Mystery Rays from Outer Space

Meddling with things mankind is not meant to understand. Also, pictures of my kids

July 19th, 2015

Definitions of “evolution”

The question on Quora was: Can someone, preferably a biologist, give me a contemporary definition of evolution, as it appears to change so greatly among scientists, particularly when evolution is challenged?

My answer was:

A trait of non-scientists is that they get frantically obsessed with definitions, rather than reality.  In fact, they tend to confuse definitions with reality, as if words had some magical power over the world.

We see this on Quora with the constantly repeated questions about “What is a species?” and “Is a virus alive?” — questions that are almost entirely pointless scientifically.  A species is whatever you want to call a species; that doesn’t change what’s out there.  A virus is whatever it is; it doesn’t change when someone tries to squeeze a word into it.

It’s a mark of someone who doesn’t actually understand science that they want definitions — perhaps because they think that words have power, and gives them control over the world.

Scientists aren’t completely indifferent to definitions, but mainly because it lets them talk amongst themselves.  Scientists don’t give a shit that there are twenty or thirty definitions of “species”, some of which are mutually exclusive.  They can natter about whether a virus is alive or not (so I’m told; I’ve never heard any virologist actually ask the question, myself), but it would never occur to them to do anything differently because of the definition.

The only real definition of “evolution” is a map with a scale of 1:1.  Evolution is what evolution is.  Trying to define it is a parlor game, like coming up with names for collectives of animals.  It’s great to know that a group of crows is a “murder”, but it doesn’t change a damn thing about the crow.  It might make you feel better to decide that evolution is a change in the frequency of alleles among a population, but it doesn’t change a damn thing about the population.

A definition of “automobile” is “a passenger vehicle designed for operation on ordinary roads and typically having four wheels and a gasoline or diesel internal-combustion engine.” Another definition is “a vehicle used for carrying passengers on streets and roads“.  Exactly how much time do you think the nice people at Ford or Mercedes spend thinking about these definitions? How much difference do these definitions make to their work? Both of these definitions seem to exclude off-road vehicles; do you think the management of Chrysler finds this worrisome, and holds regular meetings to bring their Jeep division into line? Because that’s just about the level of importance that scientists put on definitions of “evolution”.

If you’ve been confused about definitions of evolution, this is probably why – you’re asking scientists to play parlor games that they don’t really care about.  If you’re trying to understand evolution with a tidy, succinct definition, it’s proof that you don’t understand anything about evolution to start with.

In a response to a comment, I added:

I think you’ve put your finger on why people want definitions for evolution: “For legal purposes, for instance”.

Notoriously, “for legal purposes” is pretty much the opposite of looking for reality; when you start talking about “legal purposes”, you’re talking about ways to subvert the truth, to evade or distort the truth for your own purposes.

The people who insist on getting definitions for evolution aren’t trying to understand it; they’re looking for ways to pretend they don’t understand it, to use weasel words and bafflegab to try to make truth look false, to distort, to get as close as they can to outright lying as they can while being able to pretend they’re not really lying.

If you want to go and sue evolution, then definitions are about your only hope.  If you’re actually trying to understand evolution, definitions have pretty much no interest for you.

The legal department at Crysler may well be deeply interested in the definition of “automobile.  Meanwhile, down in the engineering department, the people who are actually contributing to the world instead of trying to distort and profit from it aren’t interested at all.

Thanks for the clarifying insight.

July 8th, 2015

Multicellularity

The question on Quora was  Could multicellularity be evolved in a lab in a relatively short time? If yes, has it been done?

My answer was in two parts, which I’ll merge here:

Sort of.  This study (Experimental evolution of multicellularity) selected yeast cells in the lab for a form of multicellularity in about 2 months. It’s debatable whether this is “true” multicellularity, where the cells become specialized (though there was some specialization observed: “With more generations, this form of reproduction began to include specialized cell behavior“).   Still, it was just two months.

There’s a nice explanation of the experiments here: Researchers evolve a multicellular yeast in the lab in 2 months.

This suggests that multicellularity might actually be fairly easy to evolve, and I recently learned about another line of evidence for the same thing.

In Episode 16 of Palaeocast podcastsDr Bettina Schirrmeister – University of Bristol explained “Multicellularity in cyanobacteria”. The interesting point I hadn’t heard before is that it seems pretty clear that not only are many cyanobacteria multicellular, the trait has evolved independently many times.

My intuition said that it would be rather hard to evolve multicellularity, but both experimental and real-world evidence suggest that my intuition was wrong.

 

July 6th, 2015

Evolution of virulence

A lot of people believe that, as a pathogen adapts to a new host, it will reduce its virulence.  Usually people phrase this something like, “The virus doesn’t want to kill off all its hosts.” More sophisticated people might say something similar in less teleogenic terms, like John Timmer:  “Typically, viruses that rapidly kill their host have a very short history, as they rapidly run out of places to reproduce“. [1]

Sometimes this does happen, as with spumaviruses. [2] Sometimes it sort of but not really happens, as with myxomaviruses. [3]  (Myxoma viruses are a poster child for the reduced-virulence theory, because early after their introduction into Australian rabbits, myxomavirus virulence did rapidly drop.  But the virulence dropped from over 99% to “just” 70% mortality — higher than Ebola or smallpox — and stayed at that level for decades.) And sometimes, viruses evolve to increased virulence.

