Friday, January 31, 2014

Identifying and writing bad and good evolutionary scenarios (A classroom activity)

I'm always looking for ways to improve evolution education in my classroom.  So I want to share something with you all that I tried this week in my Sex and Reproduction in Our Species (APG 310) class and that worked pretty well. 

Here's the activity (with my commentary in red) and it's yours for the taking/modifying as you wish. Cheers!
Classroom Activity:
Identifying and writing bad and good evolutionary scenarios 

Part 1. In class, in groups

1. What is evolution?

2. What are the four main mechanisms? (just names for now please)
3. What is evolution not?
4. Write an evolutionary scenario, without invoking any form of natural or sexual selection, to explain how humans lost our body fur and are now what’s often called ‘the naked ape.’
5. What are the components of natural selection scenarios?
6. What are the components of sexual selection scenarios? 
7. Could sexual selection explain human body fur loss? Why or why not?
8. What are some potential benefits to body fur loss? In what ways are they dependent on context/environment?

Students worked in groups of four through all the questions above. Then we held a discussion as a class and I wove-in helpful slides to illustrate things better than I can on the wipe board, like  family resemblance with simultaneous uniqueness (and, hence, perpetual mutation/change/evolution). And like how we can blame (at least inchoate) genetic drift for Mitt Romney's Y chromsome existing at a relatively high frequency in the next generation

Part 2. Homework, to be discussed next class
All of the numbered paragraphs below are answers that APG 201 students wrote for the following final exam question:  

Give a plausible explanation, in Darwinian terms (i.e. using the components of selection, or if you want, sexual selection), for how humans lost our body fur and are now what’s often called ‘the naked ape.’ There are many ways to answer this for full credit as long as you incorporate all the components of selection properly.” 

Read each of their answers and find at least one error, mistake, or less than ideal part in each one (must involve evolutionary theory, not grammar, etc). Then give each one an overall thumbs up or thumbs down. 

From a strict (and arguably proper) position, sexual selection only explains sexually dimorphic traits, not things found in both sexes. However, it's not something I'm going to continue to do, but I introduced sexual selection to my intro students as being more broad than that, as being a term to hypothetically explain things like naked human skin or giraffes' long necks if something like runaway selection is used (with not just mate preference but maybe just mate recognition). I'm still struggling with how to conceptualize let alone effectively apply (let alone effectively teach) these theoretical distinctions. Regardless, this opened up a great opportunity to discuss the strict Darwinian definition with my class before they evaluated these answers below.

1.    Hypothesis explaining why humans lost their/our body fur: Cloths were developed enough to the point that humans did not need their body “fur” to rely on for warmth, they used the skin and fur of other animals to keep warm thus eliminating the need for a coat of fur. Over time that trait became less and less necessary for human survival and fitness. Male and females no longer needed their fur to enable their survival. They could reproduce without fur making the fur a diminishing trait among humans, and over time was replaced with a “naked skin” which was kept warm unnaturally through use of clothing and other heat sources.

Let's hope they all see the similarities here with their answers to #4 in Part 1.

2.    Random mutations occur in the genome of every organism. The random mutations could have favored a specific group of people that lived in a warm environment, over time allowing them to lose their fur. This happens because genomes act with the environment that an organism lives with. This eventually created variation among groups; those with less fur in a warm climate were able to live longer because the environment favored them. Food and water may have been scarce and with less fur, these humans were able to release less body heat and hold on to more water, allowing them to survive longer. Humans with less fur could have also camouflaged better which allowed them to be preyed on less. Over time the humans that never lost their fur died off, and only humans with less fur, or no fur were left to mate with one another.

3.    Over time humans have slowly evolved into the modern humans we are today. Sexual selection was the cause for the loss of a lot of the old traits our ancestors had. Over time we continued to reproduce and meiosis and mitosis played a part. Genes our ancestors had didn’t necessarily carry the same genes that their parents carried which is why it wasn’t pass on. We didn’t need body fur the way we were adapting anyways, although still to this day we have hair on our bodies. There are specific genes that get passed on to us from our ancestors and it typically is only the stronger one. If we needed body fur, there wouldn’t have been a change in our genes and we would have continued to reproduce with body fur.

4.    Over time there has been an apparent loss of body fur in humans which can be contributed to natural selection. This “loss” of body fur has become the source for our existence as “the naked ape.” Fur was originally a biological method of protecting the skin against harsh climate, weather, and other outside threats. As alternative methods of protection were developed such as knowledge of constructing shelter and tools, body fur became less vital to survival. Because of variation within a population due to mutations in the genome, some humans were born with more body fur than others. While body fur was previously a necessity for survival and, as a result, passing on of traits, changing environmental situations and social/technological situations no longer demanded the presence of such a trait, and perhaps resulted in the trait as a genetic disadvantage. Those who were genetically less “furry” became more successful in their environment, allowing them to stand up to competition, obtain food, and ultimately mate. Humans with less body fur thrived and survived, meaning they were naturally more fit for the “selection” of their environment, allowing them to pass traits for lesser body fur, which led to a decline in the presence of the fur trait over generations as a result of the natural and sexual success of those with less or no body fur. Those with the trait became less for the environment, so they were less likely to survive to the point or reproducing and without the continual passing on of the trait, it eventually became significantly inconvenient, prevented survival success, and as a results, slowly became uncommon and completely overwhelmed by the presence of those carrying the trait for no body fur.

