"On November 16, 2006 Science Daily published scientific test results demonstrating that Neanderthals and ancient humans probably did not interbreed. Scientists with the U.S. Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) and the Joint Genome Institute (JGI) sequenced genomic nuclear DNA (nDNA) from a fossilized Neanderthal femur. Their results more precisely indicate a common ancestor about 706,000 years ago, and a complete separation of the ancestors of the species about 376,000 years ago. Their results show that the genomes of modern humans and Neanderthals are at least 99.5-percent identical, but despite this genetic similarity, and despite the two species having cohabitated the same geographic region for thousands of years, there is no evidence of any significant crossbreeding between the two."
Of course this makes sex with monkeys even less probable. In fact, Dave Chapelle once pointed out that AIDS could not have come from someone having sex with monkeys, because anyone who would have sex with a monkey, probably doesn't have sex with woman. Yet there has been experiments by a Russian scientist in the past:
"Dr. Il'ya Ivanov was a world-renowned expert on veterinary reproductive biology, but he wanted to do more in life than breed fatter cows. So in 1927 he traveled to Africa to pursue his vision of interbreeding man and ape. Thankfully his efforts weren't successful. To a great degree this was due to the native staff of the West Guinea research facility where he worked, from whom he constantly had to conceal the true purpose of his experiments. If they had found out what he was really doing, he wrote in his diary, "this could have led to very unpleasant consequences." The necessity of carrying out his work in secrecy made it almost impossible to do anything, although he did record two unsuccessful attempts to artificially inseminate female chimpanzees with human sperm."
He eventually tried to implant an orangutan embryo into a human womb, but the ape (Tarzan) died before the experiment could be performed, and he was sent to prison.
Still, sex with monkeys is probably more pleasant than sex with Bruchid beetles, at least for females. In this species the males unfurl an impressive penis covered with spikes and impales the female's reproductive tract. The female tries to kick the male to end copulation early and minimize damage. However she does get something out of it, she uses the copious amount of ejaculate to rehydrate and nourish herself. So the perfect female in beetles likes it quick and swallows...
In humans, kissing may also be a way for females to rehydrate: "Males, however, were more likely than females to initiate open mouth kissing and kissing with tongue contact. The researchers speculate that the exchange of saliva during kissing may have biological consequences in its own right. Male saliva contains measurable amounts of the sex hormone testosterone which can affect libido."