Some really valid points were made in a previous thread on evolution vs. creation or intelligent design. Unfortunately, as happens so often, it got heated and wandered into religion and other landmines.
Can we try it without the hype? No "show me proof of evolution/creationism", no reference to holy books, specific faiths or specific deities. And no references to things that cannot be cited from a reliable source other than the above. (Dear generic deity, the other post was so filled with unreliable stuff on both sides of the discussion that it would make a great doctoral thesis to unravel!)
One challenge was to explain diamondback terrapins or another species. I don't know DBTs well but have read the snot out of red-footed tortoises, so here is a summary of what I understand that we believe about their history.
DNA research shows at least 5 major variations in red-foots, but only one kind of yellow-foot, and both share a lot of DNA with African hingebacks, and all of the above have lots of overlap in habitat, behaviors, general shape, diet, etc. Fossils show older forms of all of the above in specific areas in South America and Africa.
The theory is that as climate changed in the combined megacontinent, some tortoises (as well as monkeys and some other species) found a way to cross whatever barriers existed between the two regions- probably a long-term drought dried up a series of rivers, marshes, etc. AND had some motivation to leave their home ranges (again, such as a long-term drought). Shortly (as in thousands of years or more) after they breached the barrier, the barrier got worse (widened, got wet again, whatever) and stopped the flow which is why there are some but not too many African-origin species in South America.
So, we now have a tortoise that is a forerunner of both the hingeback and yellow-foot some 3-4 million years ago. Possibly due to competition for food in a fairly low-nutrient habitat, one group begins to prefer deeper forest, another prefers openings and edges (yellow vs. red).
Over time, the climate in the rainforest region has changed a lot- growing and shrinking, moving north and south, sending out arms in all directions to follow the rains and changing rivers, etc. As this happens, the red-foots on the edges find themselves cut off from other populations. The Amazon itself seems to serve as the main barrier between the reds at the north end of the rainforest and those at the south end.
Differences in diet, climate, selection, etc. generate small differences over generations- the southerners develop a tendency to average much larger, get dark plastrons, loose or never develop the wasp waist, etc. compared to the northerns. They also become more cold hardy, reproduce at a smaller size, and more
Changes in climate continue and create 5 main pockets of tortoises over time that are isolated by big rivers, mountains, dry plains, etc. and in that isolation, each group changes from the others a bit more. Three groups in the north, 2 in the south. Each group breaking off the others or the main form at different times that correspond to other evidence of the changes in the rainforest.
There is DNA evidence and fossil evidence that was used to create this picture. It can show change and movement- the fact that more modern forms and characteristics of modern forms are not represented in the fossil record suggests that change has occurred.
A young earth model would have to explain continental drift, apparently large age differences between populations, large changes in a large ecosystem that is slow to change, lack of evidence of the older fossil forms in newer rock layers, etc.
Partial list of citations:
- Vargas-Ramirez, Mario and Jerome Maran, Uwe Fritz. "Red- and yellow-footed tortoises, Chelonoidis carbonaria and C. denticulata (Reptilia: Testudines: Testudinidae), in South American savannahs and forests: do their phylogeographies reflect distinct habitats?" Organisms, Diversity and Evolution, 2010.
- Moskovits, Debra."The Behavior and Ecology of the Two Amazonian Tortoises, Geochelone carbonaria and Geochelone denticulata, in Northwestern Brazil". (PhD Dissertation) University of Chicago, 1985.
- Crumly, Charles R. “A cladistic analysis of Geochelone using cranial osteologyâ€. Journal of Herpetology 16:215-234. 1982. JSTOR.
- Pritchard, Peter C. H. and Pedro Trebbau. Turtles of Venezuela (Contributions to Herpetology). SSAR, 1984. ISBN 0916984117.
Errors in dates, etc. are mine since I am doing this from memory in the middle of the night.
(Remember, keep it clean and nice. Just because we look at things differently does not make 'the other side' evil, stupid, godless, etc. and as a moderator myself, even one that has not been round much in the last few months, I will not hesitate to take action if things get past a very low simmer, on any side of the debate.)
