Instinctive Behavior and DNA: Exploring the Genetic Basis of Innate Behaviors

[precisionart]

I was wondering how instinct or other forms of 'memory' are encoded in DNA. It seems there is a reservoir of knowledge that is stored in some way. Is this currently explained in genetics?

 

[Pythagorean]

I think instinct and memory are more emergent properties that come from the interactions between genetics and environment. In the most general sense, a memory is a representation of interactions with the environment stored internally in a system and DNA can do that in a more reduced way, but the specific kind of memory you're thinking of emerges from cellular networks which DNA underlies.

DNA doesn't know about what's going on with memories and stimulus. This might possibly answer the question in your other thread about evolution and perception. On the one hand, the system has to have lots of internal degrees of freedom to sufficiently model external representations. But on the other hand, it has to keep the core code (DNA) safe, so it tends to be very stable.

But the DNA is a like a multiple choice set of answers. Protein networks in cells turn off and on genes as they're needed, and some genes may never need to be expressed for a particular organism. This is kind of the arsenal of DNA the cells have, but for the most part it is fixed. It doesn't receive any information bout what the organism is perceiving. That is the central dogma of biology.

So apparently, it's only by chance that this arrangement of molecules in this environment leads to this behavior that is so beneficial.

DNA, in its own right, has been compared to associative memory:
http://staff.elka.pw.edu.pl/~RNOWAK2/publ/assocmem.pdf

But this is a different kind of memory. You might call it uber-long-term memory.

 

[precisionart]

Good response, thank you.

I see that this thread is related to my other thread on perception. To ask the question differently...I observe directly that behavior is passed on, simply watching squirrels demonstrates this. I then ask how is behavior and capacity (tremendous and immediate climbing skill by young squirrels) passed on. Let's leave asside "soft inheritance" for now. What is the nature of this encoding? How is this information 'held' in the DNA? I have no idea about the information capacity of DNA (I would like to know), but it seems that particular structures in the brain get communicated through DNA. Does DNA have sufficient information storing capacity?

 

[Pythagorean]

It's a code with an alphabet of four letters. Little proteins come along and take a chunk of the code and make a simple copy of it called RNA, leaving the DNA safe. In a string of different combinations of these four letters in the RNA, every set of three letters is considered a "codon" and these codons are "read" by a ribosome that creates an "amino acid". So the ribosome will make several amino acids in a row and they might fold up or change geometry a bit into a functional shape and we call this a "protein" and the proteins are little molecular machines that do magnificent things at the molecular level.

http://en.wikipedia.org/wiki/Genetic_code

 

[John Kari]

instinct in embryonic brain

DNA has all the alfabets of life, and it also has the alfabets for instinct "memory knowledge".
Did you want to know how this memory looks like in embryonic brain and how it is made with the DNA?
I would like to know it too. John

 

[Ygggdrasil]

In many animals, basic instincts and behaviors are encoded in the organism's DNA. The DNA provides instructions for the animal to build specific neural circuits to perform certain behaviors in response to certain stimuli. For example, flies have an escape response triggered by certain stimuli, such as a shadow passing over them. Researchers have identified a specific nerve cell in the fly that controls this response and this nerve cell is the same in all flies of the same species. Artificial stimulation of this nerve cell triggers the escape response. The nematode worm, C. elegans is probably the animal where the neural circuitry for many innate behaviors, as well as the genetic elements controlling the development of the circuitry, is best understood (for example, see http://www.ncbi.nlm.nih.gov/books/NBK20005/).

In humans and other higher mammals, however, the situation is very different. Humans are born with very few innate behaviors and instincts. For example, whereas many animals (insects, fish, reptiles, amphibians, etc.) are fully capable of walking, feeding themselves and even surviving independently after birth, human babies can do practically nothing after birth and cannot survive without a caretaker. The difference here is that the DNA of humans does not specify a wiring diagram for the brain. Rather this wiring diagram is formed in response to the experiences of the individual. For example, if you were to take a newly born baby and cover its eyes for its entire early childhood, the child's neural circuitry for interpreting visual stimuli would not develop and the child would be blind despite the fact that the child's eyes work perfectly well. Another consequence of this strategy is that everyone will develop different neural circuits to perform the same functions. For example, whereas the same nerve cell will trigger the same escape response in all flies, activating a specific nerve in humans would likely trigger very different responses in different individuals.

