an autodidact meets a dilettante…

‘Rise above yourself and grasp the world’ Archimedes – attribution

Posts Tagged ‘biology

how evolution was proved to be true

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The origin of species is a natural phenomenon

Jean-Baptiste Lamarck

The origin of species is an object of inquiry

Charles Darwin

The origin of species is an object of experimental investigation

Hugo de Vries

(quoted in The Gene: an intimate history, by Siddhartha Mukherjee)

Gregor Mendel

I’ve recently read Siddhartha Mukherjee’s monumental book The Gene: an intimate history, a work of literature as well as science, and I don’t know quite where to start with its explorations and insights, but since, as a teacher to international students some of whom come from Arabic countries, I’m occasionally faced with disbelief regarding the Darwin-Wallace theory of natural selection from random variation (usually in some such form as ‘you don’t really believe we come from monkeys do you?’), I think it might be interesting, and useful for me, to trace the connections, in time and ideas, between that theory and the discovery of genes that the theory essentially led to.

One of the problems for Darwin’s theory, as first set down, was how variations could be fixed in subsequent generations. And of course another problem was – how could a variation occur in the first place? How were traits inherited, whether they varied from the parent or not? As Mukherjee points out, heredity needed to be both regular and irregular for the theory to work.

There were few clues in Darwin’s day about inheritance and mutation. Apart from realising that it must have something to do with reproduction, Darwin himself could only half-heartedly suggest an unoriginal notion of blending inheritance, while also leaning at times towards Lamarckian inheritance of acquired characteristics – which he at other times scoffed at.

Mukherjee argues here that Darwin’s weakness was impracticality: he was no experimenter, though a keen observer. The trouble was that no amount of observation, in Darwin’s day, would uncover genes. Even Mendel was unable to do that, at least not in the modern DNA sense. But in any case Darwin lacked Mendel’s experimental genius. Still, he did his best to develop a hypothesis of inheritance, knowing it was crucial to his overall theory. He called it pangenesis. It involved the idea of ‘gemmules’ inhabiting every cell of an organism’s body and somehow shaping the varieties of organs, tissues, bones and the like, and then specimens of these varied gemmules were collected into the germ cells to produce ‘mixed’ offspring, with gemmules from each partner. Darwin describes it rather vaguely in his book The Variation of Animals and Plants under Domestication, published in 1868:

They [the gemmules] are collected from all parts of the system to constitute the sexual elements, and their development in the next generation forms the new being; but they are likewise capable of transmission in a dormant state to future generations and may then be developed.

Darwin himself admitted his hypothesis to be ‘rash and crude’, and it was effectively demolished by a very smart Scotsman, Fleeming Jenkin, who pointed out that a trait would be diluted away by successive unions with those who didn’t have it (Jenkin gave as an example the trait of whiteness, i.e. having ‘white gemmules’, but a better example would be that of blue eyes). With an intermingling of sexual unions, specific traits would be blended over time into a kind of uniform grey, like paint pigments (think of Blue Mink’s hit song ‘Melting Pot’).

Darwin was aware of and much troubled by Jenkin’s critique, but he (and the scientific world) wasn’t aware that a paper published in 1866 had provided the solution – though he came tantalisingly close to that awareness. The paper, ‘Experiments in Plant Hybridisation’, by Gregor Mendel, reported carefully controlled experiments in the breeding of pea plants. First Mendel isolated ‘true-bred’ plants, noting seven true-bred traits, each of which had two variants (smooth or wrinkled seeds; yellow or green seeds; white or violet coloured flowers; flowers at the tip or at the branches; green or yellow pods; smooth or crumpled pods; tall or short plants). These variants of a particular trait are now known as alleles. 

Next, he began a whole series of painstaking experiments in cross-breeding. He wanted to know what would happen if, say, a green-podded plant was crossed with a yellow-podded one, or if a short plant was crossed with a tall one. Would they blend into an intermediate colour or height, or would one dominate? He was well aware that this was a key question for ‘the history of the evolution of organic forms’, as he put it.

