Lions And Tigers and Ligers, Oh My!

A full grown liger is a biiggg cat! A male lion and

a female tiger get to know each well, and their

love child is huge. It doesn’t happen in the wild

because the ranges of lions and tigers don’t

overlap, and they don’t have computer dating

services. The liger is bigger than either parent,

and this is a problem during birthing. They have

many birth defects and often die young.

When putting organisms into categories (taxonomy), we go from bigger, more general categories to smaller more specific ones. The more similar two organisms are, evolutionarily and genetically, the more levels of their taxonomic classification they will have in common.

Question of the day:

A tigon is the result of a cross between male tiger and a female lion, while a liger is the offspring of a male lion and a tigress. But are these new species? And just how far can you go when you cross-breed?

There are instances when different species mate, but the outcomes, while interesting, may or may not be new species. It helps to know the classification levels.

Kingdom (domain) - Insects, dogs and people are all very different, but they are all animals.

Phylum (Division for plants) – usually these group things by a common body plan or some other morphologic character, or a certain degree of genetic relatedness. Arthropods are all related by a chitin exoskeleton, so flies and lobsters are both arthropods, but flowering plants have fruits and conifers have cones, so they are in different divisions.

Class – these groups have more in common, either physiologically or genetically. Cows and dogs both have hair and give birth to live young, so they are both in the class Mammalia. However, flowering plants are divided into two classes, monocots and dicots, based on seed and vascular tissue differences.

Here is the classification scheme for several familiar

mammals. Cats are all in the same family, but there are

several genera, while all dogs fit in one genus and all

wolves in another. Black bears and Kodiak bears are a

different genus than polar bears, but hikers and bigfoot

monsters have reported sightings of polar and Kodiak

bear hybrids…. well hikers have been reporting them.

Order – Even more specific, this level of classification has been altered greatly by molecular biology. Armadilloes and anteaters are both in the Order Edentata – as toothless mammals. However, roses and magnolia trees are both dicots, but they belong to different orders (Magnoliidae and Rosidae).

Family – Now we are getting down to smaller differences, but still just as important.  All the big-eared bats and all the thick thumbed bats are both included in vespertine family, because they come out to feed in the evenings. On the other hand, maples and mahogany trees are both in the order of Sapindalae, but they belong to different families based on their leaf and flower anatomies.

Genus –comes from the Greek for “kin,” so these organisms in the same genus are closely related. In animals, both moths and butterflies are in the same order, but they are broken into 124 different families, and the family Nyphalidae, which contains the Monarch butterfly, has over 600 genera (the plural of genus).

Species – These are the individual distinct group of organisms. Usually, the distinction is made based on whether their breeding can produce fertile offspring. So bulldogs and St. Bernards are both species of dog, since they can make mutts.

The africanized honeybee is more likely to swarm and

migrate when food supplies are low, so they can be seen

in masses like the one above. For hives, they usually

invade an existing hive, quit out the queen and install their

own. The danger in these bees is that they are more likely

to swarm when agitated, and they will chase the agitator

for a much longer distance (a mile or more) than regular

honeybees (100 yards or so).

Sub-Species - this is like the different breeds of cats we keep or that unfortunate incident where African bees were crossed with South American honeybees and created killer bees!

Now that we have that information – let’s rephrase our question of the day. Can you breed (hybridize) different species and create a new species?

Cross-breeds are common within species (intraspecies hybridization), like with cats or dogs – not cats with dogs, you’d never want to do that! And we know they are fertile, so you end up with some dogs that are ¼ this, 1/8 that, and ¼ the other. What about between species?

Interspecies hybrids usually don’t give you fertile offspring. Since the definition of a species is a group of animals that can mate to give fertile offspring, then you would be hard pressed to create a new species by breeding different species together.

For example, the liger and tigon males are always sterile, so even though the females are sometimes fertile, they still can’t mate a tigon to a tigon. This would be necessary to make a stable species. So the chances are low on the interspecies level.

That would mean that new species coming from breeding of animals from different genera would be even less likely to produce new species. However, individuals can be hybridized. Intergeneric hybridization is easier to do in plants; orchid growers have made many different intergeneric crosses, like little Dr. Frankensteins with green thumbs.

Compare the two marine mammals that are jumping. One

is bigger, darker colored, and apparently can jump

higher. That one is the wolphin. Her name is Kekaimalu,

the offspring of a bottlenose dolphin and a false killer

whale. Her offspring, Kawili Kai, is bigger than a dolphin

as well, but is lighter colored than mama.

