Itt van egy releváns populáris cikk, ajánlom az olvtársak figyelmébe: Evolutionary Direction and Humanity's Place: Is evolution evolving or just wandering about? What leading evolutionary biologists have to say may surprise, even inspire you.
Darwin offered this automatic, mindless mechanism as an alternative to purposeful design, as an explanation for the uncanny good fit between organisms, their environments, and each other. While suggesting how one species might evolve into another as an adaptation to a changing environment — a micro evolutionary process — Darwin's theory provided no additional mechanisms for long-term evolutionary trends — for macroevolution.
If there is no direction in evolution, however, if evolution is not really going anywhere, then no additional mechanism is required.
Let us entertain the case for Nowheresville. While it might appear that life started simple and evolved to the complex, this is just an artifact of our perspective: that of a large, rare, surface animal.
We consider ourselves highly successful, but in actuality, we are not. If one is coldly objective about life — about success — it is biomass that counts. Among animals, the insects, not mammals let alone mere humans are the paraziták az autóban winners.
Animal biomass, however, even all of it rolled together, is inconsequential compared with plants. This is not the worst of it, however. Recent research has revealed the actual winners of our planet to be subterranean bacteria. Trapped in surface sediments, these denizens of the deep enter a comatose state as they embark on million-year geological cruises. Their total biomass is staggering, reducing all surface life to a mere footnote.
Granted: in terms of biomass, surface animals are insignificant. But are they not significantly more complex than bacteria? Does not this suggest a trend, of sorts, in evolution — a direction? Not at all, suggests Harvard paleontologist Stephen Jay Gould. Sure, he admits, to begin with, life randomly got complex more often then it got simpler; there was no other direction to go. Life could not get any simpler and still function.
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Eventually, however, things steadied out, and life randomly got simpler as often as it got more complex. Bottom line: Nowheresville for evolution. In fact, Gould suggests with some justification, complex life actually has a built-in disadvantage: its very complexity makes it easy prey to the mass extinctions that periodically plague the planet. Life might get more complex for a while, but then, whamo, a meteor or other mass extinction snuffs out the latest prideful, oversized surface fluff, setting things right again.
Big, boastful life comes and goes. It was trilobites one time, then dinosaurs. Now it is humans. Next time, who knows, it might be giant cockroaches!
But what példák a paraziták progresszív morfofiziológiai adaptációira there actually is an overall trend in evolution? What if civilized humans were the most complex form of life, the current culmination of a long evolutionary trend toward greater complexity and differentiation of form?
As complexity is difficult to define objectively, Bonner uses two surrogates: the size of life and the variety of different cell types in organisms.
These trends, over time, are unmistakable. While Bonner admits that mass extinctions have repeatedly set complex life back to a simpler state, he differs with Gould on the completeness of the reset. Bonner suggests that evolution is a two-step dance: two leisurely steps forward between mass extinctions, then one abrupt step backward during each extinction.
Thus in spite of periodic setbacks, evolution is going somewhere.
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Bonner suggested that evolution advanced because there was példák a paraziták progresszív morfofiziológiai adaptációira at the top. The first organisms to break through to a new level of complexity would at least initially face little competition; they would have found room at the top.
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Evolutionists and cosmologists have noted for some time that life, even the universe itself, appears to be sharply discontinuous, to be layered into distinct strata of increasing complexity. We now realize that this layering is also an evolutionary time series, the story over time of the flowering of the cosmos and life on earth, the Epic of Evolution.
The sequence is now familiar: quarks, subatomic particles, atoms, molecules, bacteria, nucleated single-cell protists and, finally, the multi-cellular plants, animals, and fungi.
But what is the mechanism behind evolution's advance, responsible for its hierarchical structure? Drawing on earlier suggestions, the polymath Jacob Bronowski suggested a macro evolutionary mechanism that simultaneously explained both the layering of complexity and its increase over time. I was immediately struck with the beauty of what Bronowski called an paraziták a hangyákon ratchet" that gave evolution its forward direction.
With the constant generation of random variations and a ratchet to keep it from going backwards, evolution had no choice but to go forward. The physical universe started with the simplest of modules, the quarks. These combined randomly to form the next higher level of modules, the subatomic particles. Entirely different from the quarks which formed them, these particles had their own, unique emergent properties.
In the immense heat of the early universe, however, these particles were immediately knocked apart again példák a paraziták progresszív morfofiziológiai adaptációira quarks.
As the universe cooled, stable subatomic particles accumulated and these, in turn, formed the basis for yet another level in the hierarchy of complexity, the atoms.
