1. In all Bilaterian species individual specimens are very similar to one another; they all have the same complex vital organs arranged in a virtually uniform manner. Some species of nematodes and rotifers even exhibit eutely: each specimen consists of the identical number of cells arranged in precisely the same pattern. Such strict uniformity of entire phenotypes is not found in other multicells (plants, Porifera and cnidarians). In those phyla, plasticity reigns. How could the same mechanism, natural selection, possibly explain the emergence of both strict phenotypic uniformity and widespread phenotypic plasticity?
2. In cell colonies (plants, cnidarians, and Porifera) the most complex and highly organized tissues are those directly involved in sexual reproduction. Natural selection explains sex-organ complexity: if those organs had not functioned with exquisite precision the lineages would have perished. But Bilaterian complexity is different. In those animals vital organs located throughout the body perform functions not directly involved in sexual reproduction. How can the identical mechanism -- natural selection -- logically account both for the existence of complex vital organs in animals and their absence in cell colonies?
3. Among cnidarians, large organisms are found in sunny habitats; in the genus Cyanea some jellyfish grow to two meters in diameter. All jellyfish are comparatively simple organisms. However, among the laterally symmetrical animals the combination of large size and exposure to sunny habitat is found only in the most transformed lineages, the terrestrial vertebrates. These animals are extremely complex. There seem to be no large, relatively simple animals (as simple, say, as annelids) living in sunny habitats. Why not?
4. Based on the fossil record the earliest Bilaterians all avoided exposure to sunlight. Somatic cells were not directly exposed until about 400 million years after those animals first appeared, and then only in lineages that produced animals with adaptive immune systems. In fact, most extant Bilaterians avoid exposing unprotected cells that divide. On the other hand, plants, Porifera and most cnidarians do not avoid sunlight; many spend all their days basking in it. What is the evolutionarily plausible explanation for this fundamental difference in the life histories and observed characteristics of the two groups of multicells?
5. Jellyfish fossils found in 2007 in Utah are estimated to be more than 500 million years old. According to University of Kansas investigators the ancient jellyfish were phenotypically very similar to present day jellyfish. It seems that, compared to Bilaterians, there has been little organismic transformation in the cnidarians (and in the Porifera). What is the mechanistic explanation for such (what some might call) unpunctuated equilibrium?
6. The theoretical problem of senescence, contrary to the opinion of some, has not been solved. Most plants, unlike all Bilaterians, do not exhibit programmed aging. An exception is found in certain bamboo species where all the individual plants live for a fixed number of years before they flower and reproduce. Then all the individual plants die. This is true aging -- the programmed cessation of mitosis following a fixed time period.
But programmed death dependent on cues from the environment which is exhibited by most plants (think of annual plants dying in the fall) is not aging; bring the geraniums inside before frost and they will survive to spring. Perhaps some annual plants do not survive indoors but with few exceptions plants do not undergo the temporal-sensitive slowdown in cell renewal that is the hallmark of aging in Bilaterians. Studies of Porifera and cnidarians indicate that they too do not age.
All Bilaterians age and investigators have actually identified (in some species) genes "for" senescence.
How could the identical mechanism -- classic Darwinian selection -- possibly account for both the presence of such a fundamental character in all the Bilaterians and its absence in virtually all other multicells?