But they can occur in animals. A wolphin was born at Hawaii Sea Park in 1985, the result of a mating between a bottlenose dolphin and a false killer whale. These species are in the same family (Delphinidae) but different genera. Named Kekaimalu, this female is fertile and has mated with male bottlenose dolphins. The first two offspring did not live very long, but her third calf is still alive and well, at ¾ dolphin and ¼ false killer whale. However, this wouldn’t be a new species unless wolphins mated with wolphins and produced fertile wolphins.

The rarest hybridization is the interfamilial hybrid. Most examples have occurred in birds, where game fowl are housed together. The Pea-guinea is a hybrid between a peacock and a guinea fowl hen. They look weird and don’t survive beyond a year or two, so there is no way that these could form a stable species.

It would take a bunch of posts to talk about why certain hybrids will work and others won’t, and why new species are not generally produced in this way. But for now - how about two exceptions?

What do you get when you cross a blueberry with a

snowberry (maggots, that is)? You get a Lornicera fly –

O.K. not a funny joke, but a pretty cool twist in

evolution. As fruitflies go, this is a pretty cool looking

one; you don’t have the ghoulish red eyes to deal with

and three stripes make it look a little like a lightbulb!

The Lonicera fly is a new species produced by natural interspecies hybridization! Just when you think you understand nature, there it goes again, kicking you in the seat of your pants.

The creation of this new fruit fly species did have a little help from humans. For about 250 years, honeysuckle plants have been imported to the North America from Europe. In the 1990’s scientists found the Lonicera fly and tried to see what other flies it was related to. Low and behold it was a hybrid of the snowberry maggot and the blueberry maggot. But why didn’t the hybrids breed with the parent species and dilute the hybrid genome back into the two stable species? How did the hybrid become a new, stable species?

These hybrid flies preferred to feed on the honeysuckle, so they lived on the imported plants, while the parent species lived on their favorites (snowberry bush or blueberry bush).  This is a kind of geographic isolation; the Lonicera hybrids find only Lonicera hybrids when it comes time to mate and they end up mating hybrid to hybrid for many generations. This resulted in a stable species, the process is called hybrid speciation.

The Heliconius heurippa butterfly has an unusually

large black bar that crosses its body. This must be

fairly obvious to other butterflies of the same

hybridization and it must also be pretty attractive.

Both male and female hybrids search out the wide

black bands. I would love to know the molecular

biology of that specificity of attraction.

The second exception is the Heliconius heurippa butterfly in South America. An interesting 2006 study in which hybridization was repeated in the laboratory showed that H. heurippa in nature is the result of breeding of two other species of butterflies. The hybrid does produce fertile offspring, both male and female, but that isn’t the end of the story. In this case, there isn’t any geographic isolation forcing hybrid-hybrid mating - they choose to mate together. Their choice is related to the fact that the hybrids have bold black stripes on its wings, while neither parent species does.

The hybrids preferentially mate with other butterflies with the bold stripes, so they are mating hybrid to hybrid and are stabilizing the new species. Darwin would blow his top – or maybe not. He never said this couldn’t happen, just that it was less likely.

Stay tuned, molecular techniques are beginning to show us that this may not be such an exception – a 2011 study identified another butterfly species created by hybrid speciation and it happens all the time in plants, like sunflowers. Three younger species, the desert, the puzzle, and the sand – seem to live where their parent species cannot, so they tend to pollinate with their similar hybrid brethren and make new species.

Next week we will ask why some birds migrate while others stay put year round.

Jesús Mavárez1, Camilo A. Salazar, Eldredge Bermingham1, Christian Salcedo, Chris D. Jiggins & Mauricio Linares (2006). Speciation by hybridization in Heliconius butterflies Nature, 41, 868-871 DOI: 10.1038/nature04738

Leaves Suck!

We have talked about the reactions of photosynthesis

before. Basically, the plant uses the energy of the sun to

fix carbon (change it from gas to solid) by adding water

to it chemically. Then it splits them again to make energy.

In previous posts we have talked about photosynthesis – carbohydrates and made from carbon (carbo-) with water added (-hydrate, as in- when you are very thirsty, you are dehydrated). Therefore, the leaves must have a constant and reliable source of carbon (from carbon dioxide in the air) and water.

Question of the day:

How do trees move the water up into their leaves, against the force of gravity, in order to carry out photosynthesis?

Water is quite massive (1kg/L or 8.3 pounds/gallon), and a mature oak tree needs 40-60 gallons of water every day. So how does this huge amount of water get to the top of the tree? Does it travel there from someplace else? Could it be absorbed by the leaf from the air in the same way carbon dioxide is brought in? Or maybe plants don’t have to drink and they use the water they make during metabolism, like the kangaroo rat we talked about last year -they don’t drink at all and seem to get along just fine.

