This paper presents a mechanism-based, cross-taxa framework linking environmental degradation to declining reproductive coherence via endocrine boundary disruption. Drawing on well-established evidence from aquatic organisms, amphibians, and humans, it argues that chronic exposure to endocrine-disrupting compounds (including pharmaceuticals, pesticides, PFAS, and plastic-associated chemicals) softens hormonal gradients and developmental timing gates rather than inducing novel biological forms. Fish and amphibians are treated as high-sensitivity early-warning indicators due to direct environmental exposure and short life cycles, with human outcomes interpreted as buffered, downstream effects. The work is explicitly non-stigmatizing, measurement-first, and Gaia-aligned, offering falsifiable predictions and clear pathways for remediation-focused policy and research. Keywords endocrine disruptionfertility declineenvironmental degradationboundary conditionsdevelopmental coherenceaquatic bioindicatorsepigeneticspopulation biologyGaia systemsreproductive biology