演化生物學家Stephen J. Gould宣稱女性的高潮根本沒有任何功能,只不過是男性射精反應的副產品,毫無目的可言。他重新詮釋了人類學家Donald Symons於1979年提出的說法:在胚胎發育之初,男女兩性都有同樣的身體藍圖。相對於天擇賦予男性射精的偶然結果,有些共同的結締組織和神經系統通路在女性身上也「偶然的」被演化塑造,導致性成熟女性偶爾會有高潮的快樂結果。陰蒂基本上就是女性的陰莖,因為這兩者來自同樣的胚胎基質。這也說明了為什麼女性高潮是藉著刺激陰蒂而非陰道達成。
哲學家Elisabeth A. Lloyd,在其著作《The Case of the Female Orgasm: Bias in the Science of Evolution》中也同樣主張:女性性高潮其實根本不具演化的意義。Lloyd也同意Symons提出的理論:女性性高潮不過是一種人類胚胎發育初期的副產品(Symons, 1979)。一個類似的現象是男性的乳頭,不具任何實際功能,完全是胚胎發育初期殘留至成體的痕跡,因此女性性高潮的存在「純屬樂趣」、「純屬巧合」。
演化生物學家Justin R. Garcia對600名大學生進行了調查,發現女性在認真的感情關係中性交或口交時達到高潮的可能性,是勾搭行為中達到高潮可能性的兩倍。類似地,一項在過去5年中對21所大學的24000名學生做的調查發現,約40%的女性在最近一次包括性交的勾搭中獲得性高潮,而男性則是80%。同樣地,約四分之三的接受調查女性說,她們在與固定伴侶的最近一次性交中達到了性高潮。
Thomas Poller和Daniel Nettle做了一個聳動的研究,根據受測者的自述,和富有男伴約會或結婚的中國婦女,比伴侶賺得較少的婦女,更常發生性高潮。亦即,男性伴侶的收入和女性高潮頻率息息相關,而且成正比,即使作者排除了包括健康、快樂、教育程度、女性個人收入等許多外在變數之後,這個收入效應依舊十分明顯。就這方面來說,女性高潮可能扮演情感上的連結角色,促使和地位較高的男性發生性行為,也因此提高受孕的機會。(然而,男人在性交中與前後的行為,有可能比他的社會資本或淨值更重要。)在動物上也可以看到類似的情況:母日本彌猴在和地位高的公猴交配時,較常展現「似高潮」的緊握反應。
William H. Masters與 Virginia E. Johnson(Masters and Johnson這兩個名字之所以成為「人類性行為研究」的同義詞,是因為他們於1966年出版的《人類的性反應》對女性性高潮的研究做出了突破性貢獻。)他們做了大量的實驗室研究,仔細觀察男女的性交過程,從而發現了著名的「子宮吸吮效應」:女性在性高潮過程中,子宮內的壓力會增加;隨著這種壓力的增加,會導致身體不由自主地吸入更多的精子,從而造成受孕機率的提高。
Robin Baker和Mark Bellis在《Human Sperm Competition》中提到兩種假設:戰斧(poleax)和上吸(upsuck)。上吸(upsuck)假設:性高潮陰道和子宮的收縮有助將精子吸入生殖腔,因此可以作為協助特定男性精子受精的一種輔助機制;女性可能會選擇性的保留或是排出不同男性遺留在他們體內的精子。在某些物種的鳥類,有時雌鳥交配後可能會完全排出雄鳥遺留在他們生殖腔內的精子,不過目前還不瞭解是透過什麼樣的機制進行。
事實上,目前對陰道排出精子量的測量發現,一般情況下,男子射精後的30分鐘內,女性排出的精子量約為總量的35%。如果女性達到了性高潮,則會排出約30%的精子(Danielle Cohen, Jay Belsky)。這5%的差別似乎不大。但心理學家假定,如果這種5%的差別始終存在,並且一代傳給一代,那麼疊加起來就會變成進化過程中的一種「選擇性壓力」。這意味著,如果女性沒有達到性高潮,那就會浪費更多的精子。因此,子宮吸吮效應證明,女子性高潮的功能,就在於把精子從陰道送入子宮頸而後直達子宮,從而提高懷孕的幾率。
批評
有70%沒有藉由性交得到高潮的女性可以由自慰得到高潮(Shere Hite, 2004; Elisabeth A. Lloyd, 2005),若上吸現象有穩定的選擇性壓力,那麼不應該只有部分的女性可以達到高潮,因為這表示未曾達到高潮的女性在演化上有先天上的劣勢。
根據蓋洛普的「去除他人精液理論」,男性的陰莖造型能夠有效的把競爭對手的精液由自己伴侶的陰道中排除。更明確的說,冠狀脊發揮作用,除去了外人精子,根據這個分析,抽插的效果就是為了要把其他男性的精子由子宮頸內抽出,聚在冠狀脊。在《Evolution and Human Behavior》中他甚至還製造了人造性器官模型和人造精液來作為實驗,發現有冠狀脊的陰莖可由人造陰道中抽出91%的精液,沒有冠狀脊的只移除了35.3%。
—20140813 補充:女性性高潮的關鍵:「The Mind」。 University of Ottawa的性學研究所受訪指出:女性高潮的關鍵:「內心越是淫蕩的女性,越容易放得開,比較容易敏感,最後升天;反觀對性愛比較「淡定」的女性,高潮就離自己比較遠」。原文指出:Women in the study who reported regularly reaching orgasm during sex seemed to be more focused on their bodily sensations during intercourse than the women who had trouble having regular orgasms with their partners, the researchers said.
