Hi! I'm Tim Tyler, and this video addresses a common objection to memetics. The idea is that "survival of the fittest" being a circular tautology is a problem for memetics, because we lack a predictive theory of meme fitnesses.
One fairly common objection to memetics is that it is vulnerable to the idea that "survival of the fittest" is a tautology - since the fittest are defined as being those that survive - and that is a circular argument.
David S. Wilson makes this point in an article titled "Flying Over Uncharted Territory" - which was a review of Blackmore’s book The Meme Machine. He says:
The oft-repeated accusation that natural selection is a tautology fails because fitness is not defined in terms of whatever evolves but in terms of the properties that enable organisms to survive and reproduce in their environments. Moths that are colored to match their background have a high fitness with respect to bird predation, but cryptic coloration may not evolve if the appropriate mutations either do not arise or are lost by genetic drift. The ability to define fitness independently of what evolves saves the concept of natural selection from being a tautology. For the meme concept to escape the same problem, we must define cultural fitness independently of what evolves. If the first four notes of Beethoven's fifth is a powerful meme only because it is common, we have achieved no insight.
Serenely and Griffiths (1999 p.334) also voice this complaint, saying:
With the possible exception of scientific ideas, we have no explanation of the nature of the fitness of ideas, nor do we typically understand why they differ in fitness. We can call a tune "a meme with high replication potential" rather than "catchy" if we like. But without source laws, this adds nothing to our understanding of musical trends.
Maria Kronfeldner also gives this objection in her 300 page critique of memetics. In her summary (p.290) she writes:
Either the analogy is heuristically trivial, because it loses its main claim, namely that memetics presents an alternative to the traditional explanation, which is given in terms of properties and interests of humans, or the explanatory units of selection analogy is trivial in explanatory terms, because it is tautological – it does not explain anything, since it merely states that those memes that have a high actual survival are those memes that have a high propensity for survival, without explaining where this high fitness emerges from.
Massimo Pigliucci gave much the same objection in a recent podcast:
[Massimo Pigliucci speaks]
We do, in fact know some things about which memes are fitter than other ones. This area is part of what is often called "Applied Memetics" (an area which also includes memetic engineering). It seems to be one of the better studied areas of the field to me - simply because social media marketing and advertising departments need to be able to predict what spreads and what doesn't in order to be able to rapidly construct successful viral marketing media without the expense of doing a lot of testing. Popular writers and musicians know what people are likely to share. Scientists often have some idea about what scientific ideas are more likely to persist. Good editors know what will sell and what will not. Military propaganda creators know which rumors are most likely to spread. Often meme fitness variations are obvious - for example, if you put "Lady Gaga" in the title of a video you create, it is likely to be viewed more than if you use "Joe Bloggs" instead. However, the area of what makes ideas spread has also been studied by social scientists.
Francis Heylighen's 1998 paper "What makes a meme successful? Selection criteria for cultural evolution" gives an early introduction to the field - breaking the meme lifecycle down into assimilation, retention, expression and transmission and observing that successful memes need strengths in each area. More recently, there have been many studies of social media on the internet that look into why memes spread. For instance see, Dan Zarella's "The Science of ReTweets" or his "The 8 Elements of Contagious Ideas".
Of course we don't know everything about this field, but it is often a challenge to determine the fitness of genes without testing them in organic ecology too.
Even if it was true that social scientists were totally clueless about what spreads and what does not - which is far from the case - then the correct attitude would not be to declare the whole enterprise of predicting meme fitnesses to be hopeless, but rather to actually do some field work - and figure out the factors that make some ideas spread while other ones do not.
The objection that "survival of the fittest" is a tautology is exactly as much of a fallacy in memetic evolution as it is in organic evolution for exactly the same reasons.
Enjoy,
The rest of Massimo Pigliucci's critical comments are here.
memetics seems completely tautological, unable to explain why a meme spreads except by asserting, post-facto, that it had qualities enabling it to spread. One might as well say that aspirin relieves pain because of its pain-relieving properties. The most interesting question — why some memes spread and not others — is completely neglected. Why did Christianity take hold during the waning days of the Roman Empire? You won’t find the answer,or any way to attain it, in memetics. (This, by the way, makes memetics utterly unlike biological evolution. The spread of genes through natural selection is not tautological because one can predict their fate through their known effects on replication and the reproduction of their carriers.)