We might be able to eliminate one possible explanation right away – what happens when you don’t water your houseplants? Do they grow or do they die? So do you think most plants need a source of external water or could get along on the water they make during aerobic respiration? Right… I think we are down to absorption or movement from some other place on the plant, namely the roots.

Keep in mind that not every plant has to move water from its roots to its leaves, take the bromeliads for instance. Many of these plants don’t have roots, we have discussed how they have special structures that help them absorb water at the base of their leaves.

You could test other types of plants to see if water on just the leaves is enough to keep them alive. How might you do that? Cover the dirt with something that repels water and then just mist the leaves – that might do it. Try it for a while and see how the plants do.

I think that you will find that they do not thrive after the moisture in the dirt is used up. For most plants, 99% or more of the water they use must be absorbed by the roots and transported up the stem (trunk if it is a tree) to the leaves.

Celery stalks and carnations are good to show the flow

of water against gravity. Dark colors show up better.

Maybe you could have races between the two plants and

then cut them crosswise to look at the size of the vessels.

I bet the smaller ones move water faster.

To model the answer to our question of the day all you need is a straw. But that isn’t very illustrative or fancy – so how about cut carnation stems or celery stalks (with the leaves) in a glass of colored water. Lighter colored flowers and darker colored water works best (I use blue food coloring), but I have had students who have really gotten into this and tried to measure the time by adding one color, then switching to another and seeing how long it takes the color to change in the flower and if all the color is lost along with the water.

Over a couple of days, the color will indeed be drawn into the petals of the flower. How does the color get there? Is the water level the same? Water is moving up and taking dye with it. So you can see that it does happen – but this still doesn’t explain HOW it happens. Hint - it isn't capillary action. Even in a very thin capillary tube, water will only move up a few centimeters. How could it possible move from the roots to the top of a redwood tree?

To answer this, you might ask what happens to the water that is being drawn up into the leaves (and flowers of the carnation model). Try putting a baggie over the end of a tree branch and tying it tight.  You will see condensation develop over a day or so. Where did this water come from?

Here are the vessels in a tree. 1) pith – it gets crushed as the tree grows 

2&3) annual growth rings made of water carrying xylem. Why 

do you see different rings if they are all xylem? Because spring 

xylem vessels are big, and summer xylem (less water available, so

less growth) vessels are smaller. The line is the change from 

small to big. 6) phloem – this is what carries the carbohydrate to 

the roots and other parts of the tree.

The answer is a process called transpiration (or evapotranspiration). The water evaporates from the leaves, out of pores called stomates, and this creates a negative pressure – like the negative pressure in your mouth when you suck on a straw. This negative pressure actually pulls water up from the roots through the xylem of the plant, to the leaves. In the case of the carnation flower or celery, it also pulled up the very small dye molecules in the water. This evaporative force is quite strong, but not strong enough on its own to lift that 350-500 lb.s (40-60 gallons) needed for an oak tree each day.

The water itself helps in the process. Water is a social molecule, it likes to stick to itself and to other things. It will climb up the sides of container, just look at the meniscus formed in a narrow graduated cylinder when water is added, or note how water travels up a thin capillary tube.

The capillary action comes from the water’s cohesive force, and helps the tree stay hydrated. Evapotranspiration’s negative pressure pulling water up is combined with water’s ability to climb up, and together this is enough to keep the tree’s leaves in the pink, no matter how tall it grows.

But like everything else, there are exceptions, like the plants that don’t have xylem. The non-vascular plants (like mosses and hornworts) only survive based on water absorption and capillary movement from cell to cell. Therefore, they cannot be very tall; you need vessels (xylem) to allow water movement and tall growth. The tallest of the non-vascular plants, the Polytrichum mosses, may get to be two feet tall, but that’s it.

Evapotranspiration via vasculature and leaf stomates leads to another question – if water is being lost through the leaves all the time, doesn’t this hurt the plant in times of drought. Well… yes. But plants have evolved some pretty neat tricks to help out.

Some plants don’t use the most forward strategy of

photosynthesis because it would drain them of all their

water during the hottest weather. CAM plants can close

their stomates during the day and only fix carbon dioxide

at night when it is cooler. We should probably talk about

these plants in more detail later this year, they have some

mighty cool adaptations.

1) Stomates can open and close to regulate water loss. Some plants can close their stomata completely during the hot day, and save their built up radiate energy to convert carbon dioxide and water into carbohydrates only at night, when they will lose less water. Cacti are a good example of this.

