The Energetic Evolution of Cannabis

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Here, we attempt to briefly describe how Cannabis came to be so varied and ubiquitous, how it has co-evolved with humans, and how it has affected the ecosystems it has been introduced to. Although it has been assisted in its conquest of the world by humans for at least the last 4,500 years, there are several characteristics of Cannabis that enable it to adapt remarkably well – and quickly – to its environment. Indeed, this is partly what makes the species such a good candidate for selective breeding programs, the like of which have given us the huge variety of cultivars available today.
The genus of Cannabis, which comprises a single species (Cannabis sativa Linnaeus); three subspecies, C. sativa Sativa, C. sativa Indica and C. sativa Ruderalis; and many postulated varieties (although the distinction, and whether the three are indeed subspecies, or in fact separate species, is still unclear despite years of debate within botanical circles), is believed to have existed for around 34 million years. It is classed as belonging, along with Humulus (hops), Celtis (hackberry) and about ten other flowering plant genera, to the family Cannabaceae, present in the fossil record since the early Tertiary period, which began around 65 million years ago.
Biologically, Cannabis exhibits many traits that enable it to flourish in a wide variety of habitats. Not all varieties exhibit all these characteristics, but for every climatic zone except polar, there is a type of Cannabis that will grow well there. As the plant is so quick to reproduce, it stands to reason that any introduction of Cannabis to an area will lead to rapid selection for dominant traits that fit the environment until a new variety is established, even without cultivation.
It can withstand large fluctuations in average temperature and rainfall (from 43F to 80F comfortably with 12 – 160in. of annual precipitation), as well as drought and frost; it will grow in all manner of soils from loamy to sandy (it does not flourish in poorly drained soils, particularly clay-based, although it does not mind temporary flooding, making it a common feature of river banks in many parts of the world). It is highly resistant to fungus, disease and weeds, has few pests, and can grow at any altitude with no apparent signs of stress on slopes. Some varieties, mainly in the hemp category, can also handle massive variations in pH (4.5 to 8.2).
Its rare dioecious nature can also be sidelined in times of genetic emergency, enabling females of a population with few males to develop monoecious traits (usually instances of male and female imperfect flowers at different points on the same plant, and more rarely true hermaphroditism where individual flowers are simultaneously male and female, or perfect) to ensure new plants will grow next season (albeit as clones of the mother) in the hope that new and more diverse male DNA will eventually find its way to them. Conversion back to strictly dioecious can then occur, allowing for rapid genetic exchange and an increase in variation in subsequent generations.
Cannabis is also a colonizer species, meaning that it is often the first plant to grow on ground newly cleared by flood, landslide or fire, and due to the ubiquitous method of seeds being distributed where they naturally fall around the branches, thick stands of it are often found in these areas. However, it is not the most aggressive species and is not so invasive that it will take over already densely populated ground. For this reason it is the perfect camp follower: it is postulated that back in the Neolithic, clearings left by human settlements would be colonized by Cannabis, and on the reappearance of the nomadic humans initial contact with the plant was made.
So it is arguable that humans have been truly crucial to its spread, and that contact in fact began closer to 10,000 years ago. The pattern of domestication runs as follows, according to a Russian study of Siberian country-dwellers in 1926: populations of Cannabis establish themselves in the wild, then invade areas of human settlement in a weed-like manner; the weed' is then recognized for its properties and utilized, and finally attempts at cultivation are undertaken.
The reason for resin production in Cannabis is unclear – it has been suggested that it may be to protect developing seeds from moisture loss (production goes up with temperature and stems may split to allow resin to run down stems, encasing them in an impermeable layer preventing loss of water); or to discourage insect and bird pests through intoxication (although the preferred method of seed distribution is surely partly through bird ingestion/expulsion, and therefore the reverse could to some degree be true – that animals actively seek out the intoxicant and therefore distribute the seeds more effectively); perhaps the resin also acts as a temporary adhesive for animals rather like burrs; and other plant adaptations.
However, the fact that an unfertilized female will produce more resin is strong causal evidence that resin is produced primarily to attract pollinators rather than distributors of seed, especially as the female largely stops producing resin after receiving pollen. To return to the idea of animal self-medication: although it is difficult to prove a link here, there is some evidence of animals (e.g. chimpanzees) seeking out flowering Cannabis as an anti-nausea treatment in times of gastric difficulty (and perhaps as it also can reportedly kill intestinal parasites), so there is a strong likelihood that its unique properties are not just known to humans.
Research into animal use of Cannabis is sparse, but is sure to increase with time, and deserves further attention. It is more than possible that we were drawn to the plant in the first place by observing such animal behavior (although I'm sure the smell would have been a dead giveaway, if nothing else), and true understanding of how the plant fits into the ecosystem would be massively aided by knowing more about its relationship with our animal brethren.