While this wiring-on-the-fly strategy has many disadvantages in the younger phases of life (babies and children are very much dependent on others for survival), this plasticity of the brain associated with the wiring strategy gives humans an unparalleled ability to learn. This neural plasticity is likely one reason why humans can learn complex tasks like reading and writing while other organisms cannot.

 

[Pythagorean]

There was an interesting distinction made in a study on neuronal regulatory function between innate behavior and learned behavior in barn owls:

Studies in barn owls have revealed that the additional learned circuits that had been assembled during a sensitive period in juvenile birds were turned on and off in the adult through mechanisms distinct from those that turn innate natural circuits on and off (disinhibition versus AMPA/NMDA ratios for the innate and learned circuits, respectively), suggesting that innate and acquired circuit arrangements can be distinguished functionally

---

if you were to take a newly born baby and cover its eyes for its entire early childhood, the child's neural circuitry for interpreting visual stimuli would not develop and the child would be blind despite the fact that the child's eyes work perfectly well.

This is an interesting phenomena. It can actually be suppressed by suppressing the signaling of the neurons involved. If you don't suppress their activity, they try to make correlations on what are essentially noise signals in the system and "hard wire" the system by misinterpreting the meaningfulness of those signals.

The hardwiring function is also discussed in the Caroni et al paper; it comes from these molecular casings that coat the neurons called perineuronal nets. This prevents further activity-induced plasticity from taking place.

Caroni P, Donato F, Muller D. (2012) Structural plasticity upon learning: regulation and functions. Nat Rev Neurosci. 2012 Jun 20;13(7):478-90. doi: 10.1038/nrn3258.
http://www.ncbi.nlm.nih.gov/pubmed/22714019

 

[John Kari]

Hi Pythagorean: I was actually wondering about dualistic nature of brain. One part has "instinct knowledge" already part of the structure from our ancestors ( ROM type, that you are not able to change). how has it been formed? The other is brain that you can "program", that means, put in and take out information.

 

[Pythagorean]

I wouldn't consider instinct knowledge as coming from our ancestors... at least not in the sense that they discovered something and it stuck in their DNA or whatnot.

It's more just that particular sets of instinctual traits happened to emerge form reduced DNA instructions and those traits were successful in producing offspring who could successfully produce more offspring. It's like following a set of instructions "go left", "go right", "go straight" but the instructions weren't written with any goal in mind... they just happened to lead to a place that enabled recurrence.

The instruction sets that were successful are what we have today, but they're not memories. They are the result of successful mutations. Babies are born with a whole set of reflexes that essentially enables their survival. When they first leave the womb and air hits their face, they begin to breathe. This isn't because a baby in the past discovered breathing at birth, it's because of mutation... and any organism that didn't have this mutation died and couldn't reproduce.

 

[Q_Goest]

In many animals, basic instincts and behaviors are encoded in the organism's DNA. The DNA provides instructions for the animal to build specific neural circuits to perform certain behaviors in response to certain stimuli. For example, flies have an escape response triggered by certain stimuli, such as a shadow passing over them. Researchers have identified a specific nerve cell in the fly that controls this response and this nerve cell is the same in all flies of the same species. Artificial stimulation of this nerve cell triggers the escape response. The nematode worm, C. elegans is probably the animal where the neural circuitry for many innate behaviors, as well as the genetic elements controlling the development of the circuitry, is best understood (for example, see http://www.ncbi.nlm.nih.gov/books/NBK20005/).

In humans and other higher mammals, however, the situation is very different. Humans are born with very few innate behaviors and instincts. For example, whereas many animals (insects, fish, reptiles, amphibians, etc.) are fully capable of walking, feeding themselves and even surviving independently after birth, human babies can do practically nothing after birth and cannot survive without a caretaker. The difference here is that the DNA of humans does not specify a wiring diagram for the brain. Rather this wiring diagram is formed in response to the experiences of the individual. For example, if you were to take a newly born baby and cover its eyes for its entire early childhood, the child's neural circuitry for interpreting visual stimuli would not develop and the child would be blind despite the fact that the child's eyes work perfectly well. ...

