Big News in Epigenetics!

The Grand Prismatic Spring in Yellowstone National Park holds bacteria like the ones in the study being discussed.
(click for credit)

The more we learn about creation, the more it surprises us. While it is true in all areas of science, it seems particularly true in genetics. When I was at university, I was taught as definitive fact that each gene in my DNA determined the makeup of one protein in my body. We now know that is false. I was also taught as definitive fact that the only way a parent can transmit a trait to its offspring is through the sequence of nucleotide bases in DNA. As a result, if a new trait appears in a population, it must be due to a change in the species’ DNA sequence. We now know that is false. For example, I was taught as definitive fact in university that cave fish are blind because of mutations to their DNA. We now know that is false, at least for one species of blind cave fish.

So we now know that there are ways to inherit traits that go beyond the DNA sequence that you inherit from both parents. For example, we know that if you train mice to fear a certain smell, the next generation can inherit that fear. It’s not that the parents train the fear into their offspring (the offspring were raised separate from their trained parent). They actually inherited the fear. How in the world can a parent pass on a fear of something to its offspring? That’s what the field of epigenetics (which literally means “on top of genetics”) wants to find out.

We know that it has something to do with how an organism regulates the activity of its genes. An organism can alter chemical aspects of the DNA that are not related to its actual sequence, and that alteration can decrease the use of a gene, increase the use of a gene, turn a gene off so that it is not used at all, or turn a gene on so that it will start being used. For example, most people are not born lactose intolerant. After all, they drink their mother’s milk or a milk-based formula. Milk digestion requires the enzyme called “lactase,” which is coded for by a gene. While everyone has that gene turned on at birth, in some people, it gets turned off later on, causing lactose intolerance. Nothing has changed in the person’s DNA sequence – the gene is still there and has not been broken. However, that gene has been turned off by epigenetic mechanisms. It is thought that this process is responsible for epigenetic inheritance. To some extent, we must be able to inherit the “off” and “on” status of our parents’ genes.

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Another Reason to Doubt the Global Climate Models

The study discussed in this article was performed in Puerto Rico’s El Yunque National Forest.

If you have been reading this blog for a while, you probably know that I am very skeptical of climate models that predict the consequences of rising carbon dioxide levels in the atmosphere. Initially, this was due to my own experience with large-scale computer models. In my early scientific research, I both wrote and used them, so I know how much their results are affected by the assumptions programmed into them. As time has gone on, my skepticism has increased, since it has been demonstrated over and over again that the climate models do not line up with the most relevant data.

Why do the climate models compare so poorly to the appropriate data? Mostly because they contain many assumptions that have not been tested. Typically, these assumptions neglect the idea that the earth has negative feedback mechanisms, which are the hallmark of nearly every well-designed system. As time has gone on, many such negative feedback mechanisms have been found, and they typically run counter to the assumptions programmed into the climate models (see here, here, and here, for example). It seems that a graduate student from the University of Virginia (Stephanie Roe) has found yet another of earth’s negative feedback mechanisms.

There is a lot of dead, decaying matter on the floors of the tropical forests of the world. As that dead matter decomposes, it releases carbon dioxide into the atmosphere. Well, decomposition is driven by chemical reactions, and chemical reactions speed up with increasing temperature. So, as the world warms, what should happen to the rate of carbon dioxide produced by decomposition? It should increase, right? That will release more carbon dioxide into the air, which will accelerate warming. This is an example of a positive feedback mechanism. In such a mechanism, a change promotes a process that amplifies the change. This particular positive feedback mechanism is programmed into the climate models that are being used to predict the consequences of increased carbon dioxide in the atmosphere.

While that assumption makes perfect sense, the real world often works differently from our simple assumptions. That’s one reason Stephanie Roe decided to test it. She went to Puerto Rico’s El Yunque National Forest, where the US Forest Service set up infrared heaters in different parts of the forest. Those heaters were programmed to keep their surroundings 4 degrees Celsius warmer than the rest of the forest. Those parts of the forest, then, should behave like the tropical forests will behave if the earth warms by an average of 4 degrees. In addition, there were parts of the forest where identical, non-working heaters were placed. They served as control areas – they stayed at the normal temperature of the forest, but they had the physical structures of the heaters present. Roe introduced various kinds of dead matter (both native and non-native) to the forest in both the warmed sections and the control sections. She then collected samples later to test the rate of decomposition in each.

