EVOLUTION

UNDERSTANDING EVOLUTION

The study of evolution encompasses all of biology.  So we face a problem in understanding evolution much as the ant faces in understanding the tree it is climbing.  It can climb all over it.  But much is hidden in the ground and under the bark.  Even the living part of the tree is mostly hidden by the dead outer layer of bark.  If all the tissues and functions that make up the tree were known, it would still be a monumental task to understand how it worked and how it was affected by its environment.

ENTRY POINTS TO UNDERSTANDING EVOLUTION

The fossil record, comparative anatomy, comparative embryology, comparative physiology, and nucleic acid analysis have been the major entries to understanding evolution used by past and present researchers.

1 - The fossil record has left a partially connected chain of organisms leading to the present living world.  It has not left an unambiguous source due to- gaps in fossil bearing sediments - soft bodied forms rarely leaving fossils - and our inability to always determine if a line of fossils was gaining or losing a feature.  Ancestral forms may appear in strata with later descendants as shown by an example in  [ http://evolutioninsights.blogspot.com/2014/05/living-fossils.html ].

2 - Comparative anatomy and related microscopical studies, especially embryology, did the heavy lifting in bringing evolution studies toward maturity.  It still is a major source of new understanding; for an unusual example connecting anatomy and psychology see [ http://evolutioninsights.blogspot.com/2014/07/evolution-intelligence-and-creativity.html ].  Many studies need a combination of factors other than anatomy considered, an example is shown in how the extreme longevity of pogonophorans was determined [ http://evolutioninsights.blogspot.com/2014/06/evolution-and-oldest-animal.html ] and [ http://evolutioninsights.blogspot.com/2013/06/evolution-in-deep-sea.html].  The anatomical similarity of pogonophorans and hemichordates is illustrated in [ http://evolutioninsights.blogspot.com/2015/05/evolution-annelids-to-chordates-middle.html ].

The sponge-cnidarian transition was first hinted at by a fossil comparison [ see http://evolutioninsights.blogspot.com/2013/07/acoelomate-evolution-1-sponges.html ] supported by a hypothetical argument based on spicules in both sponges and some cnidarian nematocysts [ http://evolutioninsights.blogspot.com/2013/07/acoelomate-evolution-2-cnidarians.html and illustrated in http://evolutioninsights.blogspot.com/2015/04/cnidaria-nematocyst-origin.html ].

The cnidarian-flatworm transition is further discussed in [  http://evolutioninsights.blogspot.com/2013/07/acoelomate-evolution-3-flatworms.html ] and illustrated in [ http://evolutioninsights.blogspot.com/2015/03/evolution-quiet-pre-cambrian-genes.html ].

3 - Comparative physiology provides many insights regarding relationships.  An example is noted in a comment about vitamin C in the previous post [ http://evolutioninsights.blogspot.com/2015/07/the-evolution-diet.html ].  The same post mentions the anatomical evolutionary connection of our appendix with the cecum of herbivores, noting that function lacking structures are often rapidly lost by lacking selection for their retention; the appendix may have value from the lymphatic tissue it contains as well as for possible retention of gut organisms for re-inoculation of a gut purged of them by diarrhea.

4 - Comparative biochemistry studies, especially DNA and RNA studies, are still the gold standard of determining close evolutionary relationships.  It is far less useful in determining relationships of phyla because rates of change can vary among the chromosomes as well as differing in different organisms.  This has been discussed in many posts, especially [ http://evolutioninsights.blogspot.com/2013/05/science-screw-up-no-1.html ]

SYSTEMATICS / TAXONOMY

Systematics indirectly confirms the reality of evolution.  When Linnaeus classified plants and animals he is thought to have assumed the different forms were created separately by special creation.  Consequently, the groups named were clustered in a hierarchy based primarily on anatomy.  When groups are determined by scientists using an evolutionary hypothesis, they approximate the relationships in the classification designed by Linnaeus.