Hi Ygggdrasil. Are you saying that if an animal's eyes were covered in the same way the child's eyes were, the animal would still be able to see?

 

[Ygggdrasil]

It depends on the animal. The "wiring-on-the-fly" strategy applies mostly to mammals (and indeed, the dark-rearing experiments were done in mammals like mice and cats and not humans), so most mammals will behave similarly to us. I would suspect, however, that dark rearing of simpler animals like insects might not interfere with the proper development of the neural circuits to process visual information.

 

[Q_Goest]

Interesting! thank you.

 

[John Kari]

Aren't human babies born prematurely, their (our) brains are still developing years after birth, I believe walking (Inuit babies are wrapped tight long time after birth) and talking are human instincts, they are complicated motor movements that has nothing to do with reflexes (breathing).
Anyways, past life memory can be something that can or can not be explained with DNA?
Strange, my cat was born blind as all cats are but cat's vision is weird, maybe because of that?
Talking about cats, behavior of my cat and African lions are similar. There hasn't been meeting with cats has there?

 

[Pythagorean]

Prematurely is defined with respect to the organism. So as a matter of technicality, no, most human babies aren't.

But yes, ignoring semantics, our enormous heads mean that mothers must give birth to their children sooner than other mammals do and a lot of brain development takes place outside of the womb. Humans are quite useless when they're born: they can't even support their own heads. Many other mammals are born practically knowing how to walk.

 

[Evo]

Anyways, past life memory can be something that can or can not be explained with DNA?

Sorry, this is a science forum, please read the rules. We don't allow mysticism.

 

[John Kari]

Hi Pythagorean. Some of the early separated twin studies are interesting. One twin has been doing the very same things in his/her life as the other one.
What happens must be in the part of DNA that develops into brain. If you just take the average of the studied twins there is no correlation but that is not what we are interested in. John

 

[Pythagorean]

Yes, twin studies are an interesting way to tease apart genetics from environment, but I don't understand what you're asking or saying.

You also have to remember that their are influences in the womb too (for example, monozygotic twins can be monoamniotic and monochorionic and these can lead to different nutrient intake rates for each which can have effects on brain development).

 

[Graeme M]

I have read a couple of threads I found via search, but none actually explain simply for me how it is that instinct is first formed and then inherited. I understand that instincts are presumably selected for, but it's not apparent to me how that happens. I just don't know enough about evolution.

Given that species change occurs through changes to DNA in germ cells being passed on through reproduction, does it follow that the same process underpins instinct formation? That is, some genetic change to germ cell DNA confers a new "hard-wired" behaviour that may or may not be beneficial. If beneficial it is selected for and over time complex behaviours evolve that are coded for within DNA. In which case at an abstract level evolution of instinctual behaviour conforms to the same paradigm as evolution of physical characteristics and given that physical characteristics at the neural level are what generates instinctual behaviours, we are really looking at the same thing in both cases? In other words is the evolution of physical characteristics via reproduction and selection all there is?

 

[Pythagorean]

Yeah, it's just like anything else that's formed. Some random mutation made a small difference statistically in the population, providing advantage to survival or reproduction. In this case, the random mutation could be in the genes that code for neural organization or individual neuron properties (including 2nd messenger signaling). The random mutation may lead to a slightly different wiring that biases towards a certain input/output relationship (e.g. a muscle reflex that triggers when skin sensors are activated) that reduces infant mortality rates. As time goes by and more mutations occur, eventually another one in some other random aspect of cell organization happens to contribute to that reflex, too, and it becomes even more selected for... one, two, skip a few million years, and you have the palmar grasp reflex.

"is the evolution of physical characteristics via reproduction and selection all there is?"

Too strong of a statement to say it's "all there is". Does it all have a physical correlate? Yes. But it doesn't necissarily have to be limited to DNA-based inheritance if epigenetics carries the information through methylation. In which case, methylation is the physical correlate.

