Marsupials and Placentals: a case of front-loaded, pre-programmed, designed evolution?
|July 13, 2006||Posted by scordova under Intelligent Design|
(adapted from a discussion at Evolution and Design )
All right guys, a potential area of ID research. Who knows how long it may take to uncover, but here is where Explanatory Filter (EF) methods may help and where IDers can make a killer breakthrough for their theory if they succeed. There will be money, fame, and glory if this enigma is solved by IDers.
Different geographical areas sometimes exhibit groups of plants and animals of strikingly similar appearance, even though the organisms may be only distantly related. It is difficult to explain so many similarities as the result of coincidence.
This form of evolutionary change is referred to as convergent evolution, or sometimes, parallel evolution.
In the best known case of convergent evolution, two major groups of mammals, marsupials and placentals, have evolved in a very similar way, even though the two lineages have been living independently on separate continents. Australia separated from the other continents more than 50 million years ago, after marsupials had evolved but before the appearance of placental mammals.
To grasp how troubling this is to the anti-teleology crowd, here are the words of Simon Conway Morris:
I believe the topic of convergence is important for two main reasons. One is widely acknowledged, if as often subject to procrustean procedures of accommodation. It concerns phylogeny[supposed evolutionary lineage], with the obvious circularity of two questions : do we trust our phylogeny and thereby define convergence (which everyone does), or do we trust our characters to be convergent (for whatever reason) and define our phylogeny? As phylogeny depends on characters, the two questions are inseparable
Even so, no phylogeny is free of its convergences, and it is often the case that a biologist believes a phylogeny because in his or her view certain convergences would be too incredible to be true.
During my time in the libraries I have been particularly struck by the adjectives that accompany descriptions of evolutionary convergence. Words like, “remarkable”, “striking”, “extraordinary”, or even “astonishing” and “uncanny” are common place…the frequency of adjectival surprise associated with descriptions of convergence suggests there is almost a feeling of unease in these similarities. Indeed, I strongly suspect that some of these biologists sense the ghost of teleology looking over their shoulders.
The placentals and marsupials supposedly evolved separately, but look how similar they are (see above) and yet how different their modes of reproduction are (see below). I can understand how that would freak out a non-teleologist!
Differences between Marsupials and Placentals by biologist Chris Ashcraft
The principal difference between the marsupial and placental mammals is the rate of gestation, or the length of time the offspring is carried in the uterus. In all non-placental vertebrates, such as the marsupials, the developing embryo is isolated from its mother’s body by the amniotic membrane. Following fertilization the embryo becomes a new organism, and the mother’s auto-immune system will attack it. The amniotic membrane isolates the embryo from all biological interaction with the parent, thus protecting it from attack. However, no nutrients cross the barrier either, and therefore its growth in the uterus is limited to the quantity of nutrients contained within the egg. The short gestation period in marsupials is due to this type of yolk-type reproduction. Except for the Paramelidae, marsupial embryos do not receive nutrients from their mother. Birth in marsupials occurs much earlier in comparison to placental mammals, and the almost helpless fetus journeys to the pouch and becomes attached to a teat for weeks or months depending on the species. Marsupials may spend as few as twelve days in the reproductive tract.
A longer gestation period results in offspring that are born more fully developed. The extended maturation time in placentals, as opposed to all other vertebrates, is a result of the placenta, which allows nutrients to travel from the mother’s system to the embryo and waste to be carried away. The embryo and the mother do not share the same blood supply, but instead the placenta is composed of several layers which are richly supplied with blood vessels, and acts as a preferential immigration barrier letting nutrients and metabolites pass through, and preventing the transfer of immunity system components. There are other significant differences between the placental and marsupial reproduction. In marsupials, pregnancy does not interrupt the continuation of the next oestrus cycle as it does in placentals, but instead ovarian inhibition is mediated by lactation or suckling stimulus. This regulatory modification is necessary since the baby is no longer carried internally, therefore, negative feedback stimulus from the babies presence must come from nursing activity instead.
Doesn’t the fact of these differences in reproduction yet similarities in structure suggest front loaded evolution? Natural selection absolutely fails as an explanation for these similarities. So how might ID research win the day?
What if the artifacts for this front-loaded evolution are still stored somewhere like a software module no longer in use. We could, in principle, attempt to trigger the software module. If we even partially succeed in triggering these software modules on the way to getting a placental to become a marsupial or a marsupial become a placental, we have evidence of front loaded evolution.
Michael Behe surely must have pondered the possibility that information for pre-programmed evolution was dormant in the ancestor creatures. At the end of his famous book, Darwin’s Black Box, he talks about front-loaded evolution, and how to actually search for it:
Work could be taken to determine whether information for designed systems could be dormant for long periods of timeÃ¢â‚¬Â¦
This is exactly the kind of research an ID paradigm can excel at. Recall what I said about functional systems with little or no selective advantage (here). Well, here is another case where functional information could exist with little or no reason for existing based on natural selection. Further, if these functional artifacts are dormant, they will be invisible to selection, but detectable via the explanatory filter! Thus if the research succeeds, it will demonstrate the superiority of the ID perspective over one that looks at biology in boring terms like fitness.
The explanatory filter (EF) which is highly oriented toward recognizing linguistic structures may help elucidate informational structures even before we identify function of these informational structures. To illustrate in the computer world, I can have large amounts of software in a system. I can identify it as software (using techniques which the EF captures) even before I understand its function or semantic meaning in the overall architecture of a system.
Explanatory filtering detects such linguistic constructs independent of functional detection (which is why fitness perspectives are inferior to detecting significant amounts of design). This would be useful for detecting dormant or artifactual information of evolutionary history if we are lucky enough to still have it sitting around in the cells of these creatures.
If the phylogeny followed an ontogeny like process, might we be able to recreate it in the lab by triggering these domant artifacts? There may indeed be dormat artifacts because we are detecting large amounts of linguistic and grammatical constructs already in sections of “junk DNA” using power law analysis, Zipf language analysis, Shannon analysis, and measures of redundancy. Specified complexity has been discovered, but the functional significance has yet to be elucidated. As the IDers know, where there is language there is also design!
Because the marsupials and placentals are so similar, they would be ideal candidates for this sort of exploration. I would wager, the differences in “non functional” pieces between marsupials and placentals are probably related to the dormant codes Behe is searching for. May the quest to find Behe’s dormant codes begin some day!
my sincere apologies to Dr. John Davison, he notes:
I proposed that marsupial and placental mammals were reading the same Ã¢â‚¬Å“prescribedÃ¢â‚¬Â information as part of my recent paper – A Prescribed Evolutionary Hypthesis.
A Prescribed Evolutionary Hypthesis. was yet another pro-ID peer-reviewed paper that explicitly mentions ID.