Life interacts with the environment. Life does not function in a vacuum.
Life in outer space does not interact; it ceases to function. Every environment is unique, each in its own way. Douglas Futuyama’s 3rd edition of Evolutionary Biology notes that: “A species is not genetically uniform over its geographic range…. At least some of these differences appear to be adaptive consequences of occupying different environments.” This is strongly suggestive of a primary environmental role in evolution. The environment is one of the two primary interacting life-changing entities.
Heredity AND environment are co-dependent. Natural selection is the genetic preservation of favorable environmentally-related traits (Darwin definition revision).
The process of natural (environmental) selection has been compared to a sieve; yet, a sieve is rigid. Futuyama also notes that: “The environment (the physical and biological factors that impinge upon members of a species, i.e., a population) is in a constant state of flux, varying on time scales ranging from hours to millions of years.” This means that all environmental conditions, everywhere they exist, are undergoing constant change (variable). Environmental selection employs a gatekeeper; the gatekeeper is more judgmental (than a sieve), selectively grading the degree of an organism’s compatibility to the existing environmental conditions.
This grading system restricts each individual organism in its passage through time, creating ongoing restrictions, expressed as organism or population (species) limitations. Therefore, environmental selection is really a more discriminating and dynamic process, with different, changing landscapes, having major geographical to micro-environmental aspects;
it is anything but rigid. Integrated into this discriminating, dynamic, process, are many different populations (different species), with each single population (members of a species) of genetically-different individual Retrospective 74
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organisms also in a state of constant change. On occasion, genetic changes within a population (a species), even within an individual organism (genetic expression may be altered by environmental conditions), can be of great environmental advantage. In the marriage of heredity and environment, the gatekeeper has become part of the family. A developing organism with ancestors having previously poor ratings of environmental passage through time can upgrade to first class passage (children will also get a free upgrade). First class passage is dependent upon continued first-class support from the environment. Later, as individuals of an environmentally well-adapted population (species) increase in number, competition for resources increasingly becomes more of a limiting environmental factor. All biologic and physical changes modify the degree of an individual’s environmental compatibility, which continually varies the outcome of environmental selection. Quantitatively, environmental selection at a given time varies directly with the sum and/or intensity of environmental limiting factors; the population number (of individuals) varies inversely with the sum and/or intensity of environmental limiting factors.
Environmentally AND genetically determined evolution (change in types of life over time) results when life comes under the selective forces of an isolated, changing environment; life will adapt or not adapt to that unique environment. The adaptation process is dependent on harmonious environmental integration into genetic expression, early in development, and the heritable transfer to offspring. The adaptation or any variability in adaptations must be supported in later more stable environments. Genetic isolation, genetic potential for survival and the time to respond to a changing environment before extinction occurs is the recipe for adaptive evolutionary success. Levinton, in the chapter on Patterns of Morphological Change in Fossil Lineages noted that “Morphological evolution occurs, only occasionally, when a population is forced into a marginal environment and is subjected to rapid directional evolution.”
Said otherwise, environmentally AND genetically determined change in types of life over time involves an environmental creation, and if it is an extremely adverse environment, death (extinction) occurs; or, on rare occasion, survival results from the interaction of environmental variation (environmental selection limiting factors) AND genetic variation (natural selection genetic bias). Environmental selection initiates a new directional change (from the genetic potential) in the surviving progeny of the heredity-environment marriage. The environment doesn’t control genetic variation from mutation, but it does influence genetic expression and genetic survival.
Levinton’s chapter on Patterns of Morphological Change in Fossil Lineages notes that: “Fidelity to the environment often supercedes the Environmentally and Genetically Determined Evolution 75
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effects of strong directional selection to jump to a new adaptive mode. The enslavement of organisms to their shifting environments is the essence of the fossil record.” In other words, the inability to adapt to a new environment is far more common than the ability to adapt to a new environment. Is this caused by an unchanging (adaptation) commitment to the pre-existing environment? Is change even a greater risk if previous prevailing environmental conditions return? Environmental extinction occurs when acquired adaptations are no longer relevant to survival of a species that is confined to an isolated changing environment (environmental creation).
From the perspective of life, significant environmental change in an isolated environment causes an extinction; or, on rare occasion, the changing environment generates an adaptation response.
Levinton, in the chapter on Patterns of Morphological Change in Fossil Lineages, further notes that: “Long periods of time with only insignificant taxa change are associated with unchanging environments such as the aerobic benthic areas from the early Pleistocene to recent times.” In other words, constant environments maintain a constancy in structures, functions and species richness; i.e., they do not undergo significant change or extinctions, they may undergo significant genetic change in this unchanging environment. This constancy pattern supports the environmentally AND genetically determined evolution model. There is even further support of the model. Levinton, in the chapter on Patterns of Morphological Change in Fossil Lineages, additionally notes that: “Even when specific taxa change (as a result of significant extinction), functional groups remain the same over long periods of time; predominant physical and biotic environmental constancy leaves little room for expectations of major directional change. This constancy may be behind the lack of common landscape phyletic change.” In other words, there is an interrupted, but general overall pattern of environmental selection similarity. That is, there is a pattern of environmental variability in the evolution of life; it’s an interrupted, environmentally-advantageous role repetition. And there is a pattern of genetic variability in evolution; it is an inheritability of environmentally-advantageous traits.
With environmentally AND genetically determined evolution, stable environments involve less evolutionary change than destabilized environments. This would mean that environmental selection acts on life at all times; it is especially active during times of an environmental extinction event. The creation of favorable new environmental conditions is often preceded by the severe environmental conditions of environmental extinction. An extinction event creates a very hostile environment for life.
