimental
test.
A New Approach to Species and Variety
Reconciling Mendel to evolutionary theory also meant that biologists had to
reexamine their definitions of species and variety. This meant replacing the
qualitative approach of Darwin with the quantitative approach of Mendel.
Bateson saw it as exceedingly unlikely that the difference between species and
variety would continue to be defined as a matter of degree.[41] While Darwin
had defined any variation between parent and offspring as a variation, the
understanding of Mendelian principles forced the geneticists to adopt a more
precise definition. Bateson supported De Vries’s principle that
“real, genetic variation” had to be distinguished from
“fluctuational varieties, due to environmental and other accidents, which
can not be transmitted.”[42] ,[43] The only way to do this was
exhaustive research. In the end, Bateson hoped to prove that variation and
heredity were real phenomena instead of mere axioms for theoretical
discussion.[44]
Mutation Theory
Ultimately, Hugo De Vries proposed the mechanism that would unite
variation, heredity, evolution, and experiment into a unified theory. De
Vries's methods modeled the new form of biological experiment popular among the
young generation of biologists at the turn of the century. In 1900, De Vries
was one of three researchers who affirmed the accuracy of Mendel’s
experiments. Since 1886, he had been studying the appearance of variations in
his cultivations of the evening primrose. He realized that these new variations
were not merely passing differences that could be explained by environmental
factors, but rather they were new traits that could be bred into future
generations. He called these spontaneous variations “mutations.”
He summarized his theory in his 1901-3 treatise Die Mutationstheorie, or
The Mutation Theory. What distinguished mutations from fluctuating
variations was that mutations signaled permanent evolutionary change. He used
breeding experiments to show that mutation could be seen as a genetic
distinction between varieties and species. A mutation could not be blended
away. It was instead a physical part of an organism’s makeup.
An
explanation of evolution through mutation represented a radically different view
of evolutionary processes than had natural selection. Bateson eventually seized
onto De Vries’s mutation theory as the mechanism underlying his theory of
discontinuity. He realized that whereas Darwin erroneously saw evolution as
“the gradual transformation of masses of individuals by the accumulation
of impalpable changes . . . the facts of heredity and variation [united] to
prove that genetic variation is a phenomenon of individuals.”[45] De
Vries extended this contrast even further. While natural selection had called
for a gradual development of new species, his theory suggested that
“species arise by a sudden step in which either a single character or a
whole set of characters together become changed. In the former case a new
variety is the result, in the latter a new species. . . is
produced.”[46]
The Extension of Mutation Theory
What De Vries started with plants, Thomas Hunt Morgan continued with
animals. Morgan was an American zoologist. He bred fruit flies in large
quantities, and in 1909 observed the spontaneous mutation of a fruit fly from
red-eyed to white-eyed. As his work became published and his fame grew, the
conception of evolution changed forever. No longer was evolution explained
through populations or even individuals, but only through genes. In less than
two decades evolutionary work had changed from the study of populations to the
study of the “independent characters of which the individual is made
up.”[47]
Morgan predicted that in the future “relationship by
common descent will be recognized as of minor importance as compared with
relationship due to a community of genes.”[48]
Morgan was right. A
new concept of evolutionary theory emerged wherein genetic mutations were the
primary mechanism of evolution and selection was relegated to a secondary role.
As Bateson said, “selection determines along which branch Evolution shall
proceed, but it does not decide which novelties that branch shall bring
forth.”[49]
Moreover, the characterization of natural selection
changed. Natural selection was no longer seen as the stern judge holding
species to the exacting standard of survival of the fittest. Instead selection
was seen as a more lenient taskmaster that could permit distinct varieties of
the same species to exist indefinitely side by side.
Conclusion
We began our discussion with the questions of how genetics became a part of
evolutionary theory and how evolutionary work changed as a result of the genetic
influence. Prior to 1900, difficulties were arising with the acceptance of
Darwin’s view of evolution. Darwin’s inclusion of inheritance of
acquired traits, his vague distinctions between variety and species, and the
dubiousness of natural selection being able to bring about a transmutation of
species on its own, raised questions as to the solidity of Darwin’s
account. Without an overarching counter-theory, however, natural selection
remained the primary mechanism by which species were thought to develop.
The
rediscovery of Mendel’s papers presented the first experimental evidence
that Darwin’s theory was fatally flawed. William Bateson, Hugo De Vries,
and Thomas Hunt Morgan exploited the experimental focus of Mendel’s work
to steer biology away from Darwin’s focus on theory back to a tradition of
experimental analysis. They changed the research work done in evolutionary
science from collecting expeditions in the field to breeding experiments in the
lab. Through their investigations, they produced the evidence for a mutational
theory of species origin. While natural selection was kept as an agent in
evolution, no longer was selection seen as having any influence on the formation
of species themselves.[50]
I maintain that this approach to evolution
was radically different from that which Darwin had proposed. Bowler confirms
that there had to have been some sort of significant schism between the two
types of evolutionary thought since "if Mendelian genetics and the Darwinian
selection theory so obviously complemented each other . . . it is strange that
biologists took several decades to recognize the fact."[51]
Indeed there
was no complementarity. The mutationists interpreted Mendel’s work as
implying a “definiteness and specific order in heredity and therefore
variation. This order [could not] by the nature of the case be dependent on
Natural Selection for its existence, but [had to be] a consequence of the
fundamental chemical and physical nature of living things.”[52]
The
simple beauty of a set of characters found in every organism overthrew the
omnipotence of natural selection. The natural selection theory -- theoretical,
qualitative, and metaphysical -- was overtaken by the genetic theory --
experimental, quantitative, and spatial. Since it captured the throne of
evolutionary science, genetics has yet to relinquish its grasp.
