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"The animal populations involved in these explosions were all marine, and it is probable that most inhabited the shallow waters of continental shelves. Their unicellular and algal food supplies were already well diversified (Lipps 1993), while established multicellular competitors, predators, and parasites were absent. There was thus a situation of considerable ecological opportunity - or empy niche space - that has never been repeated in biospheric history. ...

These early animals were all (by definition) multicellular, but consisted of relatively few cells compared with most present-day animals. Their ontogenetic trajectories were therefore much simpler than those to which most of our detailed embryological information relates. Also, since they had not been subject to a comparable history of selection for integration and canalization, their ontogenies were almost certainly more evolutionarily flexible than those of their later counterparts. ... a highly coordinated development that is resistant to change [is an evolutionarily derived state]. Mutations of genes controlling early development thus occurred, at the beginning of animal evolution, in a very different ontogenetic context to those occurring in Caenorhabditis, Drosophila, Mus, or any other present-day animal." (The Origin of Animal Body Plans: A Study in Evolutionary Developmental Biology, Wallace Arthur, Cambridge University Press, 1997, 226-227)

"In fact, the number of bacteria that normally inhabit the human body (about 700 trillion cells) exceeds the number of its own human cells (about 70 trillion)." (Biology: Fifth Edition, Solomon, Berg, & Martin, Harcourt College Publishing, 1999, p497)

”The Volvocaceans

The simpler organisms among the volvocaceans are ordered assemblies of numerous cells, each resembling the unicellular protist Chlamydomonas, to which they are related (Figure 2.11A). A single organism of the volvocacean genus Gonium (Figure 2.11B), for example, consists of a flat plate of 4 to 16 cells, each with its own flagellum. In a related genus, Pandorina, the 16 cells form a sphere (Figure 2.11C); and in Eudorina, the sphere contains 32 or 64 cells arranged in a regular pattern (Figure 2.11D). In these organisms, then, a very important developmental principle has been worked out: the ordered division of one cell to generate a number of cells that are organized in a predictable fashion. As occurs during cleavage in most animal embryos, the cell divisions by which a single volvocacean cell produces an organism of 4 to 64 cells occur in very rapid sequence and in the absence of cell growth.

The next two genera of the volvocacean series exhibit another important principle of development: the differentiation of cell types within an individual organism. The reproductive cells become differentiated from the somatic cells. In all the genera mentioned earlier, every cell can, and normally does, produce a complete new organism by mitosis. In the genera Pleodorina and Volvox, however, relatively few cells can reproduce. In Pleodorina californica (Figure 2.11E), the cells in the anterior region are restricted to a somatic function; only those cells on the posterior side can reproduce. In P. californica, a colony usually has 128 or 64 cells, and the ratio of the number of somatic cells to the number of reproductive cells is usually 3:5. Thus, a 128-cell colony typically has 48 somatic cells, and a 64-cell colony has 24.

In Volvox, almost all the cells are somatic, and very few of the cells are able to produce new individuals. In some species of Volvox, reproductive cells, as in Pleodorina, are derived from cells that originally look and function like somatic cells before they enlarge and divide to form new progeny. However, in other members of the genus, such as V. carteri, there is a complete division of labor: the reproductive cells that will create the next generation are set aside during the division of the original cell that is forming a new individual. The reproductive cells never develop functional flagella and never contribute to motility or other somatic functions of the individual; they are entirely specialized for reproduction. Thus, although the simpler volvocaceans may be thought of as colonial organisms (because each cell is capable of independent existence and of perpetuating the species), in V. carteri we have a truly multicellular organism with two distinct and interdependent cell types (somatic and reproductive), both of which are required for perpetuation of the species (Figure 2.11F). Although not all animals set aside the reproductive cells from the somatic cells (and plants hardly ever do), this separation of germ cells from somatic cells early in development is characteristic of many animal phyla and will be discussed in more detail in Chapter 19.

Although all the volvocaceans, like their unicellular relative Chlamydomonas, reproduce predominantly by asexual means, they are also capable of sexual reproduction, which involves the production and fusion of haploid gametes. In many species of Chlamydomonas, including the one illustrated in Figure 2.10, sexual reproduction is isogamous ("the same gametes"), since the haploid gametes that meet are similar in size, structure, and motility. However, in other species of Chlamydomonasas well as many species of colonial volvocaceans swimming gametes of very different sizes are produced by the different mating types. This pattern is called heterogamy ("different gametes"). But the larger volvocaceans have evolved a specialized form of heterogamy, called oogamy, which involves the production of large, relatively immotile eggs by one mating type and small, motile sperm by the other (see Sidelights and Speculations). Here we see one type of gamete specialized for the retention of nutritional and developmental resources and the other type of gamete specialized for the transport of nuclei. Thus, the volvocaceans include the simplest organisms that have distinguishable male and female members of the species and that have distinct developmental pathways for the production of eggs or sperm. In all the volvocaceans, the fertilization reaction resembles that of Chlamydomonas in that it results in the production of a dormant diploid zygote, which is capable of surviving harsh environmental conditions. When conditions allow the zygote to germinate, it first undergoes meiosis to produce haploid offspring of the two different mating types in equal numbers. “
(http://www.ncbi.nlm....bio.section.203)

blazer2000x: If the sun has always been shrinking at its current rate, then it would have charred the earth to dust if you go back just a little over ten thousand years.

”In category ninety-two, Brown claims that the sun is shrinking at a constant rate and that it cannot be more than a million years old. In support, he cites three sources (Dunham et al., 1980; Gribbin and Sattaur, 1984; Lubkin, 1979). Unfortunately, two of his sources are out of date and the third supplies evidence that undercuts Brown's claim. From the very beginning, the claim of a shrinking sun was disputed by contrary evidence (for example, LaBonte and Howard, 1981; Parkinson et al., 1980; Shapiro, 1980; Stephenson, 1982). It now appears that the sun oscillates on about an eighty-year cycle (Gilliland, 1981; Parkinson et al., 1980; Parkinson, 1983). It should be noted that several of the authors of one of the papers Brown cites (Dunham et al., 1980) recently concluded that "the solar radius changes are not secular (monotonic and uniform)" and that "the Mercury transit data convincingly disproved the existence of large secular changes in the solar radius" (Sofia et al., 1983, p. 525). More recently, the claim has again been made that the sun was once significantly larger than it is now, specifically during the seventeenth century (Ribes et al., 1987), but this study failed to account for certain systematic instrumental effects which invalidate the claim (O'Dell and Van Heiden, 1987). Measurements of the solar radius, contrary to Brown, are not a reliable measurement of the sun's age. (See also chapter three of Van Till et al., 1988, pp. 47-65, for a description of creationists' use of the "shrinking sun" claim and the evidence against it, including a note on p. 51 that a 1984 paper by Claus Frohlich and John Eddy reported an increase in the solar diameter between 1967 and 1980. The chapter comments specifically on Brown and was originally published in the September 1986 Journal of the American Scientific Affiliation, so Brown should have been aware of its existence.)”
(http://www.ncseweb.o...__8_21_2003.asp)