What do Jehovah's Witnesses believe about evolution? From Do Jehovah’s Witnesses Believe in Creationism? on jw.org:

No. Jehovah’s Witnesses do believe that God created everything. But we do not agree with creationism. Why not? Because a number of creationist ideas actually conflict with the Bible. Consider the following two examples:

Length of the six days of creation...the word “day” in the Bible can refer to a considerable length of time...
Age of the earth...Jehovah’s Witnesses have no objection to credible scientific research that indicates the earth may be billions of years old.

Although Jehovah’s Witnesses believe in creation, we are not antiscience. We believe that true science and the Bible are compatible.

Any mention of evolution is absent (which IMO is a bit surprising, considering the FAQ being answered).
Similar to Earth's age, would Jehovah's Witnesses also have no objection to &quot;credible scientific research that indicates&quot; life, including humans, evolved from simpler forms?
Or do they have a different belief?
I'll try to summarize some of the infos we can find in the JW.org site (wol.jw.org)

First, have a look at their Awake! 9/06 magazine, pages 9-10, the article titled "Did God Use Evolution to Create Life?" 

As a summary, it says that the Bible’s account of the creation of the first man, Adam, is to be taken literally. It also says that Jesus (and his disciples) took it as a true story.

Also this other article from their 1/1 2008 Watchtower magazine, titled "Is evolution compatible with the Bible ?", should interest you.