Originally Answered: Examples of observed single-cell to multi-cell evolution?
I was going to give the example of volvox, but bigGourami scooped me.
Other examples would be the slime mold amoeba, that is able to congregate into a multicellular body ... a growing stalk with a fruiting body at the top that releases haploid spores into the air.
Or the porifera (sponges). You can take a sponge, put it through a sieve that breaks it up into single cells, and it will reassemble into a new sponge on the other side.
For more example, look up "colonial organisms." These show species in that critical stage of evolution between single-celled and multicellular organism. I.e. they can survive just fine as single cells, but find advantage in organizing together into *colonies* and taking on specialized roles in those colonies.
But Creationists would just argue ... "but those aren't *evolution* ... the organism already exists that can do that. "
And this shows you the bogosity of the argument.
Evolution is, by definition, slow. Really slow. It took almost 3 *billion* years for single-celled organisms to give rise to the first multicellular organisms. So why on earth would someone say that evolution hinges on being able to "observe" this occur again within the blink of an eye of a human lifetime?!
To put this in perspective, it takes a star about 1 *million* (not billion) years to form ... so imagine someone demanding to see the formation of a star "observed directly". You would argue that we can directly observe stars in various *stages* of forming, but it is unreasonable to demand to see a process we know to take 1 million years, to occur in less than 100 years (within the observable span of a human being).
The evolution of multicellularity is about 3,000 times *slower* than the formation of a star.
And that is precisely why Creationists think the "it's still a cow" argument is brilliant! Because they are demanding to see something that they know evolutionists can't produce ... reproducing millions of years of evolution, within the blink of an eye of a human lifespan ... and they will accept nothing less or they refuse to call it "directly observed".
And that is precisely why the argument is so bogus. It says that any process that cannot occur within the span of less than 100 years, cannot be "directly observed", and therefore can be said to not occur at all.
But this is an argument that pretty much rules out most of science. If anything that takes longer than 100 years to occur cannot be shown to have occurred at all, then this rules out the formation of stars, the erosion of beaches, the movement of glaciers, the changes in global climate (a favorite target), the formation of a fossil, the formation of a diamond, the formation of a mountain range, the evolution of languages, the history of civilizations, all paleontology (the study of fossils), astronomy, astrophysics, geology, archaeology, atmospheric science. Etc.
I.e. this "argument" eliminates most of science.
An example I give is the "birth" of a 100-foot oak tree. Nobody has ever "directly observed" an oak tree being "born" from an acorn, because this process can take several hundred years ... longer than a human lifespan. So it would be bogus to say that since we cannot "directly observe" something that slow, we may as well conclude that it doesn't occur *at all*.
So how do we know about the birth of oak trees, or diamonds, or stars, or species? By observing cases of the process *AS IT IS OCCURRING* and then extrapolating from that. That is *BASIC* science ... but the Creationist will reject it because it is not "directly observed."