Marsupial Post Flood Migration

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.

A New Creation Theory of Marsupial Origins

After watching the last surviving Tasmanian-tiger walking around in a pen on film, I began to wonder how significant the difference was between the marsupial and placental reproductive system. This marsupial wolf appeared and behaved just like any other dog. Is it possible for it to belong to the same Biblical kindship group as the dingo who later replaced him? The marsupial counterparts are in many cases identical to a placental twin, and distinguishing them as unrelated is not possible without a much closer inspection than necessary for the differences we typically use to distinguish the Biblical kinds.

The exclusive presence of marsupials in Australia following the flood, and the fact that numerous marsupial / placental counterparts exist forces the creation theorist to reach out for a new explanation. If it was possible for the marsupial mode of reproduction to evolve from the placental mammal, then the exclusive existence of the marsupials in Australia might be explained through the evolution of placental mammals to marsupials. Convergent evolution occurs when several distinct kinds exist in the same biotype, and are all exposed to the same selection. This results in the evolution of similar traits or behaviors in unrelated organisms.

The animals that migrated into Australia after the flood were all exposed to similar conditions and potentially the same environmental extremes which would be necessary to trigger the obligatory convergent evolution of the trait in all local mammals. The mammals that migrated to Australia were either all marsupial by coincidence or there exists the ability for the placentals to evolve to a marsupial mode of reproduction if it is advantageous. The existence of the marsupial / placental twins makes the latter seem a possible explanation

Marsupial Benefits and Selection

Although the advantages of marsupial vs. placental birth may not be obvious, upon further examination several trade-offs become apparent. The placenta is extremely beneficial for many reasons, and allows the organism enough advantage to replace its marsupial counterpart if introduced into the same area. However, for everything there is a trade-off, and the gestation length may represent a direct exchange between what's advantageous for the child as opposed to the mother.

In particular circumstances or levels of stress, the marsupial reproductive mode may be more beneficial in reducing the deaths specifically related to the child-mother union. Carrying a child internally for longer periods can have its consequences: principally the death of one is frequently remains concomitant to that of the other. If one dies the other dies also if carried internally, but that is less frequently the case with pouched babies. If the mother is killed, a pouched baby can survive whereas birth subsequent to the mother's death never occurs regardless of the level of maturity of the fetus. Likewise, if the baby dies during gestation, a pouched baby will not sacrifice the life of the mother. Giving birth to offspring more fully developed can also have obvious disadvantages. Basically, the larger the child at birth; the more difficult the delivery is for the mother. Breech positions and such are not an issue for marsupials, but only become problematic for mammals with longer gestation periods.

At times when survival has become difficult and the death rates of mothers and children are high, the marsupial mode of reproduction may prevent high mortality rates from affecting the death of the other. Under severe environmental stress when giving birth earlier becomes advantageous for the success of the population, then the marsupial reproductive mode may be selectable from the natural variation that exists within the timing and developmental rates of these events.

Natural Variation in Gestation Rates and Birth Maturity

The nature of the reproductive system especially the timing and length of gestation appears to be provided significant evolutionary potential through genetic recombination. Likewise the level of maturity or ability to self-support oneself following birth differs greatly between animals which appear to belong to the same Biblical kindship group. For example rats are born with closed eyes, naked and fairly helpless after a 21 day gestation, while guinea pigs are born with open eyes, covered in hair and able to feed itself after a 67 day gestation period. A similar variability exists between even more closely related animals such as the Hare born with eyes open, and the Rabbit with eyes shut.

There is tremendous natural variation found among the gestation rates in marsupials. In most marsupials the broad sequence of changes in the ovary and the genital tract are similar, however the general timing of events in the reproductive cycles is different between marsupials and even between species and subspecies. For example the kangaroo differs from the basic marsupial pattern in that gestation is extended from half to occupy almost all of the oestrus cycle, and there are timing differences between the grey and red kangaroos or the wallaroos.

There also appears to be significant variability related to placental development. The placenta grows from maternal and embryo tissue, and lifestyle differences between various species appears to affect the specifics of the complex. Among placentals there are at least five different forms the placenta can take in different species which involve changes in the degree of contact and the number of layers of tissue between the maternal blood supply and the embryos.

Likewise not all marsupials have a permanent pouch and a few have none at all. There is clearly natural variability of the features which distinguish the placentals from marsupials. These variations are produced by genetic recombination, and performed in attempt to specialize the organism to specific conditions. The presence of variability within the features that distinguish the placental from marsupial suggests the ability to change from one mode to another. Although many modifications would be required, in particular those that alter the gestation rate, placental and pouch development have been established as active.

Irreducibly Complex System

The marsupial mode of reproduction is very complex, and the evolution from placental to marsupial would require the simultaneous alteration of several independent systems not to mention the development of the pouch and the physical capability necessary for the fetus to crawl to the pouch.

