Your e-mail will thus appear as a post to the main course blog, and will be a contribution to its quality.
Your evaluative response should be five hundred words, give or take, and be engaging, scholarly, and balance a strong personal voice with an ear for a wider audience.
To adopt a jargon from Business, you should take a vertically-integrated approach to your post. Take a very narrow band of the full spectrum of primary material that we are studying, and present a vision that is bright and sharply-focused. Some piece of the material critiquing Darwin will stick in your mind, and use your thoughts to evaluate that one particularity and start out with some brief notes--in an email message pane, say--and save them while your ideas solidify, and then work them up in odd moments here and there, until you arrive at a firm and well-written evaluative post. And just email that off to the address given.The Lecturer will provide a written analysis and letter grade of the quality of your insight, argument and writing to you in class.
Send your post any day before the deadline: use the exigencies of your own schedule and your preference for analysis of your abilities and progress in the course as your guide.