This is not the only surprise for evolutionists. Recent research has found that these adaptations are controlled by different genes. That surprised evolutionists because they expect the same genes would control the same changes in related species. A basic prediction of evolution is that related species should be genetically similar, because they have been evolving independently for only a relatively short period. But this expectation is routinely contradicted by biology, which seems to be unaware of the theory of evolution.
Another interesting example of this in stickleback fish are the sex-determination genes, which are located on different chromosomes in different species. As one evolutionist admitted:
This is very surprising because these species are fairly closely related.
Evolutionists believe that significant differences such as these must have somehow evolved. Evolutionists may not have a clear or compelling explanation for how or why the change came about, but not surprisingly, they believe evolution did the job. Since these differences do not fit the evolutionary expectation, they are viewed as anomalies, whereas the similarities that are expected are viewed as more informative of evolutionary relationship. It is the latter, not the former, that are more often used when evolutionists create their evolutionary trees.
This pre screening of data is known as confirmation bias. It is a well known tendency in science. Proponents of a theory are less likely to dwell on, or perhaps even acknowledge, contradictory data. Those data are viewed as outliers. This is one reason why objective theory evaluation is difficult. Don't expect evolutionists to tell us one day that their theory may not be a fact after all, even though that is what the science tells us.