Final answer:
The food-competition hypothesis for giraffe's long necks was widely accepted without testing due to its plausibility and alignment with Darwin's theory of natural selection, which was supported by other observations and experiments.
Step-by-step explanation:
The food-competition hypothesis, explaining why giraffes have long necks, was widely accepted without testing because it seemed so plausible. According to the hypothesis, giraffes with longer necks could reach leaves that other giraffes could not, thereby having a survival advantage and passing on the long-neck trait to their offspring. This theory aligns with Darwin's theory of evolution by natural selection, where those with advantageous traits are more likely to survive and reproduce.
However, previous hypotheses, such as the one suggesting animals that stretch their necks will grow longer necks, were discarded due to experiments showing that stretching muscles doesn't cause bones to grow nor changes DNA. Eventually, the food-competition hypothesis became the prevailing theory without rigorous testing because the concept of natural selection was already supported by other observations and experiments, like Darwin's work on the giant tortoises in the Galápagos. The content loaded into the scientific community regarding giraffe's neck evolution was that natural selection most likely played a key role, and thus for many years, no one questioned this assumption to further test the food-competition hypothesis.