Skepticism about the existence of ancient asexual animal taxa such as bdelloid rotifers persists, partly because asexuality is supposedly based on “negative evidence”, and partly because the long-term survival of asexuals is believed to be an extraordinary and inexplicable “evolutionary scandal”. However, this skepticism is unfounded for two reasons. First, it is true that the failure to detect sexual individuals in a species or taxon is negative evidence, and we cannot rule out the possibility that future samples will include sexuals. But we can conclude that the probability is very small, and negative evidence is widely used to draw statistically sound inferences in science as well as in everyday life. When sexual individuals are rare, the Poisson distribution describes the probability of observing a particular number of sexual and asexual individuals in a sample. When no sexuals have been observed in a sample of n individuals, the 95% confidence interval of the frequency of sexuals ranges 0 to 3.7/n. A very large number of bdelloid rotifers have been examined at high magnification without finding any with sperm, i.e. no males or hermaphrodites. The real frequency of sexual individuals must then be extremely low. If there are separate sexes, the probability of a male encountering a female is so low that sex will be of little effect and is likely to be lost by mutational pressure and/or selection. Sex will likewise be of little effect if the sexual individuals are selfing hermaphrodites. Second, ancient asexuals could only be considered “scandalous” if they were either extreme outliers in a frequency distribution of the ages of asexual lineages, or were theoretically inexplicable. But although asexual animal lineages tend to be limited to individual species or genera, the ages of most of those taxa is unknown, and hence the age distribution of asexual lineages is unknown. Thus we cannot know whether bdelloid rotifers are truly exceptional. Moreover, although theory predicts that asexuals should have a higher extinction rate than sexuals, the parameters are seldom known with any accuracy so the theory cannot be used to make predictions about the expected mean and variance of the ages of asexual lineages. Moreover, it is always possible that the ancient asexual groups have advantages that may outweigh the disadvantages of asexuality.