The connection between selection and adaptation.
What do we know about the forces of chance and natural selection in shaping the diversity (and so in some sense the adaptations) we observe?
Strictly speaking, chance by itself can never result in adaptation. Adaptations usually refer to traits that make organisms suited for their environment and so adaptations must always involve some molding by the natural selection. However, if you answered question 9 correctly on your homework two, you acknowledged that drift in some ways can influence the adaptive process for the last example.
Here is another example. A researcher working with swordtail mollies changed the size of the tail fin or sword on the mollies by pasting larger or smaller plastic tail fins (swords) on males. Sure enough as predicted from watching these mollies in nature, females preferred big tailed males, even though some of these males’ tails were only longer because of some glued on plastic.
The prediction was that the adaptation for males was to have big tail fins. However, the researcher did not stop the study there and placed artificial tails on platies or species that never sport swordtails. Well, female platies also preferred the longer tailed males. It turns out that whatever she did to make the males appear bigger made them more preferred by females in platies and mollies. So in essence the adaptation was for greater size not specifically how the size was attained in different species. Looking at the different types of mollies available, it looks like they could have increased the whole tail (as in lyre tails) or even another fin (as in sail fin mollies). Perhaps chance played a role in how males got bigger. We don’t know at this point, but the demonstration that females do not seem to care what makes a male large, just that he is large, seems to suggest a role for chance in determining whether in some species it is a large tail or a dorsal fin etc.
This story also shows how hard it can be sometime to determine the exact nature of an adaptation and why you should never assume without supportive evidence that any trait under observation is an adaptation.
Examine a new hypothesis for why zebras have stripes. Answer question one.
Zebras and stripes
A bit of History:
Adaptation has always been difficult to study. It was at a meeting in the seventies, that two biologist at a meeting drawing the best recognized evolutionists at that time, signaled that the study of adaptation was very flawed.
Skim the following paper, paying particular attention to the problems Gould and Lewontin felt were plaguing evolutionary thinking at that time. Re-read the pages describing the blue bird experiment. The Spandrels of San Marco and the Panglossian Paradigm: A Critique of the Adaptationist Programme. STEPHEN JAY GOULD AND RICHARD C. LEWONTIN Link to a pdf download of this paper can be found on the schedule. Answer question two.
A more formal introduction to the study of adaptation.
What now are the main factors limiting adaptation? Visit the website below.
http://evolution.berkeley.edu/evolibrary/article/misconcep_01
Another look at why adaptations are not perfect and difficult to study.Focus on what are the limits to natural selection.
Be able to list the reasons why “bad genes” persist.
Answer question three.
Read the limits to adaptation chapter from Stearns and Hoestra
The focus is how time lags, etc. can constrain selection and so affect the “perfection of adaptations.
Answer questions four and five.
A modern approach to studying adaptation.
How to recognize adaptation. Re-visit this page to learn how to recognize an adaptation.
https://evolution.berkeley.edu/evolibrary/article/0_0_0/misconcep_06
Answer question si.x
The following study is a good example of how we can use in some cases, experimentation and artificial selection, to study adaptation.
http://evolution.berkeley.edu/evolibrary/article/conover_01 Answer question seven.