Science & Nature Archive

Sunday, February 12, 2017

Understanding Evolution - Balancing Selection Pressures, Or Why All Features Are Tradeoffs

This entry is part of a collection on Understanding Evolution. For other entries in this collection, follow that link.


Gazelle & Cheetah DioramaTo celebrate Darwin Day, I'm going to recycle a recent Quora answer about evolution. Somebody had asked, Why would a gene that makes a gazelle slightly faster, but still much slower than a cheetah be favored by evolution?. Here's my answer.

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Because everything in life is a trade-off, and cheetah attacks aren't a gazelle's only concern.

Running faster comes at a cost. In particular, it means bigger or stronger muscles to be able to propel yourself faster. Bigger muscles take more food to grow, and more food to maintain. So, the fastest gazelle is also the most likely to starve in times of scarcity. And it's also putting more of it's food resources into those muscles instead of reproduction and/or nurturing young, and may end up not having as many offspring / surviving offspring as a slightly slower gazelle.

And gazelles have other predators besides cheetahs. One in particular is so efficient that it doesn't really matter how fast a gazelle runs - our bullets are faster. And which animals do trophy hunters target? The biggest and most impressive. It's already been documented that trophy hunting has led to bighorn sheep having horns that aren't so big (Phys.org - Intense trophy hunting leads to artificial evolution in horn size in bighorn sheep), and that size limits in fishing has led to smaller fish (Phys.org - Intensive fishing leads to smaller fish). I don't know if gazelles have been studied in this manner, but I wouldn't be surprised at all if human hunting had strong selection pressures on their sizes.

There's this whole complex network of selection pressures acting on gazelles (and all other organisms). Evolution has to balance (metaphorically since evolution isn't conscious) an organism's strategies to dealing with these pressures, and can't focus on optimizing completely for one selection pressure if it means compromising too much on other ones. So, cheetah attacks are one pressure on gazelles, and this particular pressure pushes gazelles to be faster. So, evolution pushes them to be fast enough to greatly lower their likelihood of being caught by a cheetah. But going even faster would only reduce that risk slightly, and at the cost of hurting the gazelles chances of survival/reproduction in other ways. So, gazelles are fast enough, and there's no reason to waste their limited food resources on even bigger muscles, when they could be using those resources for other activities, or even just being smaller so that they don't need as much food.

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If you want to look at it another way, it's like wondering why everybody doesn't have a Ferrari. Sure, Ferraris are fast, but they're also expensive, use a lot of gas, and have many compromises that make them less than practical everyday drivers. Evolution could make gazelles faster, but only by compromising them in other ways.

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To add one more thing - the reason gazelles just have to be reasonably fast, but not as fast as or faster than a cheetah, has to do with the way attacks actually play out in real life. As Brian Dean pointed out in his answer, it's not like a track race, where the fastest organism is the winner. Cheetah's are only sprinters, with limited stamina. Gazelles are keeping a lookout for cheetahs already, trying to make sure the cheetahs don't get too close. The usual result is that the cheetahs can only get so close before starting their sprint, meaning the gazelles have a head start. The gazelle only needs to be fast enough that it can avoid the cheetah until the cheetah gives up, which is still pretty fast, but a good deal less fast than a cheetah. And an extra few miles an hour on the gazelle's top speed is a sizable percentage difference in how much more time it has to evade the cheetah.

Image Source: Wikimedia Commons


Want to learn more about evolution? Find more at Understanding Evolution.

Sunday, February 12, 2017

Happy Darwin Day 2017

I'm cheating. This is mostly copied from last year with just a few updates.

Darwin's BirthdayToday is Darwin Day, the 208th anniversary of Charles Darwin's birth. To quote one of my previous Darwin Day posts, Charles Darwin was "the man who presented evolution in such a way and with sufficient evidence that it became obvious that it was the explanation for how life developed on this planet. Others had ideas of transmutation before Darwin, and Alfred Russel Wallace even came up with a theory of natural selection very similar to Darwin's at around the same time, so it's apparent that humanity would have eventually recognized how evolution works. But Darwin's genius in presenting all the evidence for evolution in the way he did certainly gave the field a huge head start."

If you want to see if there's anything specific going on in your neck of the woods, you can check out the list of events at DarwinDay.org, or my recent post. I couldn't find anything for Wichita Falls again this year. And I never did watch Inherit the Wind last year, so maybe I'll be able to talk my family into it this year.

To celebrate Darwin Day on this site, I'm going to provide links to a few of my previous entries. This first set of links is entirely to entries specifically relevant to Darwin or written just for Darwin Day.

And while I write way too much about evolution to list all of my evolution entries, here are a few highlights since the previous Darwin Day:

Friday, February 10, 2017

Upcoming Darwin Day Events

Darwin's BirthdayFebruary 12th is Darwin Day. Many organizations are planning events for this weekend to celebrate. You can check DarwinDay.org for events close to you. Here are a few from across Texas and Oklahoma (well, at least the ones you can still make it to - there were some events earlier this week).