Regarding irreducible complexity it should always be remembered that intelligently designed evolution occurs through genetic recombination. These reactions are not random, but instead are rearrangements performed by the cell to drive the evolution of organism. The specific capabilities of these reactions has not yet been determined, and the alteration of such complex systems should not be ruled out given our present level of understanding.

Since the development of any feature takes many generations, an examination into the reducibility of any system should look at each component to determine if they possess the following characteristics.

• Survival must be expected prior to complete formation of the new system. (Survival must not be contingent upon the presence of all the components of the system)
• The modifications must have improved benefit at increasing levels of development.

Given this particular developmental scenario, several questions may be examined to determine if the changeover to marsupial reproduction is possible, or if the differences between the two systems are irreducibly complex.

• Could a prematurely born child survive without the pouch?

• YES - Although modern science has improved the percentages, tremendously premature children survive with some regularity

• Could the child arrive at the teat and/or survive without the muscular development currently possessed by marsupials at birth?

• YES - The level of assistance afforded the child is ultimately determined by the mother, and greater or lesser extents can be awarded when necessary. The mother is able to assist the child or position herself alternatively.

• Is it necessary for the child to remain at the teat?

• NO - The pouch is not a necessary component, but simply improves the survivability of the child by keeping it with the mother.

• Is the placenta necessary?

• NO. The placental mammals are the only vertebrates which possess a placenta. All others from birds, reptiles, fish, etc., use the yolk-type reproductive system with the amniotic membrane between which no nutrients are transferred.

The placenta is extremely beneficial, but like everything else in nature, there is a trade-off. The child is much safer gestating to greater maturity while being nourished by the mother's continuous input, but being tied together also puts both at risk if either of them experiences a complication. Under times of stress, when the percentage of child or maternal deaths rates rise significantly, it may becomes instead beneficial to drop the placenta, and bare young much earlier in the marsupial manner to eliminate this threat resulting from lengthy gestation periods.

Postflood Migration or Evolution

The Bible says the ark of Noah came to rest in the Mountains of Ararat which are now in Turkey. The subsequent distribution of animals into the various regions on earth was naturally driven except on rare occasion where livestock or domestics were taken. It is possible the distribution of marsupials to Australia was caused intentionally by human, but it seems more likely that the migration of wild animals to any given continent was largely a natural process. Post flood civilization would not be expected to possess the knowledge and ability Animals basically spread out in all direction while favoring climate preferences, and post flood civilization would not be expected to have the .

Why would numerous marsupials migrate into Australia and not even one placental mammal? There appears to be no other natural mechanism forthcoming from the creation community. An explanation for this tremendously one-sided migratory pattern may require a drastic new theory such as presented here, and perhaps a reinvestigation of the evolutionary potential genetic recombination provides organisms. We are hesitant to invoke natural selection-driven evolution as a mechanism for the development of complex system, but under the direction of genetic recombination this process is not random, and exactly what is designed into these rearrangements we can not say.

It could therefore be proposed that the marsupial reproductive system can evolve from the placental method, and has done so numerous times during the evolutionary history of mammals. One possible factor effecting all who passed into Australia would be the equatorial crossing following their release from the ark in Turkey. The mammals which arrived in Australia would have been the first to cross the equator, and probably when environmental extremes were exceptional. It is possible that this evolutionary adaptation can be forced upon animals during times of severe stress or when mother/offspring mortality reaches high frequencies.

If marsupials have indeed evolved, nature must be able to select this alternative reproductive method from the pool of genetic recombinants. However, recombination is not random, and the rearrangements which affect reproductive rates and such, almost certainly do so for the purpose of effecting reproduction in a similarly profound manner. Another extreme version of this ability may therefore be suggested by the marsupial situation. If the marsupials have evolved, it would also propose the duck-billed platypus or egg-laying mammal may have also.

References:

1. Culp, G. Richard; “The Geographical Distribution of Animals and Plants,” Creation Research Society Quarterly, 25[1]:24-27, June 1998.

2. Woodmorappe, John; "Causes for the Biogeographic Distribution of Land Vertebrates After the Flood" Proceedings of the 2nd International Conference on Creationism, 1990, Vol. II, pp. 361-370.

3. Woodmorappe, John; "Studies in Creationism and Flood Geology" ICR IMPACT No. 238, April 1993.

Other Discussions on Marsupial Creation vs Evolution

• Australia's Unique Animals by Trevor Major, M.Sc., M.A. Apologetics Press
• Are look-alikes related? by Don Batten. Creation Ex Nihilo 19(2):39-41
• The Natural History of Marsupials by the Anti-Creation TalkOrigins Archive