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The mechanism proposed by Darwin to explain the evolution of life on Earth is based on a delicate balance between a positive process, that of variation, and a negative process, that of selection. The inconsistencies encountered so far in the fossil record all seem to point towards a need for a stronger positive process, one that allows for a species to be born in far shorter times than the evolutionary times implied by Darwin's theory. It is true, as Behe noted, that an organism is way too complex to be built by refinements, and it is true, as Gould claimed, that species appear all of a sudden. Selection does account for the disappearance of variations that are not fit, but variation alone (and the set of genetic "algorithms" that would represent it) is hardly capable of accounting for the extraordinary assembly of a new organism. A more powerful force must be at work.
When we find that force, we may finally write the last chapter of "The Origin of Species", which Darwin never even tried to write: we still don't know how species originate.
That force may be hidden in the process of endosymbiosis, the process by which a new organism originates from the fusion of two existing organisms, or, more precisely, by which two independently evolved organisms become a tightly coupled system and eventually just one organism.
"Structural coupling" of organisms has been shown to be an accelerating factor in evolution both by the Chilean neurobiologist Humberto Maturana (whose "autopoiesis is precisely such a process to generare progressively more and more complex organisms) and by the neurophysiologist Ben Goertzel (who notes that organisms capable of effectively coupling with other organisms are more likely to survive, and that the coupling process may account for Gould's puncturated equilibrium).
If organisms are composites rather than individuals, then Darwinian evolution can occur much faster and can exhibit sudden jumps to higher forms, and therefore explain two unsolved mysteries of life on Earth: : how prokaryotes (cells without a nucleus) evolved into eukaryotes (cells that have a nucleus) and the sudden appearance of new species in the fossil record.
The symbiotic creation of species is not such a far-fetched idea. After all, humans can be thought of as collections of organs and viruses co-existing in symbiotic relationships. Generally speaking, the transformation of primitive organisms in more complex ones may be due to the incorporation of other organisms. We know, to start with, that species may also originate by hybridization between existing species, a process that is very common in plants.
Assembling organs in a functionally coherence way is a very difficult task for anybody, including Nature itself, especially if the forces working on it are random; but mixing genomes may be relatively easy. The chemical process that can dramatically alter the genetic code of an organism to incorporate the genetic code of another organism may exploit the very peculiar structure of the DNA double helix and the very peculiar behavior of sex. Both the genetic apparatus and the sexual apparatus seem to be involuntarily conceived so as to facilitate the fusion of organisms.
While single-organism evolution may explain only gradual and localized changes in skills, the formation of composite structures would certainly result in higher levels of complexity which in turn would result in higher levels of organization.
Unfortunately, we have no idea of how the DNA of a new organism can be synthesized from the DNA's of two organisms, i.e. how a new species can be created by the symbiotic union of two species. The chemical process that allows for the fusion of two codes has not been discovered yet, but may turn out to be a relatively simple "algebra" of the four bases of the DNA.
We now know that the immune system is itself an evolutionary system. How does it know which repertory of antibodies to start with? How are new antibodies created? The answer is probably the same answer to the very mystery of the origin of species. The immune system is but a miniature representation of life on Earth. It may prove to be the ideal laboratory for researching that elusive chemical process.
The British biologist Matt Ridley, following in the footsteps of William Hamilton, thinks that evolution is accelerated even by parasites. Organisms adopted sexual reproduction in order to cope with invasions of parasites (parasites have a harder time adapting to the diversity generated by sexual reproduction, whereas they would have devastating effects if all individuals of a species were identical). Furthermore, life can be viewed as a symbiotic process which necessitates of competitors. In a sense, co-evolving parasites help improve evolution.
The emphasis in evolution has traditionally been on competition, not cooperation, although it is through cooperation, not competition, that considerable jumps in behavior can be attained.
Sex itself is but cooperation.
We have not found any evidence of multiple beings integrating in one being, but there is plenty of evidence that individual single-cell organisms sometimes join in creating "collective beings" which are better equipped to survive.
