Uncovering the primate clitoris

所有雌性哺乳动物都有阴蒂。阴蒂在性唤起、性快感和性高潮中起着至关重要的作用。然而，我们对这种结构及其演变过程知之甚少。人类阴蒂的“豌豆大小”的外部部分只是冰山一角：90%的结构隐藏在皮肤下。人类阴蒂的这些细节直到最近二十年才被揭示出来，随后使用了医学成像技术，如MRI和X射线CT。我们对灵长类动物阴蒂的了解更少。虽然在许多物种的女性生殖器周围有独特的皮肤表皮，但我们对阴蒂的内部解剖几乎一无所知。有多少神经末梢存在？阴蒂在哪里最“敏感”？组织在觉醒时是如何改变形状的？如果没有其他灵长类动物提供的信息，我们就不可能理解是什么进化力量塑造了人类阴蒂的形状和功能，也不可能理解人类的性行为，这种缺乏理解的情况并不包括男性生殖器官。男性的阴茎是一种相当的结构，研究得比较充分。这可能反映了一种社会偏见，在历史上，女性生殖器被认为比男性生殖器更少变化，因此被忽视。这种片面性也可能与研究阴蒂的技术挑战有关。与男性生殖器相比，女性的组织通常很小，精致，并且隐藏在视线之外。然而，生物成像技术的最新进展确保了这些障碍现在可以被克服。在这个项目中，我们将开发研究灵长类阴蒂的新方法。它们将使我们第一次了解阴蒂的结构，从大体解剖到微观特征，贯穿灵长类动物的家谱。尸体将来自苏格兰国家博物馆，这是英国动物园动物死亡的主要储存库。雌性样本包括狐猴、洛里斯、绒猴、猕猴、长臂猿和猿。需要对会阴区进行正中解剖，以描述阴蒂解剖结构，并在不损伤组织的情况下提取组织进行进一步分析。解剖指南只适用于人类尸体，因此解剖将是非常新颖和探索性的。一旦解剖出来，阴蒂组织将被切成非常薄的切片，用染料染色，并在显微镜下观察，这一过程称为组织学。这些“薄切片”将用于记录神经末梢的数量及其在阴蒂几个区域的分布。为了更好地了解灵长类阴蒂的3D形状，将对其他尸体的骨盆区域进行X射线microCT扫描。这将允许对整个阴蒂（包括隐藏的组织）进行非破坏性的“虚拟解剖”，通过确保阴蒂在动物的骨盆区域内保持不受干扰，使我们能够更好地了解其形状和功能。由此产生的模型将是有史以来第一次瞥见灵长类阴蒂的3D结构和形状，超越了我们目前对人类女性的有限了解。已经建立了从高度珍贵的博物馆标本中提取这种有价值的信息的可行性，拟议的项目将为进一步的研究开辟几条途径。在哺乳动物中，生殖最终需要雄性和雌性生殖器的直接相互作用。雌性和雄性生殖结构应该一起进化的观点被普遍接受，但值得注意的是，从未在我们的近亲灵长类动物中得到过检验。利用该项目开发的技术，未来的研究将探索灵长类动物生殖器的大小和形状，以及性行为中男性和女性解剖结构之间的相互作用。这些进展将彻底改变这一群体的性选择研究，并改变我们对人类生殖器和人类性行为自然历史的理解。

All female mammals have a clitoris. The clitoris plays a vital role in arousal, sexual pleasure, and orgasm. Yet we know very little about this structure and how it has evolved. The 'pea-sized' external part of the human clitoris is just the tip of the iceberg: 90% of the structure lies hidden under the skin. Such details of the human clitoris were only revealed in the last two decades, following the use of medical imaging technology, such as MRI and X-ray CT. Even less is known about the clitoris of our closest kin, the primates. Whilst distinctive skin swellings around the genitals have been documented in females of many species, we know almost nothing of the internal anatomy of the clitoris. How many nerve endings are present? Where is the clitoris most 'sensitive'? How might tissues change shape during arousal? Without this information from other primate species, it is impossible to understand the evolutionary forces that have shaped the form and function of the human clitoris, nor human sexual behaviour.The lack of understanding does not extend to male reproductive organs. The equivalent structure in males, the penis, is comparatively well-studied. This may reflect a societal bias, where female genitalia were historically thought to be less variable than male counterparts and therefore overlooked. This one-sidedness may also relate to technical challenges associated with studying the clitoris. Compared to male genitals, female tissues are often small, delicate, and hidden from view. Recent advances in biological imaging, however, ensure these hurdles can now be overcome.In this project, we will develop new methods for studying the primate clitoris. They will allow us, for the first time, to understand the structure of the clitoris, from gross anatomy to microscopic features, across the family tree of primates. Cadavers will come from the National Museum of Scotland, which is the main repository for deceased UK zoo animals. Sampled females will include lemurs, loris, marmosets, macaques, gibbons, and apes. Meticulous dissection of the perineal region will be required, to both describe the clitoral anatomy and to extract the tissues without damage for further analysis. An anatomical guide exists only for human cadavers, and dissections will therefore be extremely novel and exploratory.Once dissected out, the clitoral tissue will be sliced very thinly, stained with dyes and viewed under a microscope, a process referred to as histology. These 'thin sections' will be used to document the number of nerve endings and their distribution across several areas of the clitoris. To better understand the 3D shape of the primate clitoris, the pelvic regions from additional cadavers will be x-ray microCT scanned. This will allow for a non-destructive 'virtual dissection' of the whole clitoris (including the hidden tissue), allowing us to better understand its shape and function by ensuring clitoris remain undisturbed within the animal's pelvic region. The resulting models will be the first ever glimpse into 3D structure and shape of the primate clitoris, beyond our currently limited understanding of human females.Having established the feasibly of extracting such valuable information from highly prized museum specimens, the proposed project will open several avenues for further research. In mammals, reproduction ultimately requires the direct interaction of male and female genitals. The idea that female and male reproductive structures should evolve together is generally accepted and yet, remarkably, has never been tested in our closest relatives, the primates. Using the techniques developed in this project, future research will explore the size and shape of primate genitals, as well as interactions between male and female anatomy during sex. These advances will revolutionise the study of sexual selection in this group and transform our understanding of the natural history of human genitalia and human sexuality.