What did she find? She found that the result was precisely opposite of what is programmed into the climate models. The warmed areas of the forests had slower rates of decomposition than the control areas. Why? According to her research, it is because the warmer parts of the forest were drier. The process of decomposition is accelerated strongly by moisture, so the loss of moisture slowed down the decomposition more than the higher temperature sped it up. Thus, according to her research, increased temperatures should reduce the amount of carbon dioxide produced by decomposition. This, of course, is an example of a negative feedback mechanism: a change promotes a process that decreases the rate of change. Once again, such mechanisms are the hallmark of designed systems, so it is not surprising that it exists here on earth.

The more we learn about climate, the less confidence I have in the predictions of the climate change doomsayers.

What a Way to Bring in the New Year!

An aerial view of the Large Hadron Collider’s layout. The particle accelerator is used for high-energy physics experiments. (click for credit)

I wasn’t planning on writing a post today, but as I was going through my email, I saw a wonderful message from a homeschool graduated who used my curriculum, and I just had to post about it. I am keeping the person’s name and some of the professional details confidential (using square brackets to paraphrase and ellipses to cut), because I don’t want the person’s presence on a creationist blog to be harmful to his or her career. It’s sad that I have to do that, but many of the high priests of science are the most anti-science people on the planet, excommunicating those who do not accept their dogma.

Here is the wonderful message I received:

I am writing to thank you for your excellent high school science courses. As a homeschooler, I really appreciated the readability of the texts. The challenging material helped me to develop effective study habits, while your clear enthusiasm for each subject led me to develop a lasting interest in the sciences, especially physics. In fact, after working through Module 8 (“Gravity and Relativity”) of your Advanced Physics Course, I decided to pursue a career in physics. Though I didn’t really have any idea of what that would entail, I figured that your science courses would be an ideal preparation, and indeed they were! Largely due to to the strong foundation that your courses (Physical Science, Biology, The Human Body, Chemistry, Advanced Chemistry, Physics, and Advanced Physics) had provided me throughout middle school and high school, I was able to complete my BS in physics a year early. This helped me to be successful in the treacherous grad school application process, and I am now a [graduate student at a well-known university] pursuing a PhD in experimental particle physics; I’m [doing original research at facilities like the one pictured above]; these are goals that I have looked forward to for a long time. Your courses have been key in successfully beginning to achieve these goals…so thank you for helping to make all of this possible!

As one further note, I’d also like to add that I really appreciate how your texts touched on more advanced topics, even if only to ultimately concede that they were “beyond the scope of this course.” Though I found it a bit frustrating at the time, it really motivated me to keep pushing deeper into the subject, making it all the more satisfying to finally encounter the topic in a later class. For example, your brief description of solving the Schrodinger equation for hydrogen (page 50 of your Advanced Chemistry text) had me on the edge of my seat until finally reaching this problem in undergrad Quantum II. Currently, my Quantum Field Theory textbook tends to make the same sort of statements…and it reminds me of your superlative texts (though when I come across statements like these in QFT, it tends to make me relieved rather than frustrated – I’m happy to leave that particular calculation to the theorists!).

Anyway, I’m sure you get many messages like this, but I just really wanted to let you know how much I enjoyed your texts and how much they have aided me in the career path that they inspired me to pursue…

Merry Christmas and Happy New Year!

There are so many wonderful things to say about this student’s message to me, but I will limit myself to two:

1) I love the fact that this person was “on the edge of” his or her seat because of a solution to the Schrodinger equation!

2) This once again demonstrates that Bill Nye has no idea what he is talking about when he claims that creationist materials are a detriment to science. This student learned junior-high and high-school science from creationist materials, and those materials inspired him or her to be doing the kind of original scientific research that Nye can only dream about doing.

How Science Brought Another Atheist to Christ

John T. Tolbert, an evangelist in Asia (click for credit)

If you have been reading my blog long, you probably know that I was once an atheist. However, the more science I learned, the less intellectually tenable that position became, so I eventually came to believe in some sort of Creator. Over time, lots of additional study led me to believe in the God of the Bible. As a result, I am always interested to learn about other atheists who became Christians. Indeed, I have a category about such people on this blog. I am especially interested in those, like myself and others (see here, here, and here, for example), whose spiritual journeys were particularly influenced by science. I came across another example just a few days ago.