First, and most important, memetics has usually very little explanatory power. Too often, memetic explanations boil down to the uninformative claim that a given meme has spread in a population because it has reproduced itself successfully. The essential issue, What makes it the case that a cultural variant is preferentially transmitted?, is often dodged, or, when it is not, is addressed with sheer speculation.
There are now some nice books on the topic of why some ideas spread, while others do not:
Hi! I'm Tim Tyler and this is a video about the internalism vs externalism controversy in memetics.
One controversial issue in memetics since its early days concerns whether memes can be usefully said to be embodied in images, videos, and texts, or whether memes are things that only exist inside human minds. I cover this controversy in my book on memetics, which is now available. This video is intended to give subscribers a taste of the topic.
The controversy started in 1982 with Richard Dawkins (1982, p 109) doing a bit of an about-turn from his earlier definition of a meme as a unit of cultural inheritance - saying:
A meme should be regarded as a unit of information residing in a brain
Dawkins also said that he was insufficiently clear about distinguishing memotypes from phemotypes, and cited Cloak's conception from 1975 of i-culture and m-culture as the correct way to think about things. Dawkins held a similar view years later in the year 2000, when he said:
Well if the analogy with genes is right, there ought to be something equivalent to DNA, and that something I presume would be material in the brain. So when I pass an idea on to you, or when you pass an idea on to somebody else, something in your brain gets reproduced in that other person’s brain.
This position became known as "internalism". It is frequently contrasted with "externalism" - which holds that it is perfectly OK to talk about videos, images and texts as containing memes.
Internalism subsequently gained many supporters. Richard Brodie wrote:
A meme is a unit of information in a mind whose existence influences events such that more copies of itself get created in other minds.
Aaron Lynch defined memes as being a type of memory. Nick Rose praised internalism in his "Controversies in Meme Theory". Robert Aunger wrote a book called "The Electric Meme" about attemts to pin memes onto mental structures. In that book he wrote:
If memes could exist in brains, in speech and in artifacts, they would be the superheros of the replicator world, able to transform themselves into any shape or form at will, like the Proteus of Greek mythology. Instead, memes must be confined to one physical substrate, just as their brethren, the biological replicators genes and prions, are. I thus argue that only one substrate can be associated with memes.
However, many experts on memetics came out against internalism. Dennett is an externalist - writing in 2000:
I think the case is still overwhelming for defining memes abstractly, in terms of information
Blackmore is an externalist - writing in 2001:
We do a disservice to the basic concept of the meme if we try to restrict it to information residing only inside people’s heads - as well as landing ourselves in all sorts of further confusions. For this reason I agree with Dennett, Wilkins, Durham and Dawkins A, who do not restrict memes to being inside brains.
Derek Gatherer famously made a plea for memes to be measurable things - and not to tuck them away inside brains where they would be challenging to gain access to experimentally.
However, internalism is still alive and kicking today. A recent comment on an earlier video of mine eloquently complained:
Memes cannot expand to inanimate objects (like clay tablets) the same reason genes cannot expand to eyes, claws, fur,? etc... The clay tablet is a manifestation of memes, the same way the claw is a phenotype... I keep hearing this non-sense about the expansion of memes to computer hard-drives and so on, and it annoys me because it's simply illogical if you follow the genotype-memotype, phenotype-meme manifestation analogy.
The internalism/externalism debate has been mostly ignored in academia - since most academics are approaching the subject from a population-memetics angle - where heritable traits are the focus and the mechanisms of heredity are an implementation detail. However, internalism also appears to be still alive among academic students of cultural evolution. For example, in his recent book on cultural evolution, Alex Mesoudi, wrote:
The ideational definition of culture given in chapter 1 implies that the cultural equivalent of the genotype is the information stored in people's brains that represents their beliefs, attitudes, values, skills, knowledge, and so on. The cultural equivalent of the phenotype is the expression of that information in the form of behaviour, speech and artefacts.
Mesoudi goes on to explain how this makes cultural evolution Lamarckian.
Can we perhaps explain the extended persistence of internalism and externalism as representing two different perspectives on the same subject matter, each with their own strengths and weaknesses? I don't think so. Internalism just totally sucks. I think it persists because it is an intuitive and attractive approach which people adopt before they have properly thought things through.
