Throughout history man has had to accept the fact that all living things must die 1. Why use has had to? Because new generations of people are being born all the time so they must continue to learn and accept this fact. It is a renewing, continuing learning and accepting cycle. The phrase "throughout history" emphasizes that this is an ongoing, never-completed process. 2. Why do not use has to? This is referring to the present only, which is incompatible with the phrase "throughout history". 3. Doesn't when the order of nature or law be decribed by the simple present tense? Read #1 and #2. "Throughout history" began in the past and continues into the future. Simple present tense cannot be used for this time span. Only present perfect tense can do this.

"During World War I/in 1976/on 26 August 2016, man had to accept the fact that all living things must die". "From the beginning of human history until now/today, man has had to accept the fact that all living things must die" "On 27/28 August, 2016 [whatever day it is where you are now], man has to accept the fact that all living things must die". "On 29 August, 2016, man will have to accept the fact that all living things must die".

Past + Present.....has had to