While causal factors are not identified, the study ([1]) concludes that the decline is due to environmental factors, and neither to genetics nor to other family

While causal factors are not identified, the study ([1]) concludes that the decline is due to environmental factors, and neither to genetics nor to other family-related causes. [1] https://www.pnas.org/doi/10.1073/pnas.1718793115 https://www.pnas.org/doi/10.1073/pnas.1718793115