In Darwin's Shadow: The Life and Science of Alfred Russel Wallace ...

The Psychology of Biography /7
over time requires a model that can handle their relative effects. “We say that
two variables interact when the effect of one variable changes at different
levels of the second variable,” statistician G. Keppel explains. “Thus, an interaction
is present when the simple main effects of one variable are not the
same at different levels of the second variable.” Variables may also be additive
when “the effect of one variable simply adds to the effect of the second
variable.” 9 Such interactions, of course, make the model more complex, but
a closer approximation to what really happens in human-culture interactions:
“In an increasing number of experiments being reported in the literature,
interactions not only are predicted but represent the major interest of the
studies. The discovery or the prediction of interactions may lead to a greater
understanding of the behavior under study. In short, then, if behavior is complexly
determined, we will need factorial experiments to isolate and to tease
out these complexities. The factorial allows us to manipulate two or more
independent variables concurrently and to obtain some idea as to how the
variables combine to produce the behavior.” 10 The Historical Matrix Model
(Figure P-1) helps us visualize the additive and interactive development of
Wallace’s thoughts within his culture, as they changed over time. 11
The tension between what can be and what must be—between the power
of the individual and the force of culture—encapsulates this biography and
drives the analysis of Wallace’s life and science. To what degree does culture
mold and shape an individual’s ideas and behaviors? To what extent does an
individual’s thoughts and actions affect change in a culture? What is the relative
influence of thought and culture as they interact over time? These questions
will be asked with specific regard to Wallace in the context of nineteenthcentury
Victorian culture, to attempt to understand the complex development
of his ideas and those of his contemporaries, particularly with regard to science
and evolutionary theory.
The Historical Matrix Model presents a 5 5 6 factorial design, in
which five internal forces (thoughts) interact with five external forces (culture)
over six periods of time representing Wallace’s life. The selection of five
forces was somewhat subjective, though fewer would have eliminated significant
events and more would have oversaturated the analysis. The six time
periods are marked by significant changes in Wallace’s life and career, such
as schooling, explorations, major publications, intellectual battles, and personal
travails. The five internal forces in decreasing order of influence on the
left vertical axis represent the individual ideas and experiences of Wallace
and include: (a) Hyper-selectionism, or the overemphasis of adaptationism in
explaining the evolution of organisms, particularly the evolution of humans
and the human mind; (b) Mono-polygenism, the great debate in Wallace’s time
over the origin of humans from either a single source (monogenism) or mul-