Tag Archives: Natural Selection

10% Of Our Brains?

There is a new movie coming out later this month called “Lucy.” (See the trailer here.) The premise of this movie is that humans only use 10% of our brains, and Scarlett Johansson  gets superpowers by using more than 10% of hers. This idea that we only use 10% of our brains, but would be better if we used more, is a very persistent myth in our society.

Disclaimer: My point here is not to rain on anyone’s parade. I love science fiction movies, and if Luc Besson’s record is any indication, this one will probably be good. (Personal note: Luc Besson wrote and directed my favorite movie.) Even though I am a scientist, I am usually willing to suspend my disbelief for whatever premise the movie asks me to accept. I am not trying to convince anyone that they shouldn’t watch this movie or that it will suck because it gets some facts wrong. The release of this movie is just a convenient opportunity to talk about an oddly persistent myth.

Now back to the show…

My first exposure to this myth was probably as a child when I read the book My Teacher Fried My Brain — the second book in the My Teacher Is An Alien series. In this book, the school bully has his brain zapped by an alien device which makes him much smarter and a much more pleasant person. I can remember speculating later that very smart people like Albert Einstein probably used more like 50% of their brains.

But none of this is true. There have been several takedowns of the 10-percent-of-our-brains myth from a neuroscience perspective by people who are more qualified than I to discuss neuroscience. I am much more qualified to discuss this from an evolutionary angle.

Evolution is incremental. Traits evolve slowly over time, with each successive version of the trait being slightly better than the last. The brains of modern humans have a volume somewhere in the area of 1200 cubic centimeters (cc). Chimpanzee brains have less than a third of this volume. We evolved from an ape that was not exactly a chimpanzee, but we can use the chimp brain size as a point of comparison. Since our evolutionary divergence from our chimpanzee-like ancestors, our brains have tripled in size. This means that, during our evolution, individuals with 450cc brains survived and reproduced better than individuals with 430cc brains, and individuals with 500cc brains survived and reproduced better than individuals with 450cc brains. Our brains eventually grew to what they are now because the modern brain allowed individuals to survive and reproduce better than individuals that had anything less than a modern brain.

Human brain (top) compared to chimpanzee brain (bottom). Image from scientificamerican.com

The modern human brain is astonishingly expensive to build and maintain from a caloric standpoint. A typical adult male at rest requires 1800 Calories per day to function. That is, a man lying motionless but awake for 24 hours will burn 1800 calories just to maintain his body. This 1800 Calories is his “metabolic budget.” The metabolic budget is just the cost of every process within the body added up. Keeping the heart beating and the lungs breathing requires some of these calories. Replacing old, worn-out cells requires some more of these calories. The average adult male brain requires 414 of those Calories, which accounts for 23% of the total resting budget. Typical adult females require fewer Calories to function (1480) than adult males. The female brain requires about the same number of Calories as the male brain (400), but accounts for a slightly larger percent of the resting metabolic budget (27%).

Malcom Holliday (1986) studied the energetic cost of the brain at different stages of life. (The data above is his.) The brain is relatively more expensive at younger ages because the brain is growing very fast and because the brain accounts for a larger portion of the body’s overall mass.

Malcom Holliday (1986) studied the energetic cost of the brain at different stages of life. (The data above is his.) The brain is relatively more expensive at younger ages because the brain is growing very fast and because the brain accounts for a larger portion of the body’s overall mass.

Evolution is not wasteful. Acquiring enough energetic resources to survive was a big problem for our ancestors. Building a smaller brain would be less expensive. If the expense of building a bigger brain was not offset by the advantage it gives, it would never have evolved in the future. If humans suddenly found ourselves in an environment where our big brains were no longer an advantage for us, our brains would subsequently evolve to be smaller. (Remember that evolution does not always make things bigger, better and more complex.)