Internalism introduces a bizarre system of inheritance which destroys germ-line continuity, and introduces a Lamarckian aspect to inheritance in which phenotypes recreate genotypes in each generation.
Also, internalism typically attempts to localise memes inside brains. However, brains are not the only repository of memes these days - memes also survive and are copied by computer systems. If you look at the latest music albums, you will see that they are widely copied on peer-to-peer networks, and that they undergo occasional corruption during transmission. However, what is actually copied is a bit pattern inside computers. This bit pattern makes it into human brains only as a pale shadow that is rarely actually copied from. The computer networks handle the actual information that is copied. With the transmission of much modern music, human brains never have most of the information that is actually copied around inside them in the first place - they actually contain part of the meme's phemotype - not its memotype.
Internalists sometimes recognise that one day there will be intelligent machines with thier own societies and cultural transmission, but they rarely seem to understand how much culture is copied, filtered and transmitted by machines - even today.
Computers storing, copying and expressing memes totally destroys the internalist dream of memes having only one substrate associated with them, with only one memetic code. There are in fact, hundreds of substrates for memes, with hundreds of memetic codes. That is exactly what the externalists have been saying all along - which brings us onto the topic of externalism.
By contrast with internalism, externalism is simple, beautiful and neat. It is based on an information theoretic version of genetics, according to which inherited information is the genotype, and everything that depeds on that is the phenotype. The heritable information can be represented in practically any physical medium - a simple consequence of information portability. From this perspective, memes can exist on CDs, hard drives, paper, film and clay tablets. When people describe videos and images as being memes, they are not making a daft category error - those things really do contain memes.
Externalism features germ-line continuity. It doesn't have a crazy Lamarckian stage in which phenotypes generate genotypes in each generation. Instead there is ordinary Weismannian inheritance where memes are copied to create more memes - just as genes are copied to create more genes in DNA evolution. That is not to say that memetic evolution is not Lamarckian at all - but that is another story which I am not going to get into here.
For me, internalism represents a common misunderstanding of memetic evolution works. Internalists entertain the idea that memetic inheritance features a bizarre Lamarckian inheritance paradigm in each generation. This makes people think that memetic evolution works in a manner that is wildly different from the way in which organic evolution operates. This hinders people's understanding of the depth of the relationship between the cultural and organic realms, preventing them from effectively reusing their knowledge of organic evolution in the cultural realm.
At this stage, I think internalism offers so little in the way of benefits, and causes so much confusion, that it should just curl up and die. I identify it here as a failed doctrine. It causes serious confusion when dealing with memes inside computers and serious confusion when considering the issue of Lamarckian inheritance of memes. Internalism's claimed benefits - of a single memetic storage medium and a single memetic code - are not benefits at all - but rather are misleading falsehoods. Death to internalism!
Hi! I'm Tim Tyler and this is a video about some of the domains within biology to which evolutionary theory can be applied.
Evolution is a powerful theory with a broad range of applications to biological systems. For some reason, the application of evolutionary theory to many of these domains is widely unappreciated. So, this video contains a brief primer, to help interested parties get up to speed with some of the basic applications of evolutionary theory.
Evolutionary theory applies most directly to systems which involve copying. Essentially that means biology, since biology is the science of life, and life is that which persists via copying. Biological evolution is the domain of evolutionary theory which people tend to be most familar with. It typically deals with the evolution of plants, animals, fungi and microorganisms over millions of years. This is an umbrella category, which includes all the other processes discussed here. However, within biology, there are many sub-processes which have their own evolutionary dynamics - and those are what we will be looking at here. The approach taken in this video may be reminiscent to readers of the material in Gary Cziko's book "Without Miracles - Universal Selection Theory and the Second Darwinian Revolution". Seven of the main areas within biology which can be usefully be modelled by evolutionary theory are:
Immunology
Ontogeny
Neurobiology
Psychology
Memetics
Cybernetics
We will briefly cover each of these in turn - starting with the simplest area to understand:
Immunological evolution - In order to deal with rapidly evolving parasites, vertebrates employ an adaptive immune system which works using the principles of evolutionary theory. This uses a process known as somatic hypermutation to rapidly generate adaptive variants. It employs genetic recombination to allow a small number of genes to generate a large number of different antigen receptors which are expressed on the surfece of lymphocytes. Lymphocytes are then tested and successful ones are bred from. Lymphocytes can also produce memory cells that mediate long-term immunity. The result is a minature evolutionary process within the organism that helps it to adapt in response to rapidly-changing parasites. To most people, this is similar to the type of evolution they are familiar with - except that mutations are performed deliberately, and since there are mechanisms for actively making them, they are more likely to be somewhat biased towards being adaptive.
