DEEP ETHOLOGY: evolution

advanced aspects of "ADAPTATION"


"Adaptation" --the good fit of organisms to their environment--can occur at three hierarchical levels with different causes."

1. Physiological adaptation [homeostatic; but animals can be conformers/regulators]

2. Cultural adaptations [a decorporealized or transindividual developmental change?]

3. Evolutionary adaptation (Darwinian mechanism of selection upon genetic variation)


Organisms can be viewed as ensembles of anatomical, physiological, or behavioral TRAITS that contribute to FITNESS --an individual's ability to survive, thrive, and reproduce. the major quality animals must manifest is a capacity to COPE with challenges to its fitness. Ordinarily, there is no attribute of an organism that can be defined (including the relationships between attributes and the timing of their expression) that is not subject to natural selection

SO, when we speak of an organism's adaptations we are referring to traits subject to natural selection which persist because they contribute to fitness (or at least, contribute more than they cost). Adaptations are the means by which organisms cope with environmental changes and stresses.
An Adaptation can be manifest at any level of organization from subcellular through the ecosystem in which any level of organism -- environment conformity can be discerned. Within a single organism, "adaptation" can encompass morphology, physiology, development (through organizational effects or through differential timing of developmental events), and behavior.


"adaptations are traits (or characters) that have been subjected to natural selection" This means that the trait has "evolved" (been modified during its evolutionary history) in ways that have contributed to the FITNESS of the organism manifesting it .
    DEFINITIONS (you would expect that such a key word has come to have many subtle nuances of meaning --BUT there IS an irreducible core of meaning which you must understand.)

    An adaptation is an anatomical, physiological, or behavioral trait that contributes to an individual's ability to survive and reproduce ("fitness") in competition with conspecifics in the environment in which it evolved (Williams, G. 1966. Adaptation and Natural Selection Princeton).

    Such a definition is simply, safely, descriptive. It doesn't distinguish adaptation as a cause or as a consequence. Bullock (1977) identifies "adaptation manifested by a whole organism" as a response, ". . . a regulatory or advantageous change in response to an environmental stress by an individual or by a species in the course of evolution" (Bullock 1977)

    Reeve & Sherman (1993) speak of "adaptation" as a consequence" ". . . a phenotypic variant that results in the highest fitness among a specified set of variants in a given environments" This "definition of adaptation consists of three components: (1) a set of phenotypes, (2) a measure of fitness, and (3) a clearly defined environmental context" (the current environmental situation, involving both biotic and abiotic elements.)
    BUT, it is unlikely that any biotic environment in which an adaptation emerged is still intact -- the adaptive peak is always receding: That is, no contemporary trait can be adaptive (in Reeve and Sherman's sense) because they were selected for in an environment that no longer exists. This is sometimes called the "environment of evolutionary adaptedness" (EEA).. [more on EEA]

    Adaptation: "In evolutionary biology, any structure, physiological process, or behavioral trait that makes an animal better able to survive and reproduce compared to conspecifics. Also used to describe the process of evolutionary change leading to the formation of such a trait" (From Glossary of Animal Behavior, 4th edition Drickamer Vessey, Meikle. 1996. WC Brown, publishers)

    Adaptation: "According to strict usage in evolutionary biology, it is correct to consider a character an "adaptation" for a particular task only if there is some evidence that it has evolved (been modified during its evolutionary history) in specific ways to make it effective in the performance of that task, and that the change has occurred due to the increased fitness that results" (p.13). . . . (West-Eberhard, Mary Jane. 1992. Adaptation: Current Usages, in Keywords in Evolutionary Biology Harvard University Press)

    Below is a definition by an anthropologist writing in the Annual Review of Ecology and Systematics. I like it because it touches every important base without becoming too diffuse:

      Adaptation is . . .

      "The processes by which organisms or groups of organisms maintain homeostasis in and among themselves in the face of both short-term environmental fluctuations and long-term changes in the composition and structure of their environments." (Rappaport, 1971).

The several senses of the term "adaptation" have something in common --the idea of compensation for change: short-term adaptations are behavioral or physiological, longer- term adaptations may be developmental (environmentally induced changes in anatomy, physiology, or behavior), and the longest-term adaptations are genetic (more-or-less "programmed" changes in anatomy, physiology, or behavior; more- programmed=relatively "closed," i.e. not susceptible to environmental influences; less programmed=relatively "open," i.e. susceptible to environmental influences.)

Patterns in biology are both adaptive and constrained

Functionally, an adaptation is "a change in a phenotype that occurs in response to a specific environmental signal and has a clear functional relationship to that signal that results in an improvement in growth, survival, or reproduction" (Strearns, S.S. 1992 (The evolution of Life Histories, Oxford) p 16; citing Williams 1966a and Curio 1973)).

In the biomechanical sense, constraint refers to the necessity that organisms obey the laws of physics and chemistry. The systems definition holds that "each stage of development must proceed from where the last one left off" (Oster & Alberch 1982:450; cited by Strearns 1992); or, more convincingly, "Developmental constraints [are] biases on the production of variant phenotypes or limitations on phenotypic variability caused by the structure, character, composition, or dynamics of the developmental system" (Maynard Smith et al. 1985:265; cited by Strearns 1992:18). In concert with this definition one can interpret constraint as the progressive irreversible integration or fixation of traits.

    ADAPTATIONISM refers to the uncritical application of evolutionary ideas and principles to develop stories about how evolution must have proceeded to result in a specific trait. In other words, adaptationism involves asserting that a trait is adaptive --has evolved to "solve" a particular problem in a way that improves fitness-- when there is insufficient empirical support. It is at the heart of many quarrels about evolutionary interpretations, but they all seem to reflect a language problem: confusing assertions (that an idea is valid) and speculations (that an idea is plausible). According to some critics of sociobiology, the whole discipline is a manifestation of the adaptationist program--a systematic attempt to explain all extant phenomena in terms of plausible previously demonstrated principles.

    "Overly facile application of the term adaptation encourages the assumption that all characters are adaptive; for this reason, some authors have urged restraint on the use of the term. It remains the case, however, that persistent attempts to discern the adaptive significance of phenotypic traits--to apply an adaptation hypothesis-- have been a primary and fruitful occupation of evolutionary biologists since before Darwin" (p.17) (West-Eberhard, Mary Jane. 1992. Adaptation: Current Usages, in Keywords in Evolutionary Biology Harvard University Press)
Mismatch theory --dealing with organisms out of their usual context -- is an important idea in understanding what constitutes "normal" behavior. In Sociobiology, E.O. Wilson puts the relationship of "an adaptive trait" to "normality" quite succinctly:

    A trait is adaptive if it contributes to "fitness" -- the success of one genotype to project itself into future generations. This is maintained in a population by selection. A trait is thus "nonadaptive" or "abnormal" if it "reduces the fitness of individuals that consistently manifest it under environmental circumstances that are usual for the species." Wilson goes on, "In other words, deviant responses in abnormal environments may not be maladaptive-- they may simply reflect flexibility in a response that is quite adaptive in the environments ordinarily encountered by the species. A trait can be switched from an adaptive to a nonadaptive status by a simple change in the environment. "