If the brain was larger (and therefore more energetically expensive) than it needed to be, individuals with a smaller brain would be able to spend that additional energy on other important things. They could spend it acquiring resources to support more offspring. They could spend it on growing bigger muscles and repairing more damage. Or they just wouldn’t require as much energy to survive and it would be harder to starve to death. This is to say that a brain that wastes 90% of its potential could not possibly evolve. Compare this to a centipede that only used 10 of its 100 legs or a cheetah that had the anatomy and physiology to run 70 miles per hour but never ran faster than 7mph. Evolution would not produce these traits, either.

In summary: a brain that leaves 90% of its potential untapped would not evolve. But don’t let this fact stop you from making good movies that use this as a premise. Luc Besson doesn’t tell me how to do my job, so I won’t tell him how to do his.

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A Journey Through Plant Evolution at the Lincoln Park Conservatory

I recently spent some time at the beautiful Lincoln Park Conservatory. It is very hot and humid in the greenhouse, which may not have been the most obvious choice on a day that was already 88º outside. Nevertheless, I thought it would be a good way to talk about the evolution of plants. My specialty in biology is animals, but I have always loved the story of plant evolution. Like all other major groups of life on Earth, plant life began in the water. Early plants were very reliant on water, but plants became less and less dependent on water as they evolved. In the water, life is easy. Dehydration is not a problem. Nutrients can be absorbed directly out of the water into the cells. The water will carry sperm for reproduction and disperse the offspring. Life in the water is good, but there was a lot of space to grow on land.

The Lincoln Park Conservatory is a great place to go. A cooler day is better.

The Lincoln Park Conservatory is a great place to go. A cooler day is better.

Liverworts

One of the first types of plants to live on land were the liverworts. They are very small, with leaves that lie almost flat on the ground. Liverworts have no ability to draw water up out of the ground, as later plants are able to do. As a result, they cannot grow very tall and must be damp all of the time. They cannot survive or reproduce without being wet.

Liverworts are one of the first plants to live on land.

My favorite room contains the primitive plants: ferns, moss, liverworts, and cycads.

My favorite room contains the primitive plants: ferns, moss, liverworts, and cycads.

Moss

Like liverworts, moss also cannot draw water up into their bodies. Are able to grow a little bit taller than the liverworts because they grow in dense mats that can trap water between individual plants. This allows them to grow up to about four inches tall.

Mosses do not dry out as easily as liverworts, but they do rely on water for reproduction. The male sperm must swim through the water to find a female plant.

Like an idiot, I forgot to take a picture of moss. This one form wikipedia.org will have to do.

Club Moss

Club moss are sometimes called “ground pines” because they can resemble pine trees, but they are neither pines nor moss. Modern club moss usually only grow to be a few inches tall, but during the Carboniferous period, when they were the dominant land plant, they grew as tall as modern trees.

Club moss are one of the first type of plants to have vascular tissue, which lets them draw water from the ground up into their bodies. This adaptation is of unparalleled importance for plants on land. For this reason, club moss were one of the first types of plants to be able to grow more than a couple of inches tall. Without vascular tissue, a plant more than an inch or two has no way of getting water to the upper part of the plant. Plants don’t need very much to live, but access to sufficient sunlight is one of their main requirements. When all of the plants around you are only two inches tall, a plant that can grow to be several feet tall or taller has an enormous advantage when it comes to getting sunlight. You can grow taller than your neighbors and spread out to get all the sun you want.

Club moss (not moss). Image from bio.sunyorange.edu

Coal is made of fossilized plants from the carboniferous period. The majority of coal is made up of ferns and club moss. Sometimes coal preserves the structures of the plants it was made from and we can use the coal fossils to learn about ancient plants.

A thin section of coal clearly shows the features of the stem of an ancient plant (in cross-section). Image from http://www.ucmp.berkeley.edu

Ferns

Evolutionarily speaking, ferns are slightly newer than the club moss. Like the club moss, ferns are have vascular tissue (so does everything else from here on).

Compared to most other plants, ferns grow sideways. The stem lies horizontally underground, and the fronds grow up out of the ground from it. When you see a cluster of fronds sticking up together, they are usually from the same plant.

Fern frond

Fern frond

Structures on the underside of the fronds, called “sori,” contain spores. These capsules break open, releasing the spores, and new ferns grow where the spores land.