In the example of evolution to increasing viral virulence that I’ve usually used,  the details are a little unusual and may involve human intervention via a chicken vaccine. [4] But here’s a new example, in a more natural system: Rabbit Haemorrhagic Disease Virus in Australian rabbits. [5]

By studying the change in virulence of recent field isolates at a single field site we show, for the first time, that RHDV virulence has increased through time, likely because of selection to overcome developing genetic resistance in Australian wild rabbits. High virulence also appears to be favoured as rabbit carcasses, rather than diseased animals, are the likely source of mechanical insect transmission.

It’s important to understand the mechanisms of pathogenesis and, especially, transmission, because that’s what drives pathogen evolution.


  1. Single amino acid change turns West Nile Virus into a killer
  2. Evolution to reduced virulence: It does happen
  3. Rabbits 1, Virus 1: Evolution of viral virulence
  4. Increasing virus virulence
  5. Increased virulence of rabbit haemorrhagic disease virus associated with genetic resistance in wild Australian rabbits (Oryctolagus cuniculus)
July 3rd, 2015

Adaptive hybridization

Can a hybrid between two species might have a selective advantage?  Although hybridization is usually a deleterious event, it doesn’t have to be. The example I usually use are Darwin’s Finches.

Hybridization between this species and two others resulted in gene exchange, but only after the El Nino when hybrid fitness was much enhanced under the altered feeding conditions. … hybrids were at a strong disadvantage before the 1982-1983 El Nino event, and at a small advantage afterwards.

Evolution of Darwin’s Finches Caused by a Rare Climatic Event

I recently learned about another example that’s even better.  Quoting Darren Naish from his Tetrapod Zoology blog:

do have to give honorary mention to the amazing discovery that the females of S. bombifrons will preferentially mate with the males of S. multiplicata where the two occur in sympatry, and where this sympatry involves shallow, rapidly drying pools. The conclusion from this discovery is that hybridisation is adaptive in S. bombifrons: that is, that females are able to give their offspring a survival advantage by hybridising with members of another species (Pfennig 2007).

North American spadefoot toads and their incredible fast-metamorphosing, polymorphic tadpoles | Tetrapod Zoology

The reference is to Karen Pfenning’s Facultative mate choice drives adaptive hybridization (full paper here, at least for now).

A review paper discussing interspecies hybridization in general (and Pfenning’s paper in particular) is Mating with the wrong species can be right (full-ltext link):

… interspecific hybridisation … is very unequally distributed among and within taxa, and in some animals the rate of hybridisation even exceeds that in plants [2–4]. This shifted the debate from a specific comparison between plants and animals to a more general question: what traits and environmental conditions separate groups with frequent and successful hybridisation from those where it does not occur in the first place (pre-zygotic isolation) or leads to unviable or less fertile offspring with no or little chance to pass on their genes (postzygotic isolation)?

July 1st, 2015

Why don’t I turn into a fish when I eat fish?

The question on Quora was:

Why don’t I turn into a fish when I eat fish? Or a cow when I eat beef?

The expanded explanation for the question was:

Before this is labelled as silly, here is explanation: there are specific chemicals in our bodies whose purpose is to prevent foreign genetic material in a body and cell from being read and translated into mRNA. What are the names of these chemicals and processes? How do they work?

My answer was:

Not a silly question at all, especially if we bypass the “eat” part and ask why just, say, injecting a fish cell into our arm wouldn’t turn us into a fish, or why giving our kid a transfusion of mongoose blood wouldn’t turn him into a speedy superpowered whizzer.

There are two parts to the answer.  First, DNA needs to have an elaborate support system before it can do anything.  It needs to be in a nucleus, wrapped in histones and other proteins, with access to polymerases and other enzymes, and so on and so on.  Just shoving DNA into your bloodstream doesn’t give it access to those things, so it can’t take over your cells to make fish or mongoose type proteins.

(But if you add to the DNA a system for entering a new cell and taking over the built-in systems, then you have a virus, which essentially does exactly that — turns your cells into a system for making more viruses.)

But why not a whole cell? Why can’t a fish cell settle down comfortably into our body and just pump out fish proteins all day long?

The answer is the immune system, which is aimed at identifying things that are not “self” — that is, that don’t match the template of our own cells — and to attack and reject them.  The immune system is very good at that, and can even reject very similar cells, like those of a different human, so identifying a fish or a mongoose cell is very easy to do, and those cells would be very quickly attacked and destroyed.

(Today, the immune system is tuned for identifying and destroying bacteria and viruses and so on.  But it’s possible that hundreds of millions of years ago, much of the immune system was tuned for exactly what we’re talking about here — preventing foreign cells from moving into the friendly environment and taking over.)

In response to a question in the comments (“What about plants and simpler organisms which don’t have complex immune systems?”), I added:

You have to get very “simple” in the simpler-organisms category before they lose the parts of the immune system that recognize different cell types, although the actual mechanisms are quite different in different organisms.

As for plants, they don’t reject foreign material, at least not in the same way that animals do; you can graft different plants, or even different species, together and they’ll grow pretty happily.  Grape vines and apple trees, to name just two, often have this done.

As to how, or even whether, plants reject a more subtle invasion by parasitic plants … I just don’t know.  Hopefully a botanist can answer.

 

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