2) Leaves, especially the sun-exposed sides of leaves, are covered with a waxy substance called cuticle that greatly reduces the loss of water by diffusion through the cell wall. If water were allowed to travel through the cell membrane and wall, then it would evaporate and set up a negative osmotic and evaporative pressure that would quickly dehydrate every surface cell.

3) Here's a trick many people don’t really consider – many plants have two types of leaves! You might be able to find a tree or two with which to investigate this.

Big leaves have large surface area, so more water will be lost as compared to smaller leaves. Leaves in the direct sunlight should be structured in order to carry out the most photosynthesis, but if they are small, how can this be maximized?

Many trees have sun leaves and shade leaves. Sun leaves are smaller, thicker, have more stomata, and are located where the direct sunlight hits the tree during a good portion of the day.  Shade leaves are bigger, thinner, and have fewer stomates to reduce water loss.

Sun leaves have more layers of pallisade cells, the cells that have the most chlorophyll and do most of the photosynthesis. They are located at the ends of branches, especially on the north side, and on the crown (top) of the tree.

Sun leaves are a smaller and thicker, and they often have

fewer in and outs in their shapes. The smaller shape

reduces water loss, the thicker body provides extra layers

of cells for photosynthesis, the reduced number of cuts

and points…. I have no idea. It is a continuum, leaves that

get a good amount of light land somewhere in the middle.

Shade leaves have to rely on lower levels of sunlight (they are in the shade), so they have even higher concentrations of chlorophyll than sun leaves, although they are thinner. They can process light more efficiently than sun leaves, so they are actually very important to the plant despite their little time in the sun.

Look at the trees around you, do some have large leave on inner branches and lower on the canopy, while having smaller leaves on top or on the ends? These are probably shade tolerant trees. They have developed the ability to still do enough photosynthesis despite low levels of light.

On the other hand, do you see a tree that has just one size of leaf (not including newly formed leaves) and only has leaves on the ends of the branches? This is probably a shade intolerant tree.

The conifers are an interesting exception, some are shade tolerant, usually the firs, while others are shade intolerant, mostly the pines. However, neither type has sun leaves and shade leaves. Their shade tolerance has more to do with their branch geometry and ability to allow just about all their leaves (needles) see the same amount of sunlight.

Next  week, we will ask if there is any limit to interspecies mating, can you cross a cat with a dog? 



von Caemmerer, S., & Baker, N. (2006). The Biology of Transpiration. From Guard Cells to Globe PLANT PHYSIOLOGY, 143 (1), 3-3 DOI: 10.1104/pp.104.900213

Terashima, I. (2005). Irradiance and phenotype: comparative eco-development of sun and shade leaves in relation to photosynthetic CO2 diffusion Journal of Experimental Botany, 57 (2), 343-354 DOI: 10.1093/jxb/erj014

How Fast Is Fast

The cheetah is one quick cat, but it often confused

with the leopard. Here is a guide. The cheetah has

single black spots, while the leopard has rosettes -

dark spots or circles with light fur in the middle. The 
cheetah is taller and skinnier, with a barrel chest.

Finally, the cheetah has “tear stains” dark lines that

run from its eyes to its mouth.

Take a look at these short videos and then we will ask today’s question. Those little guys are awfully fast, especially the Chromatium. Some seem to dart all the way through the field while others move around in circles or stay mostly still. Bacteria must be the fastest things around.

The question of the day:

Just how fast are microscopic organisms? And for that matter, what is the best way to measure speed in organisms of vastly different sizes?

The fastest terrestrial animal is the cheetah; it is scary fast, to the tune of 70 mph over short distances, like in this video. From a dead stop, the cheetah can hit 60 miles per hour in just three seconds. Cheetah races are popular attractions in many zoos right now. You run and the zoo keepers time you. Then they have the cheetah run and you get to compare times – you won’t win. Biologically, they're built for this speed.

We talked a couple weeks ago about how the hyoid is the only bone in humans that is not attached to any other bone, but in cheetahs, the clavicle bones of their shoulders are built this way. They attach only to muscle, so that it offers the cat extra length in its stretch as is reaches forward for its next step.

The cheetah uses it tail as a rudder and counterbalance as it 

runs. In these pictures, you can see that its tail flattens out to 

act as a sail. It can catch wind or cut through the wind to help 

in turns and balance. This is the only cat that can flatten its 

tail without the aid of a slamming door or a rocking chair.

Any prey animal worth his or her salt will try to turn and have the cheetah run past them, but this cat can go from a top speed to near zero in a mere second. It has claws on the backs its front paws so it can slam its front legs into the ground and have them catch like extra brakes.