Sori are clearly visible on the underside of fern fronds. These contain spores.

Sori are clearly visible on the underside of fern fronds. These contain spores.

Cycads

Cycads look superficially like palms, pineapples or yuccas, but is not closely related to any of them. They were one of the dominant types of plants during the mesozoic era — the age of the dinosaurs.

Cycads were among the first plants to use pollen in reproduction. Pollen is produced by the male structures on plants, and is responsible for carrying sperm to the ovule in the female structures on other plants. Unlike the earlier plants, which require water for the sperm to swim through, pollen is carried by the wind. This is great for plants that live away from water and want to be able to reproduce with individuals that are far away. The problem is that it is fairly inefficient. Plants whose pollen is carried by the wind need to produce vast quantities of the stuff in order for some of it to get to other plants. I grew up in New Hampshire, where there a lot of white pine trees (which are not cycads, but also reproduce with wind-borne pollen). I got up many a morning to find my car completely covered in yellow pollen. All of that pollen that didn’t end up on the right part of the female plants is wasted energy.

Cycads were also among the first plants to have seeds, instead of spores like the older plants. Spores are fine, but they cannot travel over long distances or lie dormant for a more opportune time to sprout. A seed contains the plant embryo as well as nutrients to keep it alive for months or years. If a spore happens to land on the back of a bird on its way to the other side of the country, the embryo inside may not survive the trip because its mother didn’t pack it lunch. An embryo inside a seed will survive the same journey because it is surrounded in an oil-rich substance called “endosperm.” When we eat nuts, it is the endosperm that we are after.

Cycads can superficially resemble pineapples, yuccas or palms, but they are not part of the same group.

Cycads can superficially resemble pineapples, yuccas or palms, but they are not part of the same group.

Flowering Plants

Flowering plants became the dominant plants of the world during the late mesozoic, and today account for the majority of plant species.There are over a quarter million living species of flowering plants, compared to only about 12,000 species of fern, and fewer than 10,000 species of liverwort.

The flowering plants have two evolutionary advancements that allowed them to be so successful: flowers and fruit. These allow plants to solve two big problems in the area of reproduction.

Flowers represent an exchange of goods and services between plants and animals. Big, colorful, aromatic flowers are nature’s equivalent of an “eat here” sign. Flowers produce sugar-rich nectar that animals like ants, butterflies, birds, and bats like to eat. While these “pollinators” are eating the nectar, they get covered in pollen. When they go to the next flower, they drop some pollen off and pick up some more. This results in animals carrying pollen directly from one plant to the next, with very little waste. Remember all that energy that earlier plants wasted trying to pollinate my car? Flowers allow plants to use their energy more effectively. The energy this saves over relying on wind pollination is part of why flowering plants are so successful evolutionarily.

Flowers attract certain animals, which carry pollen between flowers, helping the plants reproduce.

Flowers attract certain animals, which carry pollen between flowers, helping the plants reproduce.

Spreading seeds is another problem for plants. If seeds just fall off the parent plant and onto the ground, some will roll away or get kicked away. The others will sprout right next to their parent and compete for the same nutrients and light. This will reduce the success of both the parent and the offspring. Some (but not all) flowering plants produce fruit to solve this problem.

Fruit is a sugar-rich substance that is easy to get eat, which surrounds the seed, which contains an oil-rich substance that is protected by a hard shell. In human terms, the plant “wants” you to eat the fruit, but does not “want” you to eat the seed. If you eat the seed, you are eating the tree’s offspring. If you (or another animal) eat the fruit, there is a good chance that you will swallow the seeds by accident. The hard shell protects it from being broken in your mouth or digested in your stomach. After eating the fruit, you (or whatever animal) will walk or fly away and eventually deposit the seeds far away in a nutrient-rich pile of fertilizer.

Flowering plants are better at life on land than any other plants. They can draw water and nutrients out of the soil through their roots and vascular tissue, and they are very good at reproducing and spreading their offspring without the aid of water. This is why they are beating all of the other plants.

Cladogram showing the evolutionary relationships of the plant groups and major evolutionary advancements.

