The "Peripheral Niche" Mechanism

1. In the evolution of life on any planet, there will invariably by new environmental ranges that must be penetrated by each major taxonomic group the first time.
2. When this occurs organisms penetrating the new range might find the fitness bounds that apply in more saturated ranges temporarily loosened, while the new organisms experiment with new means of adaptation.
3. As organisms adapt to the new conditions, their genomes are likely to move large distances from ancestors who were originally adapted to survive in very different niches.
4. Over the range of the variation, large movement of genome distance will register as a fitness decline, larger than one we would normally expect to see between closely related types. This process of penetration of a new niche, and large movement of genome distance might account for how major new novelties could evolve against very steep fitness losses.

To see PDF version of this file (173k) click NICHE.PDF 

(Note: This mechanism is interesting. But if you are not yet convinced that fitness falls for complex accumulations it might be better to return to 2.0 The Theory of Complex Accumulations, or skip ahead to 4.0 The Theory of Phylogenic Evolution and come back later.)

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3.1 Searching for Explanations

3.2 The "Boundary" of a Species

3.3 The Theory of "Concatenation"

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When humans discovered that light elements such as hydrogen and helium could burn as nuclear fuels in the interiors of stars, fusing into heavier elements and releasing energy, it seemed that they had discovered how the heavier elements formed. Except the process of fusion burning of light elements only continues up to element 33, iron. Beyond iron, fusion becomes an energy-absorbing (not releasing) process, so it occurs against a loss (not a gain) of energy. This required a much "bigger furnace" than the normal burning of stars. Eventually, it was discovered that a supernova would produce the energy exchange needed to form the heavier elements.

In the history of life on Earth there has also occurred large 'explosions' of whole new classes and phyla, a crude analogy to an evolutionary supernova. Only whereas astrophysical supernovae have an analytical cause, explosive radiations of life on Earth have each had a unique explanation, which can only be established empirically. For example;

• Evolution of a single type able to photosynthesize solar energy, converting carbon into oxygen, will lead to an 'explosion' of new types able to exploit the more abundant energy source.
• In turn, a slow build up of an oxygen atmosphere will eventually release an 'explosion' of diverse aerobic types, able to exist at higher metabolic levels.
• In a similar manner, a cooling of the Earth's climate, as seemed to occur at the end of the Cretaceous released an 'explosion' of types pre-adapted with endothermic regulation, such as birds and mammals.

So, in the evolution of life there can exist instances of build-up followed by release. Except each case results from a unique series of events, and has no one general cause.

The "peripheral niche" mechanism correlates empirically derived histories of large-scale, episodic build-up and release of evolutionary diversity with an analytical model of fitness.

1. In the history of life the fittest organisms evolve first and penetrate the most suitable, comfortable ranges that can sustain primitive life.
2. After this newer, more complex forms can only evolve against a fitness loss. However, new types would have no opportunity to evolve against a fitness loss in existing ranges, because these ranges would already be dominated by fit types, against whom it would be impossible to compete.
3. Because fit types will dominate existing ranges, slightly less fit types will be pushed into "peripheral niches" on the outer limits of existing ranges. Here, slightly sheltered from direct competition against dominant types, new, low fitness-yield novelties have evolutionary time to accumulate and mature.
4. The more marginal the niche, the longer new types will have to accumulate totally new novelties, even against large fitness losses.

Yet also in the past there must have existed a greater range of niches that were not yet exploited than can exist today. So, larger accumulations of totally fresh novelties, and larger subsequent 'explosions' of matured types, were possible in the past than in recent times.

Nobody has studied the psychology of it, but one difficult concept for classical physics to establish in human minds was that of a "field"; a force or 'containment' which humans could not see but was there. Today though, the 'field' concept has caught the popular imagination, despite that we now realize that the field as "lines of forces" is only a mathematical fiction. Mathematics deals with an entity called fields, just as it deals with lines, points, vectors, gradients, surfaces, and volumes, but we must interpret these as physical properties. So, the physical basis of fields is termed an 'exchange mechanism', in which a particle is 'exchanged' between physical entities. The heavier or more energetic the exchanged particle, the more tightly bound entities exchanging particles will be drawn. (The stronger the 'field'.)

Similar to the concept of a field, the "boundary" of a species is an analytical fiction. A species is a collection of individuals, also "bound" by some attribute that they share in common. Usually this is a shared attribute to reproduce or cross-fertilize, so the boundary is often just a geographical range of the species. Outside of this range, any individual would not have a reproductive mate, or the protection and comfort of the group. Also, within the species individuals can enjoy high fitness for small changes of genotype. If a male was randomly born with a slight advantage that was only a small deviation from the genome (genotype range within the group) that male could mate with any one, or many, females in the same group, to enjoy high fitness (many offspring for a small change). More importantly, staying within the species has another advantage, in that if the species has survived many generations it must be based on a proven design. In the past a narrow group of individuals in a species found themselves so felicitously adapted to their range that their offspring spread rapidly, with minimal further changes to genotype (minimal loss of fitness). So, while members of a species must be able to reproduce among each other, what they also share is an already proven design.

