The ‘fungus’ that ‘walks’
Published: 24 October 2012 (GMT+10)
Photos by Ron Oldfield
Despite intense scientific scrutiny, these ‘what-are-they?’ organisms continue to baffle.
Even after many decades of research, the experts still debate how best to classify them.1,2 For many years the organisms pictured here were labelled ‘fungus’, because part of their life cycle is like that of many fungi. Mostly, though, they move and feed like one-celled ‘animals’. Yet they make their own cellulose, like a plant. And incredibly, as we shall see, there are times when they look and move like multi-celled animals. Part of their life cycle is also very similar to certain bacteria. Just what are they?
These are the so-called ‘slime moulds’, which are tiny (about 0.02 mm long, or 1/1000th inch), and despite their repulsive-sounding name, can look very beautiful. They are found all over the world, living in rich damp soil, leaf litter, or animal manure. They come in two broad types: plasmodial and cellular.3 We will mainly consider the cellular slime moulds, one of which, Dictyostelium discoideum, has been (and continues to be) the subject of intensive scientific scrutiny.4
Slime moulds vividly demonstrate the ingenious diversity of God’s Creation. It would be hard to imagine creatures more bizarre in their behaviour, if indeed it can be said that they ‘behave’.
When conditions are favourable, slime moulds are free-living, single-celled, ameba-like micro-organisms. They are not actually ‘amebae’ as scientists would normally understand amebae to be (i.e. a type of protist, a one-celled organism). But they are so like them in appearance and form of motion that scientists usually call them by that name since no other suitable term is available. (This highlights the dilemma faced by scientists who try to ‘label’ these creatures within an evolutionary framework.)
Slime moulds creep about in or on the soil, leaf litter, logs or manure, consuming bacteria as they go. With their capacity for ‘self-cloning’ by dividing themselves into two new daughter ‘amebae’, slime moulds can rapidly multiply their numbers so as to exploit favourable environments. Each of these new amebae creeps off on its own as a completely separate entity. This can continue for as long as environmental conditions stay favourable. That is, as long as the ground is moist enough, and they can find enough bacteria for food.
But should conditions begin to take a nasty turn (usually a dwindling food supply), something utterly remarkable happens. Thousands of individual amebae from the same vicinity begin to congregate together. This they do by responding to a substance that one (or more) of them starts to secrete. It has been shown that about one in every 2,000 amebae has the ability to start producing this substance under unfavourable conditions. Other nearby amebae start to stream towards the source of this chemical. Then they too begin to secrete the same substance, which spreads out in wave-like pulses and attracts more amebae, and so on.5
Within hours, up to 500,000 amebae have clumped together in a multi-celled mass.6 This they are able to do by secreting a sticky substance which glues them together. Each ameba is still, however, an entirely independent individual. But the clump of thousands of one-celled individuals now begins to behave as if it were a single slug-like creature.
And, in some species such as Dictyostelium, something else very strange happens. The amebae pile up one on top of the other to form a steep-sided mound. Then the mound topples onto one side, and may slither away like a garden slug (up to 2–3 mm long, or 1/10th inch), with a clearly defined head end. Scientists are still figuring out the mechanisms that determine why some amebae become leaders, while others become followers, meekly falling into line behind the leaders. Amazingly, this self-redistribution of the amebae into leaders and followers during the ‘slug’ stage can occur even when the slug is cut up into smaller segments, with tiny fragments capable of forming themselves into a midget body (and able to proceed through the rest of the life cycle quite normally).6
Slugs of some species then migrate considerable distances, depositing a thick slime sheath as they travel, which collapses behind them. It has been found that these slugs, still consisting of not-quite-so-independent amebae that are now acting in unison, are remarkably sensitive to light and heat. They will move towards a weak source of heat or a light as dim as the faintly luminescent hands of a wrist watch.
The mound of clustered amebae topples over and begins to move away as a ‘slug’.
The migrating slug leaves a trail of slime behind.
‘Whoa! Here’s a good site for a launching pad.’ The slug slows and enters the ‘standing finger’ stage.
As one slug slows, another begins to lift itself higher.
The amebae at the tip push down through the mass to form a stalk, lifting the others up into the breeze.
