Monthly Archives: March 2014

Why We Eat Spicy Food

Imagine you are some kind of small mammal, like a rodent. You are minding your own business when you notice a snake sneaking up on you. What do you do? Run? Hide? Fight back? These are all are fine choices. Now imagine that you are some kind of plant. Lacking any ability to detect the presence of animals trying to eat you, you are completely unaware of the cow sneaking up on you. And even if you were aware, what could you do about it? With no ability to locomote, you cannot run, hide or fight back. Now, some plants can hide by being inconspicuous or by blending into their surroundings, but this is not the norm. Some plants can fight back with thorns or spines or hairs, but not all plants do this, either. The third option is to produce chemicals that lower the digestibility of the plant, make the plant taste bad, or are harmful to animals. These three strategies (hiding, fighting and chemical warfare) are all very cool, but it is the third option that I will be talking about today.

Those plants couldn’t run away from the water buffalo. Image from wikimedia.org

Plants actually produce chemical defenses for two reasons: The first is to prevent being eaten by herbivores, and the second is to prevent infection. Plants do not have an immune system in the same way that animals do, so these chemicals are very important in repelling pathogens.
But what does all of this have to do with us? Plants suffer from the same type of parasites that we do — viruses, bacteria, worms, fungi, and protozoa. Before the advent of the pharmaceutical industry, people had to rely on plants for medicine. The compounds that plants produce to keep themselves safe from infection can be harnessed by humans for the same purposes.
Which brings me to the point of this: spices.
Cultures across the world vary in how much spice they use in their food, particularly with meat. Consider the types of cuisine that are the spiciest — e.g. Mexican, Thai and Indian. It’s no coincidence that these countries are in the tropics. Research has shown that spices are used most in areas of the world where there is the highest burden of infectious disease: both in numbers and intensity.

The birds-eye pepper is high in capsaicin, which has antimicrobial properties. Image from wikimedia.org

The most common spices in the world — such as garlic, thyme and cloves — have been shown to be powerful antimicrobial agents. Adding these to food can prevent food spoilage and food-borne illnesses. (Please don’t rely on this as your only method of keeping your food safe.) Infectious disease is a big problem for people in the world today, and has been a big problem throughout human evolution. Food-born illnesses that are a problem for people today include typhoid fever, hepatitis B, Salmonella, Escherichia coli, Listeria, cholera, and Norovirus. Cooking with spices will not eliminate these diseases, but they can reduce the likelihood that you will catch them. Spices don’t just taste good — they can save your life.

Here’s simple experiment you can do at home to test the antimicrobial effects of spices:

I’ve made a simple bread recipe and separated the dough into two equal portions. Store-bought dough will usually contain preservatives (which prevent the growth of bacteria and mold), so you’ll have to make your own if you want this to work.

I’ve kneaded in 1.5 teaspoons of red chile powder to one half of the dough and the same amount of flour to the other, just so both conditions are as similar as I can make them. I used chile powder because I like to cook with it, but you could do this with any spice or herb you wanted:

The dough has been made, and the spice measured out.

IMG_1060

The spice and extra flour has been kneaded into the dough.

I pressed them into flat, round loaves, baked them and sliced each one in half:

IMG_1065

The bread has been baked and is ready to grow mold.

I put all four pieces into a big ziplock bag with a a couple of pieces of moldy cornbread. Mold would grow fine on its own, but seeding it with some already-mature mold helps things move along more quickly. I put a few drops of water in the bag, too, so it stays moist:

IMG_1067

The bread will stay in the bag for the remainder of the experiment. The fresh bread has been seeded with a piece of moldy old cornbread.

After about a week, the plain bread is covered in mold. The spiced bread has a little bit of mold on it, but is mostly mold-free:

At the end of the experiment, the spiced bread is almost entirely free of mold.

At the end of the experiment, the spiced bread is almost entirely free of mold.

The plain bread is covered in mold.

At the end of the experiment, the plain bread is covered in mold.

The chile powder didn’t completely prevent mold growth, but there is certainly a lot less mold on the spiced bread than on the plain bread. Depending on where you are in the world, even a little bit less spoilage could mean the difference between life and death. Try this out on your own and let me know how it worked out.

 

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Human Origins: We are apes and also fish

Last week I talked about the evolutionary origins of birds, which are dinosaurs in every sense. This week I will talk about our own species and where we came from. Spoiler alert: no, we are not dinosaurs.

