Saturday, December 5, 2009

Foure Footed Beastes

This illustration was made in 1230 AD. The tusked animals are elephants. The top panel shows soldiers riding an elephant into battle, while the bottom panel shows an ailing elephant being supported by the rest of its herd. It's obvious from the animals' fur, pig-like heads, and dog-like limbs that the artist has never seen a real elephant. The images are true to a verbal description of an elephant, as a large animal with tusks, large ears and a long trunk. But a lot has been lost, and gained, in the translation from words to image.

I find these sorts of images compelling, although it's difficult to explain exactly why this is so. On a basic level, these illustrations are funny because to modern eyes, they are so obviously wrong. More than words, an image seems to lay an authoritative claim to the truth, and when it is so transparently inaccurate, there's a cheap thrill in catching the artist out in the act of fabrication. There's also the charming naivete of this image, and the mental acrobatics of trying to put myself in the mind of someone in whose world the elephant is still a quasi-fictional beast.

In a similar vein is this image of a hyena, which appeared in Edward Topsell's book Foure Footed Beasts, in 1607. Below is a photograph of a real hyena for comparison.

The text below the illustration reads:

'This beast aboundeth near Caesarea (?) in quantity resembling a Fox, but in wit and disposition a Wolf; the fashion is, being gathered together, for one of them to go before the flock singing, or howling, and all the rest, answering him with correspondent tune: In hair, it resembleth a Fox...'

Below are depictions of a sloth (1573), and a crocodile (c. 1170), which is devouring a water serpent. As with the elephant illustrations, the crocodile's claws, long tail, and spiky backbone are all accurate features of the animal, but their translation from words into an image leaves a lot to be desired.



The crocodile image comes from a type of Medieval book known as a bestiary, which was essentially a compendium of animals. Each animal in a bestiary was the subject of a story, the purpose of which was to illustrate an aspect of Christianity. The story accompanying this image is that the water-serpent allowed itself to be eaten by the crocodile, but would then devour the crocodile's innards and escape. The crocodile symbolised Hell, while the hydra represented God.

The animals in bestiaries often speak, or perform miraculous acts. It's difficult to say whether the people reading these stories interpreted them as allegories or scientific fact, partly because the medieval mind had no concept of science as a way of thinking. Areas of knowledge that today would fall under the auspices of science were mixed up with religion and myth, with no distinctions made between these ways of explaining the world. Scientific knowledge has shaped the modern worldview to the extent that we take the scientific method for granted. So I suppose another part of the appeal of these images is the unsettling thrill of trying to imagine a world in which it wasn't yet possible to think in this way. I think the scientific method is a wonderful thing, but maybe part of me enjoys the iconoclasm of trying to recreate a Medieval concept of nature. There's something comforting about the thought that no one had to study for biology exams in the days before biology was invented.

The image below is a woodblock print of a rhinoceros, which was made by the artist Albrecht Durer in 1515. A chapter in Science, Medicine and History (ed. B.A. Underwood) charts the history of this image, which became the European world's defining image of a rhinoceros for the next 250 years.

Compared to a real rhinoceros, the print is strikingly accurate in some respects. But the plicae, or skin folds, of the real rhino have been depicted as elaborate plates that resemble Medieval armor, and the animal has a completely fanciful horn between its shoulder blades.

Durer never saw a rhinoceros. He made the print from descriptions of the animal and from a sketch made by another artist of an Indian rhino that was a gift to the Pope. It's believed that Durer may have heard about the two-horned species of African Rhino (pictured below), which had been described in classical texts. Even though the species he was drawing has only one horn, he may have tried to make his image more believable by adding a second horn, not on the nose as in the real-life African species, but on the animal's back.


Over the next few centuries, Durer's image became the defining image of the rhinoceros, and was reproduced and plagiarised, complete with its embellishments, in numerous scientific texts. Later images became even more fanciful, exaggerating the morphology of the armor plates and size of the second horn. The drawing below was claimed to show several newly discovered species of rhino, but the mark of Durer's image is obvious.

Durer's rhino and its fictitious dorsal horn even found it way into this early C17th coat of arms, of the Society of Apothecaries.


In the eighteenth century, a traveler to Africa quoted local (presumably European) hunters as saying they often saw three horned rhinos, with the third horn being positioned in the location of Durer's fictitious horn. Apparently, only male animals carried the third, dorsal horn. Continual reproductions had made Durer's image so persuasive that it had influenced people's observations of the real animal.

