With a previous paper (Niu & Wang, 1995), a general, hypothetical outline of the mechanism of carcinogenesis was proposed. With reference to the fact of starvation-induced hypermutation in micro-organisms, we propose that the hypoxia commonly seen in the cells at the centre of solid tumours might also result in hypermutation, and then p53-dependent programmed cell death. Like the apparently adaptive mutations in micro-organisms, only those genes (e.g. p53) that enable the cells to escape from apoptosis may be selected.

Division of labour is a marked feature of multicellular organisms. Margulis proposed that the ancestors of metazoans had only one microtubule organizing center (MTOC), so they could not move and divide simultaneously. Selection for simultaneous movement and cell division had driven the division of labour between cells. However, no evidence or explanation for this assumption was provided. Why could the unicellular ancetors not have multiple MTOCs? The gain and loss of three possible strategies are discussed. It was found that the (...) advantage of one or two MTOC per cell is environment-dependent. Unicellular organisms with only one MTOC per cell are favored only in resource-limited environments without strong predatory pressure. If division of labour occurring in a bicellular organism just makes simultaneous movement and cell division possible, the possibility of its fixation by natural selection is very low because a somatic cell performing the function of an MTOC is obviously wasting resources. Evolutionary biologists should search for other selective forces for division of labour in cells. (shrink)

To cope with the water deficit resulting from saline environment, plant cells accumulate three kinds of osmotica: salts, small organic solutes and hydrophillic, glycine-rich proteins. Salts such as NaCl are cheap and available but has ion toxicity in high concentrations. Small organic solutes are assistant osmotica, their main function is to protect cytoplasmic enzymes from ionic toxicity and maintain the integrity of cellular membranes. Hydrophillic, glycine-rich proteins are the most effective osmotica, they have some characteristics to avoid crystallization even in (...) high concentration, but because they are expensive they are not as commonly used as salts or organic solutes. In addition there is the question of whether the genetic information for growth in saline environment is present in all kinds of plants, both halophytes and nonhalophytes. (shrink)

From the viewpoint of an evolutionary biologist, carcinogenesis should be looked upon as a protective mechanism against destruction of DNA. Because genes expressed in embryonic cells are covered and protected by heterochromatinization, they are the most appropriate ‘alternate genes’ compared to genes that are expressed already in somatic cells. When DNA-damage occurs, the embryonic genes can be activated. Some somatic cells exhibit some features of embryonic cells.