Turning is also engineered into this fast cat. Its tail, unlike other cats, is flat, so it can use it as a rudder in turns. Also unique to cats, cheetah claws do not retract. They are always sticking out, so that they can grip the ground and push off for more speed and control in the turns. (click here for the newest mechanism identified in cheetah speed)

If we look up in the sky, there are some pretty fast animals there too. The peregrine falcon is considered to be the fastest bird, hitting over 220 mph when in its hunting dive. The falcon uses this speed to catch other birds right out of the air, as they almost always take their prey on the wing.

The difference is that this speed is achieved with the aid of gravity, it is only in diving that they can go this fast. In horizontal flight, the peregrine can manage only a measly 55-60 mph, not quite as good as the cheetah. If you tossed a cheetah out of a plane, it could achieve a terminal velocity of 200 mph, nearly the same as the falcon, the difference being that a cheetah is not accustomed to assuming an aerodynamic position going straight down. It would probably look rather scared and flail a lot – I don’t recommend trying this.

The white-throated needletail is a sleekly designed

bird, with swept back wings and a large chest. The

chest is large to accommodate huge breast muscles

and a larger than normal heart a lungs. Its tail can be

splayed out for turns, or turned into a needle shape

to reduce drag.

If you want top speed in flapping flight from a bird, bet on the white-throated needletail. It used to be considered a member of the swift family (appropriately named), but is now in its own genus. With a tail wind and the proper motivation, these small birds can reach speeds of 100 mph. Living on the northern coasts of Australia, it is bigger than you might expect for a fast bird, especially one that used to be considered a swift. It has long, swept back wings that help it pick up speed and still be able to maneuver.

Most airplanes have this swept wing design to improve flight characteristics; and as with many of humans so called ideas, we stole it from nature. However, we are getting better at stealing. New aircraft wing designs are based on the swifts’ ability to wing morph, changing the shape of its wings to take better advantage of the flying conditions at the time.

If we drop down into the seas, we can look at speed in the fishes. The sailfish is considered to be fastest. It is of course built in a streamlined fashion, meant to build the speed needed to catch the fish and octopuses it eats. It has been clocked at 68 mph, which in my book makes it faster than the cheetah, since it is moving through water, a much more dense medium as compared to air.

The long upper jaw of the sailfish isn’t just for cutting

through the water. It can skewer large fish with it while

hunting, although this isn’t its normal hunting behavior.  

Sailfish have been seen to cut mackerel in half with a

flick of the bill. Its cousin the marlin has a bill that can

cut through the hull of small boats.

So how do bacteria stack up against these speeds? Not too well, despite what we saw in the first video. The fastest bacteria, members of the Vibrio family, move about 200 µm/sec – this is about 0.00045 mph (0.00072 kph). Even my teenage son on his way to clean his room moves faster than that! However, when you sneeze, you send bacteria (and mucus) out of your nose and mouth at over 100 mph – you can almost hear the little bugs screaming.

Because we are looking at a very small area under the microscope, it appears that the bacteria are covering a good distance. But at 1000x magnification, the least magnification you would need to observe bacteria, the field is usually just 500-800 µm across (0.02-0.03 inches). This makes the bacteria appear to be moving quickly.

Vibro cholerae is a gram negative bacteria with a single

polar (meaning at one end) flagellum. This long

appendage rotates and provides the locomotive force for

this fastest species of bacteria. The flagellar motor can

spin in either direction and is driven by a sodium ion

gradient. Too much salt and it slows down; not enough

salt, it slows down. It’s like a microbial Goldilocks.

Like the fish, bacteria are moving through an aqueous (water) medium, so the density is much greater. But it is even worse for them because of their small size. The effects of density are much larger on small organisms, sort of like us trying to walk through a pool filled with caramel (not a bad idea).

But what if we measured speed in a different manner, say….. bodies lengths per second. Vibrio are approximately 2 µm (0.00008 inches) in length and they move about 200 µm/sec. This is about 100 body lengths per second. Now that seems pretty fast, especially for swimming through something thick. 

How does that compare to our other candidates:

                                                Avg. Length            Top speed (kph)               Body lengths/sec

Cheetah                                     125 cm                         112.7                                     25.0

White throated needle tail           25 cm                         160.9                                    178.7

Sailfish                                      340 cm                         109.4                                      8.9

Vibro cholerae bacteria            0.0002 cm                   0.00072                                   100

S. Giant Darner dragonfly          12.7 cm                       57.9                                       126

Australian tiger beetle                0.10 cm                        9.01                                    2502.8

So the bacteria are pretty fast, it just depends on how you measure it. But the needle tail still holds its own, even though it is only traveling through air. Comparatively, Usain Bolt moves at a top speed of about 6.2 body lengths/sec. Since humans walk upright, we could measure him at body depths/sec, which makes him sound faster, about 30 body depths/sec (assume 15 inch body depth). But we don’t all run like Usain Bolt.

