Answer to Question 1
If a researcher joined a group without telling the members that they were being studied, those members might form friendships with the researcher and feel violated when they discovered the truth. In addition, the people in the group might engage in behaviors that they didn't feel comfortable doing in the presence of an outsider, so their privacy may be invaded.
Answer to Question 2
If the behavior being observed is public behavior, there are few ethical concerns about studying those people engaging in those behaviors. If the behavior is not considered public (even if it occurs in a public location), there are ethical issues concerning invasion of privacy.
In the research by Humphreys, you could argue that the research was ethical because the men who engaged in the sexual behavior did so in a public area and with anybody who happened to be there. As such, you could say that they had no real expectation of privacy if they didn't care who participated with them.
On the other hand, you might argue that sexual activity, even if anonymous, is a fundamentally private act. Even though it took place in the rest room of a public park, the men engaged in the behavior were simply using a convenient area, but that the act was still a private act. So the researcher was invading their privacy.
This 11-month old girl demonstrates one of the abilites of a child of this age group - creating a to
Stroke Risk Factors
A good disinfecting solution you can make yourself consists of 1 part bleach to 10 parts water.
Structures of the ionized forms of some representative fatty acids (part 2)
Breakup of the Larsen B Ice Shelf (part 2)
Annotation of a DNA sequence containing part of the human beta globin gene