The Barbican is a sprawling concrete brutality as apt to divide opinion as Marmite or skinny jeans. Built in the 60s and 70s as a housing estate and cultural centre on a vast bomb-site in the City of London, it does not sound like a promising place to go botanising, but after the fire-weed was concreted over, other plants moved in…Aside from the fleabane gussying up the scheduled monuments, and the friendly rivalry of the residents’ window-boxes, the Barbican also houses a large conservatory containing more than 2000 species of plant. It is open to the public most Sundays. A highlight of the conservatory complex is the arid-zone glasshouse, which crams a surprising variety of cactuses and other succulents into quite a small space. Like many botanerds, my sickness started in childhood, when I broke out in a rash of succulents and carnivorous plants – as I enter my dotage, nostalgia grips me and I am drawn back to these plants like a homeopath to idiocy. Is this a botanic garden? Can it be justly included in my baggings? As far as I’m concerned, the key difference between a garden and a botanic garden is whether the plants have merely been plonked there to be gawped at by the proles, or whether the plants are properly labelled with Linnaean binomials and can thus be ticked off a list as God intended: The plants are labelled; Flora be praised; this is a botanic garden.
When we went to the Berlin Botanischer Garten in 2005, we saw some pretty cool stuff, including a flowering Welwitschia and some fantastic tree ferns. However, like every other botanical garden I’ve ever visited, mosses , hornworts and liverworts were effectively ignored, or – worse – treated as dreary also-rans at the start of one of those ‘evolution houses’ so beloved of curators without the wit to find something accurate to do with their cycads.Imagine my wet-gusseted delight when I heard that Berlin was building a proper home for these overlooked beauties. Judge me harshly for waiting a decade before actually visiting.
The main problem with displaying mosses is that they’re mostly quite small, so you need to be up close to appreciate them. Berlin have solved this by creating a reverse sunken-garden: you walk down some steps into a basin, around the edge of which are arrayed the mosses. It’s a lovely idea, spoilt only a little by the netting they have put over the planted area at ground level to stop clumpy-footed numpties from trudging over them in their slack-jawed pursuit of angiosperms. For my long-suffering companion this was too much: “It looks like the backyard of an abandoned bungalow”. Tsk. Sticks and stones… are all just substrates for them to grow on.Although most mosses are quite small, a few conduct water sufficiently efficiently up their stems to grow much larger. Some of the mosses in the order Polytrichales can grow to almost a metre tall, but even the smaller ones from this order, like the smoothcap below, are still rather chunky and striking: The leafy green bit of a moss that mostly attracts your attention is haploid – that is, it contains only one copy of each of its chromosomes in each of its cells. This is unlike most of the cells in your body (and those of most other plants), which are diploid, with two copies of each chromosome. The only part of a moss that is diploid are the little stalked capsules that you can see growing out of the leafy mass in the photo above. Those diploid capsules make spores through the specialised cell division process that reduces diploid cells to haploid cells. This process – meiosis – is the same one that occurs in your ovaries or testicles. The result is a mature capsule full of haploid spores, which drift away on the wind and eventually germinate into the leafy green body of the moss. It’s the leafy green part that then makes the eggs and sperm. The sperm swim to another moss plant, fertilise its eggs, and the diploid cell from that fertilisation then grows up to make the capsule.
This life-cycle is inside-out from the way humans reproduce. The only cells in your body that are haploid are your eggs and sperm, and they never have an independent existence. So that whole section of a moss’s life – from spore to leafy plant to eggs and sperm – is condensed into just the eggs and sperm of a human life-cycle. If we reproduced like mosses or liverworts, we would all start as a kind-of unfertilised ‘egg’ that grew directly into a big mass of haploid cells. That blob would then sprout vaginas and ejaculating penises all over its surface. The penises would fertilise nearby vaginas, and then a diploid baby would grow directly out of each one. That baby would have a gigantically long neck, and when it hit puberty, its head would explode in a shower of eggs to restart the cycle.