Not dinosaurs, but we are apes. Actually, let me back up a little bit. Humans are animals. People constantly talk about humans AND animals, as though there is some sort of difference between the two. In biology, an animal is defined as anything with the following traits: multicellularity (check), no cell walls (check), sexually reproducing (check). We have all of the traits of animals, and our evolutionary history is in the animal lineage. Anyway, back to apes.

Apes are a particular lineage of primates that includes the gibbons, siamangs, gorillas, orangutans, chimpanzees, and humans. The “great apes” — a group to which we also belong — includes just the gorillas, orangutans, chimpanzees, and humans. (The gibbons and siamangs are pretty good, but they aren’t great.) Back in the day, it was easy for people to believe that we weren’t. Scientists knew that we were closely related to the apes, but didn’t believe that we were actually in the ape lineage. The anthropologists studying humans and our relatives believed that, of all of the apes, humans were the ”out-group.” Said differently, they believed that the following cladogram was correct:

Incorrect ape cladogram

Incorrect ape cladogram. Humans are most closely related to chimpanzees.

Humans (and our recent ancestors and relatives, like the neanderthals, Homo erectus, Australopithecus afarensis, etc.) were classified in the group “Hominidae” and the other apes were in the group “Pongidae.” But then they did more research and found that this was not correct. With the advent of genetic testing, it was discovered that the human genome is about 99% identical to that of the chimpanzee. Human anatomy and physiology is nearly identical to that of the chimpanzees. Humans have 23 pairs of chromosomes, compared to 24 pairs in the other great apes. Upon closer examination, our chromosome #2 is the result of the end-to-end connection of two of the chromosomes from the other great apes.

Correct ape cladogram

Correct ape cladogram

From this, it is clear that we cannot continue to call humans hominidae and the non-human apes “Pongidae” for the same reason that we have to call birds dinosaurs.

As it stands, there are two species of chimpanzee: the common chimpanzee (Pan troglodytes) and the bonobo or “pygmy chimpanzee” (Pan paniscus). We are so similar to these two chimpanzees that some biologists advocate classifying humans (Homo sapiens) and chimpanzees in the same genus — either reclassifying humans as Pan sapiens or the reclassifying the chimpanzees as Homo troglodytes and Homo paniscus.

In addition to being apes, we are also fish. This usually comes as more of a shock to people than the news that we are apes. It is not through a technicality or semantics that we are fish. We are fish in the same way that we are apes or that birds are dinosaurs. We may not look like fish outwardly, but we are made up of traits — very important traits — that first evolved in organisms that were unambiguously fish: Before fish, there were no animals that had a bony skeleton. Only fish and their descendants have this trait. This alone places us in the group “Osteichtheys” which literally means “bony fish.” Early vertebrates had no jaw. The jaw first evolved from a “gill arch,” which is a bony structure that supports the gills in fish. Early vertebrates had no teeth, either, until they evolved out of fish scales. Human embryos have gills, one of which develops into a jaw. In rare cases, babies are born with (non-functioning) gills.

All vertebrates, including humans, have gill slits as embryos. Image from evolution.berkeley.edu

All vertebrates, including humans, have gill slits as embryos. Image from evolution.berkeley.edu

Most of the fish that we know are not the type of fish that we evolved from (and still are). There are three main groups of fish: The first are the cartilaginous fish (Chondrichtheys), which include the sharks and rays. The second are the ray-finned fish (Actinopterygii), which include most of the fish that we eat: trout, tuna, cod, halibut, flounder, bluefish, etc. The third are the lobe-finned fish (Sarcopterygii), which include the coelocanths, the lungfish, the amphibians, the reptiles, and the mammals. The lobe-finned fish have fleshy, limb-like fins that were the anatomical basis for the arms and legs of the land vertebrates.

Fish cladogram

This cladogram shows that humans evolved from fish.

We are fish. We are fish that crawled out of the water and evolved for life on land, but we are still fish. Outwardly, we do not look much like fish, but the anatomical, developmental and genetic traits that we have give away our heritage. That we are fish or that we are apes does not in any way detract from our humanity. Our evolutionary heritage connects us to other organisms in a way that enriches our understanding of ourselves.