Zeiler, MD. (1972). Fixed-interval behavior: effects of percentage reinforcement. Journal of the Experimental Analysis of Behavior 17 (2): 177–89.
Shere Hite. (2004). The Hite Report: A Nationwide Study of Female Sexuality. New York, NY: Seven Stories Press. pp. 512 pages. ISBN 1-58322-569-2. Retrieved March 2, 2012.
Shere Hite. (2006). On female sexuality in the 21st century. The Independent. April 30, 2006. Retrieved April 10, 2011.
Elisabeth Anne Lloyd. (2005). The case of the female orgasm: bias in the science of evolution. Harvard University Press. pp. 21–53. ISBN 0-674-01706-4. Retrieved January 5, 2012.
Diana O. Fisher, Michael C. Double, Simon P. Blomberg, Michael D. Jennions & Andrew Cockburn. (2006). Post-mating sexual selection increases lifetime fitness of polyandrous females in the wild. Nature 2006 Nov. 2.
Malcolm Potts, Roger Short. (1999). Ever since Adam and Eve.
Marlene Zuk. (2003). Sexual Selections: What We Can and Can’t Learn about Sex from Animals.
Wilson (1964)4及Taylor & Ho (1967)5利用動物(狗、老鼠)進行實驗,餵食以同位素標記的膽固醇,發現長期下來體內的膽固醇大多數都是有標記的,而自行合成的只佔一小部分,這表示膽固醇攝取量變多後合成的機制就會受到壓抑。 至於在人類是否也是依循相同的機制呢?有些研究者認為無論如何攝取進的膽固醇都會被吸收6,7,8,9,但後續研究發現,人體似乎為防止長期食物裡有太多膽固醇,故會限制吸收的總量,在經過相同的同位素標記法的實驗後,發現人的血漿裡的膽固醇中來自飲食的比例依然較少10,11,顯示人的機制應該是更傾向於抑制吸收。 到目前為止,研究顯示當人體攝取的膽固醇過多時的平衡機制有:
由上圖可以發現,儘管膽固醇的淨平衡(intake minus excretion)是增加的,但卻沒有完全反應在血漿濃度中,血漿膽固醇濃度的增加量不會超過20%,這表示增加的膽固醇是留在體內(body pool)中的其他地方而非血漿中。 而這個研究無法解釋在身體內的膽固醇是跑到哪了,研究發現兔子所吸收的膽固醇會出現在其體內的許多區域,但老鼠則是有很多出現在肝臟13。
Hooper, L., Summerbell, C. D., Higgins, J. P., Thompson, R. L., Capps, N. E., Smith, G. D. & Ebrahim, S. (2001). Dietary fat intake and prevention of cardiovascular disease: systematic review. Bmj, 322(7289), 757-763. ↩
Wilson, J. D. 1964. The quantification of cholesterol excretion and degradation in the isotopic steady state in the rat: the influence of dietary cholesterol. J . Lipid Res. 5: 409-417. ↩
Taylor, C. B., and K.-J. Ho. 1967. A review of human cholesterol metabolism. Arch. Pathol. 84: 3-1 4. ↩
Stanley, M. M., and S. H. Cheng. 1956. Cholesterol exchange in the gastrointestinal tract in normal and abnormal subjects. Gastroenterology. 30: 62-74. ↩
Karvinen, E., T. M. Lin, and A. C. Ivy. 1957. Capacity of human intestine to absorb exogenous cholesterol. J. Appl. Physiol. 11: 143-147. ↩
Borgstrom, B. 1969. Quantification of cholesterol absorption in man by fecal analysis after the feeding of a single isotope-labeled meal. J . Lipid Res. 10: 331-337. ↩
Dietschy, J. M., and J. D. Wilson. 1970. Regulation of cholesterol metabolism. N . Engl. J . Med. 282: 1128-1 138, 1179-1183, 1241-1249. ↩
Kaplan, J. A., G. E. Cox, and C. B. Taylor. 1963. Choles- terol metabolism in m a n : studies on absorption. Arch. Pathol. 76: 359-368. ↩
Wilson, J. D., and C. A. Lindsey, Jr. 1965. Studies on the influence of dietary cholesterol on cholesterol metabolism in the isotopic steady state in man. J. Clin. Invest. 44: 1805-1814. ↩
Quintao, E., Grundy, S. M., & Ahrens, E. H. (1971). Effects of dietary cholesterol on the regulation of total body cholesterol in man. Journal of lipid research, 12(2), 233-247. ↩