5.   Humans are the product of evolution over deep time, and took up until 200,000 years ago for us to be anatomically and biologically the way we are today. As time has progressed, so has temperatures. One component of natural selection is adaptation. Humans adapted to the warm climates and saw that the extra hair on their bodies was heating them up quickly. Another proponent is the fact that the sun perhaps started to burn off the hair and our DNA realized that it was no use to generate more hair, due to it being burned off. So it developed another mutation, having the result of less hair. With the bodies of Homo sapiens evolving, so have they psychologically and sexually. Homo sapiens became more “choosier” in their mate and found less hairier bodies to be more attractive. Thus, mating with less hairier mates, producing less hairier offspring.

6.    The Homo sapiens species may have begun to lose body fur in warmer areas such as the Africa regions. The body fur may have held in unneeded warmth which may have led to overheating. The overheating may have damaged the brain or hindered the general efficiency of the individual. It may have been noticeable to females of a group that certain males with less fur were stronger and more fit. This means that those individuals with less hair were more reproductively successful. This mutation of less hair is therefore selected for and inherited by descendents.

7.    Humans lost their body fur due to natural selection. Human fur was naturally unfavor because it no longer serve a purpose. As the earliest humans migrated from rainforest like environment to more savannah related environment, the need for body fur was longer desire or needed. Over time as the earliest humans reside in such climate of savannah their body fur became infested with insects, and since it was no longer purposeful over time body fur slowly became extinct in humans.

8.    A possible explanation of why we lost our body fur can be explained through natural selection. First, there is constantly variation found among individuals as a result of genetic mutations and recombination during meiosis. Perhaps an ancestor received a variation for less fur. This trait in some way helped the individual to successfully live and reproduce; it served as an adaptation for their environment. Maybe this ancestor with less fur could cool more efficiently and not have as great a chance of dying prematurely of heat stroke since this individual has survived, their offspring can inherit this advantageous trait. Due to the force of differential reproduction, more or less individuals could inherit this trait. Perhaps individuals with this trait were able to produce more offspring (say because they are living longer because they aren’t dying from the heat) than their hairier counterparts. This would then likely cause the trait to be passed on in greater numbers. If the trait continued to be advantageous, it would have been passed on and resulted in a common trait of a species, in this case, loss of body fur for humans.

9.   Throughout a species this is always variation. No two organisms are exactly alike and differences occur through combination of genes (as in reproduction) or mutations. During humans lineage, a hominid was born with less body hair than usual. This trait benefited the hominin by keeping cool when it needed to travel long distances for resources. Therefore this trait became adaptive because it helped the hominin live. Since the hominin was able to live, it was also able to reproduce and so the trait was passed on through the generations because the hominin s with less body fur lived longer and were able to reproduce more than hominins who had more body fur. The trait was “selected” because it was beneficial to the species.

When discussed as a class the next meeting, students should be able to tell the difference between selection and drift, the importance of mutation and differential reproduction for both, and issues with using sexual selection as an explanation for non-dimorphic traits. Thanks to help from the accompanying readings (linked), they will hopefully be critical of the agency-infused, and also quasi-Lamarckian, language that they need to play up in #1 and avoid entirely in #2 in Part 3 below. 

Readings to accompany Parts 2 and 3 as homework.

Part 3. Homework, to be submitted and discussed next class

1. Write a scenario for the evolution of either human bipedalism (upright walking and running) or large human brains (encephalization) by making evolution and selection into agents that might have preferences, feelings, thoughts, intentions, decisions, needs, etc…

2. Write a scientific scenario for the evolution of either human bipedalism (upright walking and running) or large human brains (encephalization). You may use a known hypothesis or invent one.

The goal is to have this final question (#2, Part 3) be answered exquisitely, that is, scientifically, conservatively, all-natural, all modern synthesis, Darwin-friendly, use/disuse-free, and agency-free. 


Holly Dunsworth said...

Some background on the exam answers... Students in that large intro class practiced on wisdom tooth loss and then I surprised them with body fur loss on the exam.

Holly Dunsworth said...

And The more I teach while I emphasize the complexity, the more misleading I think it is to ask them to write simple scenarios. But how else are they going to get the basics down?

Holly Dunsworth said...

Posting stuff like this always leads to unexpected and positive a surprises, like social media discussions about what sexual selection is.

Ken Weiss said...

You clearly raise important and interesting points in your MT posts, and it's not surprising that they trigger thoughts on a variety of related issues.

Manoj Samanta said...

Are there any human tribes anywhere with large amount of body fur (hairs), or is the body fur lost >200K years back in what we call anatomically modern human?

The reason for asking is this. If the body fur was lost in one small group of humanoid monkeys over 200K years back, it is very hard to describe possible scenarios without living their life. Were those ancient humans (hunter-gatherers) able to run faster and climb easily on trees due to less weight? Being able to climb trees can help you evade a number of animals.

Holly Dunsworth said...

For ironing out the basics of evolutionary theory, hypothesis creation is a useful device. Without a time machine, as you say, it's not easy to test these things!

Holly Dunsworth said...

Tip! Make sure to really work through the anthropomorphizing issues (if you're going to take those on) before you have them write that creative essay that asks them to anthropomorphize evolution.