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中間性
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導言 |
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生物學註腳：植物與動物
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在詳細討論人類的中間性之前，至少對較低等動物的“雌雄同體”投入匆匆一瞥可能是有用的。在自然界，存在著既擁有雌性性器官也具有雄性性器官的植物或動物物種，它們借此而增加了繁殖的機會。生物學家稱這些生物物種為“雌雄同體的”生物。除了數也數不清的雌雄同體的植物以外，也存在著許許多多的雙性動物，尤其在無脊椎動物和魚類中這種雙性動物更多。某些雙性動物既能夠作為雌性也作為雄扮演角色和繁衍後代，其他的雙性動物則在條件許可時或需要時，改換它們的性別。這就是在我們這個星球上龐雜的生命多樣性的另一個事例。在此不妨試舉幾例：
- 扁形動物門(phylum
Platyhelminthes)的渦蟲既能發揮雌性動物的作用也能執行雄性動物的職責，既能產生卵子也能射出精子到它的交配物件體內。它們這些輪換的功能既是執行著雌性的也是扮演著雄性的角色。
- 一種叫Hypoplectrus的魚在一個場合能夠作為雄性發揮作用，然後在其他的場合作為雌性產生魚卵。
- 巨大硬鱗(black
sea bass)在幼年可以是雌性，可是隨後就可以轉變成雄性。
- [(中國大陸讀者比較熟悉的魚類黃鱔，其生殖腺從胚胎到成體都是卵巢，只能產卵。但是，一旦產卵完畢，其卵巢逐漸轉化為精巢，產生精子。這種從雌到雄的轉變，在生物學上稱為性逆轉(sex reversal)。——譯者注]
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從左起：1.
扁形動物門(phylum
Platyhelminthes)的渦蟲[自然大小：約4cm(約1.5英寸)]；
2.一種叫Hypoplectrus 的魚；3.
巨大硬鱗
From the left: 1. The flatworm phylum
Platyhelminthes (natural size: ca. 4cm/1.5
inches)
2. The fish Hypoplectrus 3. The black
sea bass
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然而，當我們將目光投向較高的進化階梯時，發現這種有益的雌雄同體漸漸變得罕見起來。在哺乳動物，雌性與雄性特徵在同一個個體存在的現象是異常的和成問題的性發育狀態。對於家畜飼養者再熟悉不過的最好例子是：所謂的雄化牝犢(freemartin)是雌性牛犢，她在出生之前與其雄性孿生犢共用著一定劑量的某些激素。這些“使雌性動物雄性化”的激素足以抑制她的雌性性器官的正常發育。其結果幾乎總是導致不孕。然而，牛犢的孿生現象不會經常發生。
在此很少的舉例想必足以有了說服力。以下的內容將闡述人類的中間性。
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Intersexuality - Introduction
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Biological Footnote: Plants and Animals
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Before discussing human intersexuality in more detail, it may be useful to cast at least a cursory glance at “hermaphroditism” in lower animals. There are plant or animal species that possess both female and male sex organs and thereby increase their chances to reproduce. Biologists call these species “hermaphroditic”.
In addition to countless hermaphroditic plants, there are many double-sexed animals, especially among the invertebrates and fish. Some can act and reproduce as either females or males, others change their sex as the situation allows or requires. This is another example of the enormous diversity of life on our planet. To give just a few examples:
- The flatworm phylum Platyhelminthes can function as either a female or male, producing eggs or inserting sperm into his counterparts.These, in turn, can also act as females or males.
- The fish Hypoplectrus can act as a male and release sperm in one instance and then, in the next instance, act as a female and release eggs.
- The black sea bass may start life as a female and then turn into a male.
However, as one moves higher on the evolutionary ladder, this useful hermaphroditism becomes increasingly rare. In mammals, the existence of both female and male characteristics in the same body is an atypical, problematic development. The best example is well known to cattle breeders: The so-called
freemartin is a female calf that, before birth, shared certain hormones with its male twin. These “masculinizing” hormones were enough to prevent the normal development of its female sex organs. The result is almost always sterility. However, twinning in cattle does not occur very often.
These few reminders must suffice here. The following text restricts itself to human intersexuality.
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