He experimented in this way for some eight years, with thousands of crosses and crosses of crosses, and the more the crosses multiplied, the more clearly he found patterns emerging. The first pattern was clear – there was no blending. With each crossing of true-bred variants, only one variant appeared in the offspring – only tall plants, only round peas and so on. Mendel named them as dominant traits, and the non-appearing ones as recessive. This was already a monumental result, blowing away the blending hypothesis, but as always, the discovery raised as many questions as answers. What had happened to the recessive traits, and why were some traits recessive and others dominant?

Further experimentation revealed that disappeared traits could reappear in toto in further cross-breedings. Mendel had to carefully analyse the relations between different recessive and dominant traits as they were cross-bred in order to construct a mathematical model of the different ‘indivisible, independent particles of information’ and their interactions.

Although Mendel was alert to the importance of his work, he was spectacularly unsuccessful in alerting the biological community to this fact, due partly to his obscurity as a researcher, and partly to the underwhelming style of his landmark paper. Meanwhile others were aware of the centrality of inheritance to Darwin’s evolutionary theory. The German embryologist August Weismann added another nail to the coffin of the ‘gemmule’ hypothesis in 1883, a year after Darwin’s death, by showing that mice with surgically removed tails – thus having their ‘tail gemmules’ removed – never produced tail-less offspring. Weismann presented his own hypothesis, that hereditary information was always and only passed down vertically through the germ-line, that’s to say, through sperm and egg cells. But how could this be so? What was the nature of the information passed down, information that could contain stability and change at the same time?

The Dutch botanist Hugo de Vries, inspired by a meeting with Darwin himself not long before the latter’s death, was possessed by these questions and, though Mendel was completely unknown to him, he too looked for the answer through plant hybridisation, though less systematically and without the good fortune of hitting on true-breeding pea plants as his subjects. However, he gradually became aware of the particulate nature of hereditary information, with these particles (he called them ‘pangenes’, in deference to Darwin’s ‘pangenesis’), passing down information intact through the germ-line. Sperm and egg contributed equally, with no blending. He reported his findings in a paper entitled Hereditary monstrosities in 1897, and continued his work, hoping to develop a more detailed picture of the hereditary process. So imagine his surprise when in 1900 a colleague sent de Vries a paper he’d unearthed, written by ‘a certain Mendel’ from the 1860s, which displayed a clearer understanding of the hereditary process than anyone had so far managed. His response was to rush his own most recent work into press without mentioning Mendel. However, two other botanists, both as it happened working with pea hybrids, also stumbled on Mendel’s work at the same time. Thus, in a three-month period in 1900, three leading botanists wrote papers highly indebted to Mendel after more than three decades of profound silence.

Hugo de Vries

The next step of course, was to move beyond Mendel. De Vries, who soon corrected his unfair treatment of his predecessor, sought to answer the question ‘How do variants arise in the first place?’ He soon found the answer, and another solid proof of Darwin’s natural selection. The ‘random variation’ from which nature selected, according to the theory, could be replaced by a term of de Vries’ coinage, ‘mutation’. The Dutchman had collected many thousands of seeds from a wild primrose patch during his country rambles, which he planted in his garden. He identified some some 800 new variants, many of them strikingly original. These random ‘spontaneous mutants’, he realised, could be combined with natural selection to create the engine of evolution, the variety of all living things. And key to this variety wasn’t the living organisms themselves but their units of inheritance, units which either benefitted or handicapped their offspring under particular conditions of nature.

The era of genetics had begun. The tough-minded English biologist William Bateson became transfixed on reading a later paper of de Vries, citing Mendel, and henceforth became ‘Mendel’s bulldog’. In 1905 he coined the word ‘genetics’ for the study of heredity and variation, and successfully promoted that study at his home base, Cambridge. And just as Darwin’s idea of random variation sparked a search for the source of that variation, the idea of genetics and those particles of information known as ‘genes’ led to a worldwide explosion of research and inquiry into the nature of genes and how they worked – chromosomes, haploid and diploid cells, DNA, RNA, gene expression, genomics, the whole damn thing. We now see natural selection operating everywhere we’re prepared to look, as well as the principles of ‘artificial’ or human selection, in almost all the food we eat, the pets we fondle, and the superbugs we try so desperately to contain or eradicate. But of course there’s so much more to learn….