Single-celled bacteria form large colonies in countless ecosystems, particularly visible in seaside locations.
Soil amoebas join together in one huge organism that can react quickly to light and temperature to find food supplies.
Sponges are actually collections of single-celled organisms help together by skeletons of minerals.
These are all examples of how cells are capable of forming communities that live together and live at the same biological "pace". Whereas in a human community we are all independent and only occasionally interact, in such agglomerates of cells every unit is synchronized towards the common goal.
In 1999 the Danish biologist Sune Dano has engineered a community of yeast cells that live together as a single organism, driven by collective chemical oscillations.
Among multi-cellular organisms, ants and bees exhibit a similar behavior, although the individuals are physically disconnected and communication occurs at distance through the senses (rather than through chemical contact).
A multi-cellular organism is a collection of cells that are synchronized through electrochemical activity. Sponges and amoeba may show how multi-cellular organisms were created from single-cellular organisms. Ants and bees may show that the difference between a multi-cellular organism and a society of organisms is only the type of internal communication: they both rely on constituents that are synchronized and the only difference is how those constituents communicate (the dances of the bees as opposed to the chemical reactions of the amoebas).
If this phenomenon cannot help explain evolution as a whole, it can at least shed some light on the transition from mono-cellular to multi-cellular organisms, one of the crucial steps in the evolution of life on this planet.
The American biologist Lynn Margulis is perhaps the strongest proponent of endosymbiosis.
A fascination with the wonders of the bacterial world led the Margulis to believe that no other single force has shaped evolution in a more important way. Everything the Earth is today and everything we and other living forms do today is due to conditions that have been created and maintained by bacteria.
Margulis' fundamental thesis is that our bodies are amalgams of several different strains of bacteria: endosymbiosis of bacteria is responsible for the creation of complex forms of life.
Margulis follows the American biologist Ivan Wallin, who in 1927 was the first one to propose that bacteria may represent the fundamental cause of the "origin of species" (Darwin's unsolved mystery) and that the creation of a species may occur via endosymbiosis.
Margulis noted that not all the DNA is contained in the nucleus of the cell. As originally noted by Wallin, The "mitochondria" are organelles of the cell that function as its "power plants" and they contain their own DNA. While most DNA is organized as double sets of chromosomes in the nucleus, the DNA of mitochondria stands apart. Margulis believes that the presence of "extra" DNA in the cell is a fossil of an ancient evolutionary event: it testifies the fusion of at least two different kinds of organisms which together formed a "eukaryiotic" cell.
Margulis believes that such symbiotic merger, or "symbiogenesis", has been common in the evolutionary history of life on Earth, and actually accounts for life as we know it today. The ancestors of all life are bacteria. They fused into "protists" (algae, amoebas, etc) which fused into multicelled organisms. Margulis tracks their evolution into plants, animals and fungi.
Margulis emphasizes that the Earth is still dominated by bacteria, which not only account for the vast majority of life, but also maintain the conditions for life on the planet.
All life is either bacteria or descends from bacteria: life "is" bacteria. Bacteria are also closer to immortality than animals with bodies: cell division generates identical bacterial copies of a bacterial cell; bacteria can be killed but they do not naturally die. The life of a multicellular creature is far more fragile.
Bacteria can also reproduce at amazing rates, compared with "higher" forms of life.
Life can even be viewed as a plan for bacteria to exist forever: bodies are desirable food sources for bacteria, so one could view the evolution of bacteria into such bodies as a plan by bacteria to create food for themselves.
The biosphere is controlled mostly by bacteria, it is, in a sense, "their" environment, not ours. Margulis emphasizes that not only the atmosphere but even the geology of our planet is due to the work of bacteria (mineral deposits have been shaped by the work of bacteria over million of years, or by the reaction with the waste gas of bacteria).
