Oooer, I hadn't counted on someone agreeing with me, partially at least. What follows may be wildly inaccurate and meandering but, whatever.
The belief in an afterlife usually relies on a spiritual or religious belief. Religions started because people couldn't explain the world around them so they invented myths and gods to push they sun around the sky and such.
If you believe in an afterlife you'll probably believe than it's something other than your physical body that survives into the next life. A soul perhaps.
I believe (and there's some scientific evidence, but I can't remember what) that the soul is just another explanation for a concept we don't fully understand, consciousness. We know that the brain isn't just a vessel for the soul and that there are specific centres for speech, motor control etc. So there must be an area for conciousness.
So if the physical brain can account for "the soul"; the same brain which will rot and decay; I don't think it leaves much room for an afterlife.
Well, I hope that makes sense for you because it doesn't for me