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March 12, 2009
Bioe 109
Winter 2010
Lecture 27
Conclusions
- in the first class, I outlined a set of objectives for the course.
1. to foster an approach that may be termed “evolutionary thinking”.
- there are two components to this idea of “evolutionary thinking”.
- the first is to make the distinction between what Ernst Mayr has called “proximate” versus “ultimate”
questions.
- proximate questions usually begin with “how”; ultimate questions usually begin with “why”.
- these “why” questions may mean either “what for” or “how come”.
- in order to understand why a particular trait or character evolved, one needs to understand how
evolution occurs.
- this was the main focus of the first part of the course (“microevolution”), where we examined the
processes of natural selection, random drift, gene flow in guiding evolution.
- if natural selection is the agent responsible for the appearance of the trait, then we need to understand
the form of selection involved and the so-called “selective agent”.
- most of our attention focused on these changes at the molecular level - this is ultimately where all
evolutionary change must originate.
- the second component of “evolutionary thinking” is to understand the fundamental role that such
genetic variation plays in evolution.
- without this variability, all evolutionary change will quickly grind to a halt.
- for this reason, the study of variation – whether molecular, physiological, behavioral, etc. – is a
central focus of evolutionary biologists.
- conservation biologists have become increasingly concerned about the preservation of genetic
variation in natural populations.
- due to anthropogenic influences, natural populations of many species are becoming smaller and more
highly fragmented.
- if populations lose this reservoir of variation, their long-term persistence may be put at risk.
- the switch to evolutionary or “Darwinian” thinking deserves to be recognized as one of the most
profound intellectual events in our brief history.
- this is the so-called “Darwinian Revolution”.
- Darwin realized that the human species is not distinct from the remaining biological world.
- we are no different in possessing an evolutionary history that places us firmly in a clade with other
primates.
- this caused him a considerable degree of anguish, particularly because his wife was a devout Christian
and Darwin thought he couldn’t possibly reveal his true feelings to her.
- when Darwin proposed his theory of evolution, there was opposition from the Church of England but
the intensity of dissension was not too great (save for Bishop Wilberforce).
- by saying it was not too great, I mean that the many of the clergy of his day were able to accept the
fact of biological evolution.
- what the Church feared most from Darwin’s theory was that the social fabric of the country would be
eroded.
- the Church of England was afraid of the breakdown of a belief system that they saw as the foundation
of their society.
2. to foster an understanding of biological phenomenon in the context of their evolutionary
histories.
- appreciating the historical aspects of evolution necessitates an expansion of time scales.
- rather than be concerned with events occurring within a single generation, evolutionary studies
require a perspective involving hundreds, thousands, or even millions of generations.
- we saw how fundamental parameters of evolutionary theory, like effective population sizes, can be
strongly influenced by fluctuations is population size over time courses that stretch far into the past.
- we also saw how very small advantages in relative fitness can impart substantial change when
extended to long enough periods of time.
3. to realize the potential and limits of evolutionary change within species.
- this involved the metaphor of evolution as a “tinkerer”, rather than an engineer.
- it also involves the consideration of the idea of “constraints” on evolutionary change.
- the idea of constraints has become firmly ingrained into evolutionary thinking, even though we are
just beginning to understand what is entailed by this notion of “constraint”.
- constraints at the molecular level form a cornerstone of the neutral theory of molecular evolution.
- it is also becoming more and more prevalent in the field of macroevolution.
- as we saw in the punctuated equilibrium theory, this dominant trend of “stasis”.
4. to dispel any preconceived ideas that evolution has any ultimate goal in mind.
- this was clearly the main theme of Gould’s lecture we saw last Monday.
- the implications of Darwin’s theory are indeed poorly appreciated today both among the general
public, but also in other areas of the sciences and the humanities.
- the process of natural selection is only concerned with the present - it does not have the ability to
foresee or plan for the future.
- there are no orthogenetic trends.
- evolution does not lead to a continuous improvement in characters, or to a continuous advancement
for one of the dominant themes of macroevolution involves the loss of traits rather than the creation of
new ones.
- chance and contingency thus play fundamental roles in evolution.
- not only in the random nature of mutations, but in the importance that genetic drift plays and in the
probability of surviving periods of dramatic change.
The final exam
- set for Monday Dec. 7 from 7:30 – 10:30 pm.
- it will cover material from Oct. 28 onward – this was the lecture on the sexual selection.
- it will represent material from chapters 11 through 20.
- the format will be:
Part 1. Multiple choice. 25 questions, 2 points each 50 points total.
Part 2. Short answers. 5 questions, 5-7 points each, 30 points total.
Part 3. Essay. Answer 1 of 3 questions, 2 pages in length, 20 points total.
- each of the 3 sections should take no more than 30 minutes to complete and thus the exam should
take no more than 1.5 hours to write.
- some chapter sections are of “lesser importance”.
- these sections were not covered in class and I am unlikely to ask you any questions on them.
- they include:
1. Section 13.5 – 13.6 on life history stuff.
2. Sections 14.5 – 14.7 on human health issues.
3. Sections 15.3 – 15.4 on genome stuff.
4. Sections 19.3 – 19.4 on evo-devo stuff.
4. Section 20.4 on human evolution stuff.