Planet for lease

Feeling nostalgic? Here's a timeline showing some of the important events on planet Earth since it formed approximately 4.5 billion years ago. My personal favourite would have to be the Cambrian explosion of 500 million years ago (see 'First Hard-shelled Animals'). This was not literally an explosion, but a relatively short time period in which the major groups of modern invertebrates evolved. And I suppose anyone's 'best of' list would also have to include that classic moment, the evolution of life, which happened roughly 3.5 billion years ago.

One thing I find striking about this sort of diagram is the 1 billion years between the formation of our planet and the appearance of anyone on it. For a little less that a quarter of the Earth's history, there was nobody here. I find this concept very calming to think about, particularly while using public transport during peak hour. Thinking about the empty earth is the biologist's equivalent of the Zen Buddhist puzzle about whether a tree falling in a forest still makes a sound if no one is around to hear it. A more scientifically minded version of the question would be: If a bubble of volcanic gas erupted on the primeval Earth, and no biotic molecule had evolved yet to inhale the vapour, would it still smell like methane?
In the period before life formed, there was constant volcanic activity. This produced an atmosphere of hydrogen and ammonia gases, water vapour, methane, carbon monoxide and carbon dioxide. The oxygen rich atmosphere we enjoy today had not yet formed. It took roughly half a billion for the Earth's crust to solidify.

The planet was constantly struck by lightning and bombarded by meteorites. The atmosphere was easily penetrated by ultraviolet radiation, which may have been especially strong because it radiated from a young sun.

In short, Earth before life evolved was characterised by a series of natural disasters. Yet, in the absence of any life forms to suffer the outcome of all this chaos, even the most catastrophic events are reduced to inconsequential sound, colour and movement. Or they would would be, if anyone had been around to hear, see or feel them. For one billion years, there was complete peace on Earth.

Conditions on the young Earth seem extremely hostile to life, but it was probably these very conditions that allowed life to form. In 1953, Stanley Miller and Harold Urey used a large glass flask to recreate this environment. The flask was filled with water, representing the ocean, while the 'atmosphere' was composed of the gases listed above. Electrical sparks were discharged to simulate lightning. The aparatus was left to sit as a self-contained system. This experiment was something very like scientists playing God.

And, amazingly, Miller and Urey managed to replicate God's data. Within a week, the flask contained amino acids. These molecules are the building blocks for proteins, which in turn form most of the structural components of animals. Further lab recreations of the primitive Earth have produced all 20 of the amino acids found in living organisms, as well as sugars, lipids, and the bases for DNA: in short, the building blocks necessary for life.

The atoms needed to make these molecules are present in the atomospheric gases. It is thought that energy provided by the lightning, and perhaps by UV radiation, enabled the breaking and reforming of chemical bonds. Our modern, oxygen rich atmosphere prevents the formation of new bonds, but on a low-oxygen planet, this process would have been possible.

In order for life to form, the tiny molecules had to join together to form larger molecules. In laboratory experiments, organic molecules have been joined together by a process that involves diluting them in water and dripping them onto hot rocks, sand or clay. It is thought that the many organic molecules dissolved in seawater may have been carried by waves onto hot rocks or larva, forming proteins, before being washed back into the ocean.

Also under laboratory conditions, these larger molecules have been shown to form what are known as 'protobionts': aggregations of molecules that are not considered living, but have some of the properties of living things. Protobionts have been observed to form an outer layer of lipids that resembles a cell membrane, and to show signs of primitive metabolism and electrical excitability, the latter of which is necessary for the development of a nervous system. These observations do not prove that life evolved in this way, but they do show that this course of events would have been possible.
On a planet crowded with the protobionts' possible descendants, perhaps the only places where the relative peace of the primeval Earth still exists is in space. But then again, maybe not. Meteorites hitting the Earth in the modern era have been found to carry amino acids. If the idea that we had our origins in the action of waves on hot rocks is difficult to comprehend, this evidence makes the picture even stanger. Some scientists believe that we had at least some of our origins in space, and that our precursor molecules were brought to Earth by meteorites and comets. If amino acids could form on other planets, there is also a possibilty that life has formed on planets other than Earth. If we have company, the universe could be even noiser than we imagined.

