So how does behavoir, like nesting, making a web, etc become written down in DNA to become instinct? It had to start somewhere. Are humans rewriting their insticts, like say a generation of children who instictivly know how to use the toilet and haggle at flea markets?
I’m too lazy to go and look up this stuff myself. I can give you one keyword to put into your search engine, however: “Lamarck”. I don’t know if his theories of adaptive morphology have been wholly discredited or not.
Zarathustra
It’s just like any other evolution. Occasionally, a child is born with some instinctive behavior. Sometimes, that behavior is advantageous, sometimes, it’s detrimental, and most of the time, it’s completely neutral. If a behavior is advantageous, then that individual will be slightly more likely to live to adulthood and have kids, passing down that behavior. If it’s detrimental, that individual will be slightly less likely to reach maturity and have kids. Thus, the instictive behaviors of the next generation will be ever so slightly more advantageous, on average, and eventually, the changes will be significant.
Instinct isn’t that significant for humans, so I’ll use squirrels for an example. With their current instincts, a squirrel’s reaction to a threat is to freeze and try to avoid notice. Ordinarily, this is good, but the number one predator of urban squirells nowadays is cars, which, if anything, are less likely to kill squirells if they’re seen. Through some quirk of genetics, a squirell is born with scrambled instincts: When approached by a large predator, instead of freezing, it jumps to the side. This squirell is much less likely to become a road pizza, and so will be more likely to have babies and pass on that characteristic. These babies are in turn more likely to have cubs of their own, in time, and so on, until you’ve eventually got a bunch of squirrels in a city that have evolved the instinct to avoid traffic.
Lamarckian theory was wholly discredited for a long time, being considered correct only by Stalin (and, of course, biologists in Russia who didn’t want to be killed).
In more modern times, evolutionary theory has become more nuanced, with recognition that genes aren’t the only determinant (some other considerations shown to affect heredity are the uterine environment, certain maternal proteins found to attach themselves to chromosones and “turn off” certain genes, etc.)
V.
It seems to me it would have to develop hand-in-hand with physical evolution, say like spinnerettes on spiders, which sounds like a huge coincidence. They would also need the instructions (behavoir) to use them. Also if it wasn’t for web-spinning behavoir why would spiders with spinnerettes be more fit (have more babies) in the first place? I can’t see how the first primitive spinnerette mutation also propagate through the species while waiting for a random baby to be born with the proper instructions to use it.
there is a difference between spinning a wab and using spineretts. the spinneretts evolved, spiders used them to linetheir burrows, wrap their eggs (probably the advantage of having them to begin with) until one day, some spider was born with some weird idea of stringing the silk between two sticks (probably just randomly–no pretty shapes). she caught somthing in it and ate it, she survived to have babies and passed this instinct of weaving between two sticks to them.
a while later, one of her decendants has some weird mutation of this insinct that tells her to weave in a more orderly fassion, and so on until you have the type of spider webs we see today.
I don’t think this answers the question, you just substituted wrapping eggs or lining burrows instead of making webs. We still have the problem of how a physical mutation like the spinnerettes can continue to be selected for while awaiting the instictive mutatation to start wrapping eggs or whatever their at-the-time purpose was.
Actually, no child (human, that is) is born with any instinctive behavior… instinct, by scientific definition, is a behavior that occurs, without change or choice, in response to a stimulus… human beings don’t have any of those… witness celibacy, anorexia, etc… and no, breathing, heartbeat, etc. are not instinctive behaviors… those are simply biological necessities, not behaviors…
Infants cry when they are injured. They don’t learn to cry because it gets attention (Not one month-old ones, anyway. Todlers are a different story.). It’s ancestral memory for human infants to cry when in distress.