Ontogenetic evolution - In multicellular creatures, development is an adaptive evolutionary process. Tree roots grow around rocks, their trunks grow around obstacles and their branches seek out holes in the canopy. If you have pulled plants out of pots, you will see that there is often an adaptive fit between the roots and their containers. However the evolutionary dynamics underlying this kind of adaptation during development often remain unappreciated. It is obvious that development involves copying on a cellular level. However, evolution requires variation - and since all the cells are clones of each other what is not always clear is where variation comes in. However, if you look at the cell phenotypes, it is obvious that some kind of variation is coming from somewhere - since liver cells look totally different from muscle spindle cells, which look totally different from neurons. The variation arises not in the DNA of the cells involved, but rather from their environment and it persists via a form of environmental inheritance. This inheritance includes location, chemical concentartions, cell neighbours and other local feaures. To give an example of how such processes work, consider the evolution of plant root tips. Plant roots have identifiable tips. The tips divide, which represents a form of reproduction for them. The offspring tips inherit their physical location from their parent - and this location varies from tip to tip. Location represents the main form of evolving heritable information in this system. The plant allocates more resources to root tips in locations with moisture and yielding soil, and withdraws resources from those tips in locations that are too dry or rocky. Those resources are then used to fuel root tip reproduction - resulting in differental reproductive success of root tips, and root tip evolution. This generates an adaptive fit to the environment in which the roots find themselves.
Neurobiological evolution - Brains exhibit several interesting forms of evolution as they are used. Copying processes are ubiquitous in the brain. Since axons branch liberally any signal sent down them is copied many times - there is also variation and differential reproductive success of these signals. This results in neural spike train evolution. Also both axons and dentrites have a dynamic branching tree-like structure. The argument I gave explaining why plant roots evolve also applies to growing neurite tips. Neurons and glial cells also reproduce and undergo selection - as is documented in a book called "Neural Darwinism". There are other forms of low-level competition in the mind as well: axon tips compete for attachment points, synapses compete for neurotransmitters, and so on.
Psychological evolution At a higher level in the mind a virtual world is implemented - containing thoughts, ideas and memories. In this virtual world more copying, variation and differental reproductive success takes place. Copying takes place when memories are recalled - since this adds a memory of recalling the original memory. Copying takes place when actions are repeated or when they are rehearsed. Ideas and action plans are also copied. Lastly the mind contains a model of the world which is used to make predictions about the future. The elements that make up this model also evolve. Psychological evolution, can feature directed mutations and intelligent design. The psychologist, B. F. Skinner was among those how appreciated the evolutionary side of mental development. He wedded his theory of learning to Darwin's theory of evolution, and talked about the "extinction" of learned behaviours.
Memetic evolution - Memes also evolve over time in social spaces - resulting in social and cultural evolution. Like psychological evolution, memetic evolution features directed mutations and intelligent design. I discuss memetic evolution in a lot more depth in my book on Memetics - which is now available. Memetic evolution has snowballed, producing accumulating innovation and technological progress - which is in the process of leading towards...
Cybernetic evolution - Machines evolve too. Today machines mostly coevolve relatively slowly with humans - but the evolution of computer viruses, genetic algorithms and memetic algorithms gives us a taste of what future cybernetic evolution is likely to hold, once humans get eliminated from the innovation loop.
These, then, are seven different domains within biology to which evolutionary theory applies. Together they illustrate some of the breadth of the systems to which evolutionary theory can usefully be applied.
Hi! I'm Tim Tyler and this is a video about the virtues of adopting a meme's eye view of cultural change.
It wasn't until the 1970s - long after Darwin's discovery of evolutionary theory - that biologists started to become accustomed to the idea that it was useful to look at evolutionary change from the perspective of individual genes.