Basic instincts

This is my housemate's cat, Larry. Larry has had a few bad experiences with cars, so he has to be an indoor cat. At least once a day, he attempts to mate with this knitted patchwork blanket. Given the opportunity, he also likes an encounter with a jumper or scarf (pure wool only, he won't stoop to synthetic fibres).

After servicing the females in his territory, he likes to go hunting. His prey is a length of leopard-spotted synthetic fur with a bunch of feathers attached to the end.

All of Larry's natural impulses and behaviours have to be played out in a completely simulated environment. Sometimes characteristics of household objects (eg. hairy, moving) provide bevhavioural cues, even when, in other ways, that object bears little resemblance to anything a cat would encounter in the wild. It could be said that Larry's blanket-humping is a desparate measure from a domesticated animal. But even wild animals have been known to misread environmental cues.


In the early 1980s, biologists discovered something unusual about the Australian jewel beetle. I could paraphrase these findings, but I think they are best conveyed in the charming deadpan of a scientific paper. Here is an abbreviated version of Dr Trevor J. Hawkeswood's article on the species Julodimorpha bakewelli:

...The males are known to mistake the ends of discarded 'stubby' bottles for females and attempt to mate with them. The first published indication of this phenomenon was Douglas (1984), who published a photograph of a male J. bakewelli attempting to copulate with a 370mL beer bottle in Western Australia.

The 'stubbies' were apparently acting as 'supernormal releasers' for male copulation attempts in that they resembled large females; the shiny brown colour of the glass is similar to the shiny yellow-brown elytra of the female J. bakewelli. On two occasions, a flying male was observed to descend onto a stubby and attempt copulation, and a search yielded two other stubbies with male beetles, with genitalia everted and attempting to insert the aedagus.

A discarded wine bottle of a different colour brown held no attraction; in addition, rows of regularly spaced, small tubercules around the base of the bottle reflect the light in a similar way to punctuations on the elytra of the beetle; these along with the colour and shape of the bottle may well enhance their resemblance to females.

One of the reasons I find animals interesting is the mystery of what it's like to view the world through their minds. Although I have to take a scientific approach, part of me wants to believe that in some important ways, the minds of animals are not very different from our own. I find it exciting when Larry reads human social cues, or opens doors with his paws, because this behviour seems like evidence of a highly evolved intelligence. But at other times, his actions, like those of the bottle-copulating beetles, seem to be automatic reactions to narrow environmental cues, and not the actions of a thinking being.

The philosopher and mathemetician Rene Descartes thought that animals were 'automata': mere machines whose behaviour was a robotic response to their environment. Sadly, it seems like this view is sometimes correct.

But perhaps this is not the evidence of a vast gulf between human and animal consciousness that it appears to be. Larry's hunting of faux fur and insemination of our woollens may seem like absurd behaviour, and evidence of his lower powers of thought. But what is this animal doing living in our house in the first place? He does no work, contributes no rent, and his food is paid for by humans. By biological definitions, Larry is a parasite, yet we willingly allow him to exploit us.

Modern, urban humans also live in an environment which bears very little resemblance to the environmental conditions under which we evolved. It seems like we too can misdirect our reproductive instincts. Don't worry, this is not a reference to bestiality. I'm referring to zoologist Konrad Lorenz's famous theory on the appeal of domestic pets. Lorenz observed in the 1940s that most pets have large eyes and heads, and shortened noses, all features in common with human infants. He suggesting that these infantile features were responsible for triggering a nurturing response in adults. In the absence of the litter-loads of spawn we would have produced in our wild state, Larry's big eyes, soft fur, and button nose trick us into thinking we are caring for our own baby. Although, if my human child starting doing that to our jumpers, I'd probably put it in a bag and drown it in the creek.

