The present study is mainly concerned with the nature of the demonstrative shì 是 as the historical source of the copula shì. Tracing the development of shì in bronze inscriptions from the 11th to 3rd centuries bce and comparing the patterns of change against two purportedly contemporary texts, Shī jīng 詩經 and Shàng shū 尚書, it argues that shì is not a typical demonstrative in origin because it only occurs pronominally and is strongly associated with the structural expression of focus in its early stage of development. On the basis of these observations, shì is analyzed as a special demonstrative that combines anaphoric and focalizing force to highlight and contrast a constituent that has been introduced into the discourse. It is then compared with the expressions wéi zhī 唯之and huì zhī 惠之 with the same function in the Shang oracle-bone inscriptions (13th–11th centuries bce). The investigation of whether shì is derived from wéi zhī only finds evidence indicating a morphological relationship with zhī, while the etymological link with wéi remains speculative. In conclusion, this study claims that the focalizing force of shì is important in answering the question why it is the only demonstrative evolving into a copula. The observed development of shì confirms that the origination of copulas is often related to the morphosyntactic expression of features of information structure.
The plateau zokor (Myospalax baileyi) is a specialized subterranean rodent that lives on the Qinghai-Tibet Plateau. The species has evolved a series of strategies to adapt to its hypoxic environment and hypercapnia. p53 is a tumour suppressor gene that plays a crucial role in the cellular response to hypoxia by inducing cell cycle arrest, cell apoptosis, DNA damage repair and angiogenesis. To investigate the sequence characteristics of p53 and the response to hypoxia in plateau zokor, we cloned the p53 coding DNA sequence, analysed it, and measured the expression level of p53 at different altitudes in plateau zokor and rats. Our results show that the coding DNA sequence is 1179 bp, consisting of 392 amino acid residues. Compared to human p53, the subterranean rodents have two mutation sites in common with the human hotspots in the DNA-binding domain. Compared to subterranean rodents, plateau zokor have a mutation at residue 309. In addition, subterranean rodents have two convergent sites at residues 78 and 84. The expression levels of p53 in plateau zokor tissues increase significantly from 2260 m to 3300 m, but there was no significant difference in rats at those altitudes. Our results suggest that subterranean rodents have two mutation sites in common with the human hotspots in the DNA-binding domain, the mutation of Gly309Asp is a unique mutation site of plateau zokor p53, and there are two convergent sites enhancing subterranean rodent adaptation to hypoxic conditions. In addition, p53 is sensitive to the oxygen concentration in plateau zokor, and hypoxia upregulates the levels of p53. Generally, plateau zokor use this strategy to adapt to a hypoxic environment.