tailieunhanh - The Fetal Matrix: Evolution, Development and Disease - part 7

sẽ làm cho độ lệch lớn hơn từ các định mức hơn nếu nó cảm nhận chỉ có một sự thay đổi tinh tế. Do liên tục này, và bởi vì các quá trình cơ bản thay đổi tiên đoán thích hợp và không phù hợp là như nhau, khi chúng tôi đang thảo luận về các quá trình sinh học phổ biến, chúng tôi sẽ tiếp tục sử dụng thuật ngữ chung, | 147 The role of PARs and environmental change will make a greater deviation from the norm than if it senses only a subtle change. Because of this continuum and because the processes underlying appropriate and inappropriate predictive changes are the same when we are discussing the common biological processes we will continue to use the generic term predictive adaptive responses. Our thesis is that the repertoire of PARs creates a set of biological processes that are a key element in the survival of a species. We think that evolution has used the PAR to tune the fetus in the absence of other cues to adopt a default position -that of the survival phenotype that is the fetus is induced so that in the absence of other information it will be equipped to be born into a relatively poor nutritional environment. Certainly the evolution of hominids occurred in an environment very different from that which we now inhabit and thus the processes underlying PARs may have led to the evolution of processes that may have been more generally appropriate in past evolutionary time but now are more likely to be inappropriate. Indeed we suggest that this is an important element in the rising epidemic of heart disease and diabetes in both the developed and developing world. In considering this we need to distinguish physiological constraints acting in all pregnancies which have created the default phenotype from those pathophysiological constraints that utilise similar mechanisms to generate a more exaggerated effect. We propose that the phenomenon of maternal constraint is a core process that served the evolutionary purpose of tuning the phenotype to be on the safe side in its prediction. This default pathway is one in which survival to reproductive age in an uncertain world is more likely. Hence we term this phenotype the default or survival phenotype. Humans are unusual in that their lives now extend well beyond the normal reproductive years and therefore the disease-enhancing effects