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September 21, 2012

How Did Bilaterian Evolution Happen?


A FACT-BASED EXERCISE

PART ONE: THE PROBLEM REDEFINED

My objective in this two part posting is to consider the fact of Bilaterian evolution in a new way, one that, in my opinion, both reveals the inadequacy of conventional theory and identifies its replacement.  Reading both parts will consume only a few minutes, but it is my hope that they will inspire others to give the problems I describe sufficient thought.

Although it may seem counter-intuitive, those of us who resolutely view evolutionary biology as an historical science have certain advantages over those who primarily employ tools of observational science. We cannot observe past events and we certainly cannot climb into a time machine and perform experiments in the pre-Cambrian, but because we accept Bilaterian evolution as fact we can reach certain useful conclusions, conclusions that demonstrate the gross inadequacy of conventional theory.

To begin this exercise, the most useful conclusion to be drawn from the fact of evolution is that not a single ancestor of any animal that ever existed died as a juvenile. It is a tautological certainty: because only adults breed we know that all the actual breeders survived pre-adult life. From that indisputable fact we can infer, with utmost confidence, that every breeder was the beneficiary of “perfect” development. (Convinced as I am that reproduction by significantly mal-developed animals was extremely rare in the past—as rare as it is in the present—I place “perfect” in quotes simply to deflect potential nitpicking.)

The fact of evolution permits me to state—also with certitude—that these links of perfect development—perfect animals begetting perfect animals—in all the chains that produced all extant Bilateria never once broke: all extant animals are products of uninterrupted chains of perfection.

THERE IS NO MODEL …

In a friendly email exchange I had not long ago with a research scientist who had read my book he asked if I had a model to support my theory. If he asked that question today I would say that he could find a suitable “model” in many biology textbooks; it’s the standard “tree of life” showing biologists’ best estimate of the various Bilaterian lineages’ relationship to one another and to the founding Ur-Bilaterians.  Included in this exercise are all chains of perfect construction of actual ancestors of all living animals in all extant species of Bilaterians: millions of lineages producing millions of trillions of breeders over ~550 million years.  

BUT THERE IS A CONTROL GROUP ...

According to my theory only the Bilaterians are products of cancer selection; except in cases like flowering plants which co-evolved with certain Bilaterians, I agree with the consensus that the evolution of all other multicells is adequately explained by Neo-Darwinism’s mechanism; cancer selection played no part in their history. 

As my control, to compare with the unbroken chains of breeding Bilaterians, I nominate the jellyfish. According to this report fossil evidence shows that more than 500 million years ago jellyfish “showed the same complexity as modern jellyfish.” In other words, in their lineages the unbroken chains of perfection might be summarized as “perfect jellyfish begetting perfect jellyfish without easily discernible morphological changes” for more than 500 million years.


TO COMPARE AND CONTRAST WITH THE BILATERIANS

Although it is possible to summarize 500 million years of jellyfish evolution with a glib phrase, it impossible to describe concisely all the morphological changes that were faultlessly expressed in developing breeder animals controlled by evolving Bilaterian gene pools, but in this (slightly revised) paragraph from page 110 of Cancer Selection I tried to give some sense of the monumental changes in the lineage beginning with a population of—already complex!—vertebrate bony fish and ending with a population of large African tetrapods:

"So great was the transformation in the fish-to-elephant lineage that it would be impossi­ble to list all the physi­ological changes that occurred, but (to mention only a few of them) it is appar­ent that it required the emer­gence of am­phibian capa­bility, then reptilian character­is­tics, and still later, mammalian characteris­tics. There was a switch in repro­duction from the fertil­ization of eggs in the open sea to internal fertilization and then to inter­nal gestation, the change from cold-blooded­ to warm-blood­ed, drastic changes in digestive systems in order to survive on rough plant mat­ter—etcetera, etcet­era, and etcetera. All those gross transforma­tions required radical changes in devel­opment programs and processes and in the structure of all the vital organs and all of the organ systems but we know with tautological certitude that the surviving gene pools handled all those changes with aplomb: all of the revisions were perfectly expressed in every single breeder."
 
To further appreciate the enormity of the challenges overcome by the Bilaterian gene pools in producing unbroken chains of perfection it might be helpful to ponder the changes that were implemented in major organ systems. Take, for example, the evolutionary chain that culminates in the heart  of the elephant, an organ of great efficiency and power, weighing between 20-30 kilograms and compare that to a much simpler animal from which elephants descended. We can never know much about the anatomy of the earliest Bilaterians but all evolutionists would agree that elephants are products of a lineage that began with much smaller and simpler animals, most likely worm-like creatures that lived in the sea bottom. I think it not unreasonable for my purposes to use, as one of the simplest Bilaterian possessing a circulatory system, the extant earthworm as a proxy for such an early ancestor. Earthworms do not have hearts. Instead segments of their blood vessels are lined with muscles that squeeze the vessels and thus function as simple but effective pumps entirely suitable for such small animals. Because of their much larger size elephants need an actual heart of great size, one capable of producing blood pressure much higher than that of humans and sufficiently powerful to drive blood to all parts of their enormous bodies through thick-walled blood vessels, some of them as long as 3.5 meters.