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Dinosaurs are not Extinct

Let me get this out of the way up front: Birds are dinosaurs. Birds are not LIKE dinosaurs. They are not BASICALLY dinosaurs. They are not RELATED to dinosaurs. They are not dinosaurs *nudge*nudge*wink*wink*. They are literally dinosaurs. Period. To this end, scientists use the term “non-avian dinosaurs” when they want to describe the things we called dinosaurs when we were kids but not birds. With a little bit of genetic manipulation, you can actually turn a bird into a more recognizable dinosaur

Scientists have known this for some time, now, and the evidence is still mounting. Birds have skeletal features that clearly place them within the dinosaur lineage, but there is more exciting evidence. Within the last 20 years, scientists have discovered that many non-avian dinosaurs had feathers and were warm-blooded, just like modern birds. Although birds are the only living lineage of reptiles that are bipedal, they belong to a lineage of dinosaurs that was also bipedal — the “Theropods.”  This lineage also includes fan favorites such as the Tyrannosaurus rex and Velociraptor, as well as the Dilophosaurus, Allisaurus, Ornithomimus, and Compsognathus. More specifically, modern birds belong to the “Maniraptora” lineage, which makes them particularly close relatives of the Velociraptor and Deinonychus. As you can see, birds are not classified as dinosaurs by a mere technicality. Birds are buried so deeply within the dinosaur lineage that it is basically impossible to classify anything that we like to call dinosaurs as dinosaurs without including birds. Although birds superficially resemble the pterosaurs, pterosaurs are not the direct ancestors of birds, nor are pterosaurs true dinosaurs. The following cladogram shows the evolutionary relatedness of birds, non-avian dinosaurs, and other reptiles (for help in interpreting cladograms, go here):

A cladogram showing the relatedness among birds, non-avian dinosaurs, and other reptiles.

A cladogram showing the relatedness among birds, non-avian dinosaurs, and other reptiles.

Pterosaurs were flying reptiles that superficially resembled birds. The two are not very closely related. Image from wikipedia.org

The Archaeopteryx is a fantastic transition fossil between birds and their ancestors, possessing traits of both modern birds and the ancient Maniraptors. Like modern birds, Archaeopteryx had large wings with large feathers, and a beak. Like the ancient Maniraptors, the Archaeopteryx had small teeth, and lacked the ridged or “keeled” sternum that serves as an attachment point for the flight muscles of modern birds. The hand bones in the front limbs of Archaeopteryx were not fused together like modern birds, but separated into long fingers just like the Velociraptor.

Archaeopteryx fossil. Feathers are clearly visible. Image from ucmp.berkeley.edu

Modern discussions of the relatedness among organisms typically involve mention of DNA evidence. For example, part of the reason that we know that humans are more closely related to chimpanzees than we are to gorillas is that our DNA is more similar to that of chimpanzees than it is to that of gorillas. The reason that I haven’t mentioned this yet is because we don’t have any. DNA is a fairly stable molecule, but it will break down over time. Under the best conditions, we can sequence DNA that is tens or hundreds of thousands of years old. In warm, humid climates, however, DNA doesn’t last more than a few thousand years — this is why scientists were unable to sequence the genome of the recently discovered “hobbit” fossils (Homo floresiensis), even though they are less than 10,000 years old. It may be possible in the future, but with modern technology no one has ever extracted DNA from a sample 65 million years old.

But DNA is not the only type of molecular analysis. In 2005, a group of paleontologists discovered, wait for it, soft tissue from a T. rex that was still soft and flexible. I’m going to pause for a second to let that sink in. Take all the time you need.

Soft tissue from a T. rex. Image from nbcnews.com

By some fluke of nature, the conditions were perfect for this tissue to remain soft, flexible, moist, and mostly undamaged for the last 68 million years, which is the estimated age of the fossil. My own excitement over this cannot come close to that of the scientists who made this discovery.

Although the scientists were unable to recover DNA from the sample, the proteins were still intact. DNA works by telling what amino acids to assemble and in what order to form a protein. Similarity in this strand of amino acids can be used to determine relatedness among organisms in the same way that is done with strands of DNA. Sure enough, they compared this sequence to that of modern birds and it was a close enough match to place birds within the dinosaur lineage.

Consider this: most Americans eat dinosaurs on Thanksgiving.