William Bateson

Written by stewart henderson

June 14, 2017 at 5:42 pm

Abiogenesis – LUCA, gradients, amino acids, chemical evolution, ATP and the RNA world

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chemical-evolution-1

Jacinta: So now we’re thinking of the Earth 4 billion years BP, with an atmosphere we’re not quite sure of, and we want to explore the what and when of the first life forms. Haven’t we talked about this before?

Canto: Yeah we talked about the RNA world and viroids and abiogenesis, the gap between chemistry and biology, inter alia. This time we’re going to look more closely at the hunt for the earliest living things, and the environments they might’ve lived in.

Jacinta: And it started with one, it must have. LUA, or LUCA, the last universal common ancestor. Or the first, after a number of not-quite LUCAs, failed or only partially successful attempts. And finding LUCA would be much tougher than finding a viroid in a haystack, because you’re searching through an immensity of space and time.

Canto: But we’re much closer to finding it than in the past because we know so much more about what is common to all life forms.

Jacinta: Yes so are we looking definitely at the first DNA-based life form or are we probing the RNA world again?

Canto: I think we’ll set aside the world of viroids and viruses for now, because we want to look at the ancestor of all independently-existing life forms, and they’re all DNA-based. And we also know that LUCA used ATP. So now I’m going to quote from an essay by Michael Le Page in the volume of the New Scientist Collection called ‘Origin, Evolution, Extinction’:

How did LUCA make its ATP? Anyone designing life from scratch would probably make ATP using chemical reactions inside the cell. But that’s not how it is done. Instead energy from food or sunlight is used to power a protein ‘pump’ that shunts hydrogen ions – protons – out of the cell. This creates a difference in proton concentration, or a gradient, across the cell membrane. Protons then flow back into the cell through another protein embedded in the membrane, which uses the energy to produce ATP.

Jacinta: You understand that?

Canto: Sort of.

Jacinta: ‘Energy from food or sunlight is used..’ that’s a bit of a leap. What food? The food we eat is organic, made from living or formerly living stuff, but LUCA is the first living thing, its food must be purely chemical, not biological.

Canto: Of course, not a problem. I believe the microbes at hydrothermal vents live largely on hydrogen sulphide, and of course sunlight is energy for photosynthesising oganisms such as cyanobacteria.

Jacinta: Okay, so your simplest living organisms, or the simplest ones we know, get their energy by chemosynthesis, or photosynthesis. Its energy, or fuel, not food.

Canto: Semantics.

Jacinta: But there are other problems with this quote re abiogenesis. For example, it’s talking about pre-existent cells and cell membranes. So assuming that cells had to precede ATP.

Canto: No, he’s telling us how cells make ATP today. So we have to find, or synthesise, all the essential ingredients that make up the most basic life forms that we know cell membranes, proteins, ATP and the like. And people are working towards this.

Jacinta: Yes and first of all they created these ‘building blocks of life’, as they always like to call them, amino acids, in the Miller-Urey experiments, since replicated many times over, but what exactly are nucleic acids? Are they the same things as nucleic acids?

Canto: Amino acids are about the simplest forms of organic compounds. It’s probably better to call them the building blocks of proteins. There are many different kinds, but generally each contain amine and carboxyl groups, that’s -NH2 and -COOH, together with a side chain, called an R group, which determines the type of amino acid. There’s a whole complicated lot of them and you could easily spend a whole lifetime fruitfully studying them. They’re important in cell structure and transport, all sorts of things. We’ve not only been able to create amino acids, but to combine them together into longer peptide chains. And we’ve also found large quantities of amino acids in meteorites such as the Murchison – as well as simple sugars and nitrogenous bases. In fact I think we’re gradually firming up the life-came from-space hypothesis.