Cladogram showing the evolutionary relationships of the plant groups and major evolutionary advancements.

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The Evolution of Flight

Out of several thousand species of birds, almost all of them can fly. They all have the ability to fly because they evolved from a common ancestor that could fly. Bats can all fly because they evolved from a common ancestor that could fly. But why can both birds and bats fly? Did they evolve from a common ancestor that could fly? While they did evolve from a common ancestor, this ancestor could not fly. How, then, are both birds and bats able to fly?

In biology, there is a concept called “convergent evolution.” Some types of organisms have similar traits because they evolved from a common ancestor that had those traits. With only a few exceptions, all mammals, amphibians and reptiles (including birds) have four limbs — two arms/wings and two legs. This is because these three lineages all evolved from a common ancestor that had four limbs. Similar traits that are due to common ancestry are called “homologous traits.”

Other types of organisms have similar traits but did not evolve from a common ancestor that had those traits. Fish and whales are a classic example of convergent evolution. They both have a tail fin that propels them through the water, forward fins that help them steer, a fusiform body that makes them hydrodynamic, and a dorsal fin that keeps them stable.

The dolphin and fish share many traits that facilitate an aquatic life. Image from wikipedia.org

But there are more differences than similarities. Here are a few:

  • The tail fin of a fish is oriented vertically, whereas the tail fin of a whale is oriented horizontally
  • Fish lay eggs, whereas whales give live birth
  • Baby fish are fed by a yolk sack in their egg, whereas baby whales are fed from mammary milk
  • Fish use gills to extract oxygen from the water, whereas whales breathe atmospheric air
  • Fish are cold-blooded, whereas whales maintain a high body temperature.
  • Fish have scales covering their skin, but whales do not.
  • Whales have typical mammalian wrist and finger bones inside their pectoral fins, but fish do not.
  • Whales have hair, but fish do not.

Whales do, of course, share a common ancestor with fish, but this common ancestor is not the reason that whales have their aquatic adaptations. The ancestors of whales first evolved into a terrestrial life, then evolved back into the water, much later in life.

When two or more different types of organisms evolve a similar trait independently, these traits are called “analogous traits” and the process of evolving these analogous traits is called “convergent evolution.”

Off the top of my head, I can think of nine independent evolutionary origins of flight — that is, nine separate events of convergent evolution. There are probably more that I don’t know about. Let’s start with the three best fliers that are currently alive: Birds, bats and insects.

Birds and bats are both tetrapods, so they are stuck with four limbs. They both use primarily their front limbs for flight, but they do it differently. Bird hand and wrist bones are fused together to make a short, stumpy end bone. Feathers produce the area required to produce lift.

The bones of a bird wing. Image from wikipedia.org

When birds are in flight, they keep their legs and feet tucked out of the way so they do not interfere with flying.

Canada goose in flight. Note that the legs are not used in flight. Image from wikipedia.org

Bats have a membrane of skin that stretches between their arms and legs that help produce lift. The legs and feet of bats are very important for flight.

Bat in flight. The legs are important in forming the wings. Image from wikipedia.org

Bats have elongated fingers that make up most of the wings. They use skin that is stretched between their fingers to create the area required to produce lift.

The arm bones in the bats and birds are homologous to one another, but their wings are the result of convergent evolution.

Insects have six legs and two pairs of wings. Insect wings are inflexible, except for where the connect to the body; a little bit like the oars on a boat. There are no bones or muscles inside the wings. Birds and bats have aerodynamic bodies that allow them to pass through the air efficiently. Some insects, like the dragonflies, have aerodynamic bodies, but bees and beetles do not.

Dragonfly. Image from wikipedia.org

The pterosaurs were not technically dinosaurs, but they were close relatives. Modern birds, which are dinosaurs, are not direct descendants of the pterosaurs, but birds are more closely related to the pterosaurs than they are to bats. Despite the closer genetic relatedness, the pterosaurs flight ability resembles bats more than birds in a variety of ways. First, they did not appear to have had feathers. Instead, they probably used a membrane of skin to form their wings much the way bats do.

