Hey Doubting Too,
Let's see if I can add to the confusion:
1) why not common ancestorS as in PLURAL?
Technically singular
is incorrect. What is correct is a common ancestral population, where the population, generation by generation, evolves. Isolated sub-populations can evolve in different ways and over time become reproductively incompatible: speciation. Here we now have two "daughter" populations that are related to a common ancestor population, with many of the hereditary traits of the common ancestor population ... but not
all the hereditary traits from the common ancestor population are necessarily (or even likely) shared by either daughter population, and they each have different
new hereditary traits.
It is just convenient to talk about a common point of ancestry as a "common ancestor" rather than necessarily a factual single individual.
You can have a population of organisms in an ecosystem that supports 100 individuals, and each generation those individuals mate, reproduce and die in various quantities such that there are still 100 individuals per generation. After several generations the hereditary traits will all be mixed together without necessarily coming directly from any single individual. They come from the pool of hereditary traits in the population as a whole (which of course is where selection comes in).
One should never think of branches as being individuals, but populations, and each branch is in constant flux along it's length with new members added (reproduction) and old members dying (no longer contributing actively to the gene pool).
Thus each branching point has a common pool of hereditary traits, where some contribute to one branch and some contribute to the other.
COnfUsEd yet?
Now back to the Cambrian "million-year-explosion" with a number of already diverse common ancestor populations and the new ability to grow calcium parts from sea-water ...
Enjoy.
Edited by RAZD, : topic
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