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Testing a Claim: Ceramic Knives

This post is going to read a little bit like an episode of MythBusters. Testing claims is not something I plan to do regularly in this blog, but this particular one concerns something I’m very interested in (knives) and something I’ve written about in the past. Yes, this is going to be my third post on what makes food turn brown. See my other two here and here. This blog is about science, and science is fundamentally about testing claims; either claims made by yourself or claims made by someone else. Science typically deals with testing a hypothesis — a formal, scientific claim made by a scientist — but the scientific method can be used just as well to test less formal claims. 

 On to the topic at hand…

A friend of mine gave me a ceramic paring knife for christmas (Thanks, Jack!). In researching the properties of ceramic knives, I came across a claim that seems to be made by almost everyone advocating their use: using ceramic knives prevents food from turning brown after it has been cut. See, for example, this video

One common explanation given for this purported phenomenon is that contact with the food causes steel blades to corrode and leave brown residue on on the food. Ceramic does not corrode, so it cannot cause food to turn brown for this reason. The video I linked to mentions “ion transfer” as the mechanism of browning. I don’t know what that is, but its predictions are basically the same as the corrosion mechanism.

I have written before about one factor that makes food turn brown (here and here). You will understand this post better if you read my previous ones, but I will summarize them briefly in case you’re short on time: When a fruit or vegetable is damaged (either by cutting or bruising), it produces a brown substance that prevents bacterial infection. This process is triggered by exposure to atmospheric oxygen. 

But let’s pretend for a minute that we don’t know anything about enzymatic browning. What we think will happen will only get us so far — let’s do some science and see what actually happens. 

If the stories are true — that food will turn brown faster with steel blades because of the corrosion of the steel — then a blade made of non-stainless steel will cause a stronger effect of food browning than a blade made of stainless steel, and both steel blades will cause a stronger effect of food browning than a blade made of ceramic. 

I will use three paring knives in this experiment:

Top: The ceramic knife that was given to me. There are no markings on the blade and I threw away the package, so I have no idea what brand it is, but I know it was made in China. I’m pretty sure it is made of zirconium dioxide.

Middle: This is a handmade knife made of 52100 steel. This steel has no corrosion resistance to speak of. 

Bottom: A J.A. Henckels Zwillinge Pro S paring knife. The steel is X50CrMoV15. It is very resistant to rust and other corrosion.

 Knives_Fotor

I have selected three foods to test these knives on: apples, potatoes and onions. I have already discussed the process of browning in apples and potatoes, so they will be good for this experiment. The naturally-occurring chemicals in onions can be corrosive to steel, so this is another good food to use in this experiment. I cut each of these three foods with each of the three knives to see what would happen. 

Here is the initial setup for this experiment. The column on the left was cut only by the ceramic knife, the column in the middle was cut only by the non-stainless steel knife, and the column on the right was cut only with the stainless steel knife:

t=0_Fotor 

After four hours, not much has happened. There is a little bit of browning in the apples, but nothing in the potatoes or onions:

T=4_Fotor 

After a total of six hours, the apples are continuing to brown, but the potatoes and onions don’t look any different: 

t=6_Fotor 

After a total of nine hours, all of the potatoes are starting to brown very slightly: 

t=9_Fotor

 Twenty four hours into this experiment, the apples and potatoes are quite brown and dried up. The onions have dried a little bit but haven’t changed color: 

t=24_Fotor

At the end of the experiment, and at each documented time, there is no discernible difference in brownness between the foods cut with the ceramic, stainless, or non-stainless blades. 

The point of this is not just to test this particular claim, but that it can be very easy to test claims that people make. While this particular claim turned out to be false, other claims are true. The purpose of science is not to find a particular answer, but to find out what the correct answer is. 

This experiment also highlights the importance of comparing different experimental conditions. A poor way to test this claim would have been to cut food only with a ceramic knife and to leave it out. I am used to potatoes turning brown in just a couple of hours, but in this experiment they were still white after nine hours. (It was fairly cold in my kitchen when I did this experiment which probably explains why it took so long for the potatoes to turn brown.) If I had only used potatoes and only cut them with a ceramic knife, I might have incorrectly concluded after nine hours that the ceramic knife prevented the browning. But by comparing the three knives simultaneously, I found that the potatoes all took longer than I expected to turn brown and not just the one I cut with the ceramic blade. 

A scientist doesn’t have to be someone with a fancy degree working in a laboratory. A scientist is just someone who makes discoveries about the world using the scientific method. Go be a scientist. 

 

 

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