Austin, TX - Center for Inquiry: Darwin Day 2017
Feb 11, 12pm - 5pm

DarwinDay.org Details
Official Event Page
Facebook Page

"FREE event to celebrate the 208th anniversary of Darwin's birth. There will be something for everyone--fun learning activities for children and teens, fascinating lectures and trivia contest for adults, and professional development credit for teachers."


Tyler, TX - Darwin Day Tyler 2017
Feb 10, 5pm - 7pm
Feb 11, 10am - 4pm

DarwinDay.org Details
Official Event Page
Art & Seek Details

"This year's Darwin Day celebration features four main events: two different public science lectures, evolutionary themed video screenings, and a teacher development workshop. There will also be other events for students of all ages at the Discovery Science Place, the University of Texas at Tyler, and Tyler Junior College.

All events are free of charge!"


Nagadoches, TX - Darwin Day at SFA
Feb 10, 1pm

DarwinDay.org Details
Press Release

"The Stephen F. Austin State University Department of Biology will host its second annual Darwin Day program. The program will include a seminar by Dr. Charles Pence, assistant professor of philosophy and religious studies at Louisiana State University. Pence's seminar is titled 'Evolution and Chance: From Darwin to the Pioneers of Statistics in Biology.' "


San Antonio, TX - Trinity University: Panel Discussion on Darwin, Gender, and Race
Feb 15, 5pm - 6.30pm

DarwinDay.org Details

"In celebration of Charles Darwin's 208th birthday join us for a discussion on Darwin, Gender, and Race. Four Trinity professors will provide a panel discussion of Darwin's views on gender and race, the current scientific views on race, and the contributions of minorities and women to evolutionary theory. Following brief introductory comments, the panel will open up for questions from the audience. Also be sure to check out the exhibit at the Coates Library, Third Floor: Who's studying evolution these days? A look at modern scientists; Feb. 8-15."


Norman, OK - Norman Naturalism Group: Darwin Day! Potluck and Speaker: The EVOLUTION of Religion
Feb 12, 5pm - 9pm

DarwinDay.org Details
Official Event Page

"The Norman naturalism Group celebrates Darwin Day 2017 with a pot-luck dinner and speaker. The topic is "The Evolution of Religion". Pull out your best recipe and get ready for some more good eating and good talking."


Thursday, February 2, 2017

Texas State Board of Education Takes a Small Step Backwards on Science Education

TEA LogoAs described in the Austin American Statesman article, Texas education board approves curriculum that challenges evolution, the Texas State Board of Education has approved some troubling language for the state science standards.

If you want to see for yourself the full standards, you can find them here. Here are the four subject to the current controversy:

(3) Scientific processes. The student uses critical thinking, scientific reasoning, and problem solving to make informed decisions within and outside the classroom. The student is expected to:

(A) in all fields of science, analyze, evaluate, and critique scientific explanations by using empirical evidence, logical reasoning, and experimental and observational testing, including examining all sides of scientific evidence of those scientific explanations, so as to encourage critical thinking by the student;

(7) Science concepts. The student knows evolutionary theory is a scientific explanation for the unity and diversity of life. The student is expected to:

(B) analyze and evaluate scientific explanations concerning any data of sudden appearance, stasis, and sequential nature of groups in the fossil record;

(7) Science concepts. The student knows evolutionary theory is a scientific explanation for the unity and diversity of life. The student is expected to:

(G) analyze and evaluate scientific explanations concerning the complexity of the cell.

(9) Science concepts. The student knows the significance of various molecules involved in metabolic processes and energy conversions that occur in living organisms. The student is expected to:

(D) analyze and evaluate the evidence regarding formation of simple organic molecules and their organization into long complex molecules having information such as the DNA molecule for self-replicating life.

You can read a detailed discussion in a report put out by the Texas Freedom Network, Texas Science Curriculum Standards: Recommendations for Dealing with Pedagogical and Scientific Problems (pdf).


The Bad

Yes, the motivation behind these standards really is to promote creationism / cast doubt on evolution. Here are a few excerpts from that TFN report regarding the motivation behind three of these:

[Regarding 7 B] In a final appeal to preserve his proposal, McLeroy stated that the purpose of his standard was to argue against: "...the idea that all life is descended from a common ancestor by the unguided natural processes."
[Regarding 7 G] During the board debate, McLeroy explained that this standard: "...questions the two key parts of the great claim of evolution, which is [sic] common ancestry by unguided natural processes."
[Regarding 9 D] During board debate, Don McLeroy, R-Bryan, explained that the new standard was "basically an origin of life amendment," referencing public testimony provided previously by Ide Trotter, a well-known promoter of intelligent design."

And the history of the first one, 3A, makes it clear that this was compromise language regarding the strengths and weaknesses gambit so popular among creationists.

Moreover, the Board had actually formed an expert committee to review the standards and make recommendations on improving them, and the committee recommended removing these four particular items because "they were vague, redundant or would require too much time to teach" (quoting the Stateseman article). So, the Board is going against the advice of experts to push standards that were originally motivated by anti-science positions.