A forest of slime mould fruiting bodies, containing masses of spores ready to fly to fresh hunting grounds.
Shortly after the slug has chosen the stage for acting out the final scene, it lifts its front tip up into the air. Somehow it keeps doing this until once again the slug is standing upright, reaching for the sky like a miniature sky-scraper. The amebae in the tip now swell with water, and then secrete around themselves a cellulose wall. Here it begins to take on a plant-like characteristic as cellulose is a key component in plant cell walls.
Then another strange thing happens. Imagine a sausage standing up on end. Now imagine that you poke down on the top end with your finger, in such a way that you push the tip downwards into the sausage. Imagine now that this indented tip keeps on going right down through the centre of the sausage until it reaches the bottom. In other words, the whole mass is turning itself inside out. While the tip is thrusting itself down through the centre of the sausage, the lower and outer parts of the sausage are making their way to the top up the outside. This is exactly what happens to the slug.
As cells at the tip turn to move downwards they secrete cellulose. Thus they turn into a long, slender cellulose stalk (up to about 13 mm, or ½ inch).6 The very last group of amebae to reach the top do not move on down the inside, but sit there like the king of the castle. Thus, the long, slender stalk now has a rounded blob on the top. This structure is called the fruiting body, and looks very much like the fruiting body of many fungi, which is the primary reason that slime moulds were grouped with the fungi for many years.
The amebae that end up perched on top of the stalk (the fruiting body) become the spores. This transformation from amebae into spores is a complex process, but basically, each ameba at the top produces, and then wraps itself in, a cellulose cell wall, which acts as a weather-resistant overcoat. Now it is a spore, lying dormant and ready to be carried off by the first breeze, or by sticking to some passing creature. The purpose of this whole ‘inside-out’ manoeuvre appears to be to form a rigid stalk high enough for the wind, etc., to spread the spores. (About 70% of the amebae in the original slug become the thick-walled spores of the fruiting body, with the remaining 30% sacrificing themselves to form the supporting stalk.)1
The spores can travel enormous distances before landing. Every time you inhale, you are probably breathing in numbers of such spores. If a spore happens to land where conditions are favourable (e.g. moist ground with lots of bacteria), it will germinate and take on the ‘adult’ form. Thus the cycle of life continues.
Major problem for evolutionists
So what exactly are slime moulds? Despite the similarities, they can’t readily be classified as fungi, plants, multi-celled animals, bacteria, or protists.7 But the core of the problem is not which group to put slime moulds in, but why bother doing so? Evolutionists operate on the premise that all life is related, believing that we all have a ‘primeval slime’ single-celled organism as our ancestor. Consequently, they classify species by assigning them to positions in their ‘evolutionary family tree’ according to how ‘closely related’ they appear to be.8
Trying to support their theory of life’s origins, and somewhat challenged by the staggering complexity of single-celled organisms like Dictyostelium, evolutionists struggle to find a place for the slime moulds. In fact, experts recently acknowledged, ‘People within and outside our field don’t know where to put Dictyostelium.’2 As more is learnt of these creatures, the more difficult it becomes. For example, the cellular slime moulds have been divided into two sub-groups which, as one evolutionist writes, ‘may not be closely related to each other’!9 Other evolutionists have made the revealing observation about cellular slime moulds that ‘… it is apparent that they do not exist to fit into neat categories!’1 Clearly, the existence of slime moulds is a conundrum for evolutionists.
No problem for creationists
For Christians, it is not necessary to try to arbitrarily lump slime moulds with other organisms. Why not? Because from the Bible we can understand that slime moulds did not evolve from, or into, any other organisms (i.e. all life is not ‘cast from the same mould’ as some ‘primeval slime’). Rather, slime moulds were created during Creation Week (Exodus 20:8–11) as slime moulds, designed to reproduce ‘after their kind’ (Genesis 1:24–25). It is almost as if our Creator put slime moulds here so that we could be in no doubt about the origin of life.10 For if God were creating things to reveal His eternal power and divine nature (as Romans 1:20 implies), we would expect He would create some things which would thwart man’s attempts to explain everything by natural processes, i.e. evolution. Perhaps slime moulds are one such type of creature.