The fact that physiological barriers to reproduction seem to be absent in Cannabis would belie the argument that the plant is, in fact, several species in one genus (although species; is a difficult term to define, and interfertility does not always denote lack of speciation). It is yet another feature of the plant that would seem to greatly increase its chances of taking hold, flourishing and cementing new DNA within an existing gene-pool, and thereby increasing diversity, viability, and chances to further evolve. An introduced genetic can therefore co-operate with existing local genetics, rather than being in competition – as would be the case with two non-interfertile populations.
Physical barriers may exist, and thank who ever up there for that as it’s provided us with some lovely (apparent, if not actual) speciation – such as the Hindu Kush mountain range neatly isolating the subspecies (or species, or variety) of C. Indica prior to any human involvement. But despite these physical barriers leading to massive genetic variance through the world, any two Cannabis plants, whether Ruderalis growing wild in Hungary with a 20-week Cambodian sativa, or North American ditchweed with the finest Hindu Kush, can reproduce. Much like humans, really!
Add to this the rapid growth rate and effective reproductive cycle, which can lead to two healthy harvests in one year in some climates, and we quickly see the generations passing – in each the potential for new mutations, and with almost limitless possibilities for what will be the new dominant strain or characteristic. The genome of Cannabis is currently being researched and mapped by more than one team, and distinct markers are now being discovered that show true genetic differences between many cultivars: for example, the University of Minnesota discovered in 2006 that hemp cultivars display DNA fingerprints notably different from marijuana strains.
This research may ultimately aid the cause for legalization of industrial hemp in the US, as it can be used to prove its THC-free nature. THC testing will not always show accurate results as THC production differs through the life cycle of the plant; whereas these tests can accurately show the potential for THC production throughout the life cycle of the plant.
With scientists only now beginning to perceive just how far the genetic iceberg extends below the tip we are now uncovering, it is difficult-to-impossible to ascertain why certain features in species came to be – geneticists can often see when characteristics began to emerge, but it is often unknown why they emerge in the first place, and in response to what. In an isolated population, strains that interbreed or self-replicate through hermaphroditism may breed true for certain characteristics while varying in others, or they may not breed true for any traits, but instead display what botanists call segregated or hybrid genes.
Usually, within a few generations of inbreeding, these segregate genes will be much less common and populations will rapidly begin to breed true for numerous traits and resemble each other more. It is an homage to the majesty of nature that we see this almost insatiable desire of the Cannabis plant to adapt to fit its environment expressed in the – now often threatened – landrace varieties that have sprung up across the planet after its introduction. Huge differences in coloration, from yellows through reds to purples and blues; height ranging from less than three feet to more than twenty; fragrances from spicy to earthy, from fruity to skunky; and thousands upon thousands of different combinations of cannabinoids are just some examples of just how varied a plant Cannabis really is.
As we have ourselves spread over the planet, we have taken the tools for survival with us: our weapons and tools, our foods and medicines, and our knowledge of how to use them. With Cannabis, in every new ecosystem we have introduced it to, we can see which characteristics best suit the local environment from our earliest attempts to cultivate, and can select accordingly. This helps to speed up the evolution of the plant. For example, in temperate and subtropical zones, it is the hemp varieties and those narcotic varieties that are short-day obligate (i.e. require fewer hours of light than darkness to trigger flowering) such as ruderalis and indica, that are most adapted to the climatic conditions.
In tropical areas, the long flowering period allows for greater production of THC, and therefore resinous sativa strains are more prevalent. We recognize this: we grow existing strains that match up as closely as possible, we select from the natural variation in progeny the offspring that are even closer to what we want (say, strong and woody with few lateral branches for fiber crops), and we breed new generations from them that are increasingly close to the ideal we seek. In doing so, we are part of a cycle that is hugely beneficial: to us, for obvious reasons; to the plant, as we are enabling more effective colonization; and to the ecosystem itself, as a plant well-adapted to its ecosystem will be more successful and develop a greater degree of integration with other member species.
This at least is the traditional pattern, although it remains to be seen what consequences lie ahead due to the trend for large-scale monoculture that is on the increase worldwide. Monoculture is rarely good for the environment, and it must be stressed wherever possible that small is beautiful when it comes to agriculture.
No matter how well-adapted a plant is to its surroundings, if biodiversity is lost the whole balance of the ecosystem becomes out of synch. Cannabis is unfairly labeled as a noxious weed by the USDA, and it would be terrible to see it become truly the case through the actions of money-hungry commercial growers. Where production is small-scale, with respect paid to the environment, Cannabis is truly a crop that has a place in every ecosystem.

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