Biology is simply disgusting.At the Moosgarten in Berlin there is a vending machine where you can hire a small magnifying glass to appreciate the details of this sexy cycle. Tragically, there was one promised – but missing – bit of phylodiversity. The moss mugshot guide promised a hornwort, but there was no Anthoceros or Phaeoceros to be seen. These plants aren’t technically mosses (or liverworts), but something slightly more closely related to ferns and flowering plants. My search continues.
Another overlooked part of the vegetable empire that Berlin showcases brilliantly are the spikemosses and clubmosses. Despite the name, these are not mosses at all, but are sister to the huge group of plants that contains all the ferns, conifers and flowering plants. Clubmosses are no longer a major player in the world’s ecosystems, but during the Carboniferous (300 million years ago) their relatives were a dominant part of the forests that formed the coal we seem so keen on burning.The true clubmosses include Lycopodium, whose spores once found use as fingerprint powder, but which is now mostly used (if at all) as a pyrotechnic flash-powder in magic acts. Their relatives the spikemosses may be a little more familiar: the genus Selaginella includes one of those resurrection plants you can occasionally buy whilst exiting through the gift shop, and Krauss’s spikemoss, a plant from the Canary Islands that is becoming an option for outdoor ground-cover in the UK because of climate change: it’s hardy down to 5°C (and has the RHS Award of Garden Merit, lah-dee-dah) but I’ve managed to overwinter it in a sheltered spot in London despite it getting covered in snow this year.
I get to appreciate spikemosses in my garden only because the liberated remains of their fossilised relatives are hastening us on the way to extinction. There’s probably some lesson to be learnt here.As you can see above, the leaves of spike-mosses look rather fern-like, but what you are probably identifying as leaves are actually whole boughs of tiny scale-leaves attached to a much-branched stem. The resemblance to ferns is not coincidental though: the leaves of ferns (and of conifers and flowering plants) are probably derived from a much-branched stem – but with fused webbing rather than individual overlapping scales.
Some of the spikemosses are really extremely pretty: this sumptuous specimen is a William Morris wet-dream.
Botanerd highlights (as if more were needed)
This picture isn’t going to win any awards because the plant was trapped in a locked-off area of the glasshouse so I had to take the photo from a looong way away, but – drumroll, please! – here is an actual Amborella trichopoda, in the flesh, as it were. This plant is in the sister group of all the other flowering plants – indeed, is the sister group, as there’s only this one species in it. If you don’t think this is the most exciting thing you can experience on a holiday to Berlin in early September, then I pity you.
The minute I found out there was a botanic garden in the north of Gran Canaria as well, a return visit became inevitable.
The Jardín Botánico Canario “Viera y Clavijo” is in the outskirts of Las Palmas, and is much larger than its Maspaloman sibling. As well as showcasing a Canary Island pine woodland, it also has a impressive path carved into the side of the cliff that overlooks the site. This affords splendid views across the gardens – assuming you can stomach them.The cliff-side path is planted with lots of native flora, including the endemic maple-leaved mallow (Lavatera acerifolia): haresfoot ferns (Davallia canariensis): and especially, a whole weyr of dragon-trees (Dracaena draco): Entry is free!
Botanerd highlights: the cactus and succulent garden is fantastic. It is large, and has many mature specimens of cactuses, Euphorbia, Pachypodium, and even a Madagascan Alluaudia. Some of the specimens are vast: this Pachycerus weberi is about 8 m high, and many of the Euphorbia are similarly imposing.
Our microscopy practical always turns up something new, which is the main reason I enjoy it. This year it was a ciliate called Euplotes patella. This kneecap-shaped critter is a single-celled organism masquerading as a tiny animal. The appendages that look like long hairs or legs are bundles of extra-long cilia called cirri, which it uses to scuttle about like a microscopic woodlouse. The cirri around the front of the cell (top of the image below) are also used to sweep food into a region of its cell membrane that acts like a mouth. Euplotes will eat bacteria, yeast, algae, pretty much anything it can fit into its mouth really: much like me at Christmas.
