The Island rule—recipe for evolution or extinction?
Biologists have for many decades observed and recorded that animals isolated on islands away from mainland populations ‘evolve’ into smaller or larger species. Generally, smaller animals tend to become larger, and larger animals become smaller when isolated populations become established on islands. Biologists have coined this phenomenon the ‘island rule’. Examples include giant tortoises native to the Seychelles and Galápagos Islands, Komodo dragons, miniature frogs, Madagascar’s giant hissing cockroach, dwarf elephants, and various rodents, lizards and snakes from islands around the world. In a recent study, a species of lizard has been observed to ‘evolve’ shorter legs over a period of only six months when introduced onto an island where it did not previously occur.1,2
For the two most prominent figures in the development of evolutionary theory, Charles Darwin and Alfred Wallace, consideration of the animals on islands played an important role in developing their evolutionary ideas.3
For evolutionists, any changes that can be observed in populations are good news. But does the island rule demonstrate the sort of evolutionary changes that have created biologists from bacteria over millions of years? As creationists have demonstrated, diversification into species cannot be claimed as evidence for evolution into new kinds of animals. Speciation arises from the interplay between inherent genetic variety and natural selection and enables animal populations to adapt to changing habitat or climate. The field of baraminology investigates the boundaries between the created kinds of organisms, and helps us understand the limited, yet valuable role that speciation within kinds plays in biological diversity.4
Let’s look a little more closely at what the island rule really shows when changes to isolated populations are observed. The diagram below5 demonstrates how a large elephant can reduce in size, or a shrew can increase in size on an island. Changes in the size of sea snails can occur when they form isolated populations at different depths, in similar fashion to the island rule.
Notice something very important about the changes occurring in these simple examples. The large elephant has been replaced by a smaller elephant when isolated on the island, and the small shrew has become a larger size shrew on the island. But the elephant is still an elephant and the shrew is still a shrew. There is absolutely no suggestion that a new form of animal will ever be created by changes observed under the island rule. It is simply preposterous to use the island rule to support evolution in terms of the creation of novel genetic information, increasing genetic complexity and diversity. It simply is not observed.
Imagine for a moment the elephant scenario. The genetic variety of the elephant naturally includes differences in size. Any population of genetically diverse elephants will include individuals of all sizes, from large to small. If placed onto a smaller habitat such as an island, selective pressures can gradually lead to smaller average size over a number of generations—because of factors such as restrictions of food and possibly space for a given herd size. The genes for smaller size were already there, but were selected because smaller elephants would be better able to survive. The possibility also exists that mutations could cause stunted growth, through a reduction in growth hormone production, for example.6
What would happen, however, if the genes for large size are lost from that isolated population? Would the population of elephants somehow be more genetically diverse? Of course not! The population would be genetically impoverished. In fact, they would be liable to extinction if moved off the island or if a large predator invaded the island. Their much smaller gene pool would make them less able to adapt to environmental change. Can we therefore conclude that genetic loss, local reduction of genetic diversity and no increase in complexity is proof that Darwinian evolution created all the life on earth? No!
The same can be said for the shrew. The little shrew would have natural variation in size. Predation or other pressures on the mainland may select for smaller size in the population as a whole. Remove some to an island, and the isolated population may become larger, because the larger type may be better suited. Perhaps an absence of predators and competition for food would bring about the size change.
But evolution? Again, we see only a reduction in genetic diversity, and no increased complexity. Only pre-existing genes are involved. They are still only shrews, since shrews only reproduce more shrews. Molecules-to-man evolution is not occurring. Natural variation and natural selection have modified the population morphology, but not produced anything truly novel. And if either the elephant or the shrew are returned to their mainland habitat before genetic diversity is permanently lost, they are likely to revert to the original size distribution.
