性 (生物學)

根據生殖特徵劃分的不同群體

(英語:Sex)是一種特徵,其可決定有性生殖生物體產生雄性或是雌性配子[1][2][3]於有性生殖過程中的雄性和雌性配子會融合,而形成受精卵,之後受精卵發育成為一繼承父母雙方特徵的後代。傳統上產生較小、更具移動性配子(精子)的生物體被稱為雄性,而產生較大、非移動性配子(卵細胞)的生物體被稱為雌性。[4]而可同時產生兩種配子的生物體則為雌雄同體[3][5]

於非雌雄同體物種,其中個體的性別是透過幾個生物性別決定係統中的一種來決定。大多數哺乳動物物種都具有XY性別決定系統,其中雄性通常攜帶一X和一Y染色體 (XY),雌性通常攜帶兩條X染色體 (XX)。其他的動物染色體性別決定系統包含有鳥類的ZW性別決定系統和昆蟲的X0性別決定系統。另有與前述不同的環境性別決定系統英语Environmental sex determination,如爬蟲類甲殼動物溫度-性別決定系統[6]

物種的雄性和雌性可能是外觀上相似(性單態性)或是有外觀上的差異(兩性異形)。大多數鳥類和哺乳動物是兩性異形物種,個體性別通常透過觀察其性別特徵識別性選擇(或稱擇偶)可加速兩性之間的差異進化。

"雄性"和"雌性"通常不適用於無性分化的物種,其個體是同構的(性單態性),且配子是同配生殖的(大小和形狀難以區分),例如稱為石蓴綠藻。但有些物種個體之間存在一些功能差異(例如真菌),[7]其繁殖方式為有性生殖中的交配類型英语mating type[8]

蕈類繁殖是真菌有性生殖(交配類型)中的一種。

性系統

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性系統是一物種中的生物體,其內部雄性和雌性功能的配置。[9]

 
交配中的食蚜蠅科

動物

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大約95%的動物物種有其獨立的雄性和雌性個體,稱為雌雄異體。大約有5%的動物物種是雌雄同體。[9]這種低百分比歸因於將種類眾多的昆蟲包含在內,昆蟲中並無雌雄同體存在。[10]大約99%的脊椎動物是雌雄異體,所餘1%的雌雄同體中,幾乎全是魚類。[11]

植物

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大多數植物具有兩種性別,[12](p. 212)或是雌雄同體(雄蕊雌蕊都在同一朵花上),或是單性同株英语Monoecy[13][14]在雌雄異株的物種中,雄性和雌性生長於不同株上。[15]約有5%的開花植物是雌雄異株的,由5,000之多的獨立品種演化而來。[16]雌雄異株在裸子植物中很常見,約佔65%,但大多數針葉樹是單性同株。[17]

 
通常開花植物的花朵上同時有雄性及雌性性器官(雌雄同體)。
松樹及其他針葉樹的毬花,圖左含雌性性器官,圖右含雄性性器官。

性的進化

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不同形式的異配生殖:
A)細胞遷移異配生殖,B) 卵式生殖英语oogamy (卵子細胞與精子細胞), C) 非細胞遷移異配生殖 (卵子細胞與精原體)。
不同形式的同配生殖:
A) 細胞遷移同配生殖,B) 非細胞遷移同配生殖,C) 結合

人們普遍認為異配生殖是由同配生殖演化而來,[18]且異配生殖在不同的真核生物群體中(如原生生物藻類植物動物)各自獨立進化過幾次。[10]異配生殖的演化與雄性和雌性的起源是同一件事。[19]這也是邁向兩性異形的第一步,[20]且影響到各種性別差異的演化。[21]

然而異配生殖的演化並沒留下任何化石證據,[22]迄2006年尚無遺傳證據證明性別和交配類間的演化連結。[23]目前還不清楚是異配生殖首先導致雌雄同體的進化,或是雌雄異體的進化。[12](p. 213)

但一件來自12億年前,稱為Bangiomorpha pubescens紅藻門化石,為雄性和雌性生殖的分化提供最古老的化石記錄,顯示性別在真核生物中很早就已進化。[24]

最初的性形式是體外受精。而我們所知的繁殖形式 - 體內受精,其演化發生在後,[25]是脊椎動物在陸地上出現後才成為主流。[26]

性別比例

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本節摘自性別比

性別比是整個群體中雄性與雌性所佔的比例。費雪原理解釋說,在有性繁殖的物種中出於進化原因,性別比例通常約為1:1。[27][28]然而有許多物種會週期性或永久性偏離此種均勻比例。例子包括單性生殖物種、週期性交配的生物體(如蚜蟲)及一些真社會性黃蜂花蜂類螞蟻白蟻[29]

