Rupert Sheldrake- "Richard Dawkins Comes To Call"
Dawkins is a highly intelligent scientist and skilled author. He also can be an outright reptile and others (such as Richard Milton) have experienced his lack of personal ethics - in matters of science and freedom.
As in most of life, you take the good with the bad.
His take on the speed of light changing over time is interesting but I don't find compelling, maybe a good physicist can explane the answers to this appearent fluctuation? Or perhaps before that can even be broached we need to find out why the speed of light is a constanst in our universe.
I'm not a physicist, but remember enough from my college physics days to know that his complaint about gravity measurements is baseless, as it's considered as a constant Worldwide simply for ease of calculations: gravity is going to vary, depending on where you are in the World since it's dependent on the mass underneath your feet at any given location and even changes with time. As such, it's going to vary (increasing when there's greater mass of the mountain underneath, but decreasing due to greater altitude, decreasing due to composition of the rock underneath with less dense material pulling, etc). Gravity will change due to shifts or flows in the Earth's liquid core, etc, just as the Earth's magnetic field is constantly changing.
However, those fluctuations in gravity are known to occur, and are considered insignificant for most applications (and any applications where it ISN'T appropriate to use a constant will require use of a special device capable of generating local gravitational readings in real-time: gravimeters).
So while it's interesting to ask the question, it's hardly compelling, if that's going to be the entire basis of his approach.
If he's got a reason to suggest WHY we need to be measuring it more closely, he's perfectly capable of making his case and offer a specific hypothesis of what we're missing by not measuring it more accurately than it is currently being done. However, blind witch-hunts and gut feelings (hunches) are NOT compelling arguments in scientific inquiry: developing hypotheses is. A scientist needs to collect sufficient compelling anecdotal evidence together, and need to suggest to other scientists WHY they should look for something. His suggesting "to look for dark matter" is well outside his area of expertise and strikes me as talking outside of one's backside orifice.
I looked briefly at his credentials on his website, and I have no idea why someone who's PhD and research was in the field of botany is working in the field of paranormal research, or asking about questioning from theoretical physics except (allow me to hypothesize) it's probably MUCH harder to find an audience interested in reading about plant hormones in botany, and much easier to find an audience of laypersons interested in reading about pseudo-sciences like the paranormal and telepathy, esp from a scientist who is willing to "tickle their ears" (tell them what they want to hear). The guy strikes me a bit as a sly ear-tickler.