His name is John T. Tolbert, and he is currently working as an evangelist in Asia, primarily with the Vietnamese people. However, he wasn’t always interested in bringing people to Christ. As a child and young man, he thought that there must be a God, but his parents were divided on the subject (his father was an atheist and his mother was Irish Catholic). Because of his mother, he spent eight years in Catholic school, but he says that he never even opened a Bible. Then, when he was in basic training for the Vietnam War, he was given Mark Twain’s book, Letters From the Earth. The book was published after Twain had died, but its content focuses on his disdain for Christianity. Despite having never read the Bible, Twain’s book convinced Tolbert that there is no God.

After the war, Tolbert went to university and eventually studied to be an attorney. He ended up practicing law in Wilmington, Delaware. That’s when his life took an amazing turn. According to him:

…our law firm was retained by the pastor of a church and I was assigned the case. This pastor always brought a Bible with him, and often prayed about decisions that had to be made – right in front of me, and out loud. I had never experienced such a strange thing.

However, thinking I was so much smarter than he, after a few weeks, I challenged him. I picked up his Bible put it right up to his face, and said “How can you believe the Bible when it is wrong in the very first chapter?” He smiled, and responded, “What do you mean, Mr. Tolbert? Evolution?” I said “Yes. Six day creation, Noah’s Ark. Come on!” He smiled again, and asked me a question that changed my life. He said, “You’re a lawyer right? Do you always form conclusions before you’ve studied both sides of the evidence?”

Obviously, that statement made Tolbert realize that he had never properly investigated Christianity. So, the pastor gave him some resources that were focused on the scientific evidence for creation. As an attorney, Tolbert was familiar with the fact that evidence can be “twisted” to fit a particular view, so after reading the books, he checked their sources to see if they were being honest about the data. As he says:

There was no distortion, twisting or misquoting. I slowly pushed my chair back from the table covered with all the original source materials, and said to myself, “Evolution is the biggest fraud that has ever been perpetrated upon the world. I have been deceived.”

Now, I don’t completely agree with Tolbert’s last statement. Evolution itself is not “the biggest fraud that has ever been perpetrated upon the world.” When we knew little about genetics and the details of the cell, evolution as a creation story actually made some sense. However, the more we have learned about the details of biology (especially molecular biology and genetics), the less tenable it has become. Add to that the fact that the fossil record speaks strongly against it, and you end up having a hypothesis with little scientific merit. However, the hypothesis itself is not a fraud. I would say that the certainty with which some promote it is a fraud, at least from a scientific point of view.

Nevertheless, Tolbert’s story is fascinating. While he is not a scientist, he was trained to examine and evaluate evidence. He was given the scientific evidence for a Creator, and he ended up finding the evidence persuasive. That led him to Christ. God calls to all of us in different ways, because He desires that we all come to know Him (2 Peter 3:9). I pray that you come to know Him as well!

Mistake in Satellite Placement Used To Further Confirm Relativity

The incorrect placement of ESA satellites in orbit has been used to confirm general relativity to the highest precision yet. (click for credit)

One of the things I continually stress with my students is that science doesn’t have to make sense. In fact, most of the theories in my scientific field make no sense at all. Why do I believe them? Because they make predictions which are later verified by the data. That’s the acid test of a scientific theory. If it can make predictions about something that is not known and those predictions can then be tested by experiment or observation, the theory is scientific. If observations or experiments actually confirm the predictions, then it is a reliable scientific theory. For example, young-earth creationism is a reliable scientific theory, because it makes predictions which are later confirmed by the data.

The same can be said of Einstein’s theory of general relativity. Make no mistake: It’s a very strange theory. It says that what we see as the force of gravity is not really a force at all. It is a consequence of how mass warps space and time. Now that’s just crazy. We know that we stay on the surface of the earth because the force of gravity continues to pull us to the center of the earth. An apple falls from a tree because the force of gravity pulls it to the earth. The earth stays in orbit around the sun because the force of gravity keeps it there. Sir Isaac Newton himself gave us an equation for gravity, and that equation has been tested over and over again and found to be reliable. It begins “F =”. The “F,” of course, stands for force. Why,then, would you believe something as silly as what Einstein said? Because his theory made several testable predictions, and when those predictions were tested, they were confirmed.

One of the stranger predictions of general relativity is that mass warps space and time enough that it actually affects the passage of time. When you are near a large mass, time passes more slowly than when you are far from that same mass. According to Einstein, then, time is not constant in the universe. It ticks at different rates, depending on the mass in the area. Once again, to you and me, that’s just crazy. However, it has been confirmed in many different experiments. Indeed, the Global Positioning System would not work if we didn’t take into account that time is ticking differently on the GPS satellites than it is on the surface of the earth. Of course, one hallmark of good science is to continually test your theories, even when they have been confirmed. My publisher told me about a recent example of this being done, and it is worth discussing.