[1]
William Bateson, Darwin and Modern Science, published in William
Bateson, F. R. S., naturalist; his essays & addresses, together with a short
account of his life by Beatrice Bateson (Cambridge University Press,
1928), p. 217.
[2] Peter J. Bowler, The Eclipse of Darwinism,
(Baltimore: Johns Hopkins University Press, 1983), 6.
[3] The
evolutionary synthesis is the name given to the great resolution in the 1930's
that reconciled the discrepancies between Darwinian theory and advances in
genetics.
[4] Michael T. Ghiselin, Metaphysics and the Origin of
Species, (Albany: State University of New York Press, 1997), 3-4.
[5] The reader will please see this narration as necessary for a proper
understanding of my arguments, which I have done my best to make
explicit.
[6] 2 Charles Darwin, The Origin of Species by Means of
Natural Selection or the Preservation of Favored Races in the Struggle for
Life (Chicago: W.B. Conkey Company, 1915), 99.
[7] William Bateson,
Problems of Genetics (New Haven: Yale University Press, 1913)
11.
[8] Bateson, Darwin and Modern Science, p. 220.
[9]
Ibid.
[10] Ibid., 211.
[11] Weismann also had a positive
contribution to genetics. He proposed a theory of heredity based on cellular
entities called “germ plasms.” Though similar to later chromosomal
accounts, it was later disproved, but his ideas stimulated much of the work in
early twentieth century cytology.
[12] Robert Heath Lock, Recent
progress in the study of variation, heredity, and evolution (London: J.
Murray, 1920), 3.
[13] Ibid.
[14] "In the last decade of
the nineteenth century many of us perceived that if any serious advance was to
be made with the group of problems generally spoken of as the Theory of
Evolution, methods of investigation must be devised and applied of a kind more
direct and penetrating than those which after the general acceptance of
Darwinian views had been deemed adequate." Bateson, Problems,
1.
[15] R.C. Lewontin, “The Gene and Evolution.” Published
in Mendel Centenary: Genetics, Development and Evolution. Edited by
Roland M. Nardone Proceedings of a symposium held at the Catholic University of
America, November 3, 1965 (Washington : Catholic University of America
Press, 1968), 68.
[16] Lock, 60.
[17] Lock gives several
specific examples along these lines p. 60-5.
[18] Lock, 136. De Vries
argues that while some variation would be visible at first, the full possible
effect of selection for the trait would be exhausted in only a few generations.
After that, selection would just keep up that standard.
[19] Bateson,
Problems, 4.
[20] Bateson, Problems, 8-9.
[21]
Lock, 7.
[22] Darwin, The Origin, 5.
[23] Ghiselin,
Metaphysics, 5.
[24] Bateson, Problems, 14.
[25]
Bateson, Problems, 134.
[26] Mendel, Experiments in Plant
Hybridization, reprinted in William Bateson's Mendel's Principles of
Heredity (Cambridge: University Press, 1909), 318.
[27]
Bateson, Mendel's Principles, 316.
[28] Ibid.
[29] The
lack of association between the authors was definitely a factor in their choice
of method for scientific inquiry. Mendel had begun his work before Darwin
published his theory of natural selection, and there is little evidence to show
that Darwin's work had any real influence on Mendel's thought processes. The
reverse was also the case. Darwin was unaware of the work of Mendel. Even
though he apparently did read the work of other experimentalists in the field of
heredity, their data and technique were so imperfect as to be duly
neglected.
[30] Bateson, Darwin, 222.
[31] Mendel,
Experiments in Plant Hybridization, reprinted in Bateson's Mendel's
Principles, 337
[32] Lock 191.
[33] Bateson, Darwin,
223.
[34] Ibid.
[35] Bateson, Darwin, 221.
[36]
On this note, Lock suggests that the phenomenon of segregation led to a
reconsideration of the term "purity" in biology. By this he means that with the
concept of recessive traits, the length of time that a race had displayed a
character did not rule out the possibility that the individuals for that race
were heterozygous for that trait. A seemingly "pure" line might carry an
"impure" trait.
[37] Lewontin, 69
[38] I have tried to be
historically accurate with my uses of the terms "gene" or "character," but it
very difficult for a modern commentator to avoid anachronisms in these terms. I
apologize if this ever causes confusion.
[39] Lock, x.
[40]
Garland Allen, Life Science in the Twentieth Century (New York: John
Wiley and Sons, Inc., 1975), xv.
[41] Bateson, Darwin,
225.
[42] Ibid.
[43] Bateson expressed a sense of relief
that Darwin had not known of Mendel, for the knowledge of the variety problem
might have prevented him from being bold enough to publish his theory of natural
selection. He points out that it is much easier to put faith in a random,
insensible mechanism that to attempt to elucidate an intricate orderly
system.
[44] Bateson, Problems, 1.
[45] Bateson,
Principles, 289.
[46] Lock, 153.
[47] Lock,
220.
[48] Thomas Hunt Morgan, The Physical Basis of Heredity
(Philadelphia: J. B. Lippincott, 1919), 223.
[49] Bateson,
Darwin, 227.
[50] Lock, 157.
[51] Bowler, Eclipse,
16.
[52] Bateson, Darwin, 223.