Yet, while every species is founded around a proven design, it is still a design optimized for a particular 'spot' in the range. If the design is optimized for life in the deep forest, members of the species might survive at the edge of the forest, but not in optimal conditions. This has its own "retention" effect. Because their design is not optimized for it, individuals forced to the edge of the forest will pass less offspring to subsequent generations than those at the center. So although new novelties can evolve among individuals anywhere in the forest, the 'deep forest' design will predominate. Again, to move out of the forest will require large changes of genotype such as change of diet or locomotion, usually over several generations. But while conditions are stable fitness will accrue to easy-to-enact single generation changes (slightly bigger, stronger, sharper, etc.) Simple, fitness-rich adaptations will more likely favor the deep forest design because the better-adapted individuals will still compete better in the middle of the forest.

Only conditions will not remain stable forever. The forest can shrink, climates can change, or invaders can drive residents out. But individuals can also migrate away from the species boundary. Within the genome of any individual some genes will express attributes (call signs, mating habits) useful only within a species to which the individual currently belongs. But other genes will express homologous attributes (vertebra, heart type, etc) that could be equally useful in a new species. Because many genes are specific to the current species the individual gains maximum fitness (for all its genes) staying within its species. This is the "retention" (stasis) effect mentioned. As competition expels some individuals outwards from the species though, genes expressing homologies will encourage a split by reinforcing racial, migratory, or 'outcast' feelings. Yet as a species genotype adapts, selection "vectors" the genomes of the migratory ancestors away from what they were (members of a species that it was better off leaving anyway) into what the new species will be. When this occurs genes in the genome specific to the old species will be weeded out by selection, and ancestors will lose fitness. But genes expressing homologies will retain fitness "breaking" from a species where their host phenotypes were loosing the fitness struggle anyway. The phenotypes too (if they survive the move and found a new lineage) will be better off in a new species founding a new lineage. Just that if the genotype has vectored a large distance from a previously proven design, there is likely to be an overall loss of genome fitness among the migrated individuals. (Although in one sense, the fitness loss is only the breaking of the retention effect.)

This breaking of a species boundary when an ancestral species splits in two happens throughout evolution. Each time there will be a slight fitness loss among the species (the 'daughter') which diverged the furthest from original type. Conventional theory effectively acknowledges this, by requiring strong isolating mechanisms or other processes to force the species to split. (If there were a fitness gain, species would split too readily. But species keep high retention under stable conditions, despite constant change and mutation, so this is the fitness effect.) Only in each case, these are minor changes (such as migrating from a forest) among highly adaptable types. The split can happen many times with a new species each branch, and this is the controversy. Mammals "diverged" a large distance from the reptilian ancestor, but only over a 200 million years (myrs) period with many small branches. So, even if we accept the fitness loss, each small split in a long series might be a normal speciation, with no "peripheral" niche mechanism needed to explain it.

However, if this theory is correct, then the larger the divergence of genotype from ancestral form, the larger (roughly) will be the loss of fitness. Modern theory acknowledges that there must be natural resistance to speciation because speciation usually requires isolating mechanisms to "force" it to occur. (Note: speciation among polyploid plants or by non-sexual gene exchange might be a more random, not requiring "forcing". It would be interesting if such speciation involved any measurable fitness loss.) But existing isolating mechanisms used in conventional theory might only account for shallow to medium fitness losses, for small to medium divergence from ancestral genomes. (Only the longer the geological time, the more small changes and shallow fitness losses have time to accumulate as major effects.) But for evolution of whole new phyla, or even classes, we might require very large fitness losses, and very large "forcing" effects over relatively short geological times, which no existing isolating mechanisms can account for.

So though it is not conclusive, evolution of major new classes and phyla occurs in "peripheral" niches. These are harsh, hostile, or outlying environmental ranges, which must be penetrated the first time by members of each major taxonomic grouping. For example,

• Although the evolution of mammals proceeded for over 140 myrs, 100 myrs was in the nocturnal (nighttime) niche, which the main competitors of mammals, reptiles, would have difficulty penetrating.
• Early amphibians, evolved in the shoreline niche, peripheral to deeper waters already under domination of primitive fish and other sea life.
• Birds (though closer to dinosaurs than mammals to reptiles) perhaps evolved in a niche of trees, high peaks, or colder habitats (this is not conclusive).
• Life's largest accumulation, from prokaryote to eukaryote life, has no established theory of how it occurred. But eukaryotes evolved from a "forcing together" of smaller prokaryotes. This may have occurred in an environment providing intense concentration of life, or along an outer edge of prokaryote life, where confederation was a superior alternative to extinction.

