Matrifocality is a feature of Caribbean communities in which mothers and adult daughters often form the household core. I argue that daughter-biased parental care underlies matrifocality. Parental investment (PI) theory predicts sex-biased care, but factors promoting daughter preference are not always clearly specified. If sons are more likely than daughters to experience unpredictable hazards, then parents may bias their efforts toward daughters. In this study, I examine gender differences in rural Dominica and test PI predictions. Men were more likely to be poor and develop alcoholism and less likely to migrate or attend high school than women were. Educational outcomes showed a Trivers-Willard effect: Boys from unfavorable family environments were less likely to receive secondary education than were other boys, but there was no association for girls. PI variables generally accounted for less variance in men's outcomes than women's, suggesting that unpredictable hazards for sons may promote daughter preference and matrifocality. 相似文献
Three high-resolution climatic reconstructions, based on diatom analyses from lake sediment cores from the Canadian prairies, show that shifts in drought conditions have prevailed on centennial to millennial time scales for at least the past six millennia. These shifts in mean aridity exhibit broad regional synchrony, with particularly pronounced shifts at all sites between ∼1700–2000 cal. yr bp and ∼3600–3900 cal. yr bp , as well as at ∼5400–5500 cal. yr bp for the two sites which extend back to at least 6000 cal. yr bp . The two Saskatchewan lakes exhibited significant coherence in both the timing and direction of these shifts, whereas inferred changes at the westernmost site in Alberta were significantly correlated to the Saskatchewan sites, but opposite in sign, and exhibited more high-frequency variation on the scale of centuries. The mechanisms behind these abrupt shifts in aridity are poorly understood, but may be linked to changes in oceanic–atmospheric interactions that influence the mean position of the jetstream and the associated storm tracks. Natural shifts in mean climatic conditions may accelerate with increasing carbon dioxide levels intensifying the likelihood of extreme droughts in North American prairies. 相似文献
A new species—Strobilanthes matthewiana R.W. Scotland—from Southern India is described and illustrated. The rediscovery of Strobilanthes punctata Nees is reported. Illustrations of Strobilanthes punctata and Strobilanthes anceps Nees are presented. A list of diagnostic differences between Strobilanthes punctata and the closely related Strobilanthes anceps is provided. 相似文献
Oestocephalus , an ophiderpetontid from the Middle Pennsylvanian of both Europe and North America provides the best known basis for evaluating the relationships of the aïstopods. All aïstopods are united by the unique manner of attachment of the skull and the first cervical in which the articulating surface of the occiput is formed by the narrow circular rim of a notochordal pit. As in other aïstopods (but in contrast with all other early tetrapods), the otic-occipital portion of the braincase is ossified as a single element. The palatoquadrate ossification extends from the orbit to the back of the area of jaw articulation. These two characters may be retained from the osteolepiform sarcopterygians. Few, if any, unique derived characters unite aïstopods with other early tetrapods. Their phylogenetic position remains enigmatic. 相似文献
THE ribonuclease, barnase, produced by Bacillus amyloliquefaciens has a molecular weight of 12,382, consisting of 110 amino-acid residues. It is one of the smallest proteins containing neither disulphide bonds nor non-peptide cross-Bnks which nevertheless maintain a well defined tertiary structure1,2. The next smallest reported enzyme of similar nature is the lysozyme of phage T4, with 160 residues. The barnase structure is reversibly destroyed by denaturing solvents or heat2, in what approximates a one step, highly cooperative, transition. Studies of this reaction should be very useful in illustration approaching the general problem of sequence-determined folding in proteins. In particular, thermodynamically meaningful quantitative differences in the stability of various genetic variants and chemically modified, or synthetic, barnases could be measured. Some work has been reported on the effect of various environmental parameters on the transition3 as well as the effects of modification by carboxypeptidases4. Full utilization of such data requires knowledge of both amino-acid sequence and three dimensional structurs. The complete amino-acid sequence is reported here (Fig. 1). The sequence was obtained by conventional procedures involving analysis of peptides isolated after hydrolysis of the native or modified protein by various proteases.