Young-Earth creationists believe all modern land vertebrates are descended from animals on Noah's ark. In the 4,500 years since the Flood, the animals from the ark evolved into many new species (within their created 'kinds' – see chapter two) as they migrated from the Middle East to their present locations.
This theory is expounded in an article on the Creation Ministries International website about the origins of New Zealand's moa.[footnote 1] In the article, David Catchpoole (who wrote the preface to The Greatest Hoax on Earth) argues that the moa descended from birds on Noah's ark. These birds flew to New Zealand less than 4,500 years ago. Once there, the birds lost the ability to fly due to "some kind of mutational disorder" and evolved (within their kind) into the different moa species (at least nine different species are recognised).
The evolutionary theory for the origins of the moa also holds that they are descended from a flight-capable ancestor. However, evolutionists argue for a time scale of at least 5 million years, rather than a few thousand years.
Christian biologist Joel Duff points out several problems with the young-Earth creationist account provided by Catchpoole. Firstly, Duff criticises the young-Earth claim that characteristics like loss of flight are due to a loss of information and thus are a form of downward evolution (devolution).
But are the lack of wings really a devolved characteristic? Superficially moas might just look as if they lost wings but losing something like a wing is much more difficult than it might sound and likely requires many hundreds of mutations and many different genes. If it were as simple as a "mutational disorder" as Catchpoole calls it why do we not see birds in captivity for thousands of years losing their wings?Duff builds on this point by describing the changes required for a flight-capable bird to transform itself into the different species of moa, particularly the giant moa species.
When the original moa flew to New Zealand it surely was not as large and it would have had hollow bones like other flight capable birds. The loss of wings would have to have been compensated for by a change in posture, thickening of the bones both in diameter and the filling of the center core, increased size in the beak and changes in the distribution of feather type on the body to name just a few changes. This is not a loss of information but required changes in genes and probably new genes altogether.
Bones simply don't become dense via a loss of information or by just a simple mutation. This requires a network of genes working together in development. If God created the moa with hollow bones to aid in flight then the formation of dense bones would not be a loss of information but would be the gain of a new feature. Were it so easy to change the structure of a bone, then the many tens of flightless birds from other groups of birds such as the ducks and chicken-like birds that have become flightless in the past couple thousand years would also have dense bones but they do not.Duff then points out the remarkable rate of genetic change required by the young-Earth model.
[T]he creationist line seems to be that God created some moa-like bird with the genetic ability to morph into these large heavy-boned wingless birds – however, in the 2,000 years from the creation to the flood, they didn't experience such a change. Then just one pair of moa were preserved on the ark, then flew to New Zealand and transformed themselves in to these dramatically different birds in potentially just a few hundred years.
How could they do this starting with such a limited gene pool of only two individuals? The genetic divergence of moa from one another is very great and thus the millions of mutations that they have in their genome all must have happened since a global flood and before their extinction. This is an absolutely fantastic rate of mutation and adaptive selection of those mutations. No evolutionists would dream of such incredible rates of divergence and change in organisms as is proposed by creationists. Young earth creationists so casually toss out hypotheses about the diversification of hundreds of species from a single founding pair of the "kind" but I have yet to see the genetic models to accompany those assertions. The rates of change are absurd and not reflected in any known genetic mechanism.And Duff concludes by showing how the young-Earth model struggles to explain the evolution of species in light of evidence in the fossil record.
[T]he pattern of diversity that we see in the fossil record is exactly the opposite of what we would predict from their [creationist] model. If pairs of "kinds" stepped off the ark and from there began to populate the world and began to speciate at the same time, wouldn't we expect that we should find the greatest diversity of species today?
What we see with these flightless birds and I think most other groups is that we can identify far more extinct species than we have species alive today or even alive in the last thousand years. If speciation can take place at such a rapid pace why then do we not see both continued rapid speciation today and why are is there such a tremendous amount of diversity in the fossil record?
Because of genetic bottlenecking by Noah's ark, creationists should expect that even if there was a high rate of mutation after the flood (a completely ad hoc hypothesis), initial speciation rates would not be high and would increase over time as greater genetic diversity was obtained in large populations. Rather, what they seem to be saying is that immediate rapid species formation occurred and then locked species into their current configurations with little change in species being observed today. This makes no genetic sense to me.
 M Bunce, T Worthy, et al, 'The evolutionary history of the extinct ratite moa and New Zealand Neogene paleogeography', Proceedings of the National Academy of Sciences, Vol 106, Issue 49 (24 September 2009), pp 20646-20651; online at: http://www.pnas.org/content/
 Joel Duff, 'Consider the moa: extinct flightless birds of New Zealand' (14 March 2013) http://thenaturalhistorian.