As Euplotes is quite fast-moving and camera-shy, it was tricky to get a good image. Fortunately, one of my students got a good picture, and kindly agreed to let me license it under Creative Commons: thank you Yikai!
In the days when potted plants were more than just disposable land-filler, my Nan would try to force her wizened poinsettia to flower by sticking it into a bin-liner with some apples every night from October until December. Sum total of flowers she ever saw: zero. Ho hum. But how many poinsettia flowers can you see in the picture below?If you’re wondering whether you can include the ones that are partly off-screen, you are asking the wrong question. There are many hundreds of flowers here, not six or ten. The red leafy-looking things you might have been cruelly mislead into thinking were petals are actually brightly coloured leaves. The flowers themselves are found in the tiny yellow-green blobs in the middle… …but they are not – as it turns out – the blobs themselves. Each one of those blobs is itself a bunch of tiny petal-less flowers: one petal-less female flower, and a bunch of tiny petal-less male flowers consisting of just one anther each. This structure – a cyathium – is found in all the species of Euphorbia, the genus to which the poinsettia and 2000 other species of spurge belong. In one of the close relatives of the poinsettia – the crown-of-thorns – two coloured leaves surround just a single cyathium, making it a flower-squared: a bunch of tiny flowers masquerading as a single bloom: This means that the poinsettia ‘flower’ is really a flower-cubed: it is a set of tiny petal-less flowers grouped together into a cyathium, and then a bouquet of cyathia are grouped together and surrounded by coloured leaves. It is a flower reinvented – twice!
The cyathium is one of many re-invented wheels in the business of making flowers. All the 33 thousand species in the daisy family have flowers-squared, as do all of the arum lilies. The flowering structures of grasses are flowers-squared or cubed according to taste.Deeper down the rabbit-hole…
When I said the ‘red leafy-looking things’ on a poinsettia weren’t really petals, I wasn’t lying, but from an evolutionary point of view, that’s all a petal actually is. Petals are a ring of leaves that became useful for attracting pollinators in some long-dead ancestor of the flowering plants.
Something similar applies to the male anthers and female carpels at the centre of a flower: these are also modified leaves, wrapped around the tissue that makes the pollen and egg-cells. So even a single real flower can be seen as a cluster of smaller male and female ‘florets’ (botanists call these sporangia), themselves made of rolled leaves, and surrounded by yet more (prettily coloured) leaves. A flower is a leaf-squared, so a poinsettia ‘flower’ is a leaf-to-the-fourth-power.Oh, but we’re not done yet.
What is a leaf? Well, if you hold up the leaf of most land plants to the light, you’ll see a lot of veins. Depending on what you’re looking at, these may be arranged in neat parallel lines, or in a tree-like branching network.The latter kind gives you a clue as to what a leaf really is. A leaf is a much-branched but flattened stem with tissue stretched out across it like the webbing between the toes of a duck.
So if a leaf is a stem-squared, then a poinsettia ‘flower’ is a stem-to-the-fifth-power:
- Start with a stem
- Group a bunch of stems together with some webbing to make a leaf
- Group a bunch of reproductive leaves together with some pretty leaves to make a flower
- Group a bunch of simplified flowers into a cyathium
- Group a bunch of cyathia together with some pretty leaves to make a poinsettia
Plants: what you get when you take one good idea and run with it for 500 million years.
An old clay pit in Cornwall doesn’t sound like the most promising place to find a tropical forest, but the alleged proximity of the entrance to Magrathea might go some way to explaining it. The Eden Project’s bubble-wrap domes are now such a familiar part of the Cornish tourist board’s marketing that you’re not really expecting them to be as impressive as they actually are in the flesh:Inside the tropical biome there is a tree-top walkway that takes you up a stairway suspended in mid-air to a platform suspended in the same. This platform sways from side to side at the exact resonant frequency of the human bowel. There was probably a view. I don’t really recall. As it was the depths of winter when we visited, there was not all that much happening outside in the Cornish biome, but the clean air and high humidity supports a lush growth of mosses and lichens on every available surface.