But despite evidence that each major taxonomic transformation occurred in a peripheral niche, there is no insistence on it. All that is asserted is that divergence from ancestral genomes involves a loss of fitness. Just if this requires losses of fitness larger than existing mechanisms can explain, we should check if the transformation did not occur in a "peripheral" niche, where for reasons to be explained, a very large fitness loss is more likely.

Conventional evolutionary theory allows no real mechanism of saturation, in terms of a limit to evolutionary variety. Now saturation (next section) does not mean that all possible variety is consumed, but only that all easy-to-enact fitness-rich changes are optimized. So if new variation is needed it must come from major, difficult-to-enact changes like new body plans, new means of reproduction, or new materials or skin covering. These require major alterations of genotype over many generations, and loss of fitness. When all organisms occupying an existing range (say, the ocean) are in saturation, there is a cumulative build-up of evolutionary pressure for change. This is an evolutionary 'supernova', or to use the new term, a concatenation.

Now although the terms sound the same, a concatenation is almost the opposite of a radiation.

1. A radiation occurs when a totally new, hard-to-evolve design (eukaryote life, amphibians, mammals) has matured, a new range has opened, and easy-to-evolve fitness rich changes adapt in huge new variety.
2. A concatenation occurs "pre" the evolution of totally new types, when evolutionary pressure builds up among existing types to force a gross change in evolutionary possibilities.

This is surmise, but "pre" the evolution of eukaryote life there was a concatenation within prokaryote life. Or "pre" the penetration of amphibians onto land, there was a concatenation among ocean life. But the cause of this pressure build up (concatenation) within existing types is fitness. If there is to be a large change (say, prokaryotes to eukaryotes) there will be a large loss of fitness, so no organisms will want to initiate the change. (Again, organisms themselves do not care. There is a "retention" effect among existing types, which we can quantify as a loss of fitness for type change.) But this fitness "wall" against change will correspond to the physical edge of an existing environmental range, if the new range has not yet been penetrated by members of that phylum. The usual limit of a species, its "boundary", is its normal ecological range (the edge of the forest, lake, grassland, etc.). But most times individuals can overcome the limits of an ecological range by small adaptations of diet, movement, camouflage and behavior. (This is why the famed "tangled bank" does not work. Its ecological edge is too porous.) Beside which, while there remain easy adaptations in a confined range, evolution will continue by small, fitness-rich changes.

Yet for however long evolution grinds on with small fitness-rich changes, effects will eventually "concatenate" when all the easy changes are consumed, and all easily crossed boundaries are penetrated. Concatenation occurs not just at a species "boundary", but a phylogenic boundary of changes easily enacted within existing types.

• The phylogenic boundary for all life forms on Earth say, is the freezing or boiling point of water, or the vacuum of outer space, which no large life forms can penetrate. (Some bacteria can allegedly survive these).
• Above limits exist for modern, highly adaptable life. There were periods in our evolutionary past when dry land, cold, night, or the air could not be penetrated by large life forms, within the restricting phylogenic boundaries that then existed.
• The oceans are huge, but if enough varieties of water-life evolve, eventually that environment will saturate. Creatures can still penetrate the shorelines, and then onto land. Only to penetrate onto land the first time requires new homologies (like lungs, limbs, and non-dehydrating skin) and large changes of genome, all of which result in a loss of fitness.
• A similar analogy applies to mammals. The nighttime niche might appear as an open range ecologically, but to penetrate it new technologies are required to stay active through the dark, colder hours. But new technologies come at a fitness price, so most creatures of the era (reptiles) went with the "easy" changes; bigger size, longer claws, sharper teeth, where small, simple changes can bring big, immediate fitness gains.

Peripheral niches offer a certain protection to creatures that do penetrate them, in that removed from the direct line of fitness-rich competition, low yield fitness gains have a better chance to mature as complex new novelties.

In the new theory then, there are only two essential processes different from conventional theory.

1. Evolutionary changes form two broad categories of being either easy, or hard to enact.
2. Hard-to-enact changes will evolve against and overall loss of genome fitness, as genotypes diverge large distances from ancestors.  

The peripheral niche and concatenation are not essential processes if all the primary effects of evolution can be explained without invoking the further mechanisms. Only an empirical study of the history of life can reveal which process were actually involved. But there is some evidence that the peripheral niche and concatenation are genuine effects, which will need further study to reveal their precise mechanisms.

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