Short answers, pulled from the story.
Literacy is the ability to read and write, and illiteracy is the inability to read and write. Researchers often split its study at 1950: before 1950 literacy meant understanding the meanings of words, while after 1950 it widened to include the social and cultural aspects of reading and writing and functional literacy. Definitions from UNESCO, the OECD, and others now include digital materials, numeracy, and varying contexts.
The ancient Sumerians invented writing in southern Mesopotamia between 3500 BCE and 3000 BCE, driven by the need to manage information from trade and large scale production. Script is thought to have developed independently at least five times in human history, in Mesopotamia, Egypt, the Indus civilization, lowland Mesoamerica, and China.
The worldwide adult literacy rate reached 86.2% in 2015, up from 55.7% in 1950, rising by an average of 5 percentage points every decade. Despite this, the number of illiterate adults was 745 million in 2015, still higher than the 700 million recorded in 1950 due to population growth.
About two-thirds, or 63%, of the world's illiterate adults are women, according to 2015 data from the UNESCO Institute for Statistics. Sub-Saharan Africa has the widest gender gap, where 52% of adult women and 68% of adult men are literate. Social barriers, household work expectations, and early marriage all reduce literacy among women and girls.
There are competing views. Classical scholars such as Ignace Gelb credit the Ancient Greeks with the first alphabetic system around 750 BCE, while many scholars argue the ancient Semitic-speaking peoples of northern Canaan invented the consonantal alphabet as early as 1500 BCE. Social anthropologist Jack Goody documented both interpretations.
Educational attainment does not perfectly correlate with literacy. Literacy tests show that 90% of second-grade students in Malawi, 85.4% in rural India, 83% in Ghana, and 64% in Uganda cannot read a single word, even though they attended school. In Greece six years of primary education counts as literate, while in Paraguay only two years is required.