Origin of the domestic dog or the result of natural introgression as the dog expanded across Eurasia. In 2018, a study found a small amount of dog ancestry in 62% of Eurasian wolf specimens looked at, that hybridization had occurred across a wide number of timescales and not just recently, however in contrast there was almost no admixture detected in the North American specimens. There was introgression of the male dog into the wolf, but also one hybrid detected which was the result of a male wolf crossed with a female dog. Wolves have maintained their phenotype differences from the dog, which indicates low-frequency hybridization.
Endangered Species Act of 1973 was a substantial cause of Congress instituting the ban and many non-DDT oriented actions were taken on their behalf under the Endangered Species Act (i.e. captive breeding, habitat protection, and protection from disturbance). As of October 28, 2012, there are 2,052 total (foreign and domestic) species on the threatened and endangered lists. However, many species have become extinct while on the candidate list or otherwise under consideration for listing. Species which increased in population size since being placed on the endangered list include: Opponents of the Endangered Species Act argue that with over 2,000 endangered species listed, and only 28