Black horseflies can measure up to 1 inch in length. They

pester people and domestic animals, but worse, can carry

mosquitoes, only the females feed on blood, the gentler

males prefer nectar and help pollinate many flower species.

I could make an analogy between horseflies and humans,

but I won’

In the table above I gave you a couple more examples so that we can find an overall winner.  As always, nothing seems to top the insect world, the Australian tiger beetle can move at over 2500 body lengths/sec, while the darner dragonfly shown above is merely the scientifically confirmed fastest flying insect. However, if you want to go with the most recent estimate for the male horsefly (Hybomitra hinei wrighti), we are talking about speeds of 145 kph when he's in pursuit of a female- typical male behavior. That works out to roughly 4000 body lengths/second!

Next week we can look at plants lifting weights; they have to be in shape in order to photosynthesize!


Penny E. Hudson, Sandra A. Corr and Alan M. Wilson (2012). High speed galloping in the cheetah (Acinonyx jubatus) and the racing greyhound (Canis familiaris): spatio-temporal and kinetic characteristics J Exp Biol DOI: 10.1242/​jeb.066720

Wilson RP, Griffiths IW, Mills MG, Carbone C, Wilson JW, & Scantlebury DM (2015). Mass enhances speed but diminishes turn capacity in terrestrial pursuit predators. eLife, 4 PMID: 26252515

Look Who’s Talking

Humans have the ability to make language, although too 

many choose not to use it well. Our speech involves 

anatomy, genes, and our higher brain functions that 

allow us to attach meaning to words and abstract 

concepts. Donkeys only speak in ogre movies.

Question of the day – Why do humans speak and use a vocal language when other animals don’t?

To begin to answer this question, you first must decide what a language is. Linguists have four criteria for sounds to be a language. One, each vocalization has a certain order – the short "i" sound always precedes the "en" sound in the word “in.” Second, the must be order between vocalizations – this is syntax. Three, the vocalizations can not be tied to or defined by a specific emotional state – you can yell the word “Hey,” either to let someone know to stop doing something, or to call out to a friend you haven’t seen. And four, novel localizations are understood – you can say something that has never been said before, but those people listening to you will understand its meaning.

If sounds follow those four rules, then they are an oral language. So humans have spoken language and other animals don't - although the majority of people don’t use it very well. A discussion could be had as to whether whale song is language, whether American Sign Language is true language, and whether parrots can really talk.

But the question remains, why are humans so much better at making sounds and language. We share 98% of our genes with chimpanzees, but they can make only three dozen or so vocalizations. Humans can make hundreds of different sounds – every noise required for every language on Earth. Where did we separate from apes in terms of speaking?

Current hypotheses focus on two areas; brain molecular biology and body anatomy.  First the anatomy – we can make more vocalizations because of how our throats and chests have evolved.

The hyoid is the only human bone that is attached

to only muscles, not to another bone. Our hyoid is attached to 

tongue muscles, throat muscles, and jaw muscles. They  all

work together to help us produce thousands of vocalizations.
Next week we will look at a bone in cheetahs that attaches to
only muscles.

To make sounds, you must be able to expel air in a controlled manner, this requires rib muscles and innervation to allow controlled exhalation – we got it, apes don’t. The air that is expelled passes over the vocal folds and vibrates them – this produces sound waves. The wave that is produced is based on the way your muscles change the shape of the vocal fold cartilage, and one way to alter the laryngeal muscle tone and shape is by moving your tongue.

The tongue is a muscle, and ours goes further back in our throat as compared to that of apes. Theirs is housed completely within their mouth, but ours is attached much deeper, and we can change the shape of our voice box by using our tongue. You can stick out your tongue and move it side to side and feel your Adam’s apple move.Your adam's apple is NOT the same thing as your hyoid bone; the adam's apple is the laryngeal prominence associated with your voice box, but you can see that moving your tongue can modulate the vocal folds.

The other characteristic of the tongue that makes a difference is that it is our most sensitive touch appendage. We can make small and discrete moves with the tongue, and sense where it is in relation to our teeth and cheeks. This is another reason we can make so many different sounds, and is also why babies put everything in their mouths.

The intercostal muscles between the ribs are arranged

in several diagonal layers. The external muscles help with

inspiration, while the internal intercostals help with forced

exhalation. Humans have much more innervation of these

muscles (see the nerve traveling with the artery and vein in

Fig. B), so we can control exhalation for vocalization. It is

said that the human thoracic nerves allow for as much

control as the innervation of the hand and fingers.

