Assistant Professor, Department of Philosophy,
University of Alabama at Birmingham
Email: mabrams at uab dot edu, or: marshall at logical dot net
(This page focuses on my research. Information on my current courses
and other information for UAB students can be found
here.)
(Note: Most links below are to PDF files.)
Areas of specialization: philosophy of science, philosophy of biology, philosophy of mind/cognitive science.
Areas of competence: metaphysics, epistemology, philosophy of language, symbolic logic, decision theory.
Does my research have anything to do with normative issues or public policy?
The Unity of Fitness, in Philosophy of
Science, 76(5), December 2009
It's been argued that biological fitness cannot uniformly be defined
as expected number of offspring; different mathematical functions are
needed to define fitness in different contexts. Brandon (1990)
argues that fitness therefore merely satisfies a common schema.
Other authors (Ariew and Lewontin, 2004; Krimbas, 2004) argue that no
unified mathematical characterization of fitness is possible.
I focus on comparative fitness, explaining that it must be relativized to
an evolutionary effect which fitness differences help to cause. Thus
relativized, comparative fitness can be given a unitary mathematical
definition in terms of probabilities of producing offspring of various
types and probabilities of producing various other effects. Fitness
will sometimes be defined in terms of probabilities of effects occurring
over the long term, but I argue that these probabilities nevertheless
concern effects occurring over the short term.
Fitness "Kinematics": Biological Function, Altruism, and Organism-Environment Development,
Biology and Philosophy,
24(4), September 2009.
It's recently been argued that biological fitness can't change over the
course of an organism's life as a result of organisms' behaviors.
However, some characterizations of biological function and biological
altruism tacitly or explicitly assume that an effect of a trait can
change an organism's fitness. In the first part of the paper, I
explain that the core idea of changing fitness can be understood in
terms of conditional probabilities defined over sequences of events in
an organism's life. The result is a notion of "conditional
fitness" which is static but which captures intuitions about apparent
behavioral effects on fitness. The second part of the paper
investigates the possibility of providing a systematic foundation for
conditional fitness in terms of spaces of sequences of states of an
organism and its environment. I argue that the resulting
"organism-environment history conception" helps unify diverse
biological perspectives, and may provide part of a metaphysics of
natural selection.
What Determines Biological Fitness? The Problem of the Reference Environment,
Synthese 166(1), January 2009. The original publication is available at
www.springerlink.com.
Organisms' environments are thought to play a fundamental role in
determining their fitness and hence in natural selection.
Existing intuitive conceptions of environment are sufficient for
biological practice. I argue, however, that attempts to produce a
general characterization of fitness and natural selection are
incomplete without the help of general conceptions of what
conditions are included in the environment. Thus there is a
"problem of the reference environment"--more particularly,
problems of specifying principles which pick out those
environmental conditions which determine fitness. I distinguish
various reference environment problems and propose solutions to
some of them. While there has been a limited amount of work on
problems concerning what I call "subenvironments", there
appears to be no earlier work on problems of what I call the "whole
environment". The first solution I propose for a whole
environment problem specifies the overall environment for natural
selection on a set of biological types present in a population
over a specified period of time. The second specifies an
environment relevant to extinction of types in a population;
this kind of environment is especially relevant to certain kinds
of long-term evolution.
How Do Natural Selection and Random Drift Interact?,
Philosophy of Science, 74(5), December 2007 (© PSA)
One controversy about the existence of so called evolutionary forces
such as natural selection and random genetic drift concerns the
sense in which such "forces" can be said to interact. In this
paper I explain how natural selection and random drift can
interact. In particular, I show how population-level
probabilities can be derived from individual-level probabilities,
and explain the sense in which natural selection and drift are
embodied in these population-level probabilities. I argue that
whatever causal character the individual-level probabilities have
is then shared by the population-level probabilities, and that
natural selection and random drift then have that same causal
character. Moreover, natural selection and drift can then be
viewed as two aspects of probability distributions over
frequencies in populations of organisms. My characterization of
population-level probabilities is largely neutral about what
interpretation of probability is required, allowing my approach
to support various positions on biological probabilities,
including those which give biological probabilities one or
another sort of causal character.
Fitness and Propensity's Annulment?,
Biology and Philosophy,
22(1), January 2007
Recent debate on the nature of probabilities in evolutionary biology
has focused largely on the propensity interpretation of fitness, which
defines fitness in terms of a conception of probability known as
"propensity". However, proponents of this conception of fitness
have misconceived the role of probability in the constitution of
fitness. First, discussions of probability and fitness have almost
always focused on organism effect probability, the probability
that an organism and its environment cause effects. I argue that
much of the probability relevant to fitness must be organism
circumstance probability, the probability that an organism
encounters particular, detailed circumstances within an environment,
circumstances which are not the organism's effects. Second, I
argue in favor of the view that propensities either don't exist or
are not part of the basis of fitness, because they usually have values
close to 0 or 1. More generally, I try to show that it is possible
to develop a clearer conception of the role of probability in biological
processes than earlier discussions have allowed.
Infinite Populations and Counterfactual Frequencies in Evolutionary Theory,
Studies
in History and Philosophy of Biological and Biomedical Sciences, 37(2), June 2006
One finds intertwined with ideas at the core of evolutionary
theory claims about frequencies in counterfactual and
infinitely large populations of organisms, as well as in sets of
populations of organisms. One also finds claims about frequencies
in counterfactual and infinitely large populations--of
events--at the core of an answer to a question concerning the
foundations of evolutionary theory. The question is this: To
what do the numerical probabilities found throughout evolutionary
theory correspond? The answer in question says that evolutionary
probabilities are "hypothetical frequencies" (including what are
sometimes called "long-run frequencies" and "long-run
propensities"). In this paper, I review two arguments against
hypothetical frequencies. The arguments have implications for
the interpretation of evolutionary probabilities, but more
importantly, they seem to raise problems for biologists' claims
about frequencies in counterfactual or infinite populations of
organisms and sets of populations of organisms. I argue that
when properly understood, claims about frequencies in large and
infinite populations of organisms and sets of populations are not
threatened by the arguments. Seeing why gives us a clearer
understanding of the nature of counterfactual and infinite
population claims and probability in evolutionary theory.
Teleosemantics without Natural Selection,
Biology and Philosophy 20(1), 2005
Ruth Millikan and others advocate theories which attempt to
naturalize wide mental content (e.g. beliefs' truth conditions)
in terms of function in the teleological sense,
where a function is constituted in part by facts concerning past
natural selection involving ancestors of a current entity.
I argue that it is a mistake to base content on selection.
Content should instead be based on functions which though
historical, do not involve selection. I sketch an account of
such functions, which defines "function" in terms of changes in
objective probabilities due to changes in ancestral traits.
Short-Run Mechanistic Probability
This paper sketches a concept of higher-level objective probability
("short-run mechanistic probability", SRMP) inspired partly by a style
of explanation of relative frequencies known as the "method of
arbitrary functions". SRMP has the potential to fill the need for a
theory of objective probability which has wide application at higher
levels and which gives probability causal connections to observed
relative frequency (without making it equivalent to relative
frequency). Though this approach provides probabilities on a space of
event types, it does not provide probabilities for outcomes on
particular trials. This allows SRMP to coexist with lower-level
probabilities which do govern individual trials.
Conference on The Evolution of Cognition: Niche Construction, Culture, and Environmental Complexity, April 23-24, 2005 (I organized this with students at Duke).