The idea is often attributed to William Hamilton. Richard Dawkins helped to popularise the concept in his 1976 book The Selfish Gene.
It is not obvious that it can be useful to think of genes as being selfish agents which have a point of view. Indeed, at first, the idea was much misunderstood, with the very idea that genes might have a perspective or be selfish being mocked by those who didn't understand it. However, these days the validity of the gene's eye view is really taken for granted by most evolutionary biologists.
In a nutshell, the idea is that genes can usefully be thought of as agents who are concerned with their own reproductive success. They behave as if they want to become ancestors, and adopt structures which facilitate this.
There are a couple of different perspectives which help to explain how and why this is useful.
One is game theory. It is possible to view the evolutionary process as a type of competition between the heritable elements that underlie different morphologies and strategies. The most successful genes are defined as being those that leave the most descendants. The common result is the appearance of design without a designer. This explains how genes come to adopt forms which help them to survive. It allows us to "cash-out" talk of genes as agents with goals, desires and a perspective in more conventional causal language that drains all the teleology and agency out.
The other perspective has to do with human psychology. Human beings have built-in mental apparatus that helps us to understand the behavior of other agent-like systems - by a process involving mentally putting ourselves in the other agent's shoes. Humans use a built-in model of themselves as the basis for this type of identification process. This system underlies both empathy and our imitation capabilities. The whole system is sufficiently flexible to allow for identification with agents with different goals, abilities and aptitudes. It is possible to identify with dogs, rodents and invertebrates - and doing so allows the brain to better make use of its architectural features to predict the behavior of such systems. Interestingly, the same architecture is even useful for inanimate systems - if they have goal-directed nature or represent an optimisation process. So, for example, it is possible to imagine yourself as a ball rolling down a hill, and imagine the path that you might take. The fact that evolution is an optimisation process is what allows this technique to do useful work in the case of genes. Genes do not literally have goals - but they behave as though they want to reproduce themselves. This allows a goal-directed model to do useful work, which in turn allows human built-in mental apparatus to model these as goal-directed systems, thereby helping us to attain insights into the operation of genes by making efficient use of the strengths of our own minds.
This then brings us to the meme's eye view. Just as the gene's eye view is useful, so the meme's eye view is useful. This has long been appreciated by students of memetics - and there the memes eye view goes back over 20 years - at least to Dennett's 1990 paper "Memes and the Exploitation of Imagination". However, students of cultural evolution in academia appear to have paid insufficient attention to the work of the memeticists in this area, and are still mostly attempting to struggle along without this important idea. One rare exception to this is Stephen Shennan - who publicly called for the meme's eye view to be more widely embraced in his presentation in the 2010 "Culture Evolves" conference.
The meme's eye view conjours up a picture of memes attempting to manipulate their environment for their own advantage.
For example, a sociobiologist looking at a modern office a might see humans using machines for their own advantage. However the meme's eye view suggests another perspective. In a mutualist symbiosis, each party typically attempts to control and manipulate the other. So: the memes are also manipulating the humans into creating more memes, and are often in competition with other memes which are striving to make use of the same human resources.
For another example consider mobile phones. The typical sociobiology perspective pictures humans using phones to promote their own ends, with the employees and bosses at the phone company using the technology to promote their own ends. The meme's eye view of this set-up looks rather different: the memes are using the human bodies of the users as sophisticated data-capturing devices and world manipulators. Giving on-screen instructions to humans allows the memes to take advantage of sophisticated actuators made using molecular nanotechnology, while cameras, microphones and keyboards allow for data input. The data is then fed to a server-side computer system, which acts like a large and sophisticated brain which manages the entire set-up. The whole system is arranged so as to promote and perpetuate the mobile phone company's memes - at the expense of the memes of its competitors.
Looking back at the timeline of human evolution, one of the first objectives for the memes would have been to make room for themselves in human brains. They did this by rewarding the humans with more space for memes with increased genetic fitness. Memes for language, music and fashion were probably mainly responsible for this. The result was 3 million years of steadily-expanding cranial capacity - which resulted in much more space for the memes.
Meme reproduction requires sociable humans - so those humans who interacted more with other humans would have been rewarded by the memes. The result of this was human ultrasociality.
Humans and their memes then developed spoken language - an adaptation which can be used for spreading memes. They also developed a taste for group chanting - which allows meme transmission with redundancy and error correction.