Another anatomical difference is that humans have a free-floating hyoid bone; it is the only bone in the human body that is not anchored to another bone. By attaching to the pharyngeal and tongue muscles, our hyoid helps us to make more sounds than just hoots and grunts. While apes do have a hypoid bone, it is not located as deep in their throat as is ours. In fact, humans infant larynx and hyoid bone anatomy looks a lot like ape anatomy, but as we grow, our voice box and hyoid bone descend in our throat, while those of the apes do not. This is one reason it takes babies a while to learn to speak, muscle tone being another.

Your ribs muscles, your tongue attachment and your hyoid bone are all good reasons why humans can make more vocalizations as compared to no human animals, but our brains matter too. The shear size of our brain means that we can devote more neurons to abstract thought, assigning meanings to vocalizations – this is the basis of a large dynamic language. But there is a molecular issue as well.

The brain has several areas that work in language.

Broca’s area is involved in making sounds, while

Wernicke’s area is important for understanding

speech. The understanding comes from integrating

the sounds with memories and feelings in other parts

of the brain.

The fox2p protein is involved in vocalization and in understanding language. In songbirds with a mutated fox2p, their song is incomplete and inaccurate. In humans, defects in fox2p activity lead to severe language impairments in both speaking and in understanding. Two small mutations in the human fox2p as compared to the animal version is much of separates our language ability from theirs.

The fox2p protein acts in just about every cell, so it does have other functions. A very recent study has looked at the role of foxp2 function in auditory learning. Proper speech is closely related to auditory cues, these cues educate motor processes that are used to form sounds. In the 2012 study, mice heterozygous for either of two fox2p mutations showed significant defects in learning the motor processes to mimic auditory cues.

In similar fashion, language disorders are a hallmark of some mental diseases. Another 2012 study sought to determine if fox2p changes were associated with schizophrenia. In a population of Chinese Han, a one individual change in fox2p (of 12 studied) was significantly associated with schizophrenic patients, but was not found in normal individuals. This single nucleotide polymorphism was rare, but was associated with both depression and schizophrenia. It is evident that normal fox2p function is necessary for speech as well as other cognitive functions. And having a normal fox2p means we are able to talk about fox2p amongst ourselves.

On the down side, our ability to speak and make language also makes us vulnerable to choking to death. The lowering of the voice box in humans puts the vocal folds and larynx very close to the esophagus. This means that your hotdog is much more likely to get lodged somewhere that will block your air flow and suffocate you. Doubly bad, the act of having a hotdog stuck in your throat prevents you from using your spoken language abilities to tell your tablemates that you are choking - one of nature's cruel jokes.

Next week we will take a quick look at the speeds at which organisms can move - is distance per unit time the best way to measure this?


Kurt, S., Fisher, S., & Ehret, G. (2012). Foxp2 Mutations Impair Auditory-Motor Association Learning PLoS ONE, 7 (3) DOI: 10.1371/journal.pone.0033130

Li, T., Zeng, Z., Zhao, Q., Wang, T., Huang, K., Li, J., Li, Y., Liu, J., Wei, Z., Wang, Y., Feng, G., He, L., & Shi, Y. (2012). FoxP2 is significantly associated associated with schizophrenia and major depression in the Chinese Han Population World Journal of Biological Psychiatry, 1-5 DOI: 10.3109/15622975.2011.615860

Big Bugs, Little Bugs

The titan beetle (Titanus giganteus), is not necessarily

a gentle giant. Its jaws can snap pencils and easily cut

into human flesh…. and they fly. Calm down, the adults

don’t feed, they just look for mates, so you won’t wake

to one nibbling your toes away.

Today, the biggest insects are goliath beetles, atlas moths, and giant stick insects. But during the carboniferous period (360 -300 million years ago), there were millipedes that were 2 m (6 ft) long and dragonflies (order Protodonata) the size of eagles!

Today’s question is:

How did insects get so big in the carboniferous period, and if they were big once, why are they so much smaller now?

It wasn’t just the insects that grew large way back then, the first large plants flourished in this same time period. Some ferns grew to be 20 m (65 ft) or more in height, and the diameters of trunks were increased. While not as big as today’s largest plants, the change was significant, as plants before this period did not exceed 3 to 5 ft in height.There was plentiful carbon dioxide in the atmosphere and the environment was warm all year round. This allowed lots of photosynthesis and lots of growth.