Jacinta: But amino acids and proteins aren’t living entities, no matter how significant they are to living entities. We’ve never found living entities in space or beyond Earth. Your quote above suggests some of what we need. A boundary between outside and inside, a lipid or phospho-lipid boundary as I’ve heard it called, which must be semi-permeable to allow chemicals in on a very selective basis, as food or fuel.

Canto: I believe fatty acids formed the first membranes, not phospho-lipids. That’s important because we’ve found that fatty acids, which are made up of carbon, hydrogen and oxygen atoms joined together in a regular way, aren’t just built inside cells. There’s a very interesting video called What is Chemical Evolution?, produced by the Center for Chemical Evolution in the USA, that tells about this. Experimenters have heated up carbon monoxide and hydrogen along with many minerals common in the Earth’s crust and produced various carbon compounds including fatty acids. Obviously this could have and can still happen naturally on Earth, for example in the hot regions maybe below or certainly within the crust. It’s been found that large concentrations of fatty acids aggregate in warm water, creating a stable, ball-like configuration. This has to do with the attraction between the oxygen-carrying heads of fatty acids and the water molecules, and the repulsion of the carbon-carrying tails. The tails are forced together into a ball due to this repulsion, as the video shows.

fatty acids, with hydrophobic and hydrophilic ends, aggregating in solution

Jacinta: Yes it’s an intriguing video, and I’m almost feeling converted, especially as it goes further than aggregation due to these essentially electrical forces, but tries to find ways in which chemical structures evolve, so it tries to create a bridge between one type of evolution and another – the natural-selection type of evolution that operates upon reproducing organisms via mutation and selection, and the type of evolution that builds more complex and varied chemical structures from simpler compounds.

Canto: Yes but it’s not just the video that’s doing it, it’s the whole discipline or sub-branch of science called chemical evolution.

Jacinta: That’s right, it’s opening a window into that grey area between life and non-life and showing there’s a kind of space in our knowledge there that it would be exciting to try and fill, through observation and experimentation and testable hypotheses and the like. So the video, or the discipline, suggests that in chemical evolution, the highly complex process of reproduction through mitosis in eukaryotic cells or binary fission in prokaryotes is replaced by repetitive production, a simpler process that only takes place under certain limited conditions.

Canto: So under the right conditions the balls of fatty acids grow in number and themselves accumulate to form skins, and further forces – I think they’re hydrostatic forces – can cause the edges of these skins to fuse together to create ‘containers’, like vesicles inside cells.

Jacinta: So we’re talking about the creation of membranes, impermeable or semi-permeable, that can provide a safe haven for, whatever…

Canto: Yes, and at the end of the video, other self-assembling systems, such as proto-RNA, are intriguingly mentioned, so we might want to find out what’s known about that.

Jacinta: I think we’ll be doing a lot of reading and posting on this subject. I find it really fascinating. These limited conditions I mentioned – limited on today’s Earth surface, but not so much four billion years ago, include a reducing atmosphere lacking in free oxygen, and high temperatures, as well as a gradient – both a temperature gradient and a sort of molecular or chemical gradient, from more reducing to more oxidising you might say. These conditions exist today at hydrothermal vents, where archaebacteria are found, so researchers are naturally very interested in such environments, and in trying to replicate or simulate them.

Canto: And they’re interested in the boundary between chemical and biological evolution, and reproduction. There are so many interesting lines of inquiry, with RNA, with cell membranes….

Jacinta: Researchers are particularly interested in alkaline thermal vents, where alkaline fluids well up from beneath  the sea floor at high temperatures. When this fluid hits the ocean water, minerals precipitate out and gradually create porous chimneys up to 60 metres high. They would’ve been rich in iron and sulphide, good for catalysing complex organic reactions, according to Le Page. The temperature gradients created would’ve favoured organic compounds and would’ve likely encouraged the building of complexity, so they may have been the sites in which the RNA world began, if it ever did.

a hydrothermal vent off the coast of New Zealand. Image from NOAA

a hydrothermal vent off the coast of New Zealand. Image from NOAA

Canto: So I think we should pursue this further. There are a lot of researchers homing in on this area, so I suspect further progress will be made soon.

