Having addressed human life as meaningful from the defining characteristics of the word ‘meaning,’ we now collate human life with the criteria for significance.
Magnitude – the requirement of sufficient importance or depth – likely is the criteria most skeptics would argue is not met by human life. But magnitude is relative, even subjective. One’s belief in the impact one has on others and on humanity seems sufficient for the attribution of ‘meaningful’; while if appears entirely arbitrary for someone else to discount that meaning. In any case, it seems preposterous to say no human life had sufficient effects to be meaningful 
– consider Jesus, Buddha, Confucius, Aristotle, Martin Luther, Da Vinci, Galileo, Darwin, Lincoln, Mother Theresa, Martin Luther King, and many more. While a bit more subtle, human contemplation of the universe, being, nothingness, infinity, and ultimate reality expand the magnitude of our existence in ways unavailable to other entities in the world.
Duration – the hope of enduring achievement or life – is another criteria skeptics question relative to humankind. Perhaps the existence of 7 billion humans on the planet makes our particular role in continuation of the species appear trivial. However on careful consideration, we see the possibility of the number of our descendants, for example two children who each have two children sequentially leads to 1000 individuals with some of our genes after 10 generations (about 300 years), about 1,000,000 individuals after 20 generations (about the year 2600), and 1,000,000,000 individuals after 30 generations. 
Meanwhile our actions and impacts on others directly and indirectly are magnified immeasurably over the infinite future. Each interaction with another person influences them, however slightly, in ways that influence others living and as yet unborn. More sublime is the infinite duration time imposes on existent beings, including us, in the countless moments that compose a lifetime, and the permanence of the space-time continuum.
Possibility – reasonable opportunity to achieve meaning – is perhaps the most easily defensible. Since magnitude is subjective and we can itemize historical persons who achieved meaning in their lives, it stands that this applies to most able-bodied, mentally sound people. Only the severely impaired can rationally doubt the possibility of a meaningful life, for the rest of us it is merely a question of whether we succeed or not.
Desirability of one’s actions – for oneself and for others or the greater whole – is not assured, but clearly rests on choices made out of wisdom and deliberation. In general ethical behavior, the pursuit of the good, and resistance to evil are the means to meet this criteria of a meaningful life.
Understanding – the recognition of one’s own meaning – is dependent only on one’s effort to decipher reality, display virtue, and analyze the results. At the end of the day, a thoughtful person with a meaningful life should recognize that fact. The examination of one’s life and environment is the means to achieve the highest level of certainty of one’s meaning.
In summary, in some way, even if not immediately known to us, most able-bodied humans can meet all of the defining characteristics of a meaningful being and can with effort meet the criteria of a highly significant life. In fact, to our knowledge, human life best meets these defining features and offers the greatest opportunity for meaning compared to any other entity known to us other than perhaps the universe itself of God should He exist.