Tickets are a breath-taking £25+ per person, and I should imagine pre-booking is sensible in the summer months.
Botanerd highlights: my memory is terrorised, fragmentary. Some palms. Definitely some rubber trees. Jewelled crabs?
On the way back from Cornwall, we dropped in at the national arboretum in Westonbirt, which is run by the Forestry Commission. We’d been there once before for a wedding, but hadn’t had much time to explore the grounds. As previously noted, it was the depths of winter, so quite a lot of the trees were dormant, and my photo-roll is a bit scant. However, there are several areas planted heavily with conifers, so I spent a happy couple of hours running about trying to find fallen cones to add to my collection. I would pay good money for the cone of a Taiwania cryptomerioides (seriously – call me), but – in keeping with most of specimens of this species in the UK – Westonbirt’s coffin tree was far too young to have any. Oh well.Tickets are £15.
Botanerd highlights: trees. Lots and lots of trees. If we’d timed it better, I would have the pretty pictures to wax lyrical about the 79 ‘champion’ trees they have, which are the biggest of their species you can find in the UK. But it was too bloody cold, so I shan’t.
In pre-emptive defence, Las Canarias = winter sun ∩ not-imprisoning-the-gays ∩ relative affordability.
Eschewing the fleshpits of the Yumbo Centre, we walked for mile after sweaty mile under the very sun we had paid to enjoy, to the Parque Botánico de Maspalomas. Only to find that Epiphany is still a thing on Gran Canaria, and so a glimpse through some locked gates was all we were likely to get:Never one to let an unlikely man-god get in my way, we tried again on the morning of our flight home. The gardens are all outdoors, and showcase sub-tropical plants, including a number of the Canary Islands’ wide range of endemics. The Canary Island spurge – which looks like a cactus but isn’t – is everywhere on Gran Canaria, and looks absolutely gorgeous in the sunshine. The photo below is not at high enough resolution for you to see that is it also covered in spider webs. Hundreds and hundreds of them, each with an attendant angry arachnid. The stuff of nightmares. Yours obviously, not mine. My nightmares are wholly taken up with falling to my death from great heights. Entry is free! In addition to the botanic gardens, the Paseo los Gatos Rabiosos (officially, the Paseo Costa Canaria, and Calle las Dunas) have some pretty nice planting along them, including a lot of Norfolk Island pines (actually monkey-puzzles), none of which – tragically – had cones within scrumping distance. The latter street also takes you to the edge of the amazing dune system and nature reserve behind the beach. Botanerd highlights: along with the native spurge, the Madagascan traveller’s ‘palm’ Ravenala is the Maspalomas go-to for generic corporate planting. However, the one at the botanic gardens was considerably more majestic than most of the hotel frontage offerings.
We timed this final UK visit a bit better. Wakehurst is the country outpost of Kew Gardens, and home to the Millennium Seed Bank, which aims to preserve the seeds of 25% of the world’s seed plants by 2020.Being a contrary dick, I went hunting for plants that don’t bear seeds to photograph. Here is Cthulhu escaping from R’lyeh. And some mosses: diploidy is for wusses. Tickets are £12.50, but factor in an unexpected £10 for the car-park too, unless you fancy a 6 mile walk (or a once-every-two-hours bus) from from Haywards Heath railway station.
Botanerd highlights: the huge stand of royal ferns above are reason enough alone to visit, but Wakehurst’s pinetum also has some interesting species: Keteleeria evelyniana, which I’ve seen nowhere else before, and a lot of small firs which have beautiful immature cones with brightly coloured bract scales at this time of year.
A few months ago, I went to a creative origami lunchtime session organised by some lovely people at
$WORK. I’d done origami a bit when I was younger, but mostly just frogs and cranes, which have since helped me while away the hours when invigilating exams. However, at this lunchtime session I was shown how to make modular origami. This involves making lots of (generally quite simple) origami parts, and then slotting them together to make larger structures.