Gravity concentrated matter into galaxies and then into stars whose interiors were the nurseries where more complex atoms were forged and dispersed via spectacular supernova explosions which enriched the interstellar media. The can't-go-backwards ratchet behind physical evolution is the very expansion, and hence cooling, of the universe.
Like Goldilocks, the higher reaches of evolutionary complexity required that it be neither too hot nor too cold. If too hot, delicate new complexities were rapidly torn apart; too cold, and there was insufficient activity to merge lower-level modules together.
Complexity was delicately poised between hyperactive chaos and frozen order. Planets with liquid water bathed in a gentle flow of stellar energy appeared to favor physically the growth of complexity, but even under these favorable conditions, the rare, highly complex molecule randomly assembled from simpler modules quickly fell apart.
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Ultra-complexity, almost by definition, was highly unstable. The universe's trend toward increasing complexity had hit a roadblock. The solution? A self-perpetuating cycle of complex molecules that catalyzed each other's formation, thus making new copies faster then they could fall apart.
We call it life — a clever, information-intensive way to make ultra complexity stable via reproduction. Continuing on, modules of early bacterial life with single strands of DNA merged together, as suggested by University of Massachusetts biologist Lynn Margulis, to form more complex albeit still single-celled protists with central "libraries" of chromasomal DNA.
And, in homokozó parazita fullness szubkután parazita egy kecskében time, these in turn merged together to form the multi-celled plants, animals, and fungi. But what was the ratchet that kept biological evolution from going backwards?
The British evolutionary theorist, John Maynard Smith, suggested that to avoid anarchy, the formerly independent, competitive ways of the lower-level modules were suppressed for the good of the new, higher-level entities. A higher level could only be achieved through the orderly submission of former, independent competitors to a newly emergent higher authority.
Once the lower-level modules lost their independence, once they threw their fates together, it was united we példák a paraziták progresszív morfofiziológiai adaptációira or divided we fall.
There was no going back. Thus a single biological mechanism, the cooperative merging of formerly independent modules with varying talents into a new whole, explains both life's trend towards greater complexity and specialization, and its hierarchical, layered evolution. Is there a hierarchical level beyond that of multi-cellular organisms?
Entities at any such higher level would contain, as their lower-level modules, a number of multi-cellular organisms. We would know that this higher entity was not just an association of organisms, but was a true "superorganism," if the individualism of the formerly independent, lower-level organisms had been suppressed, had been sacrificed to a higher, superorganismic authority. Such superorganisms exist: they are the colonies of ants, bees, and termites.
Ant colonies, as pointed out by insect zoologists Bert Holldobler and Edward Wilson, perform amazing feats of coordination.
Instead of feeding off the top of the food chain, as do their carnivorous solitary wasp predecessors, ant superorganisms have developed complex schemes to tap the bottom of the food chain by herding other animals aphids and by farming fungi.
The ant farmers are especially instructive. They practice large-scale, production-line farming.
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A physically large caste scissors out leaf sections and transports them to the nest. Ever-smaller castes, in turn, dice the leaves, mulch them into pellets, and feed the pellets to the ants' fungi garden. This caste specialization allows these ants, by indirectly példák a paraziták progresszív morfofiziológiai adaptációira off leaves at the bottom of the food chain, to be numerous instead of rare.
Having achieved a breakthrough to a new level of complexity, having found room at the top, these ants have grabbed the choice real estate and pushed their ancestral wasps and other less organized insects to the periphery to subsist, the best they can, on evolutionary crumbs. The late Donald Campbell suggested that two routes have been taken to "super sociality," to the top betegség székletszag a szájból rung of the superorganisms.
In both cases, the trick was to suppress the natural evolutionary competitiveness of the lower-level modules for the good of the new, emergent, higher-level whole. This was, of course, the same trick that life had always used to break through to a new hierarchical level at the top. In the case of the ants and other insect superorganisms, this suppression of competition was achieved by having a single queen lay all the eggs for the entire colony, thus fostering cooperation among the thousands, even millions of workers — sisters all — via common motherhood.
Homo sapiens, Campbell suggested, took another route to super sociality, to top superorganism status. Humans were not biologically capable of massed common motherhood. Although unable to become literal brothers and sisters, we were, nevertheless, able to overcome culturally the normal social limits of our chimpanzee-like ancestors to achieve our own pinwormok abból, ami megjelenik massing of thousands, even millions.
Our common bond, our brotherhood and sisterhood writ large, was culturally induced via religious belief and political loyalty. The Golden Rule was our ticket to the top. Of course, we humans, new to the game of massed millions, lacked the ant's smooth genetic cooperation, constantly refined over millions of years.