Bats use fingers 2-4 (index through pinkie) for flight, and finger 1 (the thumb) for limited gripping. Pterosaurs only had four fingers, and only finger 4 was used for flight, whereas fingers 1-3 were used for gripping.

Pterosaur wing. Image from http://www.geol.umd.edu

 

Other, lesser fliers:

These are animals that fly sort of like a paper airplane. They cannot propel themselves once they are in the air — they have to jump to get their initial momentum. But once they are in the air, they can control their direction and create an air foil to slow their falling. Humans can do this with the aid of a wingsuit:

Flying squirrels: A little bit like bats, flying squirrels have a membrane of skin that stretches between their front and rear legs. This allows them to glide over longer distances than they would otherwise be able to jump.

Flying squirrel in flight. Image from wikipedia.org

 

Flying lizards: Although the word “dinosaur” literally means “terrible lizard,” lizards and dinosaurs are completely different types of reptile. Flying lizards in the genus “Draco” are not very closely related to the flying dinosaurs. The flying lizards are very unusual because they do not use any of their four limbs for flying. Instead, they are able to spread out their ribs to form fairly immobile wings which allow them to glide for short distances.

 

Flying dragon. Image from wikipedia.org

Flying fish: Flying fish are much better at flying than you would expect. They use their tail to get out of the water and get speed. Once they are in the air they can glide for fairly long distances. If they want to increase their speed, they can put their tail back into the water and give themselves another push. This makes them the only glider that I know of that can add energy to their glide without landing.

Flying Fish. Image from wikipedia.org

 

Flying frogs: Like bats, flying frogs create “wings” by stretching skin between long fingers. Unlike bats, the “wings” of the flying frogs are limited to their feet, and do not include any skin on the arms or legs.

Flying frog in flight. Image from http://endangeredliving.files.wordpress.com/

Flying snakes: To people who are afraid of snakes, nothing sounds more horrifying than snakes that can fly. But don’t worry — the flying snakes are the worst flyers of the group. They are able to flatten out their bodies to create a very minimal air foil. Their “flight” looks a lot like jumping or falling, but research has shown that they are able to steer themselves in the air. It may not seem like I should have included these in a list of things that evolved to fly, but remember that everything that evolved to fly had to go through many stages of flying ability. In the first stages, the animals would have just been jumping. In later stages, they would have a rudimentary ability to glide and navigate. For this reason, I firmly consider these snakes to be an example of incipient flight.

 

 

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Drug-Resistant Diseases

Drug-resistant pathogens are in the news more and more these days. The World Health Organization recently released a report about the declining effectiveness of antibiotics. Many believe that the age of antibiotics is coming to an end. This is very troubling, given that antibiotics are unquestionably one of the greatest advancements in the fight against disease.

Infectious diseases are caused by a variety of organisms: viruses (HIV, chicken pox, dengue fever, ebola, influenza, rotavirus), bacteria (tuberculosis, meningitis, gonorrhea, tetanus, whooping cough), worms (schistosomiasis, ascariasis, whipworm, pinworm, elephantiasis, river blindness), protists (malaria, sleeping sickness, giardia, leishmaniasis, chagas disease, cryptosporidium), and fungi (athlete’s foot, thrush, valley fever, aspergillosis).

Organisms that cause disease (such as those listed above) are not fundamentally different from the organisms that do not cause disease. Parasites are subject to evolution by natural selection just like anything else.

A toxin may broadly be defined as a chemical that negatively affects the physiology of an organism when the two come in contact. Drugs that we use to fight parasitic infections within a person’s body are toxins. Ideally, the toxicity of the drug is much greater to the parasite than it is to the host.

There are many naturally occurring toxins in the environment. Ethanol, along with many other alcohols, is a very powerful toxin to most living things. It is because of this toxicity that we use various alcohols to sterilize various surfaces (including our hands, in the case of hand sanitizers) and sometimes instruments.

