The Challenge Hypothesis was developed to explain why and how regulatory mechanisms underlying patterns of testosterone secretion vary so much across species and populations as well as among and within individuals. The hypothesis has been tested many times over the past 30 years in all vertebrate groups as well as some invertebrates. Some experimental tests supported the hypothesis but many did not. However, the emerging concepts and methods extend and widen the Challenge Hypothesis to potentially all endocrine systems, and not only control of secretion, but also transport mechanisms and how target cells are able to adjust their responsiveness to circulating levels of hormones independently of other tissues. The latter concept may be particularly important in explaining how tissues respond differently to the same hormone concentration. Responsiveness of the hypothalamo-pituitary-gonad (HPG) axis to environmental and social cues regulating reproductive functions may all be driven by gonadotropin-releasing hormone (GnRH) or gonadotropin-inhibiting hormone (GnIH), but the question remains as to how different contexts and social interactions result in stimulation of GnRH or GnIH release. These concepts, although suspected for many decades, continue to be explored as integral components of environmental endocrinology and underlie fundamental mechanisms by which animals, including ourselves, cope with a changing environment. Emerging mass spectrometry techniques will have a tremendous impact enabling measurement of multiple steroids in specific brain regions. Such data will provide greater spatial resolution for studying how social challenges impact multiple steroids within the brain. Potentially the Challenge Hypothesis will continue to stimulate new ways to explore hormone-behavior interactions and generate future hypotheses.

挑战假说是为了解释为什么睾丸激素分泌模式的调节机制以及为什么在物种和种群之间以及个体之间和个体之间变化如此之大。在过去的30年中，所有脊椎动物群体以及一些无脊椎动物对该假设进行了多次验证。一些实验测试支持该假设，但许多实验却不支持。但是，新出现的概念和方法将“挑战假说”扩展并扩展到了潜在的所有内分泌系统，不仅控制了分泌，而且还控制了转运机制以及靶细胞如何能够独立于其他组织调节其对激素循环水平的反应性。在解释组织如何对相同的激素浓度做出不同反应时，后一个概念可能特别重要。下丘脑-垂体-性腺（HPG）轴对调节生殖功能的环境和社会线索的响应可能全部由促性腺激素释放激素（GnRH）或促性腺激素抑制激素（GnIH）驱动，但问题仍然存在社交互动会刺激GnRH或GnIH释放。这些概念尽管被怀疑了数十年，但仍被继续作为环境内分泌学的组成部分进行探索，并成为动物（包括我们自己）应对不断变化的环境的基本机制的基础。新兴的质谱技术将产生巨大的影响，从而可以测量特定大脑区域中的多种类固醇。这样的数据将为研究社会挑战如何影响大脑中的多种类固醇提供更大的空间分辨率。