Yale Passamaneck and eye evolution
| 31 March, 2011 | Richard P. Grant |
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What can a clam-like creature tell us about eye evolution? Quite a bit, as it turns out. We ran a news article at the beginning of the month, on the finding that brachiopod, or lamp shell, embryos have eyes that are more closely related to those of vertebrates, than of their spineless cousins.
I caught up with Yale Passamaneck, lead author of the study, on Skype (unfortunately the F1000 budget won’t stretch to sending me to Hawaii). In this video he tells us a bit about his findings and the joys of Kewalo Marine Laboratory. The paper is free to access at EvoDevo.
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Excellent presentation. The findings are caged as such, and their possible materiality with regard to revelations in other areas of study are expressed as hypothetical. Over hundreds of millions of years, various genomes have left evidence of their existence. Let us imagine what if a photograph of each had been taken, glued to a piece of board, cut up into a jigsaw puzzle, ninety-nine percent of the pieces disposed of, and the remaining one percent scattered about. Millions of years later, we humans in our present form, come along and find specimens of the one percent of surviving specimens and seek to assemble them. Now to make matters a bit more challenging, we find some of those remnants similar to some currently living forms. We construct a timeline, as best we can, by studying datable paleontological specimens, and through time-assigned proxies, such as an iridium layer, volcanic ash layers, various sorts of leaves… at various layers, indicating large temperatures waxings and wanings. Also, we play backwards, as it were, Earth crust movements and through studies of geological formations, and through proxies of temperature variations in various Earth loci, and reconstruct temperatures at various places at various times. With all this evidence, and all these pieces, we begin to assign to the overall process, over time, a picture of the developmental steps in biological evolution. Hopefully we will not be too quick — upon finding what we interpret to be a primordial example of an eye and say (with more than a little assurance, at least), “This is the same interstitial state of the evolution of “the eye,” as though this currently living organism fills in all the blanks for all the millions (billions?) of species, and all their phenotypes, as each has come onto the scene, and most have gone. Each puzzle piece is informative. Each currently living species, or genome, or phenotype is what it is. Some literature (especially pop-science literature) seems to imply that biological evolution has been linear, in the sense of having “improved” by a process of “newer and better out-competes and is more “fit” than older and less fit. It does not seem clear to some writers/editors that fitness may be deemed to CHASE change, and change in milieu is, over the long term, erratic and abrupt. Characteristics of species not only are acquired but, also, are lost. Imagine, if there were intelligent creatures on Earth a hundred million years from now, finding only one complete skeleton of a twelve year old male homo sapiens with Downs syndrome. Okay, the odds are against it. Let’s say it is the skeleton of a female homo sapiens child of parents of mixed race, with a genetic predisposition to unexplained fractures during childhood.
Or, suppose they find the skeleton of a human child that had been attacked and killed by a Rottweiler. Or, what if they were to find the skeleton of Magic Johnson.
While it is true that pattern recognition is a useful tool, and that statistical sampling is a useful tool, we should never (in my opinion, at least) forget that even a million pieces from millions of jigsaw puzzles will provide us with more than a speculative picture of all that has come and/or gone over time. Much less should we become overly dogmatic about our wonderful abilities to discern clear pictures from a few dots sprinkled about.
Excellent points. You’d get on very well with a certain Nature editor, over at http://occamstypewriter.org/cromercrox/. He has a particular bug bear about ‘missing links’!
Thank you, #2 — no pun intended (:>) — for calling attention to the propensity of some readers to knee-jerk everyone’s motive to one or the other of a polemic.
Perhaps this will clarify this commenter’s motive:
1. Science is not dogma;
2. Dogma is not science;
3. Two extremes of dogmatism seem to be at war currently over who has a right to claim a right to one of two philosophical polarities;
4. Each, so far as this commenter can discern, is unwilling to let the data continue to be sought objectively, interpreted objectively, and to speak for itself alone.
5. A working hypothesis is a wonderful and necessary tool of human reason;
6. A dogma is not a hypothesis but, rather, a limiting philosophical constraint;
7. Fortunately nature, over the centuries, has continued to speak for itself;
8. Dogmatic models promote stereotypical thinking.
Unfortunately, those of us who actually seek to have an open mind, and let the data speak for itself (and treat a working hypothesis as something to test and continually reevaluate, rather than as a constraint) seem to be attacked by proselytizers from both sides. Each extreme tends to accuse us of “siding up” with its perceived enemy.
Please allow a plea of “not guilty” to the pot shot. (:>)