Making an environment 79
homogeneous, variant rates of reproduction implicitly measure the variance in
environmental factors. Finally, the “selective environment” is made up of those
factors which account for differential rates of reproduction between genetically
heterogeneous subsets of some population. Here, the distribution of phenotypical
traits among the population, if and when affecting rates of reproduction, becomes
part of the environment, too.
As an illustration for the distinction between ecological and selective environments, Brandon (1995, 47–49) uses the image of a field with soil conditions that
vary over certain areas or that change over time. If we plant seeds from a genetically homogeneous stock in a regular pattern, the patterns of growth and health of
the plants that emerge will provide a measure of variation in the soil conditions that
have an effect on the plants, allowing us to identify a number of relevant variables
within the plant species’ ecological environment. If we plant seeds from two or
more different varieties in the same manner, the variant patterns of growth will help
us to identify a number of relevant variables within the different varieties’ selective
environments. For example, one variety might be more affected by a change in soil
conditions than the other, so the variant patterns of growth and reproduction will
provide a measure of the relative fitness of the respective varieties. In this sense,
the organisms themselves can be interpreted as measuring instruments that are able
to determine the conditions in these two latter types of environment.
Hence, the line of distinction between the three levels of description of an
environment is drawn by distinguishing levels of conditions outside and within a
population with respect to their objective relevance to that population and its individual members. Although the external environment can be defined in disregard
of the constitution, the abilities and the needs of the particular organisms inhabiting it – apart from the question whether the reference point for “external” is the
individual or the population – the latter two can be defined only in relation to the
properties of individuals and populations. Nonetheless, there is, strictly speaking, no ontological difference among external, ecological and selective environments. There are only different levels of description that refer to different relations
between the constituents of an environment, and their respective relevance to a
population and its members.
The point that Brandon seeks to make with his threefold distinction is that external, ecological and selective homogeneity vs. heterogeneity of some environment
may not necessarily reflect each other (Brandon 1995, 64–66): a homogeneous
external environment may be heterogeneous in ecological terms, as the key factor
of reproductive relevance may lie with other members of the same population.
Such would be the case for a high population density of adult specimen in some
area that gets in the way of the growth and reproductive chances of juveniles.
Even developmental stages of an organism may become selectively relevant.
Conversely, although there will be no selective heterogeneity without ecological
heterogeneity, a physically and ecologically heterogeneous environment may still
be selectively homogeneous, as relative fitness of genetically variant sections of
the population may covary with variation in the ecological conditions, that is the
variant forms may be identically affected by the ecological conditions in question.
homogeneous, variant rates of reproduction implicitly measure the variance in
environmental factors. Finally, the “selective environment” is made up of those
factors which account for differential rates of reproduction between genetically
heterogeneous subsets of some population. Here, the distribution of phenotypical
traits among the population, if and when affecting rates of reproduction, becomes
part of the environment, too.
As an illustration for the distinction between ecological and selective environments, Brandon (1995, 47–49) uses the image of a field with soil conditions that
vary over certain areas or that change over time. If we plant seeds from a genetically homogeneous stock in a regular pattern, the patterns of growth and health of
the plants that emerge will provide a measure of variation in the soil conditions that
have an effect on the plants, allowing us to identify a number of relevant variables
within the plant species’ ecological environment. If we plant seeds from two or
more different varieties in the same manner, the variant patterns of growth will help
us to identify a number of relevant variables within the different varieties’ selective
environments. For example, one variety might be more affected by a change in soil
conditions than the other, so the variant patterns of growth and reproduction will
provide a measure of the relative fitness of the respective varieties. In this sense,
the organisms themselves can be interpreted as measuring instruments that are able
to determine the conditions in these two latter types of environment.
Hence, the line of distinction between the three levels of description of an
environment is drawn by distinguishing levels of conditions outside and within a
population with respect to their objective relevance to that population and its individual members. Although the external environment can be defined in disregard
of the constitution, the abilities and the needs of the particular organisms inhabiting it – apart from the question whether the reference point for “external” is the
individual or the population – the latter two can be defined only in relation to the
properties of individuals and populations. Nonetheless, there is, strictly speaking, no ontological difference among external, ecological and selective environments. There are only different levels of description that refer to different relations
between the constituents of an environment, and their respective relevance to a
population and its members.
The point that Brandon seeks to make with his threefold distinction is that external, ecological and selective homogeneity vs. heterogeneity of some environment
may not necessarily reflect each other (Brandon 1995, 64–66): a homogeneous
external environment may be heterogeneous in ecological terms, as the key factor
of reproductive relevance may lie with other members of the same population.
Such would be the case for a high population density of adult specimen in some
area that gets in the way of the growth and reproductive chances of juveniles.
Even developmental stages of an organism may become selectively relevant.
Conversely, although there will be no selective heterogeneity without ecological
heterogeneity, a physically and ecologically heterogeneous environment may still
be selectively homogeneous, as relative fitness of genetically variant sections of
the population may covary with variation in the ecological conditions, that is the
variant forms may be identically affected by the ecological conditions in question.