I went home with a simple 12-unit Sonobe ball that afternoon and was very pleased with myself.
Things have rather escalated from there.
Between running some of these lunchtime sessions myself now, and being asked on several occasions on Twitter about how I make the pretty things I keep tweeting, I thought it’d be useful to put together a quick guide (or a link-farm, at least)..
Sonobe units are very easy to fold, quite forgiving, and can be used to make a cube (6 units), a cumulated octahedron (12 units), a cumulated icosahedron (30), and a kind-of truncated icosahedron (90, basically a spiky football). They’re a pretty good introduction to the general principles:The 30-unit ball has the symmetries of an icosahedron (or dodecahedron). Once you’ve learnt how to construct that object in Sonobe modules, you’ve essentially learnt how to construct any 30-unit modular origami ball: they mostly involve slotting 30 edge-units into groups of three to form the 12 pentagonal faces of a dodecahedron (or equivalently/alternatively, slotting them into groups of five to form the 20 triangular faces of an icosahedron – the difference is mostly one of perspective). There are lots of variations on the Sonobe unit you can (re)invent, by adding back-folds that expose the other side of the paper, or that make the tabs narrower than the pockets, giving a more intricate look. Although the 90-unit structure is quite stable, the next one up (270 units) tends to sag under its own weight over time, but by that point it felt like a right of passage to make one. The Sonobe units can also be assembled inside-out to make inwardly cumulated polyhedra… …and they can also be assembled in pairs and then assembled into a spiked pentakis dodecahedron... …and other structures. The next unit I tried was the Penultimate edge unit (attributed to Robert Neal), which can be used to make a wireframe dodecahedron, as demonstrated by Matt Parker, the stand-up mathematician. Other variations of this subunit can be used to make pretty much any other wireframe polyhedron. Thomas Hull’s PhiZZ edge unit makes similar wireframe structures, but the modules fit together more tightly and the resulting structures are much more robust than you get with the penultimate modules. You can also make colour-change variants using the technique shown in Lewis Simon’s decoration boxes. For structures based on dodecahedra/icosahedra and made from edge-units, you can always get away with using just three colours and never have two of the same colour pieces touching. This is because you can draw a Hamiltonian circuit on a dodecahedron: that is a path from vertex to vertex that only visits each vertex once, and which comes back to where it started. You can represent this in 2D on a Schlegel diagram. If you colour alternate edges of the Hamiltonian circuit in two of your chosen colours, and the rest of the edges in the third, then you’ll avoid having any colour-clashes. I only learnt this after I started making these structures, so not all of them have this optimal colouring! The same 3-colour rule is true for the other Platonic solids, and also for the truncated icosahedron.
Francesco Mancini’s star-holes kusudama uses a similar module to the PHiZZ, but with a little back-bend that gives a nice 3D star effect. This one is a dodecahedron-shaped (30 units), but a 90-unit truncated icosahedron should also be possible.UPDATE: yes, it is possible 🙂 Lewis Simon and Bennett Arnstein’s triangle edge unit can be used to make very nice patchtwork tetrahedra, octahedra and icosahedra. They’re a bit fiddly to put together but are very robust once constructed. A similar patchwork effect for the dodecahedron can be achieved with M. Mukhopadhyay’s umbrella module; Sonobe units can be used to make analogous Battenberg-cake style cubes. The simple isosceles triangle unit (attributed variously to M. Mukhopadhyay, Jeannine Mosely and Roberto Morassi) can be used to make small and great stellated dodecahedra. The small stellated dodocahedron is particularly pleasing and makes a fairly robust decoration if made of foil-backed paper. The great stellated dodecahedron can be made from the same subunit, but is tricker to construct because a tab has to curl around into a pocket that is partly inside the next tab round. I used needle-nosed forceps to construct this, and I’m still not terribly happy with the result.