Humans have a fairly high resistance to ethanol, but not to other alcohols. Most people can drink the equivalent of a couple of ounces of pure ethanol and be fine. The same quantity of methanol or propanol (which are chemically very similar to ethanol) would lead to pretty severe physiological consequences, including death. The ability of humans to metabolize ethanol is attributed to our evolutionary history of eating fruit. Fruit contains a lot of sugar, which is a good source of energy. Ancient people who ate fruit whenever it was available had more energy available in their bodies for building muscles, repairing damage, reproduction, hunting, and whatever else they needed to do. If fruit sits on the tree (or the ground) too long, yeast lands on it and starts eating the sugar for itself. When yeast eats sugar, ethanol is produced as a waste product. If a person eats that fruit, they will also be eating some ethanol. A person who is able to withstand a lot of ethanol is able to eat a lot of fruit and gain the energetic benefits of doing so. Over time, the average human became more and more able to cope with consuming toxic ethanol. Modern humans can safely consume quantities of ethanol that would be fatal to many other organisms.

Methanol, ethanol and propanol are all very similar molecules. Ethanol is the only one we can consume.

Methanol, ethanol and propanol are all very similar molecules. Ethanol is the only one we can consume.

So what does any of this have to do with diseases? Just as humans evolved to cope with the toxicity of ethanol, pathogens can evolve to deal with the toxicity of the drugs we use to fight them.

The most toxic substance to an organism is going to be one that is “evolutionarily novel” — that is, the substance is one that the species has not encountered over its evolutionary history. Why? Because a species that frequently encounters a particular toxin will evolve physiological mechanisms to resist the negative effects of the toxin. For example, if you want to poison a human with an alcohol, you’d use methanol, not ethanol, because ethanol is more evolutionarily familiar to us.

When we use the same drug to fight the same pathogen over many years, the drug becomes evolutionarily familiar to the pathogen, and the pathogen can evolve to cope with it. For decades, physicians used the same antibiotics to treat bacterial infections, including those caused by Staphylococcus aureus. After they used the antibiotic methicillin for a long enough time, the methicillin became a normal part of the bacteria’s environment and the bacteria evolved to cope with it, eventually becoming Methicillin-Resistant Staphylococcus aureus, or MRSA.

The rate of evolution for any given species is inversely-related to the generation time of the species — species with long generation times evolve very slowly, and species with short generation times evolve very quickly.

Organisms with a shorter generation time evolve faster

Organisms with a shorter generation time evolve faster

This is because evolution is a process that happens in between generations. If new generations occur more closely together, more evolution can happen in a shorter time. The human generation is about 20-30 years. A generation for bacteria can be as short as 20 minutes — that’s 72 generations per day, over 26,000 per year, and over a half million within the span of a single human generation. For perspective, a half million human generations is about 10 million years. 10 million years ago, gorillas, chimpanzees and humans had not yet evolved into separate species. What does this mean for antibiotic resistance? It means that bacteria can evolve very quickly to be immune to a given antibiotic.

This is obviously bad news for us. Not all pathogens evolve as quickly as bacteria, but they are all pretty fast. Recent history is full of examples of drugs that worked well until the disease evolved immunity towards it.

Malaria, tuberculosis, HIV, Staphylococcus aureus, Escherichia coli, gonorrhea and many others all have strains that have evolved immunity or resistance to the drugs we use to treat or cure them. We are going to need a new way of fighting these diseases.

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Are Humans Still Evolving?

Image from telegraph.co.uk

I hear this question come up a lot. The subtext is that, because humans have mastered our environment, we are no longer subject to the same pressures of natural selection that we once were.

First, let’s review what evolution is. Evolution is a change in the frequency of alleles or traits in a population over time. Natural selection is the mode of evolution where the change is based on environmental pressures that cause individuals with certain traits to reproduce more than individuals without those traits. Natural selection does not have a goal, or a more or less advanced state. Natural selection improves a population in that it increases the frequency of traits that cause the members of the population to leave more surviving offspring. It does not improve a population by necessarily making the individuals smarter, faster, stronger, or more complex. A cheetah is not more evolved than a sloth because it is faster. Both were designed by natural selection to do what they do.