Next the memes increased human numbers - since the more humans there are, the more memes there are. Agricultural memes allowed humans to form closer symbiotic relationships with plants, animals and each other, which boosted their fitness and increased their numbers. The result was a massive increase in the worldwide population of memes.
The next problem for the memes was transmission fidelity. At this early stage, most memes were copied by using behavioural imitation - which provides very little in the way of copying fidelity. Environmental inheritance proved to be the answer here. By inventing the idea of writing memes could persist unaltered across extended periods of time.
Then there was the copying speed problem. Transcribing documents by hand was slow and tedious. However, the invention of mechanical printing presses allowed machines to take over this task from humans, resulting in much more rapid meme production and a vastly wider distribution of memes.
Today, many memes often still need the consent of a human brain to get copied - an obvious bottleneck from their perspective. The afflicted memes are currently busy sorting this issue out. Today, only a few parasitic computer viruses manage to reproduce themselves while skipping over the human brain completely. However, in the future, superintelligent machines seem likely to copy memes with the full consent of society.
To close, I would like to propose the meme's eye view as one obvious landmark to use for gauging the progress of academics in developing their understanding of cultural evolution. Academic study of cultural evolution has now fairly-clearly made it past the "Darwin" stage and the "Fisher" stage. However, it still appears to be somewhere around a hundred years behind the study of organic evolution. Since cultural evolution seems unlikely to produce a Mendel, or a Watson and Crick any time soon, the question arises of how best to measure the progress of academia in its understanding how culture evolves. The meme's eye view seems to provide a fairly suitable yardstick. At the moment, the penetration of the meme's eye view in academia is fairly clearly at an extremely low level. I think that places academia somewhere before the state of evolutionary theory in the 1970s. This metric suggests that academics still have a considerable way to go in developing their understanding of how culture evolves.
There's more about the meme's eye view in my "Memetics" book - which is available now.
Enjoy,
Update 2012-03-26: Here is what seems to be the meme's eye view a little earlier than 1990 - in Luc Claeys' 1989's book "Behavior of Information". Chapter 1 says:
Chapter 1 Living Information - To understand the theory of the behavior of information, we have to place ourselves on the point of view of information itself. To facilitate the transition from our classical "self-centered" point of view to this new point of view, this chapter will show some analogies between the life of information and the life of some living species we all know about.
Chapter 2 Information beings - The next step towards the point of view of information is to imagine that there is some consciousness associated with information. In other words, the life, the propagation and the survival of information is related to a desire to live, a desire to survive.
Chapters 5-14 (pages 48-120) are browsable - which is a fairly significant chunk of the book. Much of the rest of the text of the book can be searched.
The pictures came through in colour. However, I can't say I approve of them missing off the covers of the book.
Matt Ridley discusses cultural evolution and the origins of modern humans, and how cultural evolution leads and DNA genes follow.
He gives the example of blue eyes, claiming it was a consequence of agriculture, followed by the colonisation of northern Europe. That seems plausible to me.
Matt is asked a question about memetics 58 minutes in, and he generally expresses his approval - saying:
Q: I was wondering how a theory of memetics maps on your account?
A: Yeah, um, good question: how does the theory of memetics map on to my ideas and the meme theory that ideas behave like genes in that they replicate - essentially remember I ran through a series of slides of things that you need to find for an evolutionary system to work - memetics is concentrating on that "replictoion" slide - where I showed a picture of aeroplanes on an assembly line - memetics is talking about whether ideas replicate and copy themselves, etc, and it's therefore part of the story - but I'm focussing on the other parts of the story, at least particularly the "recombination" part. It's another analogy for a genetic evolutionary process - which is all part of the story - so it's a different emphasis - it's a different side of the same coin.
In fact, memetic recombination is surely part of memetics, in exactly the same way that genetic recombination is part of genetics.
Matt wrote a whole book on cultural evolution recently. There's a lot of "ideas having sex" - but memes are only mentioned on one page. That was a spectacularly disappointing turn-out.
