什么是性倾向的生物学根源?

What are the biological roots of sexual orientation?

关于性倾向生物学根源的研究进展,本文从4方面加以评述:内源性生物学根源、外源成因作用的生物学基础、理论和分歧以及研究建议.在决定性分化和性腺分化的基因网络和性翻转研究中发现,内源性发育障碍和性翻转的发生概率不足以解释当代社会性少数群体发生率的1‰.当代社会性少数群体主要成因是外源的环境和社会因素,通过表观遗传机制、脑内奖励/强化系统、人格特质或素质以及神经信号和遗传信号间交流的分子生物学基础而发生作用,构成其间接的生物学根源.在此基础上,建议今后加强研究4项课题.文中对人类繁衍的基础是否必须是异性性倾向驱动,性别决定的Y染色体及其进化前景是否乐观,成人个体是否会自发地发生性翻转,性倾向在人群中的分布模式等问题,加以评论并给出了作者的看法.

This paper contains first a consideration of the biological roots of sexual orientation. Next the paper reviews the different points of view about the SRY gene and the Y chromosome. The paper then discusses three models of the distribution of sexual orientation. The paper concludes with four suggestions for future investigation on the question of the biological determinants of sexual orientation. The biological roots of sexual orientation are considered from two perspectives： endogenous and exogenous. The endogenous roots are the consequences of genes and prenatal development,while the exogenous roots are the consequences of postnatal development which include environmental,societal,and cultural factors. Both the endogenous and exogenous factors influence the acquisition of non-heterosexual orientation through induced changes in neural and genetic information processes as well as changes in the communication between gene and brain. The SRY gene determines the sex of the fetus,including the primary genital cell and its hormone secretion. Then,the sex differentiation in the prenatal brain is influenced by the sex hormone＇s neural organizing effect. The brain＇s sex differentiation in the prenatal period and early years of an infant＇s development are potent determinants of the adult＇s sexual behavior. The occurrence rate of sex reversal in prenatal development was reported as one thousandth of the sexual minority in a demographic assessment,therefore neither the sex related gene（SRY） nor gonad differentiation as well as the variations of sex development seem to be the dominant biological cause of non-heterosexual orientation. The exogenous influences on the biological mechanism for non-heterosexual orientation occur also in the neural,hormonal,and epigenetic mechanisms as well as the communication between neural signals and genetic signals of an individual. These influences by the exogenous factors come from the society and the culture. The exogenous factors that influence a person＇s sexual orientation usually evoke excitatory processes in the lower sex centers of the sexually dimorphic nucleus（SDN）,which are under the regulation of the higher neural circuits between the sub-cortical sex centers and neocortices,including orbital frontal cortex（OFC）,anterior cingulate cortex（ACC）,and ventral medial prefrontal cortex（vmP FC）. Although evidence for sexual orientation from neurobiology exists,it is not definitive. The question remains whether or not the observed biological factors are the behavioral prerequisites or the behavioral results. The non-heterosexual behavior must activate the brain stem reticular formation and get reinforcing effect from the reward/reinforcement system in the brain（mesolimbic dopamine system）,so that the memory system puts the non-heterosexual orientation as an acquired behavior model. The processes are similar to those involved in the formation of other compulsive attractions,such as to the internet. The changes in neural signal processing must be connected with gene or epigenetic expression,because any form of long term memory is accompanied by new protein synthesis. Especially,the sex hormone evokes sexual arousal more rapidly than a neurotransmitter does,due to sex hormone receptors with special double exciting units which are distributed not only among post-synaptic membranes,but also both inside the cell plasma and cell nucleus. The questions as to whether the SRY gene is either degenerative or evolutionary and sex reversal under a natural environment are relevant to the understanding the biological root of sexual orientation. The paper gives a promising answer by some new findings in the comparative investigations between the Chimpanzee and the human Y chromosomesas well as between human being and reptiles.