The opposite is true for Paolo Bascetta’s star module, which makes a great great stellated dodecahedron, but a rather *eh* small stellation. This module needs duo paper (i.e. paper that is coloured on both sides) for best effect.Dave Mitchell’s Electra module can be used to make a icosidodecahedron: it’s unusual in that each module corresponds to one vertex of the structure: the edge units described up to this point combine together to make each vertex. I’m not that happy with my Void kusudama (Tadashi Mori): I should have used duo paper, but it was really tricky to put together. Maybe one day. It’s one of the few structures here that is back to the original octahedral/cubic 12-unit structure. I’m not sure the 30-unit version would be stable. UPDATE: Yeah, I don’t think the 30-unit version is do-able. I think the units are too wide to actually fit into an icosahedron: I couldn’t even manage it with glue, so I don’t think it’s just a stability issue. However, I did do a better 12-unit version, with duo paper and a little reverse fold on the outer edge to expose the second colour properly, which I’m quite pleased with: Tomoko Fusè’s little turtle modules are extremely flexible: they can be used to make pretty much any polyhedron that is made of regular polygons. However, because the flaps are only one paper layer thick, they don’t fit together terribly tightly, so I’ve only found them robust enough to make smaller structures without the help of glue. However, with glue, I’ve made a rhombicosidodecahedron, which is cool because it is built of pentagons, triangles and squares (all of the polygons found in the Platonic solids)… …and also a pair of snub-cubes, which are even more interesting as the snub-cube has two non-superimposable mirror images, like hands, amino acids and amphetamines. I found Maria Sinayskaya Etna kusudama in Meenakshi Mukerji’s Exquisite Modular Origami book. It’s a really pretty model, and robust once it’s assembled, but it can be a bit fally-aparty during construction: I used very small clothes pegs to hold it together as I was making it. Meenakshi Mukerji’s compound of five octahedra (inspired by Dennis Walker) is also a bit fally-aparty, but I like it as – unlike many of these models – it genuinely is the polyhedron so-named, rather than something where you have to squint at the holes in the wire-frame and imagine faces there. The five intersecting tetrahedra are actually a lot easier to make than they look. Francis Ow’s 6-degree modules themselves are easy to fold, and the vertices are a lot more robust than they might appear. The most difficult bit is getting the modules interlinked in the right way. I’ve managed it twice, but only whilst staring at the YouTube video and performing assorted “purple = green” gymnastics in my head. Michał Kosmulski’s page has lots of lovely illustrations, instructions and inspirations. I found Tung Ken Lam’s blintz icosadodecahedron (also credited as Francesco Mancini’s UVWXYZ intersecting planes model) there. It has the same symmetry as the Electra icosadodecahedron above, but you can see the six intersecting pentagons more clearly. Both have the same underlying structure as the Hoberman sphere – that expanding/contracting plastic stick model thing beloved of science fairs. This last one is a bit of a cheat as (in theory, and mostly in practice too) the structures above are held together by nothing more than friction. Valentina Gonchar’s revealed flower star kusudama has to be glued, which is kind-of cheating, but I couldn’t resist as it is two structures in one: Things I’d still like to do:
- Build a much larger PhiZZ ball (270 units): this would be useful for demonstrating the structures of viral capsids. UPDATE: Done!
- I’ve not yet found a good great dodecahedron model: they exist on Pintrest, but I’ve yet to find any instructions for one.
- I have lost wherever it was I found the instructions for this inwardly cumulated rhombic triacontahedron: I’d quite like to rediscover them so I can credit the inventor! UPDATE: this isn’t where I originally saw it, but AresMares by Gewre has a video tutorial, and a kind commenter has let me know the designer is Silvana Betti Mamino – thank you!
- Invent my own module 🙂
Tardigrades make me squee. These little relatives of the arthropods and velvet-worms are found in the water around mosses, and they are quite easy to find if you have a cheap microscope and a little patience. Like spiders, they have eight legs, but unlike the legs of a spider, they’re plump and stumpy, and end in the little ‘fingers’ you can just about make out in the photos below. Ignoring the excess of legs, it’s easy to see why they’re sometimes called water-bears.