Jacinta: Yes, we need to explore the exploitation of proton gradients, the development  of proton pumps and the production of ATP, leaky membranes and a whole lot of other fun stuff.

Canto: I think we need to get our heads around ATP and its production too, because that looks pretty damn complex.

Jacinta: Next time maybe.

 

Written by stewart henderson

July 29, 2016 at 8:51 am

something to send you to sleep

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sleep-apnea-machine.jpg

sleep apnoea mask – looks great, feels even worse?

I went to a Science in the Pub talk last night, not knowing what to expect. The three speakers were all researching sleep, and the focus was mainly on insomnia and sleep apnoea. How fortunate, for I’m having a problem with insomnia at the moment. I may well have a problem with apnoea too, but because I sleep alone I can’t monitor it. Sleep apnoea is about blocked airways that reduce the intake of oxygen, causing sleep disturbance. Here’s an extract from the Better Health Channel on the subject:

In most cases, the person suffering from sleep apnoea doesn’t even realise they are waking up. This pattern can repeat itself hundreds of times every night, causing fragmented sleep. This leaves the person feeling unrefreshed in the morning, with excessive daytime sleepiness, poor daytime concentration and work performance, and fatigue. It’s estimated that about five per cent of Australians suffer from this sleep disorder, with around one in four men over the age of 30 years affected.

So it’s much more common among older males, and it correlates with excessive weight and obesity. Some years ago, when I had a sleeping partner, she expressed a concern about what she thought might be my sleep apnoea, but since then I’ve lost a lot of weight, and my overall health – apart from my bronchiectasis – has improved, so I don’t intend to worry needlessly over that, but it was interesting to hear about the CPAP mask and other treatments being offered, including the possibility of surgery to the uvula and tongue. Also that the evidence is mounting about the long-term effects of sleep apnoea, upon the heart particularly, though not surprisingly with obesity, confounding factors are hard to control for. The problem I’m having at the moment, though, is ‘advanced circadian rhythm’ insomnia, which has only been happening over the past few weeks and which I’m hoping will sort itself out. Our roughly 24-hour circadian rhythms, our body clock, when running at its best, gives us at least eight hours sleep, optimally between 11pm and 7am, though there is enormous individual variation, and huge variation in tolerance of sleep deprivation, possibly due to genetic factors. Amongst the many varieties of body clock-related sleep disorder, two were focused on last night; delayed-phase and advanced-phase circadian rhythms. The terms are largely self-explanatory. In the delayed-phase type, you stay up late and find it hard to get up in the morning, a common teenage problem (or habit). In the advanced-phase type, which I’m now experiencing for the first time in my life, you find yourself falling asleep alarmingly early, and then waking up – and being alarmingly wide awake, at 4am or sometimes even earlier.

The Circadian Sleep Disorders Network is a great place to learn about the problems, and possible solutions for having a body clock that’s out of synch with the day-night cycle or with your work or other commitments. These problems can lead to all sorts of stresses, but what I took from last night’s session, though it was never explicitly stated, was that your attitude to wonky sleep patterns might be causing more stress than the patterns themselves. In my case, though it’s irritating, I tell myself I needn’t stress over it as I have to get up around 6am for work anyway, and as long as I’m awake and fully operational until 5pm, or 7pm for cooking and eating dinner, it’s no big problem. I’ve not noticed excessive daytime sleepiness or poor concentration (but maybe I’m not concentrating enough). Though I do hope it will right itself, just because being abnormal feels – abnormal. Then again, I’m abnormal in so many other ways that are far more stressful.

Advanced-phase sleep disorder is apparently much less common than delayed phase, though that might just be that it’s less often reported precisely because it doesn’t disrupt work routines. The main treatment is the use of bright light, though I’ve found myself falling asleep in the bright light of the lounge room, or in my bedroom with a bright reading lamp left on. But there’s more to it than just leaving the light on. Here’s a summary from the Sleep Health Foundation:

Bright light visual stimulation should occur in the evening before you go to bed. The light should be brighter than normal indoor lighting. You can obtain it from specialized light boxes, or portable devices that you can wear, e.g. eye glasses. A few examples can be found by a web search for “bright light therapy”. You may need an hour or two of bright light therapy before bed. Some will benefit from nightly use for a week. Others will need longer, sometimes several weeks, to get maximum benefit. It is best used late in the evening, perhaps turning the bright light device off half an hour before bed.