Times of mass extinction involve massive amounts of habitat loss over a short time. Most environmental extinctions are not mass extinctions, but are due to different degrees of habitat loss. Most habitat loss is a local
phenomenon and may only reduce biodiversity within a species (population); however, at times, habitat loss is significant enough to eliminate species, even genera. Fatal competition mostly occurs between members of the same population (species); it primarily increases fitness of individuals within that population. Increased fitness does not lead to extinctions of species, but becomes more important as essential resources are depleted from the environment. Variation in availability of an essential resource constrains the life within that environment; this essential resource in short supply becomes a limiting factor of environmental selection.
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Environmental biology is the study of the conditions of life and their impact on past, present and future organisms. Population isolation is environmental (creation—may be biological). Recall that Darwin clearly recognized the significance of geographic isolation in The Origin of Species.
Speciation is an isolating mechanism. Species are mainly significant as a breeding population of individuals; i.e., individuals selectively breed only with members of the same species. Isolation restricts genetic flow. This isolation creates a unique environment for that population, which allows environmental selection to interact with genetic potential in that population. The environment that was created by isolation continues on as time passes. With environmentally AND genetically determined evolution, as environmental stress increases, life will adapt, or not adapt, to a changing unique environment, depending on the genetic variation available. Assuming no escape from an isolated changing environment, if the environmental stress exceeds the ability of an organism’s normal range of response to manage an environmental challenge, organism survival comes into question. The survival outcome is dependent upon the product of an interaction between environmental variation and genetic variation.
For the individual organism and its offspring, this interaction makes all the difference.
The origin of species through natural selection may not be the driving force of evolution. Speciation does not necessarily create significant change (Levinton). Genera of small body size have far more species than those of large body size. If speciation was the driving force in evolution, morphological evolution would be more prominent on small forms, but the reverse is so (Levinton). The driving force of evolution may well be the product of early developmental organism interactions between environmental variation (variable environmental selection) AND genetic variation (natural selection genetic bias), in a changing, isolated environment. The creation of a changing, isolated environment Retrospective 78
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must occur to initiate this life-changing phenomenon. Environmental selective forces in the changing isolated environment and their influence on then-present genetic patterns (preserved genetic variation) join and produce the successful change, something new. In a word, the driving force of the changes in types of life over time is (genetic) adaptation (to an isolated changing, environment).
Could speciation be over-rated? In simple life forms, speciation itself seems to lose relevance. For simple life, fatal competition doesn’t cause speciation; it doesn’t even fit. Members of a vegetative-reproducing population do not vary from one another unless something occurs that leads to a change in gene expression. The origin of a simple life “species”
may be due to a genetic change in expression of a (pheno) type in a changing, isolated environment. If this change in type has survival advantage (an adaptation) it will likely become established and predominate in a vegetative-reproducing population. For complex animal life, the origin of species is only a behavior adaptation (sexual selection) to minimize genetic incompatibility in organism development and sexual reproduction. Sexual reproduction within a species constrains (as well as it enhances) complex life’s genetic variation, and this aids in formation of a potential adaptation. The conditions of life, including sexual selection, isolate breeding populations in time and space. Under increasingly stressful conditions of life in an isolated environment, organisms utilize existing genetic bias and somehow integrate an environmental influence into expression of a newly-designed (pheno)type.
An environmentally-supported change in a developing organism (an adaptation) must also be supported by a breeding population for the change to continue. Gene pool isolating mechanisms, including sexual selection, results in the origin of species, which genetically supports preferable adaptations. Speciation in complex animal life is increasingly the result of sexual selection, an ancient, complex animal life behavior pheno(type); speciation is only indirectly associated with (not caused) by other isolating factors in the environment. A species is a sex club; it supports harmonious reproduction and development in complex animal life. Flowering plants have thrived because they are better at sexual reproduction than other complex-life plants. In flowering plants, their sexual reproduction is dependent upon intimacy with co-evolved pollinating insects, often a single species. It was different species of plants that were first described and placed into the taxonomic system;
classification was based on differences between sexual components. Botany is fundamentally about sex. However, plant speciation itself can become unclear (discussed in epilogue). In the chapter, Domestication: Evolution in Human Hands (wheat species discussion), of The Evolving World, David Mindell states: “The process of hybridization among disparate forms and Alone 79
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of increase in the number of chromosomes via duplication (sometimes of entire genomes) is a common method of speciation in plants, and the increase in genetic material allows for the evolution of novel traits and protein functions.” Speciation is the vehicle carrying the changes in types of life over time; however, speciation is far less significant than adaptation to a changing, isolated environment. In complex-life, the formation of a new species can take a very long time. Identifying a newly-evolved species and documenting an environmental advantage that is only found with this new species would be coincidental. In complex life, the origin of a species may or may not involve a detectable change in expression of a (pheno)type in a changing, isolated environment. A complex life breeding population (gene pool) often includes different (pheno)types, including any new (pheno)type change with a survival advantage—an adaptation; this adaptation will likely become established so as to predominate in the sexually-reproducing population. At all times, environmental selection is the gatekeeper for survival of an adaptation.
As early complex animal life gained variation in (pheno)types, a change in behavior (a phenotype change) included a sexual selection of preferable (pheno)types, which led to further genetic isolation. Sex complicates the conditions of life. Geographic isolation affects the variation available to sexual selection possibilities in the isolated gene pool. Fatal competition primarily increases fitness of individuals within the breeding population;
this doesn’t necessarily originate a new species. Natural selection competition for limited resources affects sexual selection, but it is not the same as sexual selection or competition for breeding rights. Natural selection is the (genetic) preservation of favorable variations and the (environmental) rejection of injurious variations (Darwin—but embellished). Any gene expression change in (pheno)type involves an interaction involving both environmental variation and genetic variation.
For any of this to make sense, it will require a better understanding of the phenotype. This requires some knowledge of genetics.