Brittle Star Photos

Here are some pictures of a brittle star, which were taken by a classmate in my marine zoology subject. Brittle stars are echinoderms, and are related to starfish.

I think this one was about three cm across. These photos were taken by pointing the camera down the microscope lens. The photos down the bottom show the underside of the animal, with its star-shaped mouth visible.

A Kick up the Blastopore

"When I view all beings not as special creations, but as the lineal descendants of some few beings which have lived long before the first bed of the Cambrian system was deposited, they seem to me to become ennobled."
-Charles Darwin, The Origin of Species


In the popular imagination, evolution is an ape with incrementally improving posture. Human beings came from monkeys. Before that, we crawled out of the ocean. But both these primal ancestors are relatively recent arrivals on the earth. Vertebrates are only 400 to 500 million years old. But our ancestors have been around since life first evolved. What did they look like before they developed bony skeletons?

If you trace the evolutionary line back far enough, we are descended from invertebrate animals. So far, I haven't come across any theories on what our invertebrate forebears looked like. Perhaps this is because no one knows. Invertebrates make poor fossils because of their soft, fragile body parts. However, human beings are more closely related to some groups living invertebrates than to others. Perhaps this offers clues as to what our invertebrate ancestors looked like. Try to guess who our closest invertebrate relatives are. Do see any familiar faces below?



What about the molluscs? I hear a lot of stories around the zoology department about octopi in laboratories who wait until their researchers go home, then climb out of their tanks and switch off all the lights in the lab. I'm not sure if these stories are true (perhaps this can be the subject of future blogs), but look at that big brain! Surely the octopus is kin. I'm not too sure about the bivalve, though.


Or what about the platyhelminths? No one really wants to be closely related to a tapeworm, but they can't be discounted.


How about the nematodes? Is that primate-level intelligence brewing behind those unassuming piercing mouthparts?




Or the echinoderms? Sea cucumbers certainly look like a certain part of the primate anatomy, but is this evidence of family ties?



How about the cnidarians, with their very economical use of the same orifice for multiple bodily functions? (see a previous blog). Surely they're not our nearest invertebrate cousins?


The annelids are also contenders. Do you have an inner bloodsucking leech?




My personal favourite would have been the arthropods. There is something familiar about insect faces. You can at least look them in their two eyes, which are located above a mouth, and see something not too different from a basic vertebrate face. Or less different than a blind tube sporting a bunch of piercing hooks, anyway.

But the answer is surprising.

The winner is: ECHINODERMS. Starfish, sea cucumbers, anemones and their ilk are our nearest invertebrate relatives. This does not necessarily mean that our invertebrate ancestors looked like starfish (although part of me really wants to believe they did), but that echinoderms and vertebrates had a more recent common ancestor than vertebrates and any other invertebrate group.

One important piece of evidence for this relationship is as follows. At a very early stage in our lives, all of us (you, me, echinoderms, tapeworms) looked a bit like this:

Before our body plans formed, we were all big, fat, amorphous balls of cells. Those were the days! Our balls of cells each had a little hole called a blastopore in them. In all other groups of animals, the blastopore developed into the mouth of the animal. In vertebrates and echinoderms, it formed the anus. Our guts run in reverse. The thing that sets vertebrates and echinoderms apart is that, compared to other animals, we are all talking out of our arses.

Prac book drawings

I spent a lot of last year drawing bones, mostly skulls, with a foray into forelimbs. Here are some of the highlights. I had to memorise the names and locations of all these bones for my exam. I managed it okay, but the day after the exam, I couldn't remember them any more. Luckily I have my sketchbook to reminisce over. I think you can make these pictures bigger by clicking on them.