Nice picture to give scale, but humans and the

Arthropleura never co-existed. Even though the

species alive today aren’t as big, you still have

to beware. Many centipedes are venomous and

some millipedes can emit hydrogen cyanide gas.

Plants were evolving lignan in this carboniferous period (carbonis = coal, and ferrous = producing). Lignan is the stiffest of the plant molecules and is what allows them to grow tall.  This is also what gives the carboniferous period its name, as the lignan of plants is the major component of the coal that formed from their remains.

Horsetails, another type of plant of the carboniferous age and which are still around today, also grew much bigger. Horsetails today do not get any taller than about 1 m (3 ft), but in the carboniferous period, they were often 10-15 m (33-48 ft) tall.

But it was the arthropods that get all the publicity. Scorpions almost a meter in length deserve to have a lot of attention paid to them! And consider the yuck factor of a 7 inch cockroach scurrying around at your feet.

The plants got big during the Carboniferous period.

Some lycophyte trees were 30 m (98 ft) tall and had

trunks of 2 m (6.5 ft) diameter. Their closest

relatives today are the club mosses, which are about

20 cm or less in height. Talk about deflating your ego.

What allowed these animals to grow so large? Scientists think it was related to the lignan. With lignan, the plants could grow larger and support more photosynthetic material. The carboniferous period is when the first forests appeared.

With more and bigger plants, more carbon dioxide was converted to carbohydrate, and more oxygen was produced as a result. The oxygen content of the air in the carboniferous period reached levels of 35% or more (today it is about 21%).

More oxygen in the air meant that more oxygen could be transferred into the blood of animals.  They could carry out more oxidative phosphorylation and produce more cellular energy (ATP), especially since there was all this plant material around to eat to gain carbohydrates (or plant-eaters to hunt down and eat). This growth spurt especially applied to animals without traditional circulatory systems. Insects, for instance.

Insects use spiracles on the sides of their bodies to take in air. The oxygen and other gases are moved through a system of smaller and smaller tubes (called trachea) to bring the oxygen to all the cells of the body. The carbon dioxide produced during cellular respiration is removed in the same way.

The spiracles of a flea are on the side of its abdomen

and the air travels through the tracheae to bring

oxygen to every cell. It seems like he would drown if

he took a dip in the hot tub.

This is not a particularly efficient way to move gases in and out of cells. A slightly bigger bug must have a much more voluminous system of trachea, and at some point, the respiratory system would have to be bigger than the entire volume of the insect! There would be no room for all the other organs. But with a high concentration of oxygen, the spiracle/tracheae system is efficient enough, and the insects can grow very large.

High oxygen in the air also meant high oxygen in the water. Carboniferous era fish and amphibians grew large as well. Some toothed fishes of this time were impressive predators, and were more than 7 meters (23 ft) in length. Isopods in the oceans were also huge. Even today some of these crustaceans can be pretty impressive. Bathynomus giganteus can grow to more than over 16 inches in length. 

So big plants brought big oxygen levels, which brought big animals. But why are the arthropods so much smaller today as compared to then? Well, the oxygen levels are lower now, so according to a 2006 study the inefficient spiracles system could not support the large body. Insects had to get smaller.

Here is an isopod that grabbed a ride when a deep sea remotely operated 

vehicle was recovered. They look even creepier from the front with 

silver eyes. Isopods are related to shrimp and crabs; I think we’re going 

to need much more butter and lemon.

But there is an additional hypothesis that may also contribute to the small size of many insects, especially flying insects. According to a 2012 study, the size of flying insects is related to another aspect of oxygen. When the explosion of plants in the carboniferous period raised the oxygen levels, the air became more dense (oxygen is a heavier gas). The insects were able to become better fliers, since their wings could move more air.

The data says that one reason flying insect

got smaller was to avoid being easy catches for the birds

that were becoming better fliers and hunters. Really?

Name me a couple birds that would go after this guy if

he was flying today.

Millions of years later, birds evolved. As they became better fliers (their ability was also based on their ability to move air over their wings), they became better hunters. Better hunting birds could catch flying insects (and terrestrial insects for that matter) better. So it became a disadvantage to be big. The smaller insects now had a reproductive advantage; they were the only ones surviving to have offspring. Over a period of time, the insects grew smaller on the whole.

So today we have fairly small arthropods and insects, although my wife has personally never seen a small insect. According to her they are all large enough to carry off small children and have evil looks in their eyes.

Matthew E. Clapham1 and Jered A. Karr (2012). Environmental and biotic controls on the evolutionary history of insect body size Proc. Natl. Acad. Sci. USA DOI: 10.1073/pnas.1204026109

Next week – ideas for long studies on the nature of science.