The Good

The standards aren't actually that bad. All of them could be handled by textbook publishers and teachers strictly keeping to real science, and not injecting any creationism or other pseudoscience. Let's look at them again on a case by case basis.

(3) Scientific processes. The student uses critical thinking, scientific reasoning, and problem solving to make informed decisions within and outside the classroom. The student is expected to:

(A) in all fields of science, analyze, evaluate, and critique scientific explanations by using empirical evidence, logical reasoning, and experimental and observational testing, including examining all sides of scientific evidence of those scientific explanations, so as to encourage critical thinking by the student;

Well, it says specifically 'all sides of scientific evidence'. Creationism is manifestly not science, so this shouldn't be a backdoor for creationism. As far as real science, this is a little overwhelming for a high school biology class. I mean, all sides of the scientific evidence supporting evolution in general could be an entire class unto itself. Even 150 years ago, in The Origin of Species, Darwin had an entire tome full of evidence for evolution, and the evidence has only grown stronger and more abundant since.

Granted, there are different 'sides' within current evolutionary biology - the relative influence of genetic drift vs. natural selection, how much of the genome is truly junk DNA vs. possible other functions, etc. So, teachers could delve into these current topics, but it seems a bit of a deep dive for high school biology.

(7) Science concepts. The student knows evolutionary theory is a scientific explanation for the unity and diversity of life. The student is expected to:

(B) analyze and evaluate scientific explanations concerning any data of sudden appearance, stasis, and sequential nature of groups in the fossil record;

Well, if you're sticking to real science, this is simply a discussion of gradualism vs. punctuated equilibrium, and perhaps some background on taphonomy and taphonomic biases in the fossil record. And that's all a decent discussion to have, showing students the evidence in support of both gradualism and punctuated equilibrium. In fact, there's evidence for both, so it's probably not an either/or discussion, but rather how they represent opposite extremes regarding the rates of speciation, and what might drive the different rates of change. Although like I said above, this is getting pretty in depth for a high school biology class.

(7) Science concepts. The student knows evolutionary theory is a scientific explanation for the unity and diversity of life. The student is expected to:

(G) analyze and evaluate scientific explanations concerning the complexity of the cell.

Well, yes, cells are complex. I remember learning about that back when I was in high school, and making a model stuffed full of organelles. And if you really want to get into the origins of the complexity, symbiogenesis is one of the topics to discuss in the origin of eukaryotes. And there's an entire field of study for abiogenesis, concerning how life first arose. But again, this might be more detailed than most people expect from high school biology.

(9) Science concepts. The student knows the significance of various molecules involved in metabolic processes and energy conversions that occur in living organisms. The student is expected to:

(D) analyze and evaluate the evidence regarding formation of simple organic molecules and their organization into long complex molecules having information such as the DNA molecule for self-replicating life.

Lots of good stuff to discuss here, as well. I'm sure that teachers would at a minimum bring up the Miller-Urey experiment, as well as other more recent experiments that used different conditions thought to be more representative of the early earth. Teachers could start discussions on the RNA World. And of course, there's that whole field of abiogenesis that I already linked to. But like I said for each of the other questionable standards, and like the expert committee said, this is getting awfully detailed for a high school biology class that has to cover all the other standards and curriculum.

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So, it's troubling that these standards were motivated by creationist misunderstandings of science, and that the Board members went against the recommendations of experts regarding the standards. But at least the letter of the standards isn't horrible, and textbook publishers and teachers can stick to real science. I just hope teachers with creationist sympathies don't use these standards as an excuse to teach junk science.


Updated 2017-02-03: Made numerous small changes

Friday, January 13, 2017

Evolution Book Available Online - From the Beginning

From the BeginningLet's end the week on a positive note. A few years ago, I bought a children's book about human evolution, From the Beginning: The Story of Human Evolution. It was actually a recommendation on a biologist's website, Pharyngula - An updated book list for evolutionists. As PZ Myers put it, it's "An older book that may be hard to get, but worth it for the wall-to-wall drawings of the organisms scattered along the human lineage, from single-celled prokaryote to modern humans." And I have to agree. It may be a little bit outdated by this point, and I did notice a few places where I would have liked to have seen a few things worded a bit differently, but overall, it's a very good overview of human evolution, going all the way back to the very beginning of life. In fact, I'd even recommend it for adults, not just kids.

Well, I got to thinking about that book today, and did a google search on it. And I found something that made me a little excited. The entire book is available online for free from the author's website. So, now I can recommend it to others whole heartedly, knowing that they don't have to hunt it down, but can access it immediately. So, here's the link:


From the Beginning: The Story of Human Evolution (pdf)


If you want to see some of Peters' other books, you can find them here: David Peters Studio - Books.

Well, I guess I'll have one downer in this post, more of a note of caution. As good as that book is, and as talented as Peters is as an artist, he's gotten into a little bit of academic controversy the past few years. He's come up with rather fanciful interpretations of certain fossils, which haven't exactly been accepted by the mainstream scientific community. You can read more about that here, Scientific American blogs - Why the world has to ignore ReptileEvolution.com. Just keep it in mind if you decide to browse Peters' stuff.

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