Sunday, 23 October 2016

Dawkins 2015 WSJ interview on memes

Dawkins interviewed by WSJ in 2015. It is four minutes long. Memes are the topic.

Wednesday, 19 October 2016

Metamorphosis: the symbiosis hypothesis

Symbiology is a core concept in cultural evolution. Cultural creatures act as though they are parasites, mutualists or commensals with their human hosts. This is fundamental to understanding the dynamics of their evolution. That's all about cultural evolution for this post - the rest is all about symbiology.

As part of my interest in symbiology I have recently explored the controversial work of Don Williamson on the origins of larvae. Williamson has promoted the idea of radical hybridization being involved in the origins of caterpillars into butterflies - and many other larval forms. For example here is his paper, Caterpillars evolved from onychophorans by hybridogenesis. Basically, Williamson claims that ancestors of modern butterflies may have had their eggs fertilized with sperm from velvet worms. Williamson's work has been widely ridiculed and castigated.

Like many students of symbiosis I am attracted to the possibility of biological metamorphosis arising as a result of fusion between widely separated forms. However, I think that there are more possible mechanisms than radical inter-species hybridization.

I have long thought that another possibility for the evolution of biological metamorphosis involves extended symbiosis. This idea shares the idea that larvae and adults started out as individuals members of separate species - but doesn't depend on the viability of radical hybrids. In an extended close symbiosis, parties can transfer genes gradually - via viruses or sperm-mediated gene transfer. They can also assimilate their partner's traits gradually through learning and ordinary natural selection. Radical hybrids are not needed in this kind of scenario - instead evolutionary assimilation can be gradual.

This symbiosis-based theory seems like a clear possibility to me. It holds that at one stage a wasp-like creature planted eggs in a caterpillar-like creature. These parties developed a close relationship and coevolved until one party assimilated the other. Their mutual descendants are caterpillars into butterflies. It is fairly well known that symbiosis promotes horizontal gene transfer. Mutualism, or at least mutual dependence, probably increases its likelihood.

The symbiosis hypothesis would be boosted by discoveries of wasps that have evolved mutualisms with their egg incubators. Wasps are commonly parasites and their incubators are destroyed my multiple wasps during wasp reproduction. However if a relationship develops in which one wasp hatches from one worm, the situation starts to look a bit more like the caterpillar into butterfly metamorphosis scenario. Such cases are in fact known - for example, see here for an example involving a single wasp egg per incubator. Exactly how parasitism might turn into mutualism in this case is not obvious - but there are plenty of other cases where parasites have evolved into benign partners and then into obligate mutualists.

Like Williamson's idea this theory would be boosted by genetic evidence which supported gene transfer. However, since it is not obvious what the ancestral species were, such evidence may remian elusive. The theory doesn't depend on such evidence existing - maybe no gene transfer was involved and one partner assimilated the other one via learning and natural selection. That makes the theory harder to refute - which is not normally considered a virtue among scientists. However, I think we need an alternative to radical hybridization that preserves the idea of separate origins - which itself is strongly suggested by the phenomenon of metamorphosis, according to multiple lines of evidence.

References

Monday, 3 October 2016

The significance of symbiosis in evolutionary theory

Before the discovery of the importance of symbiosis, evolutionary theory worked with a few fundamental operations - prominently including splitting and mutation. The history of life was viewed as a branching tree with branches diverging, but not converging again, at least not once they had fully divided. Life had an associated family tree.

Symbiosis represented a significant revolution in evolutionary theory because it introduced a new operation into the fundamentals of evolutionary theory: merging or joining. If splitting looks like this:

-> ->

...then joining looks like the time-reversed operation - like this:

-> ->

Before the 1900s, merging and joining operations were not completely foreign to evolutionary theory. The fusion of male and female gametes was a find of merging operation, though one that was confined by species boundaries. It was also known that some creatures lived inside other ones - such as gut bacteria - and that parasites regularly forged new associations with their hosts. However such intimate relationships were not widely thought to involve permanent fusion between previously unrelated organisms. Instead they were mere ecological associations.

The pioneers of symbiosis were mostly Russian. Though they discovered symbiosis early in the 20th century, their theories were ignored in the west until the 1960s, when it was discovered that mitochondria contained their own DNA lineages. Over the next 30 years, evidence accumulated that unrelated organisms could fuse together permanently, generating new kinds of recombination operation distinct from sex. Gaining or losing symbionts could be profound and dramatic evolutionary events - sometimes triggering speciation. The phenomenon was not confined to bacteria, but affected organisms of all sizes. We now know that eucaryotic cells are unions of many free living ancestors, that viruses carry DNA between all kinds of different species, and that around 10% of the human genome shows signs of origins outside our own species. Horizontal gene transfer has turned the tree of life into a web. Multi-cellular organisms are now widely viewed as being menageries.

In modern times, the evolutionary significance of symbiotic unions is familiar to us, so it is sometimes hard to appreciate the scale of the revolution the idea represented, and the resistance that it faced at the time. Evolution was generally though of as being gradual - yet in symbiogenesis, entire genomes could join forces in an evolutionary instant. This idea violated established dogma and was widely rejected and ridiculed for over 50 years. An avalanche of facts and data eventually vindicated the idea. At the time, this was the the biggest revolution in evolutionary theory since Darwin - eclipsing the discovery of DNA, kin selection and Mendelian inheritance, in my humble opinion.

In cultural evolution, the story went rather differently. In 1975, Ted Cloak pioneered a symbiosis-based version of cultural evolution, in which human hosts cultivated cultural symbionts inside their brains. Richard Dawkins went on to popularize the idea in the 1976 book The Selfish Gene. These cultural "memes" were sometimes characterized as being "viruses of the mind". However, in academia, symbiosis was very slow to catch on. Many academics didn't seem to cotton on to the fundamental concept of a cultural organism - instead opting to model culture as an aspect of the host's phenotype. This was a bit like modeling smallpox without the concept of the smallpox virus - and instead talking about horizontal and oblique transmission of the smallpox rash phenotype. Many of the researchers in the field are still laboring under the resulting hangover. Symbiosis enthusiasts were one tribe of biologists and cultural evolution enthusiasts were another. The intersection included Ted Cloak, Richard Dawkins and Ben Cullen - but only a few others. What this meant in practice was that concepts such as parasitism, mutualism, domestication, parental care and arms races tended to get neglected by most students of cultural evolution.

The slow uptake of symbiology among cultural evolution researchers is an aspect of cultural evolution's scientific lag. Most anthropologists long ago demonized evolution and expelled it from their halls as a dastardly idea that they wanted nothing to do with. The important topic of cultural evolution subsequently suffered from lack of attention and funding - and progress has been slow as a result. It wasn't until the 1980s that symbiology gained acceptance among mainstream evolutionary biologists. There's clearly still a long way to go before most students of cultural evolution start applying the idea properly.