Evolution of Aging

On monday, we will discuss the following hypotheses of aging:

Antagonistic Pleiotropy is the concept 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. This hypothesis recognizes that most traits have both costs and benefits, and are tradeoffs. The tradeoff in antagonistic pleiotropy is improved health in youth, but disease in old age.

Declining power of selection hypothesis of aging: Genes for maintenance and repair of the body are selected for more strongly at early ages (pre-reproduction) than after reproductive
age. 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.

Disposable Soma hypothesis; This hypothesis recognizes that the nonreproductive part of the body (the soma) exists only to support the reproductive part of the body. At any moment in time an adult can devote energy to the maintenance of the body or to reproduction. Put simply, after successful reproduction, the soma is “disposable”, and genes are passed on. This tradeoff is vividly illustrated in adult salmon, which appear to do all their aging at once, immediately after a single reproductive effort. In many animals, bearing offspring shortens lifespan. There is some evidence of this in humans too.

Optional readings for the weekend:

age-old-question

understanding-aging

There is no writing project due.Keep working on your final projects. Congratulations to those who have already presented their topics. Excellent work so far!! And good luck to those getting ready to present this upcoming week.

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Update!

Here is the handout of slides for mondays lecture:aging

Diet Lecture Slides & Handout

The lecture will be an overview of some evolutionary considerations of food. These include the concept of the paleolithic diet, which proposes that humans are healthiest when eating what our stone age ancestors ate. We will explore a variety of concepts through the lens of a Thanksgiving meal.

The following links contain the same information. If you want to print out the file, use the printer friendly link below:

Printer friendly handout:diethandout

Color slides best for viewing on your computer:dietslides

This link describes some of the differences between eating wild turkey (the paleolithic variety) and “broad-breasted white”, the most common bird found in grocery stores: About a Bird

Another good read is this recent New York Times article about disappointing results of multiple vitamin trials: Vitamin

Next weeks topic: Diet

We are going to focus on diet next week. We have already talked about trans fats, and I think we have said enough about it already. Diet, as you know, is a huge topic, with far more information that we can cover in one week. But we will talk about lactose intolerance, spices, and maybe carbohydrates. 

There will be no writing project for next week, since most of you are working hard on your presentations!

I will post the lecture handout when it is ready.

Reading and Slides for 11/17/08

Here is a preview of the slides for this monday’s talk:

Evolution of Diabetes

This is an extra reading that I did not include in the original list. Dr. Kuzawa wrote this chapter for a new book “Evolutionary Anthropology”. This work explains his hypothesis about the fixed needs of the brain and the role of blood glucose in stressed infants.

kuzawa-chapter-for-evolutionary-anthropology

This one is not on eReserve. Email me if you are unable to download it here.

Also, in case you missed it. Evolutionary medicine made the New York Times with a mention of David Haig, the Harvard scientist who wrote the reading on reproductive conflict:

New York Times article

Diabetes and Development

Cardiovascular disease (CVD) and diabetes are perhaps the most consequential diseases in America in terms of deaths, economic impacts, and effects on quality of life. Despite intensive efforts and millions of dollars worth of studies, our understanding of CVD and diabetes remains incomplete.

The fine work of Chris Kuzawa from Northwestern University shows how environmental influences during development can cause diabetes. Please complete the reading prior to class. It will also be hard to do the writing project without first doing the reading.

Reading: also on eReserve

1. Kuzawa – Diabetes and Development

Writing project:

There appears to be switch activated in underweight babies that leads to diabetes later in life. Early on, many underweight babies are insulin resistant. Insulin resistance is a pre-diabetic state.  In these small babies, less glucose gets metabolized by muscle tissue. As a result, less energy is devoted to growth and building muscles and bones. On the flip side, more glucose is available for other uses ‐ like the brain and perhaps white blood cells. 

Kuzawa proposes that because humans have particularly large brains (recall Dr. Trevathan’s lecture) glucose gets diverted to the brain from the rest of the body in times of stress. In this view, insulin resistance feeds the brain.

1) Try answering this:  What might be the consequence of slower growth, and higher blood sugar in these infants? Are there situations in which more energy available to the brain or immune system might be helpful? 

2) If that is too tough, try this: Large brains appear to have benefits and costs to the developing baby. Try to name three downsides to having a very large brain in an infant. What might be the benefit?

3) Extreme extra credit. Can genetic conflict (recall two lectures ago) have something to do with insulin resistance in an infant?

Special Guest Wenda Trevathan

The author of the textbook “Evolutionary Medicine” will be visiting on 11/10/08 to lecture on evolutionary considerations of human reproduction and childbirth. The readings for this lecture include:

Evolutionary Obstetrics. Trevathan WR.  Chapter 8 in in Evolutionary Medicine (1st edition) 1999. Eds Trevathan WR, Smith EO, McKenna JJ. Oxford University Press. pages 183-207. (On eReserve)

You should consider re-reading the first reading of this class (pages 22-29), also written by Dr. Trevathan:

Introduction and Overview of Evolutionary Medicine. Chapter 1 in: Evolutionary Medicine and Health. 2008. Trevathan WR, Smith EO, McKenna JJ.  Page 1-54. (on eReserve)

An optional reading is nausea-in-pregnancy

Have a great weekend!

Writing Project due next session

Writing project:
Some have suggested that the age of weaning of infants from the breast is subject to  parent offspring conflict. Eg. infants might want to breastfeed longer than the mother would like. Breastfeeding tends to suppress ovulation and delay pregnancy.   Give an evolutionary hypothesis for why infants might exhibit behavior that promotes longer breastfeeding.  What behaviors might these be? The infant has 1/2 maternal derived genes and 1/2 paternal derived genes; which of these would these be expected to prolong breastfeeding?

Update: I reloaded the slides from todays lecture. Click again below…

Click Below for the lecture handout from today:

conflicts-in-pregnancy