You’re missing part of the scientific point of what is a true instinct… not each and every infant cries when it is injured… some react in an almost shocked silence… an autistic child may not react at all… in order for a behavior to be classed as an instinct it must occur in the same way in response to the same stimulus each and every time… if I weren’t so new to this forum, maybe I could figure out how to underline some of this… it is absolutely key to the discussion of instinct that it be understood that there can be NO variation in the behavior in reaction to the stimuli… a male prairie chicken MUST do his dance when presented with a suitable female in mating season… (in males of the human species, I believe my ex was unique in having to… oh, wait, that’s another thread altogether…)
Look up instinct in any biology book… the explanation of it will be clear and if you try to apply that to any human behavior you will see that it cannot work… I think what we have here is a slight misunderstanding of what instinct itself truly is…
Fluffinator’s right-
The things that humans do without decision are called reflexes- a baby reflexively sucks, there’s also a moro reflex (don’t remember how to spell it) and they reflexively grasp at anything put in their hand.
An INSTINCT is a more complex set of involuntary actions that are innate- the web-spinning, hibernation, mating dances.
None of these are present in humans.
What about a baby smiling?
fluffinator said: "… it is absolutely key to the discussion of instinct that it be understood that there can be NO variation in the behavior in reaction to the stimuli… a male prairie chicken MUST do his dance when presented with a suitable female in mating season… "
That definition would seem to mean that no animal has
instincts.
Based on the definition above, if only one member of a set lacks the behaviour then it is not instinctual.
I am willing to bet there are prairie chickens born from time to time that do NOT do a mating dance or do it a litle diferently from the other guys.
In any population there are huge variations in all types of behaviour in reaction to stimuli.
I’m with diver. Human behaviour relies a lot less on instinct than other animals. Make like you’re gonna punch someone in the face, but pull the punch. Did they blink? Yes, unless they have conditioned themselves to overcome their blink reflex in which case they’re likely to get an unecessary eye injury. Do the same to an animal. Did they blink? Yes, unless they are blind; I also suspect that with repeated pulled punches, they would get tired of blinking.
Cockroaches instinctively run for darkness when you turn the lights on, but not always. What if you never ever crushed them? Their inherited habits vary pretty quickly over time, since they have so many generations.
A male and female bird in adjacent cages will begin a courtship ritual (some species, some times) when the visual barrier is removed. What happens if you do this ten times a day? My example is a college biology class where we were supposed to describe stereotyped reactions like courtship. We removed the barrier, and the birds didn’t do much but hop away from the ruckus. They didn’t flirt or preen or any of that. Why? Were they the same sex? No, they were just tired of being teased by humans. They didn’t waste energy on courthship when it afforded them no biological advantage.
Intinct defeating by conditioning.
I believe you have missed the point, or rather misunderstood the evolutionary process. I don’t know anything specific about spider evolution, but let’s presume a basic arachnid develops egg-wrapping behaviour. Perhaps over time stronger “siks” develop – random traits appearing in some individuals and which are then selected for by those individuals higher survival rates. (Note: some traits may carry along of course even if they’re not all that useful if something else compensates for for them, matter of coincidence)
Over time a trait establishing a rudimentary spinnerete (from some prior structure) appears in some individuals which gives them some advantage. Slowly, generation by generation, selection occurs to the point where we have the tools for a spider. Not at all the factor involved might be obvious, perhaps a variety of small cumulative advantages. Along the way, at some point the spider begins to pick up some extra meals through catching whatever in quasi webs or tunnel linings. Some of these little guys begin to develop web behaviours. Bit by bit.
Nothing “awaits” anything in evolution, no purposes, no goals. Just good luck or bad luck. (Or just neutral luck)
"it is absolutely key to the discussion of instinct that it be understood that there can be NO variation in the behavior in reaction to the stimuli… "
fluffinator, by this definition instinctive behavior cannot evolve as this relies on the idea that organisms vary. If they cannot evolve, then they should not be present, unless you believe in strict creationism. If all male prarie chickens do the same dance the same way then the dance has no value for the female as an indicator of fitness.
Also, we can’t really be sure how much human behavior is learned versus instinctive as it is unethical to do the appropriate experiment.
John