The saga of Durer's rhinoceros can be read as a cautionary tale about the hazards of observer bias, not to mention the pitfalls of plagiarism. The modern scientific method stipulates that results must be able to be replicated by another party. This means modern science largely avoids the problems of falsification and bias that seemed so rampant in the middle of the last millennium. But these images are a reminder of the enduring possibility of human fallibility, and of truth being in the eye of the beholder.

My favourite historical scientific image is this drawing, made by Nicolas Hartsoeker in 1694.



This is a human sperm cell, or spermatazoon. Spermatozoa were discovered by the Dutch microscopist Anton van Leeuwenhoek in 1677. At the time this drawing was made, one school of thought on the origins of human life held that an entire miniature person was carried in the head of the sperm. The only contribution of the mother was to nourish and protect the baby. This theory was known as 'spermism'. As you can see, this drawing shows a tiny person curled up inside the cell. Since male babies would, in turn, carry their own offspring in miniature, the generations of humanity could be imagined to be like a set of Babushka dolls, which had originally all been contained in the testicles of Adam. And since a whole person was contained inside the cell, some people concluded that sperm cells had souls. This idea was used to support the argument that masturbation was a sin.

I had trouble researching this image because many sources gave conflicting information. Some sources claim that Hartsoeker, and sometimes also van Leeuwenhoek, claimed to have actually seen the little person, or 'homunculus', sitting in the head of the sperm. According to other sources, no such claims were made. Although the artist had seen sperm cells under the microscope, and believed in spermism, he would not have been able to see through the cell membrane to determine whether the homunculus was present. It's possible that in creating the image, he was merely representing a concept, as opposed to drawing from life what he thought, with his biased vision, he was seeing.

Somehow, the second scenario is much less appealing than that of a seventeenth century scientist gazing through a lens and thinking he could make out a little person in his own sperm, in the same way that children think they can see a face in the moon. Perhaps the first scenario has gained traction because it has much more comic potential, and seems to fit better with our ideas about the ignorant dark ages of science. If this is the case, maybe our modern minds are not so far above biased interpretation as we like to believe.

Thursday, November 19, 2009

Batting average

Here are some photos from a field biology camp I went on in September. It was held in the Strathbogie Ranges, in northern Victoria. I was in the bat group. Our project was to work out whether higher temperatures resulted in more insect activity and therefore more bat activity. We trapped the bats using a harp trap, which looks like this. The frame is strung with fishing line, which the bat flies into. It bounces off the trap and into the canvas bag below.


The first two nights of the camp were very cold (down to zero degrees), so we spent a lot of time walking around in the bush late at night but catching nothing. This was great preparation for a major part of real field work: dealing with frustration and disappointment. Then it warmed up, and we woke up one morning to this miraculous sight.


We caught two species of microbat: the Southern Forest Bat and the Little Forest Bat. It's difficult to tell which is which from the photos, because the two species look very similar, and are distinguished by (among other features) subtle differences in their fur and the morphology of the tips of their penises.


Here's an echidna I ran into one day. I took a video (pasted at the end of this entry) because echidnas' rolling gait always makes me laugh. Echidnas are mammals, because they produce milk, but unlike most mammals, they lay eggs. This is not their only reptilian feature. They also have a reptilian-style pelvis, which explains why they walk with their legs splaying out to the side, like a lizard. However, their archaic physiology shouldn't be taken as a sign of low intelligence. According to our lecturer, Kath, laboratory tests have shown that echidnas have the intellect of a domestic cat. I probably wouldn't want to stroke one on my knee, though.


However, I suspect that Kath might. Here she is demonstrating how to capture an echidna bare-handed. Understandably, the echidna was not happy. Being an intelligent creature, it communicated its disgust in a way it was sure humans could understand: by pooing all over Kath's pants. This was fortunate because one of the groups was collecting mammalian faecal samples, and was able to scrape the poo into a zip lock bag.


Here's a Mountain Brushtail possum, or bobuck, who is being measured and having his details recorded. The possum looks a bit dopey because he has just been sedated. This possum would later wake up to find that while he was out of it, he had gotten a tattoo. Fortunately, it wasn't a dolphin, or text from Kabbalah. Possums aren't that stupid. The tattoo was an identification number so he can be included in a long term population study of bobucks in the Strathbogies.