One of my first-year undergrads spotted this one in a sample of moss I pulled out of the down-pipe from my bathroom. The fact that my skin flakes and spittle contributed in some small way to this microteddy’s food-chain makes me feel about as paternal as it is possible for me to feel.
All science is either physics or stamp-collecting.
This rather mean-spirited dismissal of chemistry and biology as “stamp-collecting” is attributed to Ernest Rutherford, the physicist usually (not wholly fairly) credited with discovering the atomic nucleus and the proton.
Shortly after Rutherford’s death in 1937, particle physicists discovered the muon, pi mesons, kaons, the electron neutrino, the anti-proton, the lambda baryon, xi cascades, and sigma baryons. It took physicists the thirty years following Rutherford’s death to make sense of this veritable album of subatomic stamps.
Nature has a sense of irony, but its comic timing needs work.
There’s nothing wrong with stamp-collecting. Science very often begins with stamp-collecting, because it’s only once you have enough stamps that you can start reliably identifying patterns in the stamps, and – from there – finding the interesting exceptions and edge-cases:I have been an on-off collector of carnivorous plants since I was very little. Most of them attract insects, kill them, digest them to tasty soup, and then absorb that soup. The soup contains useful nutrients that are missing from the soil in which they are rooted, so this helps them grow and set more seed. But there are many plants that tick some of these carnivorous boxes, but not all of them. Roridula is one I’ve blogged about before: it subcontracts out the digestion part of the process to an assassin bug. Another plant that walks the line is a kind of passionflower: The charmingly-named stinking passionflower bears sticky hairs on tentacle-like growths around its flower buds. There is some evidence to suggest that these help protect the flower bud from hungry insects while it develops. Similar sticky hairs are also thought to protect the flower buds of a number of other plants.
The stinking passionflower kills insects, and even appears to digest them, but it doesn’t benefit from the nutrients this releases. However, it does benefit from not having its flowers damaged by herbivorous insects. This presumably means it sets more seed, so the ultimate effect – more baby plants – is the same as for ‘true’ carnivory.Is this plant carnivorous or not? Well, whether you ultimately choose to paste this stamp into the carnivorous plant album or not is very much less interesting than the reasons you have for making that decision. I’m just glad that someone discovered this particular stamp and took the care to stick it somewhere for us to study. Here’s to collectors and taxonomists, the unsung heroes of biology.
Organisms evolve adaptations to increase their fitness
There are few ideas in science that explain as much of the natural world as does natural selection, but there are few ideas in science that are more frequently misunderstood.
Often the misunderstandings are deliberate or disingenuous, but I’ve seen quotes like the one above even in undergraduate essays and popular science books.
There are two subtle problems with what is written above.
Firstly, adaptations do not evolve in individual organisms, because evolution isn’t something that happens to individual organisms. Evolution is something that happens to populations over time. A mutation that predisposes pea plants to making flowers that are purple will initially arise in a single, particular plant cell. But only if this plant’s offspring prosper (at the expense of peas with differently coloured flowers) will the population as a whole change over time.
Adaptations like flowers that attract pollinators – and the mutations that underlie them – arise in particular individuals, but they can only become more (or less) common in populations considered as a whole. Individuals mutate, but only populations evolve.
Biologists usually think of evolution as the change in frequency of an allele in a population over time. An allele is one of the various forms a particular gene can take. In the peas studied by Gregor Mendel, flower colour was determined by a single gene, which came in two variants: one variant – one allele – resulted in purple flowers, the other allele resulted in white flowers.