Something to think about if this keeps up. Another treatment is with melatonin, the ’sleep hormone’:

One option is to take a 2mg slow release melatonin tablet (Circadin™) as close to your new (later) bedtime as possible. A second option is to take a small dose of melatonin (0.5 mg), about half way through your sleep period. This could be at a time when you wake up on your own. To change your hours of sleep, you should gradually delay your bed time (e.g. 20 minutes later each night) until you get it to the time that you want. As you delay your bedtime, you will also be delaying the time of your bright light exposure and melatonin intake.

Obviously, neither of these treatments are simple or guaranteed to be effective. Cognitive behaviour therapy was suggested by the experts, if these approaches were unsuccessful, but I know next to nothing about that. For now I’m not too worried, I just hope the problem goes away without my noticing.

Written by stewart henderson

July 5, 2015 at 10:12 am

reveries of a solitary wa*ker: wa*k 1

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(Being a thousand words or so of mental drivel)

I’d prefer not to be coy about the title but I’ve a job to protect.

the delightful enthusiasm of children

the delightful enthusiasm of children

Began watching documentary series chronicles of the third reich, yet another rake-over of that terrible but ghoulishly fascinating period, and it kicked off with noted historian Ian Kershaw saying that the regime was unique in that it aimed to overthrow the entire Judeo-Christian system of ethics that sustained western Europe for centuries. Bullshit I say. No such thing. What nazism was overthrowing, or delaying or subverting, was the progress of western Europe, for example the Renaissance and the Enlightenment, movements towards democracy, individual liberty, internationalism, none of which owed anything to the Judeo-Christian belief system. This lazy thinking and remarking continually goes unchallenged. At the height of Judeo-Christian control we had monarchical dictatorships, divine right, religious authoritarianism, extreme corruption, torture, rigid hierarchies, feudal slavery, etc, a world of inhumanity and brutality. Not saying that Christianity caused this, life wouldn’t have been any better in China or Japan, doubtless. Depended on chance and ‘birthright’ as to how well you fared.

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Reading the big bio of Darwin by Desmond and Moore, thinking how so much that was radical or extreme becomes mainstream within a few generations, such as materialism, atheism, democratic principles, equality for women, humans as apes. Chartism’s aims – extension of suffrage, taxation reform, the repeal of laws too unjust to be enacted nowadays, all horrific to the upper classes, who armed themselves with crowbars to protect their homes and privileges. And among them, quite a few favouring transmutation (though not of the Darwinian kind – more a sort of Lamarckian progressive development towards the human pinnacle) and atheistic science. Makes you think of today’s accelerating trends, e.g gay marriage. All these ideas were opposed because they would bring down civilisation as we know it. Rock n roll was another one.
Also thinking how science threatened and continues to threaten religion. Moslem student asked me last week, do you think humans come from apes? Could see what his hopes were, was happy to crush them and move on. No doubt he’ll return to Saudi, ask the question again and be reassured as to his human specialness. But maybe not. But in Darwin’s day, so many associates, Sedgwick, Henslow, Lyell, Owen, Whewell, even Herschel, even bloody Wallace, couldn’t countenance our ‘demotion’ to a primate, on grounds some of them didn’t even recognise as religious. How can it possibly be argued that religion and science are compatible? Only if we have a very different religion, and perhaps a very different science – panpsychism, spooky action at a distance, positively conscious positrons.