What about Matt's ideas about cultural recombination (starting around 22 minutes into the video)? Memetic recombination is probably ancient - predating the split with chimpanzees. For example, this video 27 minutes in, apparently shows a combination of chimpanzee ideas. They barter too a little - but they don't really have many artefacts to barter. So yes, recombination may well be important - but we are probably just talking about a cultural snowball that eventually got big enough to start picking up speed on its own. If you want an event to pin the birth of the recent human explosion on, the end of the last glacial cycle looks as though it is the most obvious candidate.
The other thing to say is that trade is not really the same thing as memetic recombination. Trade might well increase the rate of memetic recombination - but they aren't the same thing. I gave some examples of memetic recombination in my own book on memetics. My examples were "portmanteaus" - like:
cyborg - comes from cybernetic and organism;
ginormous - comes from gigantic and enormous;
Why doesn't trade qualify? Trade is more like two ecosystems exchanging organisms. That does "recombine" things - in a sense - but we don't usually describe moving creatures around between ecosystems as being a form of sexual recombination. IMO, memetic recombination ought to cleave functional units - at least sometimes - or it isn't really playing the same functional role that recombination plays in the organic realm.
Lastly, it is worth noting that recombination within minds doesn't discriminate between ideas that are the product of individual learning and social learning. Individually-learned ideas can recombine - and that has nothing to do with trade, or socially-transmitted memes.
Now that cultural evolution is making such good progress in academia, can memeticists just leap onboard?
I don't think so - not just yet, anyway. Apart from the whole issue of long-winded terminology, although these are very similar theories, they have a different emphasis and history - and memetics is still much, much better in some areas. The approaches obviously need to fuse - but at the moment they still have some significant incompatibilities.
Alex Mesoudi - in his recent book - has a soundbite which encapsulates one of the differences in the approaches of academic researchers in cultural evolution and memetics.
Mesoudi says:
In a typical cultural evolution model, a population is assumed to be composed of a set of individuals, each of whom posseses a particular set of cultural traits. A set of microevolutionary processes is specified that changes the variation of those traits over time.
I can verify that this is a pretty accurate description of what most cultural evolution models in academia are like.
By contrast in memetics, there are organic creatures and cultural creatures - two interwoven lifecycles to consider. These typically play the role of host and endosymbiont. The endosymbionts are usually parasites, or mutualists. All the standard models of symbiosis in biology are thus applicable to the cultural realm, and can simply be imported.
On page 7 of Culture and the Evolutionary Process, Boyd and Richerson give what appears to be an argument against such cultural creatures. They say:
This does not mean that cultures have mysterious lives of their own that cause them to evolve independently of the individuals of which they are composed. As in the case of genetic evolution, individuals are the primary locus of the evolutionary forces that cause cultural evolution and in modelling cultural evolution we will focus on observable events in the lives of individuals.
This seems to be fundamentally the wrong approach. It is like saying: to study the evolution of AIDS, we should focus on on observable events in the lives of the AIDS sufferers. Yes, that method will result in some progress - but it is a fundamentally misguided approach - because it ignores the HIV virus itself.
I have looked at a lot of the literature and I don't think this is just a case of model simplification to produce something tractable. Cultural evolution researchers have a real blind spot when it comes to cultural creatures - although they do sometimes receive an occasional mention - usually as an "analogy". I give some examples of this in my book.
A more correct and complete model would include cultural creatures and organic creatures in a symbiosis. The cultural creatures do evolve outside of their organic hosts. Books get burned. CDs get scratched, hard disc drives crash, and computers filter and process memes. Yes, you can attempt to model these as "microevolutionary transmission processes" - but that produces nasty complexity - it is much better and much simpler to just recognise cultureal avolution as dominated by symbiosis - and then reuse existing symbiosis-based models.
OK - so cultural creatures may sound like something out of science fiction - but they are essential for understanding human culture. These things have genotypes, phenotypes, and their own lifecycles - it is just obvious that they are best treated as symbionts - if you stop and think about it for a moment or two.
Due to only attempting to model half of the creatures in the relationship, cultural evolution in academia has become a feeble and dumbed-down version of memetics - which got this right from the very beginning. The academic researchers involved apparently need to pull their socks up in this area - before they go very much further.
My "Memetics" book has shown up on 
Matt Ridley discusses cultural evolution and the origins of modern humans, and how cultural evolution leads and DNA genes follow.
Now that cultural evolution is making such good progress in academia, can memeticists just leap onboard?
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