I'll have to admit that I created these, they reflect my worldview (or perhaps I should say universview), so I am probably guilty of loading the dice a bit. But I'll have a go anyway.
Imagine that in the not too distant future, travel between the Earth and the Moon or Mars is regular, as well as fairly safe and inexpensive. Observers discover, located North and South of the Earth's orbit -- for lack of a better way to describe that part of space -- but no further than Mars, hundreds or thousands of mumblephysics tunnels, that allow inexpensive transport to distant parts of the universe. When we start exploring we discover that the far end of most of these tunnels is a star system very much like the one where Earth is located, including an Earth-sized planet located in an orbit very close to 1-AU in mean size.
Further observation and exploration onto these planets finds that they all contains abundant plant, insect, and sea life, but few if any mammals or reptiles. However, when the first samples of these plants and animals are studied closely it is discovered that every spices found exists on the Earth, or was made extinct in the last few thousand years. The alien examples are discovered to be identical to their Earth counterpart down to the genetic code.
How will this lack of interstellar or intergalactic diversity be explained?
Imagine that tomorrow a litter of puppies are born which have much larger brains, opposable thumbs, and a larynx and mouth that makes them capable of human speech. As they grow, they quickly learn to speak and understand humans and are abnormally -- at least in terms of how humans act to other humans -- loyal and obedient. Then, within the next few weeks nearly every litter of puppies born in the world exhibit these same traits, but few if any are born in feral packs, or in other canid spices closely related to the domestic dog.
How will this sudden evolutionary jump be explained?
I've often thought of the first experiment as an idea for a story or series of stories. Actually, I'd be more interested in telling the stories of how these worlds were used by the population of Earth and how a new society would develop then in telling the story about the academic arguments. I also proposed this as a panel idea for ConSecration, and it still might work as a panel topic with the right panelists and moderator.
I used the term "mumblephysics tunnels" to avoid having to deal with any preconceived ideas about these kind of connections. I used "mumblephysics" instead of the more common "technobabble" since I wanted to be clear that these tunnels were found, not created by human technology.
I could see the second one making an OK panel, but its probably a bit too weighted towards one side. Frankly, if this happened, I would not be the first one claiming that it was a miracle or proof of God's existence; and I'd probably not completely believe it was happening until it was very strongly verified.
I apologize for any remaining spelling errors. I large number of words in this post are either so badly misspelled that TextPad's spelling checker cannot find them, or are missing from its dictionary.