We are allowed to live in it, thanks to the work of bacteria, which maintain the proper balance of chemicals in the air. If all bacteria died, everything would die. It is their world. Everything other form of life exists because they exist. (On a smaller scale, if you "fumigated" your body and destroyed all bacteria that live in it, your body would not be able to perform vital functions such as synthesizing vitamins and would die).
The mitochondria which dot all cells of all living beings are former bacteria, using oxygen to generate energy.
The property of bacteria that intrigues Margulis is that they trade genes, rapidly and easily. DNA is loose inside bacteria's "bodies". Bacteria reproduce by simply splitting their DNA in two. This yields two offspring identical to the parent (same genes). The change of genes occurs only when genes are traded among bacteria. Bacterial sex ("conjugation") is about making a new bacterium out of an existing bacterium by adding genes donated by another bacterium.
The new bacterium resulting from the "engrafting" can even change sex, if the "sex" gene is received from the other bacterium (the "sex" gene specifies whether a bacterium is a donor or a receiver).
This process is not really related to our sex: sex is about two beings making a new being which partially inherits genes from each parent.
When bacteria "create" a new being, they do so by splitting (there is only one parent and the new being is identical to the parent). When bacteria trade genes, a being is changed into another being. We don't have either of these processes. I cannot split myself into identical copies of me, and I cannot mutate into another being by absorbing somebody else's genes. (Incidentally, bacteria can also trade genes as plasmids and viruses).
This process of "recombination" occurs even among bacteria of different species. It is as if I could absorb genes from an eagle and turn into a human with wings, and making children who are also humans with wings. The genetic material of bacteria is extremely flexible and versatile.
Margulis thinks that this is the process that enabled life to evolve rapidly. Scale is crucial: what Margulis realized is the extent to which bacteria rule the planet. They account for a vast portion of the atmosphere and the geology of the planet.
They spread in ancient times and are still spreading today at fantastic speed. Any phenomenon that involves bacteria is involving billions of rapidly moving and mutating beings. Once life was created, once the first bacteria appeared, things happened quickly and on a massive scale. Bacteria spread quickly, thanks to their reproductive efficiency and to their ability to feed on ubiquitous organic compounds.
The first bacteria were "fermenters", feeding on the sugars available on the surface of the planet. They were followed by photosynthesizers: photosynthesis enabled these bacteria to feed on light. Then came bacteria ("cyanobacteria") that could tolerate oxygen and could therefore feed on water (extract hydrogen atoms from water).
Each new type of bacteria was "polluting" the Earth and therefore changing the environmental conditions for future generations of bacteria. Pollution is an integral part of the evolution of life. The power of bacteria is that their "gene trading" habits made it relatively easy to adapt to whatever new conditions climate and their own doing were producing.
The history of life is the history of a planet blanketed with rapidly reproducing and rapidly changing beings: the bacteria.
Not surprisingly, Margulis subscribes to the vision that the Earth as a whole is a living being.
Protoctists were born about 2 billion years ago from the fusion of bacterial cells. "Endosymbiosis" is the process by which a being lives inside another being.
Eukaryotes (living beings who cells have a nucleus and whose DNA is confined in that nucleus) evolved from those protoctists.
Mitochondria are visible remnants of this process of endosymbiosis.
Experiments by the Korean biologist Kwang Jeon showed that even virulent pathogens can become organelles. Margulis deduces that predators can become symbionts, that a deadly infection can become a bodily part.
Margulis extends this paradigm to bodies made of several organs, and suggests that those organs also were accumulated the same way, that they are also due to the fusion with independent organisms by endosymbiosis.
While Darwin was emphasizing competition as the driving process of evolution, Margulis is emphasizing cooperation.
Margulis also introduces the novel idea that life has "free will" and has used it to influence its own evolution. It is not only humans who can affect their environment to direct their own evolution: the whole environment is doing the same. Living beings make decisions all the time and are thus responsible in part for their own evolution, as first speculated by Samuel Butler, a contemporary of Darwin.
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