Natural Selection can be difficult to observe in natural populations. In the video linked below I examine a fascinating example of possible adaptation via natural selection of cliff swallows to the challenge of fast-moving vehicles in their environment. In the paper we will examine it was observed that over a period of 30 years, the number of road kill cliff swallows decreased dramatically despite population densities increasing more than 100%. What might account for this observed reduction in fatalities? It has been proposed that changes in the behavior or changes in physical characters of the birds are allowing them to escape collisions. Could the action of natural selection be involved in either of these possibilities and how might we be able to tell? There are many explanations we must exclude before concluding this is a solid example of natural selection in the wild and I examine some of those alternative hypotheses.
At the end of the video I have some discussion about how the fitness values of a trait can change in different environment and how the overall fitness of the organism is determined not by a single trait but the combination of all of its traits which can make measurement of natural selection on a single trait difficult in the wild populations in which there are so many variables at play.
Paper cited: https://www.sciencedirect.com/science/article/pii/S0960982213001942?via%3Dihub
Cover photo credit: Cliff Swallow Joe-Galkowski
Naturalis Historia 