 

[BillTre]

Yes. Instinctive behavior will (to the extent that it is genetically determined) will be underlain by the same selection process as everything else.
The genes involved will direct developmental processes (perhaps with some environmental input, such as visual stimuli to promote normal visual system development).
This results in a nervous system whose functioning underlies behavior, including instinctual behavior.

The genetic component of behavior control can be pretty exact.
bendless: is a fruitfly mutation that, among other things, blocks an escape instinct.
The reflex occurs when the fly sees a increasing area of dark in its visual field (potential approaching predator). This triggers a giant escape fiber (axon) to fire, which triggers leg motoneurons to fire, which causes the fly to jump off the substrate, which in turn turns on (lack of contact between feet and substrate) the the flies flight system (fly flies away).
The bendless mutation deletes a particular synapse between the giant fiber and the leg motoneurons, blocking that step in the behavior and therefore to escape response.

bendless was found in a genetic screen for mutations in which this behavior (which is normally strong) does not occur. Flies in which the behavior occurred (and therefore did not have mutations affecting this behavior) ended up dead in the test apparatus (fell into a pot of oil). The survivors did not jump, did not die, and carried mutations. Thousands to millions of flies were tested in this way, which amounts to a selection (artificial not natural). Geneticists like selection screens because most of the initial work to find the mutants is done by the selection process making screening the huge numbers of flies feasible.

Mutations in several different genes were found in this screen indicating there are many ways (genetically) to modify this particular behavior.

 

[jim mcnamara]

FWIW - there is a whole field of Evolutionary Biology that deals with Evolutionary Psychology, and one that looks at social behavior under Natural Selection - see: E O Wilson 'The Social Conquest of Earth',
D Buss 'Evolutionary Psychology: The New Science of the Mind'

So none of what you are looking for is hard to find.
PS: Instinct is not a very well-defined term, IMO.

 

[bassamnfs]

I guess that DNA codes the location information of every cell in relationship to other cells, sort of a 3D map (a blue print) of how to build the body (identical twins have almost identical physical parameters), if my guess is correct do we know what is the mechanism that interprets the code in DNA into coordinations? This is interesting because as I understand ribosome translates the information coded in DNA to proteins and I'm not aware of any other thing that performs similar task but ribosome.

 

[BillTre]

Positional information is probably something like what you are thinking about. In embryology, cells have to know their location to develop properly and positional information is an interpretation of how this is done. Some molecules have been found in gradients, in certain parts on embryos (like the developing visual system), that could provide a coordinate system for the interpretation of a cell's position and its appropriate development for that location.

However, location in developing embryo would not be directly coded in the DNA. There would be a lot of intermediate steps involved where particular gene products, expressed in particular cells, would have effects on the developmental processes that in turn result in the right cell being in the right place.

These things are very indirect and are generated by cellular and developmental processes (whose protein components are encoded in the DNA) rather than being a description written down directly in some DNA code.

 

[Ygggdrasil]

I guess that DNA codes the location information of every cell in relationship to other cells, sort of a 3D map (a blue print) of how to build the body (identical twins have almost identical physical parameters), if my guess is correct do we know what is the mechanism that interprets the code in DNA into coordinations? This is interesting because as I understand ribosome translates the information coded in DNA to proteins and I'm not aware of any other thing that performs similar task but ribosome.

At the broad level, the locations of certain cell types in the body is genetically programmed genetically, but at the fine level, this is not true for vetebrates. For example, in examining the wiring between nerves and a particular muscle in mice, researchers found substantial variation in the wiring diagram even between the same muscle on the left and right side of the same animal:

Conventionally, the organization of a neural circuit is studied by sparsely labeling its constituent neurons and pooling data from multiple samples. If significant variation exists among circuits, this approach may not answer how each neuron integrates into the circuit's functional organization. An alternative is to solve the complete wiring diagram (connectome) of each instantiation of the circuit, which would enable the identification and characterization of each neuron and its relationship with all others. We obtained six connectomes from the same muscle in adult transgenic mice expressing fluorescent protein in motor axons. Certain quantitative features were found to be common to each connectome, but the branching structure of each axon was unique, including the left and right copies of the same neuron in the same animal. We also found that axonal arbor length is often not minimized, contrary to expectation. Thus mammalian muscle function is implemented with a variety of wiring diagrams that share certain global features but differ substantially in anatomical form, even within a common genetic background.

http://journals.plos.org/plosbiology/article?id=10.1371/journal.pbio.1000032

Thus, especially for neurons, the specifics of connections and positions are not genetically predetermined, but instead formed in an experience-dependent manner.

