I will attempt to answer questions posed to me by email at this blog.
One recent question was:
“Something you mentioned in class – “evolution has bigger effects the younger you are.” does not make immediate sense to me, and I was hoping you can explain this in a bit more detail.
This relates to evolutionary hypotheses for aging and senescence:
That statement is a way of introducing the concept of Antagonistic
Pleiotropy – that a gene for survival or a gene that promotes
reproduction early can be selected for even if it kills you at a later
age. So selection favors juvenile survival at the expense of old age survival.
Also, genes for maintenance and repair of the body are selected for
more strongly at early ages (pre-reproduction) than after reproductive
Antagonistic pleiotropy is controversial though. And if you think
about it, in humans as in other animals, infancy and early childhood
is a period of high mortality. So it is not true that selection has
resulted in human children being immune to disease.
Another way to think about this is that because of mortality from all
causes there are more infants and young children on the planet than
adolescents, adults, and the elderly. This means that if a gene has an
effect in a youngster (either positive or negative) it will affect
more individuals than a gene that affects older people. This concept
applies even if you are talking about infants vs 20 year olds.
This argument is also known as the “declining power of selection” hypothesis of aging. For this: imagine a gene mutation that prevents cancer at age 10 and another gene mutation that prevents cancer at age 100. The gene that prevents cancer at age 100 will not have any effect most of the time because most people are dead by age 100 (this remains true even if you take senescence out of the equation – random accidents will claim many lives). The gene that affects 10 year olds is more likely to be expressed and have a benefit simply because most people are alive at age 10. Therefore the old-age gene will be invisible to natural selection, the 10 year old gene will be subject to positive selection.
More to this story… this will be the topic for a future lecture.
Thanks for the note. Good question!
A second question regarded writing projects:
For the writing assignments do you want us to cite sources at the end of the paper, or is that not necessary? Are the writing assignments supposed to be researched topics or more of our opinions and ideas? Also, for the final presentation, are we doing those as a group or are they to be done individually?
My answer is here:
You do not need to cite sources for the weekly writing projects. They can reflect creative thought, ideas and opinions, in addition to researched ideas. But additional research beyond what we cover in class or in readings is not required for these (usually!). The final projects will be done individually.
Emergency Physician, Educator, Researcher, interested in the microbiome, evolution, and medicine
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