Back in 2014, the European Space Agency launched several satellites into orbit around the earth. Satellites are generally put in a circular orbit, so their distance from the earth never changes. However, a malfunction in the rocket used to place two of the satellites caused them to be put into an elliptical orbit. As a result, their distance from the earth regularly varied. The ESA corrected the orbits as much as they could, but they remain elliptical to this day. The difference between their closest and farthest distances from the earth is about 8,500 kilometers.

While this was a disappointing mistake, two physics research teams realized that they could use it to further test Einstein’s prediction of time being affected by how close you are to a massive object. After all, at regular intervals, these satellites moved closer to and farther from earth. Their position could be accurately measured in real time, using the International Laser Ranging Service, which shoots lasers at the satellites and measures the time it takes for the light to reflect off them and return.

The teams independently examined the time measured by the clocks aboard the satellites, and they each produced a graph similar to the one at the top of this post. Both of them showed that the time measured by the clocks aboard the satellites varied just as Einstein had predicted: As the satellites drifted away from the earth, time started passing more quickly for them. As the satellites drifted towards the earth, time passed more slowly for them. What makes their results noteworthy is that this test is more precise than any other that has ever been done. Their results tell us that the maximum error in Einstein’s prediction is about 0.003%.

Like it or not, the general theory of relativity is the best description scientists have for gravity, as these misplaced satellites have further confirmed.

Students Compare Homeschooling to Conventional Schooling

Students who transition from homeschooling to conventional schooling note that homeschooling allows them to learn more and have more realistic social experiences. (Credit: IowaPolitics [left] and Audio-Luci [right] | Flickr Creative Commons)

How does homeschooling compare to conventional schooling? I have read lots of different opinions written by educators, parents, and politicians. However, I haven’t read a lot from students. This is somewhat understandable, since many homeschooled students never experience a conventional school, and the vast majority of conventionally-schooled students never experience a home school. However, I recently read a paper published in the journal Cogent Education that summarized the views of 40 Australian students who had experienced both forms of education. Their views were quite enlightening.

Many of them valued the flexibility that home education gave them. They could choose to focus more on the areas that interested them. This was especially true if their parents took a less-structured approach to their curriculum. They also valued the freedom that comes with homeschooling. They could choose the times they studied, played, slept, etc. This was especially helpful when they were doing long-term projects. In contrast, they found the conventional school they attended to be limiting because of time tables, commutes, and the necessary fact that the classes were geared to teach students of average ability. This wasn’t true of all the students, however. Some found the structure and regulation of a conventional school to be a nice change of pace.

What I found more fascinating were the cultural differences the students noticed between home and conventional schools. For example, based on his interviews with the students, the author notes:

The most common cultural feature of home education has been family recognition that each child is unique and programmes require individual tailoring.

He discusses how the students saw that play out in homeschooling. He then discusses what the students thought about how that works in conventional schools:

In conventional schools there was written and verbal recognition that each child was unique and needed personalised learning programmes, however, delivering this type of approach was restricted by the structures of conventional schools.

This is something I have always stressed in my talks with homeschoolers. One very important benefit that homeschooling gives you is the ability to tailor your child’s education to meet his or her specific needs.

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Homeschooling In Israel

A shelf with books in Hebrew (click for credit)

Many people think that homeschooling is unique to the United States. However, nothing could be further from the truth! Homeschooling is a worldwide phenomenon. For example, I have spoken at homeschooling conventions in Canada, South Africa, Australia, New Zealand, South Korea, and Thailand. In addition, I have spoken to homeschoolers in one country that I can’t mention because it is illegal to homeschool there. In my interactions with homeschooling families all over the world, I have seen lots of differences. In South Korea, for example, many families homeschool because they think the school system is far too demanding. In high school, for example, South Koreans use the “five hour rule,” which states that if a high school student gets even five hours of sleep a night, he or she will not be able to go to college. On the other hand, many homeschoolers in the United States (myself included) choose to homeschool because the schools are not demanding enough of their students.

Despite the differences among homeschoolers worldwide, there are many similarities. One example of this comes from a country that I have not yet visited: Israel. Two senior lecturers from Western Galilee College in Akko, Israel recently published a small study in which they interviewed 30 Israeli homeschooling mothers to find out why they homeschool and what benefits they have seen as a result of homeschooling. While reading the paper, I was struck by the similarities between homeschooling in Israel and homeschooling here in the U.S.