In the picture below, 'TS' stands for transverse section, which is a paper-thin slice of an animal that has been preserved on a microscope slide. Preparing the specimen like this shows where all the bones, organs and muscles are located in that part of the body. I think I've labelled the vertebrae wrongly, but you get the idea. The little spots on either side of the specimen are feathers. As well as the chicken embryo, I've had to draw transverse sections of a baby turtle, a rat embryo and a tadpole. It was like a petting zoo, only all the baby animals were inside out.

Fish out of water

My mother is a fish.
-William Faulkner, As I Lay Dying.

A staple illustration of biology texts is the diagram of vertebrate forelimbs. The bones, for all their different shapes and sizes, are the same bones. The same basic structures have been used to make legs, flippers and wings.
The beginnings of these later-evolved bones can be found in the fins of the modern-day lungfish and the coelocanth (both pictured below), which are believed to be living fossils from the time fish began to take to land. The structures that became our arms and legs were originally made for moving through water. Our bodies have been bequeathed to us by fish.



But it’s not only our arms and legs they have left us. The earliest fish were jawless animals who sucked, tore and filtered their prey from the water. One theory says that the lower jaw evolved from a bone that was originally an arch to support the gills. The structure that, in human beings, allowed the development of speech, with all the implications of that revolution, might have started out as a bony strut that helped fish to breathe oxygen from water. Maybe the only response to a revelation like this is to let your mouth hang open, and gape wordlessly like a stunned mullet.

Toad dissection

I decided to photograph and talk about a toad dissection I did this week. Some people (Lorelei?) might not want to see these pictures. A few of the Queenslanders amongst you are likely to have done a toad dissection at school. I wish I could preface this entry with some illuminating comment on the ethics of dissection, but in order to do this sort of thing I try not to think too hard about the morals of what I'm doing. Sometimes I feel a sympathetic pain in the same body part as the part of the animal I'm cutting. I am a hypocrite. But enough of my moral flabbiness, and on with the toad.



Here's my toad. I picked it out of the other toads in the tub because it was a very pretty shade of pale yellow. It's illegal to breed cane toads, so the toads we used were captured in Northern Queensland and crated down.



This is always the saddest part of the dissection.




Once I've made the first cut it's easier to think of the toad as a specimen, and not an animal. Here (above) I've cut through the skin to reveal the abdominal muscles. Toads have no external genitalia (both sexes have a multi-purpose cloaca), so it's only once you get inside that you can tell what sex it is. This is a male toad, because it has a vocal sac. You can see the vocal sac in the photo immediately above. It's the black-and-white flecked section of skin beneath the lower jaw.



These pictures were taken after I cut through the muscle layer. The internal organs are known collectively as the viscera. In the above picture, where the chest muscles and vocal sac have been severed, you can see the white roof of the toad's mouth.


Here's a close-up of the viscera. The following organs are visible:

Lungs: the pale yellow, honey-comb sacs on either side of the body. As well as breathing with their lungs, toads can breathe and absorb water through their skin.

Heart: dark red, in the centre of the chest.

Stomach: pale pink tube on the lower right hand side of the photo. It is attached the small intestine, which is the thinner, coiled tube.

As it turned out, there was something wrong with my toad. The large grey ball in the middle of the viscera is the gall bladder, which is abnormally enlarged. Normally the toad's liver would be dark brown-red and cover a large portion of the viscera. However, this toad's liver is visible as the two shrunken, pale brown masses on either side of the gall bladder. Humans with poor liver function can have a yellow complection. Maybe the yellow colouring I initially took to be the sign of a particularly beautiful toad was actually a result of liver disease. The demonstrator told me that if my toad was a human, it would be an alcoholic.

At this point my camera ran out out of batteries, so I can't show you the toad's kidneys, which were located under the rest of the viscera, or its internal testes, which are small yellow things that sit above the kidneys. Neither can I show you inside its heart, which I had to remove, slice through and put in a petri dish. Underneath the viscera I could see the toad's backbone sitting against its skin. I ran out of time to draw the nervous system, so I wanted to take the toad home in my lunchbox to finish the prac, but the demonstrator wouldn't let me.

Next week I'm doing a pigeon.