为什么只有男人有小鸡鸡？

男性的小鸡鸡是他们身体中一个特殊的器官，与其它生物相比较常见。这个问题涉及到生物学和进化学的知识，以及性别差异的起源和演化。

生物学角度来看，男性和女性在生殖器官上有着明显的差异。男性的小鸡鸡是一种外部生殖器官，用于尿液排出和性交。然而，女性则没有这样的结构。这是由于在生物进化的过程中，不同的性别发展出了不同的生殖策略和特征。雄性的小鸡鸡是该策略的结果，为了最大限度地传播自己的基因。

在人类进化的历史中，雄性通过尺寸和形状的多样性来吸引雌性。因此，人类男性的小鸡鸡变得更加突出，并且有着不同的大小和形状。这是一种进化上的竞争策略，目的是吸引潜在的伴侣，并增加后代的数量。这也解释了为什么人类男性在性成熟之后，小鸡鸡会变得更加明显。

英文翻译对照 (English Translation):

Why do only men have penises?

The male penis is a unique organ found in their bodies, which is relatively common compared to other organisms. This question involves knowledge from biology and evolutionary science, as well as the origin and evolution of gender differences.

From a biological perspective, males and females have distinct differences in their reproductive organs. The male penis is an external genitalia used for urination and sexual intercourse. However, females do not possess such a structure. This is due to the development of different reproductive strategies and features between genders during biological evolution. The male penis is the result of this strategy, aiming to maximize the spread of their own genes.

Throughout the history of human evolution, males have attracted females through diversity in size and shape. As a result, the human male penis has become more prominent and varies in size and shape. This is an evolutionary competition strategy aimed at attracting potential mates and increasing the number of offspring. It also explains why the male penis becomes more noticeable after reaching sexual maturity.