If – perhaps – the purple flowers were more attractive to pollinators like bees than the white, then the purple-flowered peas would tend to be fertilised more often, and would leave more offspring. The next generation of pea plants would then inherit a larger proportion of alleles causing purple flowers, and a reduced proportion of alleles causing white flowers. The purple allele would therefore increase in frequency at the expense of the white, and the population as a whole would become more purple over time.For similar reasons, fitness is not a property of individual pea plants either; it is an average property of purple-flowered peas versus white-flowered peas. Any particular purple-flowered pea plant might get trampled by a cow and produce hardly any pea-pods; any particular white-flowered pea plant might get lucky and find itself in a cosy, well-fertilised spot near a beehive. But on average, the purple-flowered plants will do better and they will bequeath their purple-flower alleles disproportionately to the next generation: that is what we mean by the purple-flowered plants being ‘fitter’.
The second problem with the original statement is actually the smallest word: it’s that seemingly insignificant ‘to’. That ‘to’ is short for ‘in order to’, and there’s the rub. ‘In order to’ implies teleological agency and long-term purpose, which are not properties that you can reasonably attribute to natural selection.
Natural selection is a mindless algorithm, not a purposeful process. In essence natural selection is just this:
- Organisms vary, and some of that variation is inheritable. Some peas have purple flowers, some have white, and this is (partly) due to purple- and white-flowered peas having different alleles of a particular flower-colour gene.
- More offspring are produced than can survive and reproduce, so they will compete, and some variants will – on average – have greater success at making offspring than others. Pea plants produce more offspring peas than are ever likely to germinate, grow and get fertilised themselves. Some variants in the offspring may be better at competing for light, nutrients or pollinators: e.g. some flower colours may be more attractive to pollinators than others.
- Those variants will contribute disproportionately to the next generation, and the frequency of their alleles will increase over time. If the purple-flowered peas are more attractive to pollinators, they will get fertilised more often, and contribute a larger number of seeds into the next generation. These seeds – and the plants that germinate from them – will inherit their parent’s purple-flower alleles, so we will see an increasing proportion of purple flowers as the generations tick over.
- Rinse, repeat.
The match between the purple flowers and the purple preference of pollinators strikes us as clever and sensible and non-random, and it is all those things. But the process of natural selection that created this apparent design is just the mindless consequence of variation, heredity and differential reproductive success: it has no goals, no aims, no purpose.
Equally, this is a passive process for the pea population: they are subject to evolution by natural selection, but they are not active participants in the process.The peas do not strive supernaturally to make more purple flowers. The peas do not get magically instructed by the bees to make purple flowers. The peas certainly do not know what DNA sequences they would need to invent in order to make their flowers purple: new flower-colour alleles arise by mutation, which is just as mindless as natural selection, and even more heedless of what might be useful.
Populations do not evolve in order to do anything. Populations evolve, period. Purple flowers arise and become more common in pea populations because purple flowers happen to be attractive to bees; peas do not choose to evolve purple flowers in order to attract more pollinators. Mutation just throws up new alleles, and natural selection (and other important processes) make them more or less common over time.
It can become tedious describing this process passively and long-windedly every time: “purple flowers have become more common in the pea population because flower colour is highly heritable, and purple flowers are fertilised more frequently by bees”. If you want to write this more succinctly, you could say “purple flowers have evolved in peas because purple flowers are more attractive to bees” without loosing too much meaning.
Unfortunately, you might well see someone reword this as “peas have evolved purple flowers because bees prefer them”. This isn’t exactly wrong, but the ‘have evolved’ makes it sound very much like the peas are doing something actively, rather than having something done to them passively, and it’s all too easy to interpret this phrasing incorrectly. This puts us on the slippery slope to misconception.
If this is then reworded further to “peas evolved purple flowers to attract bees”, it sounds very much like like peas are active players in the process, and that they have a long term plan of improving their attractiveness to bees. This is almost guaranteed to mislead, unless you have your evolutionary biology filter turned up to maximum.
Do not write:
Some species evolved an adaptation to do some task
Write this instead:
An adaptation that does some task evolved in [a population of] some species
Given human nature (particularly on this subject), some people will still misinterpret your meaning, but at least you’re not implicitly misleading them with your language.