Infectious disease was a huge problem for our ancestors. Good thing we cured them all. (In case there was any doubt, that last sentence was full of sarcasm.) While it is true that medical advances have greatly reduced the burden of infectious disease in the west, they are still a big problem in most of the world. Malaria, tuberculosis, HIV/AIDS, respiratory infections, and diarrheal disease each kill over a million people a year worldwide, mostly in developing nations.

Even in the medically-advanced United States, tens of thousands of people die every year from influenza alone. We may not have schistosomiasis or malaria, but we still have people dying of infectious disease in large numbers. If there exist any alleles in our population that confer resistance to diseases that we face, however slight, then we are evolving. If for example, people with a particular allele have even a 0.1% increased chance of surviving influenza, then that trait will increase in frequency in subsequent generations.

If diseases are not killing us randomly, then those diseases are causing us to evolve. If we cure those diseases, then the cure will also cause us to evolve. If a disease is killing people who do not have a particular trait, then the frequency of that particular trait will increase. If we cure the disease, then the frequency of that particular trait will begin to decrease again. Both the increase and decrease of the trait frequency are evolution. I think this is where a lot of people get hung up — because we are not “improving” we must not be evolving.

Our evolution is not limited to the effects of infectious disease. If you look at population growth in the world, it is not the same everywhere. Traits that occur at higher frequencies in the parts of the world with higher fertility rates will get passed on at a higher frequency. This is also evolution.

Average fertility rate by country. Most of the world’s population growth is happening in central Africa. Image from wikipedia.org

Evolution takes place over the course of many generations. Individual human observers will therefore have a difficult time observing human evolution. It may not look like we are evolving, but we certainly are.

 

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The Tragedy of the Commons

In my recent post on greed, I explained how the underlying psychology that leads some people to have an intense and selfish desire to acquire wealth evolved. In doing so, I focused on how these traits favored individuals that had them in the past. One reader pointed out that this leads to resource depletion in humans (which it does), and wanted to know whether this or any other “bad outcomes” occur in other species.

The drive to leave more surviving offspring than other individuals is integral to the evolution of all traits. Reproduction is the only currency of natural selection, and all traits are tied back to this in one way or another. Survival is an important trait, but it is only important so far as living longer allows one to leave more offspring. Social behavior is important for some species, but only if it improves survival and reproduction. The same goes for intelligence, opposable thumbs, wings, or any other trait.

It’s obvious to see how the drive for reproduction can be bad for other species. For example, if an animal enhances its survival and reproduction by being a predator, the survival and reproduction of its prey will suffer — being eaten for lunch certainly qualifies as a “bad outcome.” For this post, though, I’ll focus only on how the evolutionary ambitions of a species can hurt itself.

Parasites have the same drive to reproduce that other organisms have, although the drive is based entirely on physiology instead of having a psychological component. Their lifestyle requires them to be careful (in physiological and evolutionary terms) about how fast they consume their resources (their hosts). If they reproduce too fast inside their hosts, the host will become so sick that it cannot transmit the infection effectively anymore. The virulence (pathogenicity) of a parasite is carefully tuned to suit the host. If a parasite jumps to a new host species, the virulence may be too high to be good for the parasite. This is exactly what happens with ebola.

The ebola virus sometimes infects humans, but we are not its primary host. In humans, ebola is very contagious but it kills the host very quickly — too quickly to infect enough other hosts. For this reason, ebola outbreaks in humans tend to “burn out” fairly quickly and do not infect large portions of our population. Humans are the virus’s resources, and by reproducing so quickly, the resources are depleted and the virus population dies out.

Electron micrograph of an ebola virion. Image from wikipedia.org

In the boreal forests of North America, the Canadian lynx (Lynx canadensis) has a 9- to 11-year cycle of population increase and decrease. The Canadian lynx specializes in hunting the snowshoe hare, and they are very good at it. Lynxes that are better at catching snowshoe hare will get more resources, and are able to have more offspring. These offspring will inherit a superior ability at catching snowshoe hares, allowing them to have more offspring of their own. Hares are renowned for their rapid reproduction, but the lynx is renowned for its ability to kill hares. When the lynx population gets too big, they will kill so many of the hares that there is not enough food left to support the lynx population. The lynxes starve to death and the population crashes.

