Register | Sign In


Understanding through Discussion


EvC Forum active members: 65 (9162 total)
4 online now:
Newest Member: popoi
Post Volume: Total: 915,806 Year: 3,063/9,624 Month: 908/1,588 Week: 91/223 Day: 2/17 Hour: 0/0


Thread  Details

Email This Thread
Newer Topic | Older Topic
  
Author Topic:   "Microevolution" vs. "macroevolution."
EZscience
Member (Idle past 5153 days)
Posts: 961
From: A wheatfield in Kansas
Joined: 04-14-2005


Message 31 of 63 (300657)
04-03-2006 3:31 PM
Reply to: Message 30 by ptman
04-03-2006 3:04 PM


Re: Back to the beginning
ptman writes:
I would contrast this to what I think is generally called "emergent properties" where differences of scale result in observations of small scale that do not explain observations on the larger scale.
You have a valid parallel here.
Ernst Mayr did a good job of discussing the emergent properties of biological systems in his book Toward a New Philosophy of Biology.
Thus complete knowledge of cellular functions would really tell us nothing about what to expect from organismal behavior, and complete knowledge of organismal behaviors would tell us nothing about population behavior, etc. etc.
The parallel is that observations of microevolutionary change, and even complete understanding of the forces and processes at work, were it possible, would really tell us nothing about patterns of macroevolutionary change and the forces and processes that guide the divergence of taxa at species level and higher. (Thus I would take issue with Jar's idea expressed below that we might find macro to be just the accumulation of a lot of micro if we had all the intermediates). Granted, similar forces such as natural selection will likely prove to be important in both cases, but they will act differently on separate gene pools than they do on connected gene pools.
I see this as further functional justification for the biological species concept, simply because macroevolutionary changes cannot begin to accrue until speciation and blockage of gene flow between populations. Macroevolution requires separate gene pools as a starting point, and yet the most initial stage of macroevolution (a speciation event) is probably the only 'macro' process we are ever likely to be able to observe directly.

This message is a reply to:
 Message 30 by ptman, posted 04-03-2006 3:04 PM ptman has replied

Replies to this message:
 Message 35 by ptman, posted 04-03-2006 5:20 PM EZscience has replied

  
EZscience
Member (Idle past 5153 days)
Posts: 961
From: A wheatfield in Kansas
Joined: 04-14-2005


Message 37 of 63 (301182)
04-05-2006 2:07 PM
Reply to: Message 35 by ptman
04-03-2006 5:20 PM


Re: Back to the beginning
ptman writes:
If you did have a complete set of intermediates, you would only be able to define arbitrary breakpoints between them and the sum would be Macro but the individual changes would be Micro.
Your thinking is rather linear and evolution is not.
Think in terms of a heavily pruned tree with only a few branches extending to give rise to others.
The branch points are speciation events.
Looking at terminal branches on different sides of the tree (extant species in disparate orders, for example) they can all be traced back to a common branch deep in the tree, a branch that now represents the divervence of some higher order taxon, even though it was originally only a speciation event.
The tree represents macroevolutionary structure, or phylogeny.
This is the only useful application of the concept.
The tree structure doesn't really hinge in any way on the presence or absence of 'intermediates' - remember these are only defined a posteriori as forms that apparently fit well between an earlier form and a later form.
They are not in any way essential to make sense of higher evolutionary processes. We now have far more powerful molecular tools to infer the structure of the tree than simply searching for fossil intermediates.
And the branch points, or 'breakpoints' as you call them, are not in any way arbitrary. That is incorrect. They are inferred speciation events that *had* to occur at certain points in order for taxa to diverge, unless you reject outright the idea of commonality of descent. Just because we may not know the exact details about how and when particular speciation events occurred in phylogenetic history, this does not make inferences of their occurrence in any way arbitary.

This message is a reply to:
 Message 35 by ptman, posted 04-03-2006 5:20 PM ptman has not replied

  
Newer Topic | Older Topic
Jump to:


Copyright 2001-2023 by EvC Forum, All Rights Reserved

™ Version 4.2
Innovative software from Qwixotic © 2024