I need an explanation for this Sociology question to help me study.

Memo 2: due January 29
What does the concept of “migrant selectivity” mean? What factors influence migrant selectivity and how might migrant selectivity change over time.

For the short memos, I would like you to respond to each question with a coherently organized, logically argued essay of 300-500 words in length. Each question can be adequately answered, relying on assigned readings and lectures; no outside reading is required. However, please make sure to accurately cite any source that you use. Each essay must be typed and properly edited (such that spelling and grammar are correct).

According to 3 readings then write this memo.