 

Canadian Lynx (Lynx canadensis). Image from wikipedia.org

This is obviously not a complete list of how resource consumption can result in problems for non-human species, but it shows that it can be a real problem. Most resources are limited, and the tragedy of the commons applies to everyone, human or not.

 

 

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What Causes Greed?

This week’s topic was requested by a reader. If you would like to request a topic, let me know in the comments or on twitter.

Before we begin, be sure to read my post on the naturalistic fallacy. Science cannot condemn or justify any behavior — it can only identify the behavior and explain why it exists. In this post I will attempt to explain greed as I understand it, without mixing in any of my own ideology or the ideology of anyone else.

My dictionary defines greed thusly: “Intense and selfish desire for something, especially wealth, power, or food.” It is the wealth part that I will focus on.

To understand greed, or many other human behaviors, we first have to understand evolution — the human mind, of course, is a product of evolution. Every behavior and thought that we have is not necessarily the direct result of natural selection, but natural selection lays the foundation for our behavior. Natural selection works on a relative level. Traits are successful if they are passed on more frequently than other traits, which means that more individuals with that trait must be born and survive than individuals with other traits. Traits will evolve faster if there is a greater “selective advantage” — that is, the difference in survival and reproduction between individuals with and without the trait is very large.

If a squirrel, for example, has three offspring that survive, it and its traits are doing better than a squirrel that only has one offspring that survives. But it is not doing as well as a squirrel that has 10 surviving offspring. For this reason, natural selection does not give animals a target number of offspring that they want to have over the course of their lives but not exceed. If a squirrel has 10 surviving offspring but could produce more, it will lose the evolutionary race to an individual that could produce more than 10 surviving offspring and does. Said differently, natural selection does not produce squirrels that are satisfied with a particular number of offspring and will not have more. Rather, natural selection produces squirrels that will produce as many surviving offspring as they can. This is true for all organisms, not just squirrels.

For all organisms, resources are the most important thing for reproduction. It takes a lot of calories to produce an offspring, and raising it (in species that provide parental care) takes even more. Animals will produce as many offspring as they can, and it is resources that determine how many this really is. There is a large selective advantage for individuals who can acquire the most resources because they can produce more offspring that are healthy and survive long enough to reproduce themselves.

Modern humans aren’t so different. Estimates vary, but it costs somewhere in the area of $100,000 – $200,000 to raise a child to age 18 these days. This means that you need to have at least this amount of money coming in for every child that you want to have.

But let’s go back in time for a minute. Back in the day, let’s say 50,000 years ago, there was no money. If someone got a windfall of resources by killing a mammoth, they couldn’t put it in the bank, or even horde it underneath their mattress. If they did not use this material wealth, it would rot.

Modern wealth is easily storable, so it can be accumulated in ways that was not possible in the past. Prehistoric people could not stuff an uneaten mammoth under their mattress for later, but modern people can easily stuff the equivalent of a thousand or a million mammoths into a bank account or a mutual fund and keep it for as long as they want.

As animals, we have a strong drive to do better than everyone by as much as possible. Humans obviously have complexities to our behavior that make us more nuanced, but this drive is still rattling around in our brains and affecting our behavior. Just like the squirrel that tries to have more surviving offspring than the other squirrels, people like to have more wealth than others. Natural selection has made us very interested in acquiring more resources than other people.

There is an old joke about a farmer who is granted a wish, but whatever he wishes for will be doubled for his neighbor. He can’t wish for a wealth of gold because his neighbor will be given double the gold. He can’t wish for five strong sons because his neighbor will get ten strong sons. He eventually decides to wish for half of his crops to be destroyed. This solution, or one like it, is the only way he can come out ahead of his neighbor. Coming out ahead, as I have already discussed, is the only way to win at natural selection.

Nobody particularly needs a billion dollars, but lots of people want it. When natural selection built us with an interest in accumulating more wealth than other people (what you might call an intense, selfish desire for it), it did not build an off switch.

And that, in a nutshell, is why we have what we call greed.

See the followup to this post: The Tragedy of the Commons

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