For example, the mothers generally thought that homeschooling made their children more inquisitive. I find that is true of homeschooled students in the U.S. as well. I teach at a university where there are some homeschool graduates (and some who are still being homeschooled) as well as a lot of public and private school graduates. I find that the homeschool graduates are significantly more likely to participate in class, and they are even more likely to ask me questions that go well beyond the requirements of the course. The homeschoolers are simply more inquisitive than their peers.

The mothers in the study also thought that their children had more self-confidence and weren’t afraid of being labelled as “different.” This is something I see with homeschooled students all over the world. Regardless of the culture they are in, homeschooled students are more likely to challenge the “norms” of the culture and do what they think is right, regardless of what their peers think. In my opinion, that is one of the major benefits of homeschooling. In this era where people actively seek to punish and even harm you if you rebel against the groupthink that has infected the culture, it is more important than ever to produce young people who are willing to be different.

By far the most important benefit that these mothers identified was that their children were not poisoned with age prejudice. This is also true of homeschoolers throughout the world. Group schooling (government or private) promotes the idea that students should only make friends with people who are roughly their own age. After all, children spend most of their school day cloistered away in ghettos, surrounded by children who are roughly their own age. As a result, they don’t get much experience interacting with people of other ages. Homeschooling is generally quite different.

While homeschooled children will spend some time with friends their own age, they tend to spend most of their time with family members, which span the age spectrum. In addition, when homeschooling groups get together, all ages are generally included. This produces a very healthy environment for socialization that is sadly lacking in most schools. As a result, homeschooled children are more likely to socialize with people of all ages. I remember being struck by this the very first homeschooling event that I attended. I saw the high-school students playing with the elementary kids and actually enjoying themselves. I also had young people introducing themselves to me and engaging in conversation. I have spent time with students of all backgrounds throughout my teaching career, but I almost never see healthy, age-independent socialization except when I am at a homeschooling event.

Despite these similarities, there are differences between homeschooling mothers in the U.S. and the homeschooling mothers in this study. For example, none of the mothers mentioned any religious motivations for homeschooling. While the number of mothers in this study is small, I would suspect that if if the same study were done in the U.S., the majority of mothers would have included religion as at least part of their motivation for homeschooling. Also, while it might have been an artifact of the study, there was no mention of academic achievement. The mothers mentioned many benefits of homeschooling, but academic achievement was not among them. Once again, had this study been done in the U.S., I would suspect that academic achievement would have been mentioned by several mothers.

In the end, it seems that homeschoolers around the world have some differences among them, but those differences pale in comparison to the things that they have in common. I hope more research like this is done, because the more we learn about homeschooling, the more we see its benefits worldwide!

Is This Object from an Alien Spacecraft?

An artist’s impression of the strange object named ʻOumuamua (click for credit)

On October 19th of last year, Dr. Robert J Weryk discovered a new object in the night sky. It was too small and far away to appear as anything but a tiny speck of light in the Pan-STARRS 1 telescope, but it was definitely moving. Subsequent analysis of its path shows that it may not be a part of our solar system. Based on its trajectory and speed, it probably originated in interstellar space and is just “passing through” the solar system.

If that’s true, it is the first object from interstellar space that has ever been seen by human researchers. Its technical name hasn’t been quite decided, since it is apparently the first of its kind. However, its name will start with “I1” – “I” for interstellar and “1” for the first one seen. However, it has been “nicknamed” ʻOumuamua, which is derived from the Hawaiian word for “scout.”

Once again, it is too small and far away to be seen as anything but a white dot in our most powerful telescopes. Indeed, there are many telescopes that cannot even see it, because it doesn’t produce enough light. However, based on the wavelengths of light that it reflects from the sun, it is thought to be red in color, highly elongated, and probably flat. That leads to the artist’s impression shown at the top of the post. Once again, these inferred characteristics are not the result of direct observation but, instead, are based on calculations that explain the wavelengths of light we receive from the object when it is viewed at different times.

