Final answer:
There isn't an exact number for experiments testing Darwin's hypothesis on natural selection, as it's a broad and ongoing field of research. Studies like those of the Grants with Galápagos finches and genetic research contribute to this field. Modern efforts continue to expand our understanding of evolution and biodiversity.
Step-by-step explanation:
It is challenging to give an exact number of experiments conducted worldwide to test Darwin's initial hypothesis regarding natural selection, as this has been a field of ongoing scientific inquiry since the mid-nineteenth century. Charles Darwin and Alfred Russel Wallace independently conceived the actual mechanism for evolution by natural selection after their extensive expeditions. For example, Darwin's observations of the finches in the Galápagos Islands led him to propose that species are modified from original mainland species.
In a noteworthy long-term study, in the 1970s, biologists Peter and Rosemary Grant observed evolution by natural selection in Darwin's finches, with documented changes in beak sizes over the generations based on food availability. This study is one example of the numerous experiments and research projects that have taken place to support or test aspects of the theory of evolution by natural selection.
The incorporation of genetic research by scientists like Dr. Hebert and the discovery of new species add to our understanding of biodiversity and evolution, demonstrating the vibrancy of research in this field.