Can we try it without the hype? No "show me proof of evolution/creationism", no reference to holy books, specific faiths or specific deities. And no references to things that cannot be cited from a reliable source other than the above. (Dear generic deity, the other post was so filled with unreliable stuff on both sides of the discussion that it would make a great doctoral thesis to unravel!)
One challenge was to explain diamondback terrapins or another species. I don't know DBTs well but have read the snot out of red-footed tortoises, so here is a summary of what I understand that we believe about their history.
DNA research shows at least 5 major variations in red-foots, but only one kind of yellow-foot, and both share a lot of DNA with African hingebacks, and all of the above have lots of overlap in habitat, behaviors, general shape, diet, etc. Fossils show older forms of all of the above in specific areas in South America and Africa.
The theory is that as climate changed in the combined megacontinent, some tortoises (as well as monkeys and some other species) found a way to cross whatever barriers existed between the two regions- probably a long-term drought dried up a series of rivers, marshes, etc. AND had some motivation to leave their home ranges (again, such as a long-term drought). Shortly (as in thousands of years or more) after they breached the barrier, the barrier got worse (widened, got wet again, whatever) and stopped the flow which is why there are some but not too many African-origin species in South America.
So, we now have a tortoise that is a forerunner of both the hingeback and yellow-foot some 3-4 million years ago. Possibly due to competition for food in a fairly low-nutrient habitat, one group begins to prefer deeper forest, another prefers openings and edges (yellow vs. red).
Over time, the climate in the rainforest region has changed a lot- growing and shrinking, moving north and south, sending out arms in all directions to follow the rains and changing rivers, etc. As this happens, the red-foots on the edges find themselves cut off from other populations. The Amazon itself seems to serve as the main barrier between the reds at the north end of the rainforest and those at the south end.
Differences in diet, climate, selection, etc. generate small differences over generations- the southerners develop a tendency to average much larger, get dark plastrons, loose or never develop the wasp waist, etc. compared to the northerns. They also become more cold hardy, reproduce at a smaller size, and more
Changes in climate continue and create 5 main pockets of tortoises over time that are isolated by big rivers, mountains, dry plains, etc. and in that isolation, each group changes from the others a bit more. Three groups in the north, 2 in the south. Each group breaking off the others or the main form at different times that correspond to other evidence of the changes in the rainforest.
There is DNA evidence and fossil evidence that was used to create this picture. It can show change and movement- the fact that more modern forms and characteristics of modern forms are not represented in the fossil record suggests that change has occurred.
A young earth model would have to explain continental drift, apparently large age differences between populations, large changes in a large ecosystem that is slow to change, lack of evidence of the older fossil forms in newer rock layers, etc.
Partial list of citations:
- Vargas-Ramirez, Mario and Jerome Maran, Uwe Fritz. "Red- and yellow-footed tortoises, Chelonoidis carbonaria and C. denticulata (Reptilia: Testudines: Testudinidae), in South American savannahs and forests: do their phylogeographies reflect distinct habitats?" Organisms, Diversity and Evolution, 2010.
- Moskovits, Debra."The Behavior and Ecology of the Two Amazonian Tortoises, Geochelone carbonaria and Geochelone denticulata, in Northwestern Brazil". (PhD Dissertation) University of Chicago, 1985.
- Crumly, Charles R. “A cladistic analysis of Geochelone using cranial osteologyâ€. Journal of Herpetology 16:215-234. 1982. JSTOR.
- Pritchard, Peter C. H. and Pedro Trebbau. Turtles of Venezuela (Contributions to Herpetology). SSAR, 1984. ISBN 0916984117.
Errors in dates, etc. are mine since I am doing this from memory in the middle of the night.
(Remember, keep it clean and nice. Just because we look at things differently does not make 'the other side' evil, stupid, godless, etc. and as a moderator myself, even one that has not been round much in the last few months, I will not hesitate to take action if things get past a very low simmer, on any side of the debate.)