A love-hate thing with Darwin, all his stuffy aristocratic connectedness, his family’s money, but then his boldness of ideas, but then his timidity born of an unwillingness to offend, a need to be admired, feted, but two kinds of glory, the one for a grand idea that might just outlast the opprobrium of his elite class in mid-nineteenth century England, the other for being a model member of that class, civilized, restrained, highly intelligent, pushing gently outwards the boundaries of knowledge. The tension between immediate, hail-fellow-well-met acceptance and something more, his dangerous idea, something barely digestible but profoundly transformative.

cover

Keep reading about the hard problem of consciousness, without greatly focusing. Don’t really believe in it. We’re surely just at the beginning of getting to grips with this stuff – but how much time do we have? Dennett talks of the mind as cultural construct, Cartesian theatre as he calls it, and you don’t need to have ever heard of Descartes to wonder at how memories, rehearsals, fantasies can be played out inside the head, inaccessible to everyone but yourself, but without the boundaries of the skull, or of a theatre, no straightforward boundaries of space or time, yet composed of reality-bits, physical and emotional. One of my first serious wonderings, I seem to remember (not trustworthy) was about this boundary-less but secret place-thing called the mind. Not sure about a cultural construct, seemed very real and self-evident to me, and a wonderful safe haven where you can think and do things for which you’ll never get arrested, never have to apologise, a theatre of blood, sex and brilliance…

But I don’t think I thought then, and I don’t think now, that this was anything other than a product of the brain because to me the brain was like every other organ, the heart, the liver, the kidneys, the lungs, they were all mysterious, I didn’t know how any of them worked, and though I knew that I could learn a lot more about them, and would over the course of my life, I suspected that nobody knew everything about how any of them functioned, and the brain was just more complex and so would contain more mysteries than any of the others perhaps put together, but it had to come from the brain because, well everybody said thoughts were produced by the brain and these were just thoughts after all and where else could they come from – there was no alternative. And it seems we’re slowly nutting it out, but humans are understandably impatient to find answers, solutions. We like to give prizes for them.

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Also reading Natalie Angier’s Woman, a revised version of a book brought out in the nineties. It’s a popular biology book from a good feminist perspective, and I’m learning much about breast milk and infant formula, about the breast itself, about menstruation, about the controversies around hysterectomies and so on, but her style often irritates, drawing attention to too much clever-clever writing rather than the subject at hand. It’s a tricky area, you want your writing lively and engaging, not like reading an encyclopedia, but especially with science writing you want it all to be comprehensible and transparent – like an encyclopedia. Angier sometimes uses metaphors and puns and (for me) arcane pop references which have me scratching my head and losing the plot, but to be fair it’s worth persevering for the content. But it shouldn’t be about persevering.

how did blue whales get so big?

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a baby blue

a baby blue

Cetaceans came into being when a group of mammals left the land some 55 million years ago, to return to the oceans (creatures first left the oceans for the land some 375 million years ago). The closest land species to whales are the artiodactyls or even-toed ungulates, a large group which includes sheep, goats, cattle, giraffes, camels, llamas, pigs and deer, but another artiodactyl species, the hippo, is most closely related to cetaceans. But, of course, since returning to the oceans, the creatures who finally evolved into cetaceans were able to become ‘super-sized’. The blue whale, likely the largest creature ever to exist on this planet, can tip the scales at over 170 tonnes, and can measure well over 30 metres.  The largest dinosaur unearthed so far, Argentinosaurus, a titanosaur sauropod (that’s to say a really effing big dino – named for the ancient mythical titans – with a long neck and tail and a comparatively small head, like the brontosaurus of my youth, now sadly out of favour) weighed around 75 tonnes.

Cetaceans have managed to fill a diverse range of ecological niches. Some of the best-known are the blue whale (a filter-feeding baleen whale or rorqual), the orca (often called a killer whale, but in fact it’s the largest species of dolphin) and the sperm whale, the largest of the toothed whales. Their success, and especially that of rorquals, may owe much to the abundance of krill in the oceans. Some researchers have also attributed the great growth spurt of the blue whale over the past few million years to this ready supply of food. It’s been estimated that, in the southern oceans alone, the krill biomass may be as much as 500 million tonnes, twice the biomass of humans on the planet.

