Replies to various posts:
>No problem. Abrupt appearance and stasis are the two most obvious features of the fossil record. <
Both of these are notable features of the fossil record, but the numerous transitional forms and the evidence for lengthy time intervals are also important features.
>And since virtually all mutations are negative<
The vast majority of mutations are neutral. Of the remainder, many are positive, though probably the majority are negative.
>Evolutionary biologists, isn't this the process [of increasing complexity] in a nutshell?
>1. The evolutionary process (a family of processes which includes variation, natural selection, genetic drift, etc.) favors only reproductive success in some particular environment/ecosystem.
>2. Some fraction of the reproductively successful species will be more 'complex' ('complexity' needs to be defined) than their predecessors.
>3. Reiterate 1 & 2 throughout geological history with its diversity of changing environments and ecosystems.
>4. Result: A diverse community of species characterized by a broad spectrum of 'complexity values,' with the maximum complexity value tending to increase in time.<
Yes, this is correct. A simple example, well-studied, comes from muricid gastropods (the ones used to make Phoenecian purple). Today, there are big muricids with lots of spines, as well as little ones without spines, and many options in between. The oldest known muricids, from the Cretaceous, are small and spineless. If the ancestors were towards the small end of the range of practical sizes for a muricid, then random variation in size and number of spines will produce a gradual increase in the average size and number of spines. It is an increasingly flat bell curve with a lower limit. However, in some areas there are also distinct shifts in the average at times in the geologic past, suggesting that natural selection was favoring increases in size and spininess. Both these features could be antipredatory.
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