My point is not to catalogue all the anatomical changes needed to transform a gene pool capable of producing a simple circulatory system in submarinal worms into one capable of producing the elephants’, but to encourage profound appreciation of the enormity of those changes (and uncountable others in other organ systems) that were all actually expressed in every single ancestral animal with utmost precision.   

PERFECT MITOSIS

If it is a tautological certainty that all the breeding animals were beneficiaries of “perfect” development then the same logic informs us that all their vital organ systems had also been “perfectly” constructed.  Again, this is self-evident: no Bilaterian reached maturity unless its vital systems had been perfectly formed and were functioning with sufficient efficiency to support the specimen’s developing body.  

Further thought informs us that those perfect organs in perfect bodies all were composed of individual somatic cells and that each of those cells came into existence as the result of a process seldom mentioned by writers on animal evolution: mitosis.

Because I am covering in this exercise the entire history of Bilaterian life on this planet I am not going to assert that every act of mitosis in every developing breeder was “perfect.”  Nor am I ignoring the likelihood that corrective mechanisms such as post-mitotic cell repair, apoptosis or autectomy of mal-formed cells played essential roles in some lineages. What I can say is that all the mitoses required to produce all those particular animals was of an order of efficiency sufficient to ensure precise construction of all essential organs in all the breeders.

SOME VERY LARGE NUMBERS

At this point I think it useful to ponder the enormous numbers that were involved in the chains of perfection that led to the existence of all living Bilaterians.

I lack the taste and the ability for estimating great numbers and then expressing them in symbols familiar to the mathematically proficient but here in outline are the diameters of the problem that any theory of Bilaterian evolution must address:

1.       The number of extant animal species according to this site is estimated to range between 3 and 30 million. Of that number only about 20 thousand are non-Bilaterians (sponges and cnidarians). Another source gives the total of 12 million. Yet another says it’s less than 8 million. Let’s assume that the actual number of extant Bilaterian species is ~10 million.

2.       Next, estimate the number of actual breeding animals that were direct ancestors of all the actual specimens now comprising those ~10 million species during the ~550 million years since the origin of the first Bilaterians.
 

3.       For the next step estimate the number of somatic cells in a typical breeder when it reached maturity. In extant Bilaterians the smallest number is about one thousand for some nematodes, for a human, ~10 trillion.
 

4.       Finally, estimate the number of individual acts of mitosis that occurred during development in all those successfully constructed breeders over ~550 million years of evolution. (Consider this: humans take about 13 years to reach physical maturity and during those years many of the ~10 trillion cells require replacement.)
Although the number (10 ̽ ?) in paragraph 4 can only be imagined (trillions of trillions?) it is not in any way fantastical because we are considering only what actually happened in actual ancestral animals.  

(I chose to limit the number of breeding animals to the ancestors of living animals. If we were to include all the ancestors of all animals that were produced in lineages that went extinct after, in many cases, hundreds of millions of years, the paragraph 4 number (10 ̽) would be much larger.)

SOME SMALLER—BUT HUGELY SIGNIFICANT—NUMBERS

In attempting to compare the relative difficulty of constructing complete animal bodies we need to consider some smaller but very significant numbers, those of the different cell types in any fully developed multicellular organism. In a summary on page 114 of Cancer Selection I show the number for the typical jellyfish at about 10 and for giant sequoias, about 30. For fish it’s about 120 and for humans, about 200.

Returning to our fact-based exercise, the challenge of  explaining the successful construction throughout Bilaterian history of all breeding animals needs to consider not only the total number of mitoses required but the degree of difficulty presented by the (in many lineages) increasing number of different cell types.  As I wrote on page 113 of CS:

"It is several orders of magnitude more difficult to start with a zygote and end with a (ten) trillion-cell organism containing 200 different kinds of cells—a human—than it is to construct a (ten) trillion-cell organism having ten cell types—a giant jellyfish."


This is because in each somatic cell type that possesses a full complement of genes (in humans, most of them) in order to produce a single cell of a particular type all the genes used exclusively to manufacture any of the 199 other types of cells must be neutralized.

SUMMARIZING …

By focusing on the actual breeding Bilaterians and by covering their entire history of ~550 million years it becomes clear that the problem faced by evolutionists is to identify the mechanisms responsible for the transformation of the gene pool capable of producing simple Ur-Bilaterians into gene pools that produced—through uncountable numbers of individual acts of mitosis—the greatly diverse and extremely complex Bilaterians that now exist. In other words how did the Bilaterian gene pools manage to produce in great numbers and in staggering variety the most complex, precisely constructed things known to exist in the universe? Conventional theory says this was accomplished by the same mechanisms that enabled the jellyfish gene pool to produce over the same period nothing but jellyfish. My theory says jellyfish mechanisms were not sufficient and that a central role was played by cancer selection, the destruction of juveniles (and their genetic material) as the direct result of errors arising during the formation of somatic cells, in other words, as a result of imprecise mitosis. I will explain in my next posting how this one mechanism worked and why it was essential to understanding what actually happened.


Comments and questions are welcomed here.


At this site you will find links to additional material including my original Letters to the Journal of Theoretical Biology and  the 1992 Nature review of my book.

Copyright © by James Graham 2012

This page was archived at the WayBack Machine on April 19, 2015.