Young earthers typically believe that God did not make every species currently in existence at the moment of creation, instead making ancestor creatures of each "type." The decendents of these then speciated to give all of the species we currently have. Usually young earthers acknowledge that animals that are morphologically similar are closely related, however, with the discovery of DNA and genetic studies some animals have been moved out of their original category. For instance, probably most of us would initially place the hyena in with the canines because of their similar morphology. However, genetic studies show that the hyena is not closely related to the canines--according to evolutionary theory the canines and the hyena share a common ancestor back further along the line. Young earth creationists don't want to push the classification of "type" back too far, though (since canines, felines, bears, and hyenas all share the same common ancestor if you go back far enough, and that's too much evolving for a young earther to allow!), so hyenas are placed in their own type. So, since young earthers have accepted genetic evidence in some cases, it is inconsistent and even dishonest to ignore it in others.
All of this leads up to
Chlamydomonas, specifically
Chlamydomonas reinharditii. These are phytoflagellates, tiny unicellular biflagellated photosynthesizing protists. They reproduce asexually (sexual reproduction is present as well, but it is chiefly a method to produce dormant spores to survive difficult times) by multiple fission, in which the cell increases its size 2^n times and then divides n times into 2^n number of daughter cells, n being 2, 8, 4, 16. The daughter cells formed are enclosed inside the mother cell's cell wall, which then bursts to release the daughter cells, which swim off on their own. However, it has been reported on several occasions that the
Chlamydomonas daughter cells do not swim off separately because their cell walls are linked together at points and their cytoplasm is continuous. This produces a little "colony" of
Chlamydomonas cells similar to
Gonium.
Gonium is a colonial biflagellated phytoflagellate occuring in groups of usually 8 or 16 cells. The cells are joined at points and the cytoplasm is continuous among the cells. However, sometimes when cells of the species
Gonium dispersum undergo multiple fission and release the daughter cells, they are unjoined and swim away remarkably like
Chlamydomonas. Indeed, genetic studies of
Chlamydomonas and
Gonium show similarities in both coding and noncoding regions (see papers below and
this link), with
Chlamydomonas reinharditii being most closely related to
Gonium, most likely a direct descendant of the original ancestor.
Gonium is a simple colonial organism, and there is no division of labor among the cells. However, there are a variety of more complicated organisms in the same order, Volvocida, that have been shown by genetic testing to be related. The most complicated of these is
Volvox, a colonial organism in which some thousands of somatic cells in a globe surround germ cells on the inside of the colony. Asexual reproduction in
Volvox involves multiple fission of one of the germ cells to produce a tiny daughter colony. The somatic cells undergo programmed cell death at only four days old, releasing the daughter colonies.
While
Gonium is a flattened disc, all of the other Volvocida members are globular. This is important because the initial colony embryos have the flagella pointing in towards the center of the globe, making them useless for locomotion. In order to function, they must invert. This inversion is carried out by the action of InvA, a novel kinesin, which acts on the microtubules at the cytoplasmic bridges to bend the sheet of cells. This protein is required in
Gonium as well, where it switches the concavity of the colony so that the flagella are on the convex side. InvA is coded for by the gene
invA.
Chlamydomonas,
Gonium,
Pandorina,
Eudorina, and
Pleodorina all have a gene that is a orthologue of
invA, and the gene in
Chlamydomonas, IAR1, has been inserted into an inversion-incapable
invA Volvox mutant, causing inversion. This is yet another instance of novel use of a pre-existing protein (also demonstrated in another case by the ability of the
Chlamydomonas ortholog of
gls to return asymmetric cell division to a
Volvox gls mutant).
The next major hurdle after cytoplasmic continuity and embryonic inversion is germ-stroma division of labor in
Volvox. This is caused by two gene expression regulators,
regA, which represses chloroplast protein synthesis in somatic cells (required for germ cells to pass on chloroplasts, stalling the usual transition from biflagellated stage to nonflagellated reproductive stage), and
lag, which keeps germ cells from developing somatic features like flagella and eyespots. It currently is unclear whether these genes are new inventions in
Volvox or if they are present in ancestors but not used for this purpose.
The close genetic and morphological similarity among the Volvocida members show that they have a common ancestry and are closely related. The genetic and morphological similarity between
Chlamydomonas reinharditii and
Gonium show that these two have a relatively recent common ancestor. The upshot of all of this is that unicellular to multicellular evolution is not "naive," it's a fact.
Coleman A. W.; Mai, J. C. "Ribosomal DNA ITS-1 andITS-2 sequence comparisons as a tool for predicting genetic relatedness." J Mol Evol 1997, 45:168–177.
Kirk, David L. "
Volvox as a Model System for Studying the Ontogeny and Phylogeny of Multicellularity and Cellular Division." J. Plant Growth Regul. 2000, 19:265-274.
Kirk, David L. "Seeking the Ultimate and Proximal Causes of
Volvox Multicellularity and Cellular Division." Integ. Comp. Biol. 2003, 43:247-253.
Cole, Douglas; Reedy, Mark. "Algal Morphogenesis: How [i[Volvox[/i] Turns Itself Inside-Out." Current Biol. 2003, 13:R770-R772.
Kirk, David L. "A twelve-step program for evolving multicellularity and a divsiton of labor." BioEssays 2005, 27:299-310.
Liss, Michael; Kirk, David; Beyser, K.; Fabry, S. "Intron sequences provide a tool for high-resolution phylogenetic analysis of Volvocine algae." Curr. Genet. 1997, 31:214-227.
Nozaki, H.; Itoh, R.; Sano, H.; Uchida, M.; Watanabe, M.; Kuroiwa, T. "Phylogentic relationships within the colonial Volvocales (Chlorophyta) inferred from
rbcL gene sequence data." J. Phycol. 1995, 31:970-979.