Here's a male Superb Fairy Wren in breeding plumage. Another group was capturing these birds with a fine net strung between trees, and fitting them with leg bands. This was so individual birds could be identified, in order to give an idea of their social structure. I've seen groups of fairy wrens around and always assumed that they consisted of one colourful male and his harem of brown females. But in fact each group consists of just one breeding pair. The other brown individuals are subordinate males, often offspring from previous years, who stick around to help the breeding pair raise their young. Other females are chased out the territory.

Continuing the theme of previous blogs about promiscuous birds, fairy wrens have one of the highest proportions of illegitimate young of any birds - about 70 per cent of offspring come from extra pair matings. Male fairy wrens have been observed picking up yellow flowers in their beaks and offering them to females in other territories in the hope of gaining matings. This kind of behaviour is known as the 'sneaky fucker' strategy, which is the official biological term. So many words in biology have complicated Greek or Latin roots. I'm all for this kind of simplification.

Here's a small-eyed snake, the bite of which will cause kidney failure. Luckily, this was only a baby.


I saw my first wombat on camp. It had a bad case of mange and was caught in the headlights for a few seconds as we drove between bat study sites. However, wombats were active around our camp, as this great photo shows. This picture, along with a lot of the better shots in this blog, were taken by my fellow bat-person, Stan.

I'll leave you with this message (the first video), spoken in bat by one of our subjects. The clicking sound is a sonar hunting call made by the bat. Bats use echolocation to 'see' insects in the dark. The call would not usually be audible to humans, but we can hear it through the Anabat sonar detector sitting on the table. It translates the sound into an audible pitch. Unfortunately, the detector does not, as my Mum suggested, translate into English. I'll let you decide what this bat is saying.

video video

Thursday, August 13, 2009

It's just not natural

I find it funny when conservative politicians and religious leaders attempt to categorise human sexual preferences, gender roles, relationships or parenting arrangements as 'natural' or 'unnatural'. Anyone who appeals to the natural world to justify their own position on human morality clearly doesn't know much about nature. It's likely that when such people think of nature, they form a mental image that looks something like this picture:


Look at this wholesome, monogamous, nuclear swan family. Mum and dad swan form a lifelong pair bond, stake out a territory, and raise a brood of cygnets every breeding season. Admittedly, these are black swans, which might be off-putting for some conservative politicians, but you have to admit that all in all, it's a lovely sight.

Unfortunately, there are some animals in our community who don't share these good, solid swan values. I hope this isn't too shocking, but I'm about to show you a picture of some filthy, dirty sex.


Of course, if you're an earthworm, life in the humus layer means everything you do is filthy and dirty. But, as you can see, the two mating worms are joined at two points. This is because earthworms are hermaphrodites. They mate by matching their male and female organs in a complementary fashion. It's thought that the evolutionary reason for this is that producing both sperm and eggs allows the worms to maximise their reproductive output in an environment in which it might be difficult to meet other worms. After mating, the worms move on and will probably never see each other again. Put simply, worms are promiscuous lady-boys who like it both ways because this gets them twice the amount of sex. And, being hermaphrodites, they become both single mothers and absent fathers at the same time.

You might think it's ridiculous to expect invertebrates to stick to good old fashioned values like monogamy. But some invertebrates manage it. Bonellia viridis is a marine invertebrate from a relatively obscure phylum known as Echiura. Members of this species are either male or female, and form lasting, monogamous pairings. If simple marine creatures can manage this, why is it so difficult for a complex primate like a human being? If only we could become more like Bonellia, the world would be a better place.


Yes, if we were more like Bonellia, a woman of marriagable age would lie in wait until a baby boy drifted her way. Then she would swallow him and imprison him in her reproductive tract, feeding him off her bodily fluids until he matured and began to pump out sperm on tap. This what happens in the Bonellia world. The female lies on the ocean floor until she meets with a tiny free-swimming larva. The larva is then sucked inside the female's feeding tube and remains as a parasite in her genital sac, with the sole purpose of sperm production, for the rest of his life. Yes, folks, there's no such thing as divorce in the Bonellia world. Those guys really know how to make a relationship last. What a great example to set for their larvae!