Real life examples confirming this can be readily seen in classic evolutionary icons. Charles Darwin used the speciation of finches on the Galápagos Islands as evidence for ‘evolution’. But he failed to realise that populations fluctuate back and forth with changing climatic conditions, and no net evolutionary progression actually occurs.7 Similarly, the famous peppered moth, so often paraded as ‘evolution in action’, only ever demonstrated that moth populations could adapt to their environment (not to mention that aspects of the studies were staged!).8
A famous evolutionary paleontologist, the late Stephen Jay Gould, used the ‘geographical isolation principle’, or island rule, to develop his own ideas of evolutionary processes from which he coined the term ‘Punctuated Equilibrium’. He incorrectly suggested that the rapid changes in isolated populations are where the bulk of evolution has occurred throughout history. He saw islands as ‘our great laboratories of evolution’ that were the driving forces of biological radiation.9 In 1996 he wrote, ‘ … evolutionary events are concentrated in episodes of branching speciation within small, isolated populations.’10
But how can this be? As demonstrated by the examples discussed above, if anything, the island rule offers a stronger explanation for extinction of organisms than for ‘evolutionary’ radiation. Ironically, in an essay on the study of land snails on the Tahitian island of Moorea, Gould reported that they were driven to extinction in the 1960s, following the introduction of a predatory snail to control an agricultural snail pest.9
The idea that adaptations are quickly acquired by isolated populations in response to environmental conditions, which leads to evolutionary radiation and increased diversity, is false. It is precisely the problem of small isolated populations of low genetic diversity that threatens many organisms with extinction today. It is true that in some cases geographical isolation on an island has enabled some species to survive, safe from predators, while their mainland cousins have perished. A good example is the quokkas of Rottnest Island off Western Australia. However, history is also littered with examples of extinctions of genetically isolated and vulnerable species. Of 23 Australian bird species that became extinct since 1788, 17 are from continental or oceanic islands!11,12
Also, geographic isolation results in a subset of the original complete population reproducing locally. This subset will not have all the variety of genes from the parent population and will therefore display a narrower range of features. This can result in a distinct variety of the animal or plant developing, if it can survive the isolation (not having the full range of genetic variety, it may not be able to adapt). Such geographic isolation could have contributed to the development of sub-types within the created kinds after the biblical Flood of Noah’s day.
Modern instances of the island rule in action have nothing to do with molecules-to-man evolution, but only with the natural variation already present within the genes of the pioneering animals.
Isolated populations are more likely to suffer eventual extinction, rather than herald a new age of increased diversity and radiation. Therefore, the island rule, while demonstrating natural variation inherent in a population, offers no hope for evolutionists desperately needing a mechanism for the myth of Darwinian Evolution.
References and notes
- Bryner, J., Short legs win evolution battle, livescience.com/, 4 June 2007. Return to text.
- Catchpoole, D., Lizard losers (and winners), Creation 30(1):35–37, 2007; creation.com/lizard. Return to text.
- Gibson, L.J., Species on islands: evidence for change, grisda.org, 4 June 2007. Return to text.
- Batten, D., Ligers and wholphins? What next? Creation 22(3):28–33, 2000; creation.com/liger. Return to text.
- Leonard, A.W., What makes sea creatures large or small, livescience.com, 4 June 2007. Return to text.
- But it is loss of functionality, not upwards evolution. See Wieland, C., The evolution train’s a-comin, Creation 24(2):16–19, 2002; creation.com/train. Return to text.
- Wieland, C., Book review: The beak of the finch, J. Creation 9(1):21–24, 1995; creation.com/beak_finch; Wieland, C., Darwin’s finches, Creation 14(3):22–23, 1992; creation.com/finches. Return to text.
- Wieland, C., The moth files: An update on the peppered moth fiasco, Creation 25(1):14–15, 2002; creation.com/moths; More about moths, creation.com/moth. Return to text.
- Gould, S.J., Eight little piggies: reflections in natural history, Penguin Books, London, pp. 23–40, 1993. Return to text.
- Gould, S.J., Dinosaur in a haystack: reflections in natural history, Penguin Books, London, p. 333, 1996. Return to text.
- Extinct Australian animals, en.wikipedia.org, 4 June 2007. Return to text.
- Islands may form by different geologic processes. Some islands are actually parts of a continent, separated from the main landmass by shallow water. Evidence suggests that these islands were once part of the mainland. An example of a continental island is Kangaroo Island. Oceanic islands are found in archipelagos fringing the edge of a continental shelf. They are mainly volcanic, with some limestones. Examples include Lord Howe Island, Norfolk Island, Macquarie Island and Surtsey. Return to text.