Does this 1250-words text have any problems?

Job ID: 31830361

Budget: $10 – $30 USD

This introductory text on psychology was already edited by the native speaker but then a couple of MINOR changes were made.
I need a native speaker, the professional to check, discuss and EDIT every problem he would find with grammar, commas and other punctuation, British spelling, sentence structure, clarity, etc.
Do you see many problems in the sample below?