Some young animals are not so lucky. This lizard has two mummies. The desert-dwelling whiptail lizard (Cnemidophorus uniparens) is a species in which, as in a prison or boarding school, the entire population is female. This may seem like a sure way to go extinct. But, along with a few species of reptiles, fish and insects, these lizards have a special feature that allows them to survive. Whiptail lizards can reproduce by parthenogenesis, which means that they can lay eggs that hatch into young without being fertilised. While these lizards can become single parents, the chances of a female ovulating increase if she engages in ritual courtship behaviour with another female. This behaviour resembles that of related, non-parthenogenic lizards, and may include mounting. Then, after a female has laid her eggs, changes in her hormone levels cause her to behave like a male, and court another lizard who is pre-ovulatory.

With creatures like this in the world, it's nice to see that there are still animals like the Sand Tiger Shark (also known as the Grey Nurse Shark), who do it the old-fashioned way. No funny business there. Boy shark meets girl shark, then here come the little nippers! Just a normal family - Mum, Dad and a couple of extremely sharp-toothed embryos who devour each other in the womb. Ultimately, just one of the offspring is born, having grown big and strong on the flesh of his siblings.

via videosift.com

One reason the natural world is a useless place to look for moral guidance is that animal behaviour is a result of evolution. The evolutionary process has no moral dimension, and represents only the triumph of superior function. And, on a more obvious level, virtually every human behaviour, from cooperation and maternal love to rape, infanticide, and cannibalism, are all technically natural to the extent that they have parallels in nature. American sex researcher James Weinreich has said that 'If animals do something we like, we call it natural. If they do what we don't like, we call it animalistic'.

But enough talk, because here comes our young swan family again. The cygnets will soon be growing adult plumage, finding mates, and raising young of their own. But what's this? Maybe only a mother would know, but one of the cygnets doesn't look at all like papa swan. Junior does, however, bear a striking resemblance to that handsome male swan from the couple in the next nest...


In the last few decades, advances in DNA sequencing have blown apart previous assumptions about bird mating systems. Now that the paternity of the offspring can be analysed, it has been shown that extra-pair matings are common in many species. One of my lecturers, who has a particular interest in adulterous birds, conducted a study and found that on average, 15% of cygnets in a black swan population were fathered by a male other than their mother's mate. An average of 38% of broods contained at least one illegitimate cygnet. It appears that the swans are putting up a veneer of respectability, while secretly acting just as they please. Which, if you're a conservative politician or religious leader, is probably something that comes very naturally indeed.

Friday, July 24, 2009

Foot fetish

I could stay on the internet all day looking at pictures of geckos. Geckos are the fluffy kittens of the reptile world.

The house I grew up in was inhabited by these native robust velvet geckos (below). The term 'robust' is appropriate. From time to time, two geckos fighting on our ceiling would lose their footholds and fall onto the floorboards with a loud smack. Fortunately, it takes a lot of force to burst a gecko. Usually they would merely sit looking stunned for a few seconds, then run up the nearest wall.


At the time I never thought about what might allow them to walk on our ceiling in the first place. It's easy to see how an animal might stick to a smooth surface like glass using vacuum suction, or to many surfaces using a sticky substance like mucus. But it's more difficult to understand how it would walk on a dry, comparatively rough surface like a ceiling.

The answer is that geckos' feet are able to 'share' electrons with the surface they are walking on. Chemistry is not my strong point, so please bear with me as I try to explain this.

Here are some pictures of the undersides of geckos' feet. Note the distinctive ridged patterns.



Traditionally, having hairy palms is meant to be a sign of madness. In the case of geckos, it's a sign of awesomeness. At a higher magnification, it's possible to see that the ridges are composed of extremely fine hairs. Each hair is split at the end into hundreds or thousands of smaller branches.


Like all matter, the hairs on the underside of a gecko's foot are made up of atoms. Here's a diagram of an atom. It probably looks familiar from high school. As you can see, the atom is made up of three kinds of smaller particles. In the centre are the positively charged protons, and the neutrons, which do not carry a charge. The electrons, which are negatively charged, orbit the other particles, like the planets orbiting the sun. The number of electrons (which, in a typical atom, is the same as the number of protons) determines what kind of element the atom is. For example, a hydrogen atom has one electron, while an atom of gold has seventy-nine. The foot of a gecko is made up of many different kinds of atoms, including carbon, nitrogen, hydrogen and oxygen.