 

[rootone]

How about instincts such as an antelope fleeing if it senses a predator nearby.
There won't be a specific gene for that, but every antelope will do it, so it must be 'hardwired' in some sense.

 

[Pythagorean]

How about instincts such as an antelope fleeing if it senses a predator nearby.
There won't be a specific gene for that, but every antelope will do it, so it must be 'hardwired' in some sense.

There's lots of genes involved in organizational outcomes. Untangling learned vs. Innate behavior can be difficult. I think detecting and fleeing a predator is a learned trait, but it's likely made up of many inherited traits (like the startle reflex to get adrenaline going, and innate motor generation patterns that have been honed for running) that easily enabled the learned behavior.

Just to demonstrate how "dumb" the system is as a result of random genes working together, the detection system for doing this does so for a deer (and other "skittish" animals) by being "overly sensitive" (letting a lot of false positives through when identifying threat) If your intention was to feed a deer and pet it, it would still run away from you because its better to be safe when you don't have sharp teeth and claws and giant muscles ... whereas animals like wolves, who have a little more threat tolerance, where able to form an evolutionary relationship with man (in which dogs emerged).

 

[Andres Pineda]

Yeah, it's just like anything else that's formed. Some random mutation made a small difference statistically in the population, providing advantage to survival or reproduction. In this case, the random mutation could be in the genes that code for neural organization or individual neuron properties (including 2nd messenger signaling). The random mutation may lead to a slightly different wiring that biases towards a certain input/output relationship (e.g. a muscle reflex that triggers when skin sensors are activated) that reduces infant mortality rates. As time goes by and more mutations occur, eventually another one in some other random aspect of cell organization happens to contribute to that reflex, too, and it becomes even more selected for... one, two, skip a few million years, and you have the palmar grasp reflex.

"is the evolution of physical characteristics via reproduction and selection all there is?"

Too strong of a statement to say it's "all there is". Does it all have a physical correlate? Yes. But it doesn't necissarily have to be limited to DNA-based inheritance if epigenetics carries the information through methylation. In which case, methylation is the physical correlate.

If the response to breath when outside the womb was an evolutionary trait, we would all be dead, right? Given a small population of "humans" in the early days, there would not have been enough opportunities to evolve that trait. Logically, the trait to start breathing would have to be an innate ability for the species. Same as the desire to suckle and have a heartbeat.
If these types of traits are indeed encoded in the DNA, why can't we insert new traits, such as a memory of how to solve quadratic equations? You can extend that idea to any amount of capabilities.

 

[Pythagorean]

If the response to breath when outside the womb was an evolutionary trait, we would all be dead, right? Given a small population of "humans" in the early days, there would not have been enough opportunities to evolve that trait. Logically, the trait to start breathing would have to be an innate ability for the species. Same as the desire to suckle and have a heartbeat.
If these types of traits are indeed encoded in the DNA, why can't we insert new traits, such as a memory of how to solve quadratic equations? You can extend that idea to any amount of capabilities.

That high level of behavior isn't encoded in DNA; the components of it are. Form is defined by DNA, but function is a property of the relationship between the organism and the environment, both vastly broader subjects than DNA.

A more likely scenario is that those reflex behaviors evolved from similar but different reflex behaviors in the ancestry. For example, primitive fish invented lungs. All creatures that have lungs descended from these primitive fish. But the fish evolved lungs from gas bladders that helped them control buoyancy. Thus, all the components were in place (a bladder that could fill with air and a nervous system to control it). It's only through a long period of small changes that the air bladder (and it's supporting systems) evolved into a lung and in turn, each descendent of the primitive fish evolved their own take on lungs, adapting it's form and function to each species' survival niche.

Of course, this was the same with limbs, too. We owe a lot of our shape to fishes :)

 

[berkeman]

Thread is closed temporarily for Moderation...

Update -- some personal speculation has been removed, and this old thread will remain closed.