Hey lyx2no2,
Whee! I get to marry a cousin.
There's a series of jokes that all have the pattern "you may be a redneck if ..." (the term "redneck" implying ignorant country bumpkin with sunburned neck from long hours of hard field work), and one of my favorites is "you may be a redneck if you get married for the third time and still have the same in-laws"...
I’m not sure what “it” is, yet. “It” refers back to this entire:
"IT" is the division of a parent population into separate daughter populations that are no longer sharing genetic material by breeding.\
The question is whether reproductive separation is sufficient to declare speciation. So the idea is to compare the degree of similarity between the two branches to see if there is sufficient divergence to match the assumed level for arbitrary speciation. You have the same amount of difference, but in space instead of time.
But what does “when such a divergence becomes sufficiently clear” mean? How is “sufficient difference” determined? What do the little, black, horizontal bars in the image represent? Who is John Galt?
John Galt had the opportunity to drink perfect coffee.
The black horizontal bars represent the variation in the population at each specific level, with thicker bars for more numbers in that size - like a normal distribution of variation of a trait in any population.
How does one calculate the 98% similarity with an extinct species? I’m assuming, here, that one looks at some portion of a gene ...
That's why I prefer "traits" to "genes" - traits are seen in the visible parts of the fossils, the result of gene expression, rather than the gene itself. This is also more important for evolution, as evolution is based on selection of the phenotype - the expressed genes combined with the development of the organism.
When comparing fossil skeletons you can compare proportions of bones, size, distribution, etc. without needing to refer to the actual genes that led to such differences.
Are they comparing the ratios of all those little measurements they seem to be continually making with their calipers instead?
Yes, indeed. Well done. A little known aspect of paleontology is the exhaustive comparative anatomy that goes into cataloging species, variations in the species and why scientists feel they have found a "new" species.
Yes a lot of it is subjective, but the issue is consistency. Some people are "lumpers" - grouping a lot of variation into a small set of species - while others are "splitters" - dividing the variations into lots of species. Lumpers and splitters are each internally consistent, so they end up with the same overall pattern, just with a different number of nodes along the way.
Enjoy
we are limited in our ability to understand
by our ability to understand
Rebel American Zen Deist
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