Darwin, in his Voyage of the Beagle, laid out the theory about the formation of coral reefs, and atolls in particular, forming and only growing in shallow, warm, oceans but growing upward as land subsided or oceans rose. His theory has largely been confirmed by evidence from boring deeply into Bikini and some other Pacific ocean coral islands. Over a thousand feet of coral rock could be found in some locations.
I expected the growth represented generation after generation growing on top of the previous generation. I thought some would get quite old by growing upward for a while, but I was surprised by the coral shown in the accompanying photo taken recently in the children's room of the Kalamazoo Public Library.
The photo shows skeletal part of a brain coral that appears to be growing from the middle of a similar coral underneath it. I was told it was donated by a local resident years ago after it had been collected in the Florida Keys region.
Below is a photo of a brain coral on the reef of Heron Island near the Southern end of the Great Barrier Reef. The green wavy line next to it is the exposed mantle of a giant clam.
Corals and sponges are examples of invertebrates that could continuously grow upward as a reef sinks so that essentially the same organism remains near the surface for a very long time. The first part and the last part would have the same genetic makeup, baring mutation, but would it still be the same individual. It becomes a semantic problem to make a distinction.
So, what's the point?
The preceding is just an example of how organisms may almost suspend evolution. As a result the long time between sexual generations means little chance for change as compared to most animals we know. The one I have blogged about the most, the pogonophorans, happened to be the connecting ancestral group linking vertebrates to the protostomes.
Joseph G. Engemann May 30, 2014
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