Actually, to all objective appearance, true!
While fraud is indeed not uncommon in biomed fields, psychology, and even some fields in technology or the physical sciences, it is almost entirely unknown (insofar as committed by researchers, as opposed to, say, Chinese fossil merchants) in evolutionary biology, paleontology and so on. After nearly one hundred years, Piltdown remains the only real case of intentional fraud that may have been committed by a research scientist in a field related to evolutionary science. (Even this is not certain as the identity of the hoaxer is not certain.)
BTW, I don't think this reflects any generally higher moral character on the part of scientists working in fields related to evolution. As usual it's a case of "follow the money". Bioscience is were the most money is, and where the most fraud is as well.
An interesting observation. In commercial science ther is the possibility of scoring some fast bucks. In academic science, the only real reward is in the hope that your work will be a lasting contribution to the total body of knowledge. As such, there is little incentive for fraud.
There have been several frauds -- the midwife toad stands out, but these have been exposed so quickly that the hoaxer got little benefit.