This question is totally pointless.
People do not specialized in just manual or just manual testing. All developers do both. However, well establish practice is to employ people for testing and for development separately. Nevertheless,
both categories of workers participate of all kind of testing, but perhaps from different points of view and to different extent.
For better understanding, please read this:
Joel Spolsky,
Top Five (Wrong) Reasons You Don't Have Testers,
http://www.joelonsoftware.com/articles/fog0000000067.html[
^].
—SA