Behavior OnLine Forums  
The gathering place for Mental Health and
Applied Behavior Science Professionals.
 
Become a charter member of Behavior OnLine.

Go Back   Behavior OnLine Forums > >

Notices

Reply
 
Thread Tools Display Modes
  #1  
Old August 15th, 2007, 12:03 PM
James Brody James Brody is offline
Forum Leader
 
Join Date: Jun 2004
Location: Philadelphia area
Posts: 1,143
Default "Evolving Evolution"

"Despite much recent controversy about the theory of evolution, major changes in our understanding of evolution over the past twenty years have gone virtually unnoticed..." So begin Rosenfeld & Ziff in a great review! Goes from lac-operon through contemporary models for the creation of body plans...strongly recommended review of three, related books and their fundamental contributions to evolutionary understandings...JimB

http://www.nybooks.com/articles/18970

Volume 53, Number 8 · May 11, 2006, By Israel Rosenfield, Edward Ziff

From DNA to Diversity: Molecular Genetics and the Evolution of Animal Design
by Sean B. Carroll, Jennifer K. Grenier, and Scott D. Weatherbee

Endless Forms Most Beautiful: The New Science of Evo Devo and the Making of the Animal Kingdom
by Sean B. Carroll
Norton, 350 pp., $25.95

The Plausibility of Life:Resolving Darwin's Dilemma
by Marc W. Kirschner and John C. Gerhart
Yale University Press, 314 pp., $30.00

"1. ...At the heart of Darwin's theory of evolution is an explanation of how plants and animals evolved from earlier forms of life that have long since disappeared; but his theory says nothing about the factors that determine the shape, color, and size of a particular fish, whale, or butterfly. Darwin and his contemporaries realized that understanding the evolution of animal forms and understanding how a fertilized egg develops into a whale, cow, or human being must be deeply connected; but they didn't know how to make the connection...In 1961, Jacques Monod and François Jacob discovered that E. coli bacteria actually have a mechanism that controls the production of the enzyme for digesting lactose...

"2. In 1894, the English biologist William Bateson challenged Darwin's view that evolution was gradual. He published Materials for the Study of Variation, a catalog of abnormalities he had observed in insects and animals in which one body part was replaced with another...The abnormalities Bateson discovered resisted explanation for much of the twentieth century. But in the late 1970s, studies by Edward Lewis at the California Institute of Technology, Christiana Nüsslein-Vollhard and Eric Wieschaus in Germany, and others began to reveal that ...(v)ery similar genes, exercising similar controls, were subsequently found in nematodes, flies, fish, mice, and human beings.

What they and others discovered were genes that regulate the development of the embryo and exert control over other genes by mechanisms analogous to that of the repressor molecule studied by Monod and Jacob. Eight of these controlling genes, called Hox genes, are found in virtually all animals—worms, mice, and human beings—and they have existed for more than half a billion years...Fruit flies and worms have only one set of eight Hox genes; fish and mammals (including mice, elephants, and humans) have four sets. Each set of Hox genes in fish and mammals is remarkably similar to the eight Hox genes found in fruit flies and worms..."animals descend from one or a few ancestors. However... different animal forms are not primarily a function of distinct gene pools that have evolved over millions of years...In Sean Carroll's view, what creates diversity is the patterns in which genes are turned "on" and "off." The different appendages found in centipedes, fruit flies, lobsters, and brine shrimp are created by varying combinations of Hox gene activity in the developing insect or crustacean embryo... Genes remain intact, but under new patterns of control...Complexity and variety are created, at least in part, by combining the activities of old genes in new ways...

"3. A powerful new theory adds considerable weight to this view, putting Carroll's work in a larger perspective. In The Plausibility of Life, Marc W. Kirschner and John C. Gerhart ... agree that Hox genes make an important contribution to the mechanisms of evolution, but they argue that there are a number of other fundamental properties of organisms that give direction to evolution...Darwin thought that at any given time variations in the forms of organisms were purely random. This is true of the neo-Darwinian view as well. However, recent research has shown that even though mutations are random, the effects of a mutation will be restricted, and may alter only one part or trait of an organism...individual parts of an animal can evolve independently of each other...This independence means that mutations can occur within a single region of an embryo that may or may not be beneficial; in any case, fewer of the mutations will be lethal (&) gives nature a much greater freedom to experiment with variant forms through random mutations... Another kind of core process that can, by constraining development, create forms that are more likely to succeed is what Kirschner and Gerhart call "exploratory behavior," such as the method used by ants when foraging for food..."

Good introduction to great stuff...one quibble, however:

"For example, though the giraffe has a long neck, it has seven cervical vertebrae, the same number as humans, whales, and all other mammals. Hox genes control this number, but they may also control cell proliferation and consequently the size of the vertebrae...Giraffes with large vertebrae and longer necks could feed off tall trees and were consequently selected over other giraffes. Changes in gene regulation, not new genes, gave rise to the long-necked giraffe."

Eeagh!

The longer necks were probably not due to tall leaves but to lady giraffes who liked tall guys...not that it matters here...

JimB
Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT -4. The time now is 11:25 AM.


Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2024, vBulletin Solutions Inc.
Copyright © 1995-2023 Liviant Internet LLC. All rights reserved.