Of course the behaviour of humans has had a massive impact on blue whales, especially in the century of so before 1966, when they came under international protection. The Antarctic population before whaling has been estimated at between 200,000 and 300,000,  possibly as much as ten times the current population, though numbers are difficult to determine. You can’t help but wonder what would have happened to whale – and krill – populations without human depredations.

Researchers and analysts point to two main and perhaps complementary reasons for whale ginormity; the abundance of food, and the lack of restraint on size in an oceanic medium. I’ll focus on the second reason first. This presumably has to do with physics, my weakest subject, so I want to get it straight in my mind.

Allometry is the study of the size of organisms and what it means in terms of growth, behaviour, environment and other constraints and factors. Allometry helps explain how a large oxygen-breathing mammal can survive in and transport itself through its chosen medium. Whales are ‘neutrally buoyant’ – that’s to say, their body’s density is equal to the density of the water around them. This means that they don’t have to expend the energy that land animals have to in counteracting the effects of gravity – scuba divers have to learn the correct breathing underwater to achieve this neutral buoyancy. Every step we landlubbers take involves a lifting up of our bodies against the gravitational force pinning us to the earth. The endless gentle push of gravity is what makes us wrinkle and sag over our lifetime. Okay, let’s not think about that anymore. Locomotion in the water has much to do with allometric scaling, because the rate of oxygen consumption per gram body size decreases consistently with increasing body size. Other factors include shape and type of movement, which influence the laminar or turbulent flow around the organism. All of this is very complicated and can be worked out with equations – the Reynolds equation, which relates turbulence to velocity, being of prime importance, though hard to work out in nature, especially with cetaceans, who seem to break all the rules. That’s to say, there’s much about their physiology and how it’s adapted to water that we still don’t know.

Of course, aquatic mammals have to pump blood around their bodies and get air into their lungs just like land mammals. Interestingly, mammals have much the same heart-body mass ratio, whether they’re mice or elephants, land or aquatic. That of course means that the blue whale has the biggest heart of any mammal, and that also goes for a number of other organs. Scaling is much the same, for example, for lungs, and for lung capacity, and for blood, which represents around 5.5% of body mass. So, for mammals of similar form, larger ones can travel more quickly, because it requires the same expenditure of energy to move a body length. The large body length of a blue whale enables it to move great distances in search of food or for other purposes at less metabolic expense. It also enables them to dive for much longer than other cetaceans. Whales have a lower heart rate and can carry more oxygen through their bloodstream than smaller marine mammals. These are just some of the advantages of size in the oceans.

Of course, greater mass requires greater volumes of food to sustain it, but krill seems to have provided just about all a blue whale needs in that department, though it’s also partial to a class of small crustaceans called copepods, and it’s happy, too, to consume any other stray crustaceans and little fishes it catches up in its lunge dives through the krill – described recently as ‘the largest biomechenical event on earth’. Its feeding system and technique is adapted to these small but vastly numerous life forms. For all its size, a blue whale’s throat opening won’t allow it to swallow anything larger than a beach ball, yet it can eat up to 40 million krill a day. It’s jawline is huge, extending over halfway down its body, and the jaws can open to almost a ninety degree angle during lunge diving, allowing it to scoop up about 100 tonnes of krill-infested water in about ten seconds. The water is then squeezed out through the baleen with the help of its  ventral pouch and massive tongue.

So it’s understandable why the blue whale has grown to this size, which raises the question – has it ended its growth spurt? There’s a bit of an argument going on about this. Obviously the present moment is but a snapshot, and we can never be certain about where evolution is heading, but often growth spurts in species occur at a rapid clip, and then things stabilize. The blue whales are relatively recent, judged as having split from an ancestor at around 10-15 million years ago, but it may be that they grew to their present size quickly after the split. We have no way of knowing as yet, unless we find a massive blue whale fossil dating back more than 10 million years, which is unlikely. However, other ways of knowing might crop up. There’s also an argument that these rorquals have reached their limit due to feeding limitations and oxygen supply limitations. Lots of interesting research questions to ponder over.

Written by stewart henderson

August 26, 2013 at 8:02 pm