If you think of one of these atoms, it's possible to imagine the electrons moving around in orbit. At certain times in the orbit, there are likely to be more electrons in certain areas of the atom than in others. This gives one end of the atom a slight negative charge, and the other end a slight positive charge. One end of a gecko's foot hair atom might be negatively charged, and be adjacent to the end of a ceiling atom that has a positive charge. This results in an attractive force, like that between magnets.

Obviously, because the electrons are in constant orbit, the attraction between the two atoms will be fleeting. However, as the electrons circle around, the charges on the two electrons swap. The previously negative end of the foot atom now has a positive charge, and vice versa in the ceiling atom. The attraction is therefore maintained.

As far as I can tell (again, this is not really my subject area), these kinds of attractive forces must exist between all kinds of matter. Perhaps, at this very moment, there are attractive forces occurring between you and your chair. I spend most mornings trying to overcome the attractive forces between myself and my bed. But if you can imagine the entire surface area of a gecko's foot hairs spread flat, it's possible to appreciate the large number of potential attractions that are compressed in the relatively small area of the foot. It's thought that the geometry of the foot, rather than any properties of the substances in it, is responsible for its remarkable adhesive power.

Geckos now have their imitators. Some scientists from the University of California have invented what they describe as a 'hard plastic gecko-inspired synthetic adhesive'. They believe this product may be useful for medical products, sporting goods and 'climbing robots where a controllable and reusable adhesive is needed'. Imagine! In the future, we could all be living in houses inhabited by hard plastic, gecko-inspired robotic geckos. I'm looking forward to the time when my evenings are interrupted by two pimped up gecko-bots blasting each other off the ceiling in a tiny ball of flames.

Thursday, July 16, 2009

Not quite Attenborough

I've just spent a few weeks at my parents' house in the Sunshine Coast hinterland. I spent some time in the bush, getting all David Attenborough in the hope of a blog-worthy sighting. Unfortunately I didn't see very much, despite sitting at a water hole (the one in the photo below) for two hours in the hope that something interesting would come along. Perhaps the cold weather was responsible for the lack of animal activity. Alternatively, as I realised some time into my stake-out, the oversized, bright red puffy parker I was wearing wasn't exactly subtle camouflage gear.

I did see, and take a bad photo of, an agitated scrub turkey. If you're from Queensland, you already know that scrub turkeys are not a particularly noteworthy sighting. But they do have some interesting habits. And in the absence of, say a Richmond Birdwing butterfly, let's talk about scrub turkeys.

Here's a picture my dad took of a scrub turkey nest further further along the same river. The male turkey constructs a mound of rotting vegetation, which is typically a metre or so high and several metres across. Unlike many other birds, scrub turkeys are not monogamous. The male waits until a female comes along and decides to lay an egg in his nest. Obviously, the male turkey is not the father of the egg, but he isn't completely cuckolded. In exchange for providing the nest, he is allowed to mate with the female, in the hope that his genetic offspring will be incubated by the male in whose nest the egg is laid. Several different females may lay eggs in the nest of a single male.
The male turkey doesn't need to sit on the egg, because the heat given off by the rotting vegetation is enough to incubate it. He can measure the temperature of the mound with his beak, and adds or removes leaves with his large feet in order to keep the temperature constant. When the young hatch, they scratch their way out of the mound, and run off into the rainforest. Their father (who is most likely not their biological father) provides no parental care, and their mother is long gone, probably off the rainforest attempting to mate with with as many different males as possible. Scrub turkeys are truly the bogans of the bird world, hence their diminutive name of scrubbers.

My other exciting sighting was up at the dam (above). Admittedly, a cane toad is not really an interesting find. But this cane toad was dead, lying on its back, and appeared to have had its abdominal skin torn open and its organs and forearm muscles removed. One of the reasons for the rapid spread and population growth of cane toads is that most parts of their bodies are highly toxic, and so they have very few native predators. However, in the last decade, there have been reports of crows and magpies learning to eat cane toads by flipping them onto their backs, thereby avoiding the poison glands. They then eat the internal organs, which are not poisonous. This could have been the fate of this toad. I promise this is the last gory toad picture for this blog.

I also came across some intriguing insect larvae, which were too small to photograph, and which I haven't yet had the chance to identify. I have to admit, apologetically, that David Attenborough would have done it better. Perhaps I'll do another stake-out in Summer, when the heat drives more animals towards to the water, and puffy red parkers are unnecessary.

Friday, June 12, 2009

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.