Perl, W., and P. Samuel. 1969. Input-output analysis for total input rate and total traced mass of body cholesterol in man. Circ. Res. 25: 191-199. ↩
Hopkins, P. N. (1992). Effects of dietary cholesterol on serum cholesterol: a meta-analysis and review. The American journal of clinical nutrition, 55(6), 1060-1070. ↩
Jacobs DR, Anderson JT, Blackburn H. Diet and serum cholesterol. Do zero correlations negate the relationship? Am J Epidemiol 1979;l 10:77-87. ↩
Hopkins PN, Williams RR, Kuida H, et al. Predictive value of a short dietary questionnaire for changes in serum lipids in high-risk Utah families. Am J Clin Nutr 1989;50:292-300. ↩
Castelli WP. Epidemiology of coronary heart disease: the Framingham study. Am J Med 1984;76(2A):4–12. ↩
Martin MJ, Hulley SB, Browner WS, Kuller LH, Wentworth D. Serum cholesterol, blood pressure, and mortality: implications from a cohort of 361,662 men. Lancet 1986;2:933–6. ↩
Castelli WP, Garrison RJ, Wilson PW, Abbott RD, Kalousdian S, Kannel WB. Incidence of coronary heart disease and lipoprotein cho- lesterol levels. The Framingham Study. JAMA 1986;256:2835–8. ↩
Klag MJ, Ford DE, Mead LA, He J, Whelton PK, Liang KY, Levine DM. Serum cholesterol in young men and subsequent cardiovascular disease. N Engl J Med 1993;328:313–8. ↩
Stamler J, Daviglus ML, Garside DB, Dyer AR, Greenland P, Neaton JD. Relationship of baseline serum cholesterol levels in 3 large cohorts of younger men to long-term coronary, cardiovascular, and all-cause mortality and to longevity. JAMA 2000;284:311–8. ↩
Clarke R, Frost C, Collins R, Appleby P, Peto R. Dietary lipids and blood cholesterol: quantitative meta-analysis of metabolic ward stud- ies. BMJ 1997;314:112–7. ↩
Howell WH, McNamara DJ, Tosca MA, Smith BT, Gaines JA. Plasma lipid and lipoprotein responses to dietary fat and cholesterol: a meta- analysis. Am J Clin Nutr 1997;65:1747–64. ↩
Weggemans RM, Zock PL, Katan MB. Dietary cholesterol from eggs increases the ratio of total cholesterol to high-density lipoprotein cholesterol in humans: a meta-analysis. Am J Clin Nutr 2001;73: 885–91. ↩
Herron KL, Vega-Lopez S, Conde K, Ramjiganesh T, Roy S, Shachter NS, Fernandez ML. Pre-menopausal women, classified as hypo- or hyperresponders, do not alter their LDL/HDL ratio following a high dietary cholesterol challenge. J Am Coll Nutr 2002;21:250–8. ↩
Herron KL, Vega-Lopez S, Conde K, Ramjiganesh T, Shachter NS, Fernandez ML. Men classified as hypo- or hyperresponders to dietary cholesterol feeding exhibit differences in lipoprotein metabolism. J Nutr 2003;133:1036–42. ↩
Greene CM, Zern TL, Wood RJ, Shrestha S, Aggarwal D, Sharman MJ, Volek JS, Fernandez ML. Maintenance of the LDL cholesterol:HDL cholesterol ratio in an elderly population given a dietary cholesterol challenge. J Nutr 2005;135:2793–8. ↩
Greene CM, Zern TL, Wood RJ, Shrestha S, Aggarwal D, Sharman MJ, Volek JS, Fernandez ML. Maintenance of the LDL cholesterol:HDL cholesterol ratio in an elderly population given a dietary cholesterol challenge. J Nutr 2005;135:2793–8. ↩