The similar features they have in common with fungi, plants, bacteria, protists and animals, would indicate these were all made by the same Designer. At the same time, the stark differences between slime moulds and other organisms defy any attempts to draw an ‘evolutionary family tree’—just as if the differences were put there for precisely that purpose!
The amazing and unique slime moulds testify to the truth of what the Bible says, i.e. that what may be plainly known about our Creator can be clearly seen by understanding what He has made—so that men are indeed ‘without excuse’ (Romans 1:19–20).
References and notes
- Eliott, S., and Williams, K.L., Modelling people using cellular slime moulds, Australian Natural History 23(8):608–616, 1991. Return to text.
- The Dictyostelium Virtual Library (a website maintained by Northwestern University, Chicago), http://dicty.cmb.nwu.edu/dicty/kessin_devreotes.html, 22 March, 2000. Return to text.
- Cellular slime moulds differ from the plasmodial slime moulds in that when swarming together to form a slug-like aggregation, they do not lose their cell membranes but retain their identity as individual cells. Curtis, H., Biology, Worth Publishers, New York, NY, USA, p. 428, 1983. Return to text.
- The life cycle of slime moulds has long fascinated evolutionists looking for clues as to how multi-celled creatures evolved (supposedly) from ‘primitive’ single-celled organisms. Additionally, Dictyostelium is regarded as a good ‘model organism’ for scientific study of cell and developmental biology. Given its similarities to infectious ameboid-related diseases such as malaria and amebic dysentery, for example, it is widely employed in medical research. Dictyostelium is now also the focus of DNA and genome sequencing projects. See Ref. 2. Return to text.
- This substance was first called acrasin, after Acrasia, the witch character in Edmund Spenser’s Faerie Queene (a long allegorical 16th century pro-Puritan poem), who attracted men and turned them into beasts. The mystery substance was later identified to be cyclic AMP (adenosine monophosphate)—an important ‘chemical messenger’ in human physiology. See Ref. 3, p. 120. Return to text.
- Bonner, J.T., Differentiation in social amebae, Scientific American 201(6):152–162, 1959. Return to text.
- The classification of the slime moulds remains contentious and uncertain, particularly as new biochemical and genetic research is forcing a major rethink of the entire classification system. Presently, however, slime moulds are most commonly placed within the ‘Kingdom Protista’ (or ‘Protoctista’, the one-celled eukaryotes, i.e. cells possessing a membrane-bound nucleus). Examples: http://titan.iwu.edu/~jdey/diversity-slimemolds.html; http://www.bio.umass.edu/biology/conn.river/protoc.html. Return to text.
- Slime moulds are a huge obstacle to this idea. Evolutionists concede that these organisms can no longer be classified as fungi because … ‘slime “molds” are now known to be quite unrelated to the fungi.’ (!) See: Introduction to the “Slime Molds” (University of California Museum of Paleontology website), http://www.ucmp.berkeley.edu/protista/slimemolds.html, 7 March, 2000. Return to text.
- The two sub-groups are the Dictyostelida and the Acrasida. Ref. 8. Return to text.
- This theme is explored in great detail in ReMine, W.J., The Biotic Message, St Paul Science, St Paul, MN, USA, 1993. Return to text.
Reading this story explaining the life cycle of this "creature of sorts" made me think about the story of the body of Christ as a whole and it's growth over time, as well as, our individual growth as a Christian. God is amazing.
Never mind the problem of classification - just imagine the coding required to generate such "intelligent" manoeuvres!
So which day of creation do you think they would have been formed on?
Good question! Traditionally 'fungi' have been thought of as 'plants', which would indicate Day 3 of Creation Week. But some might argue that slime moulds' ability to coalesce and 'creep' opens up the possibility of Day 6. My view leans towards Day 3 (though I wouldn't be adamant about it). Trees, for example, indubitably created on Day 3, are hardly static: see, e.g., Pulsating plants.
I'm surprised that atheists haven't claimed them as the missing link between protozoa and multi-celled creature! The just-so stories usually begin with 'Then, lots of cells clumped together to form multi-celled organisms...'
Amazing--a timely reminder in a world that usually only sees an image which may not even be accurate. Here is detail that shows exquisite design behind the big picture. Well done.