a. Story of ulcers
https://www.ncbi.nlm.nih.gov/pubmed/1558442 (You may need to paste this reference into a browser)
b. Story of fever
The evidence from initial studies on lizards........
........... leads to these recommendations.
https://health.clevelandclinic.org/2015/05/kids-fevers-when-to-worry-when-to-relax
based on https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4145646/
newest hypothesis
Researchers isolated immune cells from mice and then put them in incubators set to a normal body temperature (about 98.6 degrees F) or a feverish temp of 104 degrees F. They found the immune cells that grew in the febrile environment produced a suite of molecules called heat shock proteins. One of these proteins, known as Hsp90, quickly set in motion a cascade of events that eventually directed the immune cells to the infection.
from https://www.discovermagazine.com/health/how-fevers-help-our-immune-system-hunt-down-infections
An interesting perspective to add. What good is staying in bed from a population perspective?s
2. Adaptations are not often easily identified because the molding of adaptation by natural selection is not perfect.
Think of changing a fighter jet, while being in flight and fight, having to survive what new and old adversities send its way.
In most texts these contributing factors are listed.
Gene flow: Is important because most human population moved from place to place as small groups of founders. Some groups are still isolated. Makes genetic drift through founder effects a significant driver of evolution.
Time lags: Controversial for humans. Will be discussed further in presentations and later lectures if time.
Lack of genetic variation: Often tauted as the primary cause of the imperfection of adaptation. May not be as important as once assumed, except in extinction events. More on this in Monday's lecture.
Today we will focus on the following.
Constraints
There are physical and historic constraints. For our purposes the most important are historic.
Example: Perhaps a different arrangement of leg muscles and bones would produce cheetahs that run faster — however, the basic body form of mammals is already laid out in their genes and development in such a mutually constrained way, that it is unlikely to be altered. There really may be “no way to get there from here.”
Trade-offs
Example cheetahs: Changing one feature for the better might change another for the worse. Perhaps “faster genes” are in the population — but there is a trade-off associated with them: running faster for short distances means the cheetah’s metabolism requires even more energy or that the cheetah’s legs must become hazardously delicate. Although longer limb bones increase stride, their chances of failing due to bending loads increases as well. In this case, perhaps it would get no net increase in fitness as a result of the “faster genes.”
Copied from https://evolution.berkeley.edu/survival-of-the-fit-enough/
3. Human applications of constraints and trade-offs.
a. Film to be viewed in class.
https://www.youtube.com/watch?v=pcnCJqDa1us&list=PLFk1ZL_Upr_9cBmUMtXWs6bjz1xwdRIIb&index
What are examples of human compromises and trade-offs?
Does Nesse agree with letting fever run its natural course?
What is the smoke detector principle?
How is back pain a result from an historic constraint?
On senescence: Homework for Monday.
The Classic paper on the evolution of Senescence is G. C. Williams, Pleiotropy, Natural Selection, and the Evolution of Senescence. Evolution 11, 398-411 (1957). His theory is summarized with others on the following website.
http://www.nature.com/scitable/knowledge/library/the-evolution-of-aging-23651151 (Homework paper)
But some new evidence may argue caution in accepting these hypotheses.
Homework for Monday
Read the paper from Nature that summarizes current theory on aging.
Answer the following questions:
What is pleiotropy?
What is the selection shadow?
Be prepared to discuss the antagonistic pleiotropy hypothesis.