Reaven GM, Abbasi F, Bernhart S, Coulston A, Darnell B, Dashti N, Kim H, Kulkarni K, Lamendola C, McLaughlin T, et al. Insulin re- sistance, dietary cholesterol, and cholesterol concentration in post- menopausal women. Metabolism 2001;50:594–7. ↩
Goodrow EF, Wilson TA, Houde SC, Vishwanathan R, Scollin PA, Handelman G, Nicolosi RJ. Consumption of one egg per day increases serum lutein and zeaxanthin concentrations in older adults without altering serum lipid and lipoprotein cholesterol concentrations. J Nutr 2006;136:2519–24. ↩
Wenzel AJ, Gerweck C, Barbato D, Nicolosi RJ, Handelman GJ, Curran-Celentano J. A 12-wk egg intervention increases serum zeax- anthin and macular pigment optical density in women. J Nutr 2006; 136:2568–73. ↩
Mayurasakorn K, Srisura W, Sitphahul P, Hongto PO. High-density lipoprotein cholesterol changes after continuous egg consumption in healthy adults. J Med Assoc Thai 2008;91:400–7. ↩
Katz DL, Evans MA, Nawaz H, Njike VY, Chan W, Comerford BP, Hoxley ML. Egg consumption and endothelial function: a randomized controlled crossover trial. Int J Cardiol 2005;99:65–70. ↩
Njike V, Faridi Z, Dutta S, Gonzalez-Simon AL, Katz DL. Daily egg consumption in hyperlipidemic adults–effects on endothelial function and cardiovascular risk. Nutr J 2010;9:28. ↩
Shin, J. Y., Xun, P., Nakamura, Y., & He, K. (2013). Egg consumption in relation to risk of cardiovascular disease and diabetes: a systematic review and meta-analysis. The American journal of clinical nutrition, ajcn-051318. ↩
這樣的悲傷可能有一大部分來自於低落的可掌控性(Allen R. et al., 1993 [2]),而這來自於覺察原則的確立與不可改變性:現實世界中的規則是如此的堅定不移、掌控了整個世界,人的所有掙扎都是徒勞無功的。舉例來說,肉眼可見的簡單物理世界,幾乎可以用古典力學以蔽之,雖說更複雜的現象物理暫時無能為力,但我們知道那是來自於人的無知,而不是原則多變或毫無規則。
A nihilist (虛無主義者) is a man who judges of the world as it is that it ought not to be, and of the world as it ought to be that it does not exist. According to this view, our existence (action, suffering, willing, feeling) has no meaning: the pathos of ‘in vain’ is the nihilists’ pathos — at the same time, as pathos, an inconsistency on the part of the nihilists. —Friedrich Nietzsche, 1901 [5]
參考資料 [1] Dienstag, Joshua Foa. (2009). Pessimism: Philosophy, Ethic, Spirit. (pp. 22). Princeton University Press. Translated by Yi-Hung, Liu. [2] Allen R. McConnell, Christine M. Bill, William N. Dember, Anthony F. Grasha. (1993). Current Psychology: Developmental, Learning, Personality, Social. (pp. 195-215). [3] 不熟悉以演化意義來解釋意識的人可能會覺得有很大爭議,可以參考這樣一個淺顯易懂的形容:人感知到外在訊號,叫做知覺(看到一道光);對外在訊號的解釋,叫做詮釋(可能是來自月亮的一道光);對於詮釋的進一步詮釋,則是意識(為什麼今天的月亮這麼圓呢?)。而這樣的逐步過程,恰好符合演化的順序。(改自:陳穎青,2012,意識如何誕生——一個演化角度的假設,內容推進實驗室,http://www.contnt.net/2012/06/blog-post.html。) [4] Clifford Geertz. (1973). The Interpretation of Cultures. Basic Books. [5] Friedrich Nietzsche. (1901). The Will to Power. Section 585. Translated by Walter Kaufmann. [6] Edith Hamilton. (1993). The Greek Way. Chapter 11, The Idea of Tragedy. W. W. Norton.