COUNTER ARGUMENTS TO EVOLUTION

No one knows the mind of God.  Lacking direct revelation of the creation of diversity that is not clouded by inspired story, parable, and limitations of knowledge among inspired writers, we are left with only science to give us a clear look at the details of how God did it.  Even the best intentions of christian writers can go astray as noted in [ http://evolutioninsights.blogspot.com/2014/09/evolution-and-error-of-irreducible.html ].  My recent post [ http://evolutioninsights.blogspot.com/2015/07/creationevolution-debates.html ] might be helpful in providing greater understanding of other arguments.  The tools of science are adequate to prove the existence of evolution, but not the existence of God; they are inadequate to prove God does not exist.

BIOLOGICAL SCIENCE

The complexity of the interrelationships of biological sub-disciplines is most fully appreciated in the study of evolution and ecology.  Genetics is also an excellent organizing principle making sense of the diversity of life and evolutionary processes.  One or more of the first three entry points are often missing or insufficiently well known in the education of today's biological scientists.  For those well versed in genetics and molecular biology, just realizing the limitations of those areas are cause for not rejecting the older scheme of phylum relationships, prior to the invalid acceptance of Ecdysozoa and Lophotrochozoa as natural groups.  The post of 2013/05 listed at the end of 4 above tells why.

Joseph G. Engemann    Kalamazoo, Michigan    August 1, 2015

SALVAGING DATA FOR EVOLUTION STUDIES

MOLECULAR DATA

It occurred to me within the past day that I have ignored one of the things I learned in my youth - how to get some use out of discarded materials in the city dump!

Such experiences were something few children in modern cities get.  So many of the products we use are not designed to be repaired, just throw the whole thing away and get a new one, or at best, get a module to replace a portion.

So my criticism of the Ecdysozoa and Lophotrochozoa studies [post of May 31, 2013] overlooked the fact that, if the errors introduced by linking most ancient ancestors were taken in to consideration, and some such ancestors were omitted in a new analysis, the remaining data might lead us closer to the reality of the ancestral paths.  Even so, the inadequate sample sizes and the limited portion of the genomes examined are unlikely to be very useful.

I don't think it is worth trying because the sample sizes were already inadequate and might still be if clusters could be reanalyzed omitting the nematodes in the Ecdysozoa study.  Nematodes need omission not only because they may have extreme retention of genomic identity giving them "long-branch attraction" to diverse distantly related groups, but they also are a separate lineage that is not basal to any other major modern group.

The Lophotrochozoa represent newer evolutionary events.  Because uncertainty due to variable length of lineages from common ancestry of early coelomate animals, and the "long-branch attraction" problem affecting some of the members descended from annelids via the Pogonophora, the relationship of various "lophophorate" clusters can not be determined with simple corrections.

EMBRYOLOGICAL DATA

As discussed in my posts regarding isopod egg comparisons it is clear that the old idea of the "biogenetic law" where animals were thought to repeat some steps of their evolutionary development in their individual embryonic development is not valid.  But I hope I made it clear that the concept is still a useful model that may suggest investigation for support from other evidence.

The isopod eggs, and ecological factors involved in deep-sea selection, helped me see how the Pogonophora explain the close relationship of ancestry of deuterostomes to advanced protostomes.  Judging from the number of views of my blogs on the topics, I think people studying such things are unlikely to know about them and thus will be unable to apply the concepts.

ANATOMICAL DATA

Amazing data can be found in studies of anatomy.  But it is increasingly unlikely to be helpful, not because it can't be, but because modern researchers are swamped with so much useful information they will never get far into older studies and approaches.  Anatomy and its changes not only reflect evolutionary history but are intimately connected with the genomes of animals.

The environment imprints it natural selection role on structure, development, and the responsible genes.  But the complex interaction is so nebulous I pity the researchers of today who are certainly more technically advanced than I have ever been.  The day is not long enough, nor their life long enough, to have much chance of putting it all together.  Still, I anticipate the continuation of the string of remarkable advances science can make in many areas.  I hope they can still get the benefits study of the humanities can make in their lives.

Joseph G. Engemann    Kalamazoo, Michigan    January 23, 2015

EVOLUTION - THE PROTOSTOME-DEUTEROSTOME LINK

ORIGIN OF DEUTEROSTOME EMBRYOLOGY

Annelid theory as a working hypothesis

Since Gans and Northcutt (1983) provided evidence of a close relative of annelids having some features of development resembling deuterostomes, as noted in the previous post, it is reasonable to evaluate other evidence.  Inversion of systems, the primary evidence supporting the annelid theory, has been deemed inadequate by those who comment.  But much other evidence is available.  The biggest impediment had been the drastic embryological differences between protostomes and deuterostomes.