人類學家和人口統計學家對人類性別比特別感興趣。在人類社會中,出生時的性別比可能會因母親生產時的年齡[30]以及性別選擇性墮胎英语Sex-selective abortion殺嬰等因素而造成相當大的偏差。接觸農藥和其他環境污染物也可能是重要的影響因素。[31]截至2014年,全球出生性別比估計為107男孩相對於100女孩(1,000名男孩:934名女孩)。[32]

參見

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參考文獻

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  1. ^ Stevenson A, Waite M. Concise Oxford English Dictionary: Book & CD-ROM Set. OUP Oxford. 2011: 1302 [2018-03-23]. ISBN 978-0-19-960110-3. Sex: Either of the two main categories (male and female) into which humans and most other living things are divided on the basis of their reproductive functions. The fact of belonging to one of these categories. The group of all members of either sex. 
  2. ^ Mills, Alex. Biology of Sex. University of Toronto Press. 2018-01-01: 43–45 [2023-10-03]. ISBN 978-1-4875-9337-7 (英语). 
  3. ^ 3.0 3.1 Purves WK, Sadava DE, Orians GH, Heller HC. Life: The Science of Biology. Macmillan. 2000: 736 [March 23, 2018]. ISBN 978-0-7167-3873-2. A single body can function as both male and female. Sexual reproduction requires both male and female haploid gametes. In most species, these gametes are produced by individuals that are either male or female. Species that have male and female members are called dioecious (from the Greek for 'two houses'). In some species, a single individual may possess both female and male reproductive systems. Such species are called monoecious ("one house") or hermaphroditic. 
  4. ^ Royle NJ, Smiseth PT, Kölliker M. Kokko H, Jennions M , 编. The Evolution of Parental Care. Oxford University Press. 2012: 103. ISBN 978-0-19-969257-6 (英语). The answer is that there is an agreement by convention: individuals producing the smaller of the two gamete types – sperm or pollen – are males, and those producing larger gametes – eggs or ovules – are females. 
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  18. ^ Kumar, Awasthi & Ashok. Textbook of Algae. Vikas Publishing House. : 363. ISBN 978-93-259-9022-7 (英语). 
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  20. ^ Togashi, Tatsuya; Bartelt, John L.; Yoshimura, Jin; Tainaka, Kei-ichi; Cox, Paul Alan. Evolutionary trajectories explain the diversified evolution of isogamy and anisogamy in marine green algae. Proceedings of the National Academy of Sciences of the United States of America. 2012-08-21, 109 (34): 13692–13697. Bibcode:2012PNAS..10913692T. ISSN 0027-8424. PMC 3427103 . PMID 22869736. doi:10.1073/pnas.1203495109 . 
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  23. ^ Sawada, Hitoshi; Inoue, Naokazu; Iwano, Megumi. Sexual Reproduction in Animals and Plants. Springer. 2014: 215–216. ISBN 978-4-431-54589-7 (英语). 
  24. ^ Hörandl, Elvira; Hadacek, Franz. Oxygen, life forms, and the evolution of sexes in multicellular eukaryotes. Heredity. 2020-08-15, 125 (1): 1–14. ISSN 1365-2540. PMC 7413252 . PMID 32415185. doi:10.1038/s41437-020-0317-9 (英语). 
  25. ^ Armored Fish Pioneered Sex As You Know It. Animals. 2014-10-19 [2023-07-10]. (原始内容存档于2021-03-02) (英语). 
  26. ^ 43.2A: External and Internal Fertilization. Biology LibreTexts. 2018-07-17 [2020-11-09]. (原始内容存档于2022-05-24) (英语). 
  27. ^ Fisher, R. A. The Genetical Theory of Natural Selection. Oxford: Clarendon Press. 1930: 141–143 –通过Internet Archive. 
  28. ^ Hamilton, W. D. Extraordinary Sex Ratios: A Sex-ratio Theory for Sex Linkage and Inbreeding Has New Implications in Cytogenetics and Entomology . Science. 1967, 156 (3774): 477–488. Bibcode:1967Sci...156..477H. JSTOR 1721222. PMID 6021675. doi:10.1126/science.156.3774.477. 
  29. ^ Kobayashi, Kazuya; Hasegawa, Eisuke; Yamamoto, Yuuka; Kazutaka, Kawatsu; Vargo, Edward L.; Yoshimura, Jin; Matsuura, Kenji. Sex ratio biases in termites provide evidence for kin selection. Nat Commun. 2013, 4: 2048. Bibcode:2013NatCo...4.2048K. PMID 23807025. doi:10.1038/ncomms3048 . hdl:2123/11211 . 
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  31. ^ Davis, Devra Lee; Gottlieb, Michelle and Stampnitzky, Julie; "Reduced Ratio of Male to Female Births in Several Industrial Countries" in Journal of the American Medical Association; April 1, 1998, volume 279(13); pp. 1018-1023
  32. ^ CIA Fact Book. The Central Intelligence Agency of the United States. (原始内容存档于2007-06-13). 

延伸閱讀

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外部連結

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