What are the origin and development of life writings?
This is a very wide question and one that I can only give you some initial thoughts about. It is the subject of books. However, the sometimes reliable Wikipedia has some good pages on the development of life writing, most widely known as biography.
The genre (text type) perhaps came to prominence with the Roman author Plutarch's Lives in which he outlined the life stories of prominent Romans of the past.
In Western Europe, the medieval period saw a number of narratives of lives, particularly as they related to spiritual life. The Book of Margery Kempe has a claim to be the first autobiography (i.e. life writing written by the person whose life is being described and one of the first works of the period written by a woman. Similarly Julian of Norwich's Revelations of Divine Love (also, confusingly, written by a woman despite the name) has strong autobiographical elements about her religious experiences and visions.
The modern biography might, arguably be said to have its origins in the work of James Boswell whose The Life of Samuel Johnson tells the life of one of the most celebrated men of the age, Dr Samuel Johnson, author of the first modern dictionary in English amongst other claims to fame.
The lines between fiction and biography have become interestingly and creatively blurred in much modern writing. Fictional writing in the nineteenth century often took on the form of fictional biographies, tracking the development of a life over a long period such as Dickens' Oliver Twist, which attempted to do just this.
Novels like AS Byatt's Possession deliberately meld the lives of fictional poets and their works into the fabric of fictional narratives, such as in the creation of Randolph Henry Ash, one of the characters within her novel who bears a striking similarity to the real Victorian poet, Robert Browning, and is conjectured by Byatt to have had an extra-marital affair. Conversely, post-modern authors like Kurt Vonnegut often include details of their own biography and, indeed, themselves, within otherwise fictional narratives such as the novelist's own appearance in the middle of his genre-defying biography/war/sci-fi novel, Slaughterhouse Five. Dave Eggers' A Heartbreaking Work of Staggering Genius is both wonderfully ironic in its title but also a genre-breaking work of autobiography, telling of the death of his parents six weeks apart from different cancers and the resulting choice to bring up his younger brother. The autobiography, however, skirts and plays with the bounds of fiction and realism in interesting ways that Eggers was later to approach in different ways when he wrote the 'true novels', based on the biographical accounts of migrants to the USA, most notably Valentino Achak Deng's story of his time escaping the civil war in Sudan and settling in the US in What is the What and Abdul Rahman Zeitoun's treatment as a Syrian American in the aftermath of Hurricane Katrina, recounted in Zeitoun.