Monday, January 30, 2006
Posted by Anonymous Coward at 5:04 PM
Simply saying that the virulence of a pathogen within the population goes up when population density goes up, down when resistance goes up. By population resistance I refer to a combination of factors such as pre-existing immunity (ie through vaccination), innate immune status, general health and nutrition level, hygeine habits (ie frequency of handwashing), food preparation habits, agricultural practices, etc. etc. It is the inverse of susceptibility.
This law is built on the fact variants with a capcity for lethality have always existed within the various quaspecies of pathogens continuously circulating within human and animal populations.
However, since infectious spread is severly compromised by high virulence, such strains can take hold when infectivity is saturated in extremely densely populated groups with high susceptibility. Thus the emergent "killer strains" everyone talks about in the news are not some new creation from thin air, but normally latent strains whose prevalence is increased by changes in human behaviour that increase population density and/or decrease resistance. Unfortunately these two factors are often coupled. For example poverty which decreases resistance through its effects on nutrition and health, tends to be prevalent in overly populated cities.
So don't be afraid of H5N1 or any other pestilence that might be cast down upon our poor helpless souls by the Almighty. Instead, fear the dark side of irresponsible civilizations: poverty, malnutrition, inadequate health care and lack of education within our massive, rapidly growing, and highly interactive global population.
Posted by Bayman at 12:59 PM
U of O's resident influenza expert Earl Brown weighs in with some cutting scientific insight on the H5N1 scare in the latest BMI bulletin.
Posted by Bayman at 10:14 AM
Friday, January 27, 2006
I think Tony brought up an interresting point, wich is worth a post rather than just a comment. I think the fact that behaviour can be inherited is undisputed. Some call these intincts, but basically, any kind of gene that can influence the chemical makeup of the brain or neuronal connections that statistically favours a particular behaviour which increases reproductive sucess will be evolutionarily stable. Now something as complex as behaviour is definately multigenic and so drastic changes in behaviour will require a more flexible system then something that solely relies on genes. The advantage of a flexible system, is that any kind of new situation, never encountered before in nature can elicit an appropriate behaviour which can even be passed on by teaching. Even blocking the irrational behaviour of a primate on a GT with suicidal tendencies. Does one need mirror neuron to learn? Not necessarily, ants are able to couple in a teacher/pupil pair to teach with both positive and negative reinforcements where food is and how to collect it. Is new behaviour heritable? There is a possibility that through imprinting one could potentially pass on new epigenetic changes affecting behaviour to its offspring. Evolutionarily speaking, this does not seem to be a stable strategy. Such a change may or may not be beneficial, and it can easily be erased in the next generation. There is however another way it can be passed on. According to Dawkins, brains are replicating machines, and ideas can be replicator. These self replicating ideas are called memes. In an objective point of view, the only "purpose" of a meme is to replicate, and to do so it must "infect" a brain. If a meme is good at being passed around it will remain stable in the memepool and be part of the culture. The meme does not need to be beneficial to the individual per say, since the individual does not need to survive or reproduce for the meme to replicate. It needs only to be catchy. For example the meme of religion is a particularly successfull one. It is debatable wether this meme is beneficial to the individual harbouring this mind virus. Yet it is good at getting passed on. It has very sucessfull co-infectors that complement it, such as the promise of life after death, or the fear of hell. The point is that behaviours can easily be horizontally heritable, but one must think outside of genes and reproduction to fully understand how they can be passed on...
Posted by Anonymous Coward at 10:16 AM
Thursday, January 26, 2006
So this past weekend at the Super-Fun Snow Jam of the Century, sitting on a GT snow-racer at the top of a cliff, working up the courage (ie insanity) to plummet down onto the ramp projecting over the ravine below, my thoughts inevitably turn to evolutionary biology. At first, I mostly ignored the whimpering and frantic looks from Mannie the German Shepherd, who was directly blocking my path, and tried to kick her out of the way. However, as I now know, German Shepherds are BIG and HEAVY and this one was determined I was not going down that hill. Then it dawned on me - this dog was herding me. I guess from a shepherd's point of view, her behaviour made sense. I was big and stupid enough to choose to rocket down to my own demise, but no idiot would want their sheep sent over a cliff, off a snow jump and into a ravine filled with running water.
Now here's what gets me. This dog has never seen a sheep in its life. Since it was probably cruelly ripped from its mother's bosom in infancy, neither did it ever have the chance to learn herding behaviours from its parents. Yet it does a great job trying to shepherd everything in site. A born shepherd. No doubt her offspring (if she still had reproductive capacity) would be the same. Heritable behaviour. Just like Rob's pointer hunting dogs.
That seems interesting to me, but maybe its not news to anyone else. At any rate, what seems even more intriguing to me is that not only are behaviours/skills heritable from one generation to the next, but they can be taught and learned between individuals (even unrelated individuals). As V.S. Ramachandran points out in the doco Rob posted, this ability is an obvious evolutionary advantage in terms of speeding up adaptation to environmental challenges. He suggests the capacity to learn is unique to humans and could be a function of mirror neurons. I tend to disagree; although humans might be the most prolific learners/teachers, you can clearly teach a dog tricks.
At any rate all this seems to suggest to me that behaviours learned by an individual after birth could be programmed into the genetic makeup of germ line cells and thus passed on to offspring. Thus, a university professor or celibate priest, by teaching or preaching ideas could reproduce their genes without ever gettin' it on so to speak. This doesn't seem to fit with current biological theory as I understand it, so can someone please explain to me why I'm wrong?
Posted by Bayman at 10:26 PM
Saturday, January 21, 2006
An article on mirror neurons by a very influential neuroscientist, V.S. Ramachandran.
A short and simple PBS doco on mirror neurons.
Mirror Neuron talk is also included in the Emerging Mind lectures 2003 from the BBC (also with V.S. Ramachandran) and I thought these lectures were an excellent listen.
Posted by rob at 9:07 AM
Friday, January 20, 2006
Posted by Anonymous Coward at 2:41 PM
Wednesday, January 18, 2006
Posted by Anonymous Coward at 3:42 PM
Posted by Anonymous Coward at 11:24 AM
Monday, January 16, 2006
(Fixed link for real)
Posted by Bayman at 10:32 PM
Friday, January 13, 2006
Posted by Anonymous Coward at 11:27 AM
Tuesday, January 10, 2006
Posted by Anonymous Coward at 8:29 AM
Monday, January 09, 2006
Posted by Bayman at 10:33 AM