In another thread about mice and snake attacks it was mentioned that memory cannot be passed on through genetics. Ok fair enough it makes sense. Then what exactly is “instinct”? Why does my beagle take off after rabbits and chipmunks and such when it was never trained to? It probably would not even know what to do with them when they caught them. Why does it seem certain animals are afraid of others at birth when they were never taught?
I’m not entirely sure, and the dividing line can be murky, but one point is that instinct is defined not in terms of information, or sensory recognition, but simply behaviour.
Does that help at all?
The difference is that learned behaviours are controlled by the brain while instincts are formed through evolution.
Behaviours related to memory are formed by trying something, consciously evaluating its success (for instance, whether it leads to a reward like food), and repeating successful behaviours while discontinuing unsuccessful ones. Everything is happening in the brain.
Instinct is similar in the end result, but it has a different way of establishing itself. Instincts come into place by random genetic variations. Individuals whose instincts give them a survival advantage have a better chance of having many offspring, so good instincts tend to be passed on to descendants. Individuals with poor instincts are more likely to die early and/or have fewer offspring so the poor instincts do not stick around in the population over many generations.
That’s somewhat useful, though I wouldn’t really agree that ‘instincts are formed through evolution and NOT controlled by the brain.’ The brain is still in the equation.
How about - instincts are formed in the brain purely as a result of parental genes, (which have in turn been shaped by evolution) whereas memory and learning are formed in the brain as a result of sensory information, body feedback, and other inputs that do not in themselves have anything to do with genetics.
So, for species with advanced enough brains to understand them, I suppose there’s no theoretical reason why the same evolutionary forces that shape instincts could form abstract thoughts or visual information, which would SEEM to be memories. However, there’s no guarantee that those ‘instinctive memories’ would be anything that had been learned or understood by some ancestor on his own the first time - just anything that there’s a survival benefit in suddenly knowing without learning it the usual way. They could almost be described as genetic hallucinations.
I think the crux here is that there’s no Lamarckian inheritance – i.e. a behaviour learned during the life cycle of an individual cannot be passed down through genetics. In order for eventual offspring to inherit a certain behavioural trait, it must have been present in the parent from birth, i.e. it either must have inherited it itself, or a convenient mutation in the genome must have occurred.
It’s a little tricky to talk about how instinctive behaviors are inherited, because there’s still so much about the brain that we don’t understand. I’d agree with Half Man Half Wit’s point about Lamarckian inheritance.
One thing I like to keep in mind is that instinctive behaviors are performed whether they make sense or not - animals don’t think about it, they just do it. This would include my puppy shaking his rope to kill it, insects attempting to mate with pheremone-soaked inanimate objects, etc. Darwin had a great example on the Galapogos. The marine iguanas there have gone for hundreds or thousands of generations without any land-based predators. The only danger in their lives comes from the ocean, so they’ve developed an instinct to get to land as quickly as possible whenever they’re in trouble. Darwin spent an entire day with an iguana picking it up and throwing it into the ocean. The iguana would realize it was in danger, and so immediately swim back to the land, where Darwin would pick it back up and throw it back in. The iguana never figured out that it’d be safer remaining in the ocean. It was a purely instinctive reaction.
Epigenetics provides a model of environmental influence on the genome that may be expressed through subsequent generations. Whether there will ever be a viable (testable) model that describes epigenetic transference of learned behaviour is another thing entirely. However, I heard a radio show on the BBC which suggested that Pavlov was able to breed mice to respond to the sound of a bell with a reduced learning curve in subsequent generations.
So it may be that conditioned responses may indeed be heritable via some epigenetic mechanism. It is also possible that such epigenetic effects may eventually create permanent changes in the genome, by influencing DNA replication.
Si
Too late to edit…
Apparently Pavlov withdrew the claim quoted above, stating that he had been deceived by his assistant (scientific shorthand for caught falsifying results) - none of the original sources I found for the quote highlighted this fact. In particular, Rupert Sheldrake presented this information as fact which was not challenged by the real scientist who was acting as a counterpoint. He claimed to have verifiable results to back up his claims of morphic fields, but if this is the sort of thing he is trotting out, then he can sit in the back with the Electric Universe guys.
:rolleyes:
However, the research on epigenetic influence on the genome is ongoing.
Si
As far as I know, epigenetics is mostly a factor in direct cellular inheritance, but has only a very small transgenerational effect. However, I’m not a biologist and all that.
One important difference between epigenetic and ‘ordinary’ inheritance would be that in the epigenetic case, the inherited factor would gradually ‘thin out’ over subsequent generations, while once you’ve got a change in the DNA of an organism, it’s there to stay (subject to the usual laws of inheritance, of course).
Epigenetics is an important process, no doubt. I don’t know of any studies looking at how it affects neuronal development, though, let alone proposing a direct link between epigenetic inheritance and instinctual behavior. Not saying it doesn’t happen - just that we don’t know yet.
At the same time it’s interesting to note the flexible interplay between instinct and current environment. Spiders in space don’t do so well with their webs at first, but then get things figured out and produce decent webs. This would seem to imply that the instinct provides a drive/goal and probably a general approach to achieving the goal, but both seem to be modified by dynamic information in the brain (e.g. is gravity present, did that last web look like crap, etc.).
And as usually if I make a declarative statement in a field where I probably shouldn’t, somebody just goes and proves me wrong – turns out there is significant epigenetic transgenerational inheritance, at least in mice.