And howsoever the matter we speak of is abominable, yet it is not fruitlesse, but helps much to the knowledge of some other things in the searching out of the secrecies of nature.
—Giambattista della Porta
Natural Magic, 1658
Many people are convinced that human hybrids, that is, hybrids involving human parentage, do not exist (other than ancient hybridization between various members of the genus Homo), and that they cannot exist. But it’s a head-in-the-sand mentality, given that there is actually quite a bit of evidence to the contrary (multiple eyewitness reports, videos, and even specimens). Perhaps it’s just that many people feel more comfortable denying the very possibility of such things than they do discussing the evidence of their existence. Obviously, the manner in which such things would come into being, would involve acts that would violate longstanding cultural and ethical taboos, something that most people simply do not wish to discuss. And yet, such information has great relevance not only for biology, but for humanity as a whole.
As indicated by the reliability arrow, the various types of human hybrids listed at right occupy a continuum between fact and myth. Some, such as pig × human or cow × human are closer to fact. Others, like bear × human and horse × cat lie closer to myth.
Wikipedia states the following:
The Kinsey reports rated the percentage of people who had sexual interaction with animals at some point in their lives as 8% for men and 3.6% for women, and claimed it was 40–50% in people living near farms [Laws and O'Donohue 2008, p. 391], but some later writers dispute the figures, because the study lacked a random sample in that it included a disproportionate number of prisoners, causing sampling bias. Martin Duberman has written that it is difficult to get a random sample in sexual research, and that even when Paul Gebhard, Kinsey's research successor, removed prison samples from the figures, he found the figures were not significantly changed.
By 1974, the farm population in the USA had declined by 80 percent compared with 1940, reducing the opportunity to live with animals; Hunt's 1974 study suggests that these demographic changes led to a significant change in reported occurrences of bestiality. The percentage of males who reported sexual interactions with animals in 1974 was 4.9% (1948: 8.3%), and in females in 1974 was 1.9% (1953: 3.6%). Miletski  believes this is not due to a reduction in interest but merely a reduction in opportunity.
Human Origins: Are we hybrids?
On the Origins of New Forms of Life
Cat-rabbit Hybrids: Fact or fiction?
Georges Cuvier: A Biography
Prothero: A Rebuttal
Branches of Biology