Why am I blogging about this? Partly, because it may very well be the first interstellar object we have observed in our solar system. Any first discovery like that is important. The other reason is because of something suggested by Harvard astronomers Shmuel Bialy AND Abraham Loeb. They offer some scenarios that explain both the characteristics and the interstellar origin of the object. Among them:

Alternatively, a more exotic scenario is that ‘Oumuamua may be a fully operational probe sent intentionally to Earth vicinity by an alien civilization. (emphasis theirs)

Since I am on my way to speak at a science fiction convention (something I do almost every year), I thought it was only appropriate to write about it. Dr. Weryk (the object’s discoverer) disagrees, as do I. Nevertheless, I plan to work this in to at least one of the panel discussions on which I am participating this weekend!

Meet The New Apex Predator

A portion of the wind farm that was analyzed in the study being discussed (click for credit)

An apex predator is defined as a predator with no natural predators. People, lions, killer whales, and bears are typical examples. Now we can add one more to the list: wind turbines. Research indicates that in the U.S. alone, wind turbines are responsible for killing more than half a million birds every year. More than 80,000 of those birds are raptors, the former apex predators of the air.

While China and the U.S. lead the world in the amount of power generated by wind farms, India is not too far behind. As a result, a group of researchers from the Indian Institute of Science decided to study the ecological impacts of wind turbines. They analyzed turbines that have been installed in an Indian Mountain Range called the Western Ghats. Some of those wind turbines are pictured above. Specifically, they wanted to see if the predatory nature of wind turbines had other effects on the local ecosystem. Not surprisingly, it did.

First, they found that predator birds were four times less likely to be in the areas where wind turbines are installed compared to areas where they are not installed. That’s not surprising. Animals tend to avoid areas where they are preyed upon. Of course, the opposite is true as well. Animals tend to flock to places where they will not be preyed upon. As a result, the population of fan-throated lizards (a favorite meal of predator birds in the area) is significantly higher around wind turbines.

Interestingly enough, the effect of wind turbines was not limited to populations. The lizards’ behavior changed as well. Apparently, life is so carefree for the lizards living near the wind turbines that they have lost some of their fear of predators in general. The researchers tried to simulate predator attacks and found that they could get significantly closer to lizards that live near the wind turbines than they could get to lizards living where there are no wind turbines. Based on subsequent blood tests, the researchers concluded that lizards living near wind turbines have significantly less corticosterone (a stress hormone) in their blood.

So in the end, the ecological effect of wind farms goes beyond the slaughter of birds (and bats). It “trickles down” the food chain as well. The authors say:

By adding an effective trophic level to the top of food webs [by being an apex predator], we find that wind farms have emerging impacts that are greatly underestimated. There is thus a strong need for an ecosystem-wide view when aligning green-energy goals with environment protection. (bracketed statement mine)

I predict that as more research is done, we will see many more unexpected ecological effects from wind farms.

Another Failed Evolutionary Prediction

A common fruit fly, Drosophila melanogaster (click for credit)

The acid test of a scientific theory is whether or not it can make testable predictions about things that are not known. If it can’t, it isn’t really a scientific theory. If it can, those predictions should be tested by observation or experiment. If the results of the test confirm the predictions, you can have more faith in the theory. If they do not, you must either alter your theory or abandon it. One of the main reasons I am a creationist is that creationism has made many testable predictions, and many of those predictions have been confirmed. In fact, creationism has a much better track record when it comes to confirmed predictions than does evolution (see here and here).

Recently, I ran across another study that demonstrates another failed prediction of evolutionary theory. It studied the alcohol dehydrogenase protein (ADH) as made by fruit flies. Fruit flies often consume alcohol because they feed on rotting materials, and the ADH they make allows them to do that. How do they make ADH? They have a gene that gives the necessary instructions to the cell. That gene is, in effect, a “recipe” for ADH.

Studies have already shown that the common fruit fly (Drosophila melanogaster) tends to feed on alcohol-rich things (like rotting fruit) more than a similar fruit fly, Drosophila simulans. The evolutionary explanation that has always been given for this fact is that these two fruit flies had a common ancestor, and that ancestor had a gene that made less efficient ADH. As a result, the common ancestor didn’t eat alcohol-rich things.

The evolutionary line that led to the common fruit fly experienced mutations in the ADH gene, and those mutations ended up making the ADH more efficient. Natural selection then caused those fruit flies to survive, because they could now survive by eating a lot of rotting fruit, while the other flies could eat only a little rotting fruit. That process continued over time, eventually leading to the common fruit fly we see today, which eats a lot of rotting fruit. In evolutionary biology lingo, we would say that the common fruit fly underwent “positive selection” in its ADH gene, while the other fruit fly did not.

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