What does the phrase the dominate primordial beast was strong in buck mean​

Read the excerpt from the common sense of bicycling: bicycling for ladies. the bicycle is capable of such high speed that there is a strong temptation to ride so fast as to cause over exertion or excessive perspiration. on the other hand some people ride too slow, causing a zigzag and uncertain movement. while exercising reasonable caution, be a fearless rider. when you come to a steep hill, if the road is clear, let it go as fast as it will. if you rid yourself of that ghost of fear, coasting is one of the greatest delights of cycling. which is the best paraphrase of the text?