Embryological evidence

My doctoral thesis research included a comparison of development of two species of isopods with very different life cycle rates of development as well as a new embryological structure in one species.  The rapidly developing egg of the Michigan species was smaller, had a thinner egg shell, and two appendages on the egg.  The Tasmanian one had a thicker egg shell and no appendage; but on the each side of the embryo within the egg was a yolk filled bulge in the position from which the other ones had their egg appendages develop.

Otherwise, both embryos packed the egg fully.  They both developed in a folded position, legs outermost.  But the flattening differs so the Tasmanian one filled up space with the yolk filled bulge.  The Tasmanian species has less change from ancestral crustacean features; they also lack the abundant source of food from deciduous tree leaves as available for the Michigan ones.

The main point of this isopod egg observation is that the evolution of a new feature in the egg goes counter to what many biologists think was perhaps a valid portion of the discredited “biogenetic law”.  The law is not absolute, especially as my observation showed me, evolution can occur by the development of new features in the earliest life stages of an organism.  Clearly, embryological stages do not faithfully repeat steps in the evolution of the organism. 

Since the pogonophorans are likely candidates as intermediates, in spite of the general opinion that they were an evolutionary dead-end, what do they contribute to the story?  Well, they have lost the annelid digestive system in the adult, their segmentation has nearly disappeared, and they live in an abyssal world with a very low rate of input of food.  Such a regime would drastically select options or mutations that save energy. 

Why protostome spiral cleavage became deuterostome radial cleavage

The thinning of the egg shell would not constrain the early dividing cells into the packed spiral pattern of ancestral protostomes but it would conserve resources otherwise used for a strong egg shell.  Consequently, the loss of structural integrity of the egg shell would not impose the constraints for efficient use of space as in spiral cleavage.

Limited energy and resulting low reproductive potential puts survival at a premium for the individual.  Thus, although the first cell divisions (cleavage) of protostome eggs end the potential of the daughter cells to each develop into individuals, it is possible for each of the early dividing cells of the deuterostome egg.  Injury or death of one of the first few cells of a deuterostome egg would not necessarily result in death.  In fact, identical twins, triplets, and other genetically identical individuals could not have developed if deuterostomes had retained the features of spiral cleavage.  The survival advantage of this feature for pogonophoran species in the nutrient poor abyss should be an obvious benefit.

In both cases it is a loss, loss or reduced production of shell, loss of control of early developmental specification.  As discussed in an earlier post, loss can occur more rapidly than gain of a feature.  The rates are relative to other factors such as food supply, generation time, and value of the features for survival.  But clearly, pogonophorans are excellent candidates for the missing link connecting embryological features of protostomes and deuterostomes.  The conclusion is hypothetical.  The event described was undoubtedly a Pre-Cambrian occurrence.  But the conclusion is based on comparative evidence consistent with similar conclusions that will be presented for other evidence.

Interesting, but somewhat irrelevant to the current discussion is the fact that the Michigan isopod egg appendage had the cellular appearance of adult respiratory tissue and must aide their relatively rapid development.

References

Engemann, Joseph G.  1963.  A Comparison of the Anatomy and Natural History of Colubotelson thomsoni Nicholls, a South Temperate, Fresh-water Isopod and Asellus communis Say, a North Temperate, Fresh-water Isopod.  Ph.D. Thesis, Michigan State University, East Lansing.  146 pp.

Gans, Carl, and R. Glenn Northcutt.  1983.  Neural crest and the origin of vertebrates: a new head.  Science, 220:268-274.

Acknowledgements

A United States Fulbright Grant for study in Australia, aide of staff and use of facilities at the University of Tasmania and Michigan State University, as well as a Faculty Research Grant at Western Michigan University, were instrumental in my making many observations involved in this series of blogs.  Many individuals deserve my thanks as well.

Joseph G. Engemann     June 24, 2013