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Evolution
- Thread starter rocala
- Start date
Parenthetical aside......
It's good to be stumped.
Evolutionary phenomena can be complex.
Having all the answers is typically a sign of hubris.
Not having them keeps it interesting.
Birds that did not build little fortifications to hold their eggs tended to not have as many surviving offspring as those who did. Over many generations, the birds that did a better job of building nests to protect their eggs had more surviving offspring, who also built better nests. But clearly, there are other ways of protecting eggs so that offspring will survive: penguins hold the eggs on their feet, peregrine falcons don't bother to make a nest per se, but find a nice ledge with a little gravel way high up and make sure they spend enough time keeping the eggs and chicks warm and fed. And so on.
Papoon
Active Member
This does not explain how a genegic mutation resulted in building fortifications however. That is the kind of question that the theory tends to gloss over. I'm not trying to refute evolution BTW, but sometimes the explanations given for examples like this are somewhat glib, and tend to have a subtext that evolution is teleological. The theory is not a theory of innate teleology.
Definitely not teleological; it's a descriptive theory of how pressures in the environment and behavior interact to create variation and selection across a population over time--always as it operates in the now, based on what's available from the past.
The interaction between the environment, genes, and behavior is complex, admittedly, and it is unlikely that there is a single gene tied to building of nests in birds--which would help explain the variety of nesting practices across the species.
Deathbydefault
Apistevist Asexual Atheist
You can always say you aren't an authority on evolution and make an educated guess.
rocala
Well-Known Member
1/ Are we saying that lots of species threw twigs together and some got lucky with an intricate design?
2/ A lot of of effort and research went into nest building and the result became an inheritable quality?
rocala
Well-Known Member
Yes that would be the normal situation. I am sure that all those present were aware of my lack of expertise, but to be blunt I do not have an educated guess on this. I remain a devotee of evolution, but to be honest devoting my self to something which stumps me is very annoying, it smacks of 'faith'.
Deathbydefault
Apistevist Asexual Atheist
Perhaps birds as they were originally made nests of a kind on the ground and were simply pushed upwards by predators.
That's my guess in most of the situations I've seen presented, not sure if it is to your aid.
The birds of origin that survived were those kept warm by their parents body heat and soft material.
I would strongly discount #2. Earlier populations would have made generally simpler nests, but there would have been variation in how much time and effort individuals put into nest building and the resources available and so forth. Some would be somewhat more elaborate than others. Selection pressures (climate, isolation of populations, predation, etc.) would have operated. Even mate selection (for example, as is the case in many species of birds, males build nests and females select which male/nest they will brood with) could then effect the survival of offspring. Nest designs that didn't have good survival tend to get eliminated from the population, those that increase survival will increase. Just as with evolution of the eye, ostrich feathers and any other features, the incremental changes over time can become quite complicated, intricate, ornate. Look up bower birds, for example.beenherebeforeagain Hi, I do see the point that you are making, but it does not really cover the dilemma that I am in.
1/ Are we saying that lots of species threw twigs together and some got lucky with an intricate design?
2/ A lot of of effort and research went into nest building and the result became an inheritable quality?
So, I guess you could say they got lucky--incrementally over time, to eventually come up with an intricate "design," although design is not exactly the proper word because it's not like a human engineer or architect designing something intentionally.
A Vestigial Mote
Well-Known Member
There simply have to be sections of the brain that become devoted to an instinctual knowledge-base in animals. This is regardless whether evolution is the key to life or not. There are spiders that "fish" for moths bu hanging from a thread doused with pheromones. These spiders, when born, are not accompanied or watched over by their parent for any length of time. How do they know how to do this? To make a single strand of web from a ceiling of a cave, or branch of tree, then create a single strand of web covered in the pheromone and then swing it in a circle in the air and wait for a moth to arrive? How do they "know". The only explanation is that their brain contains these activities inherently, they are informed by instinct.
And is it really such a stretch? Are there not such instincts within even ourselves? A baby born into water will start into reflexive movements that are attempts at "swimming", they also hold their breath and will open their eyes. How could they know that such things would be beneficial to survival when in the water? It has to be there, inherently. On an even smaller scale - are you the driving force behind moving your hand off of a hot stove top? Do you consciously feel the burn and then decide to move your hand? No - your hand is moving well before you consciously realize exactly what happened. Survival instinct is built within us all to do exactly the things necessary to keep us out off harms way as much as is possible via these types of inherent maneuvers.
And is it really such a stretch? Are there not such instincts within even ourselves? A baby born into water will start into reflexive movements that are attempts at "swimming", they also hold their breath and will open their eyes. How could they know that such things would be beneficial to survival when in the water? It has to be there, inherently. On an even smaller scale - are you the driving force behind moving your hand off of a hot stove top? Do you consciously feel the burn and then decide to move your hand? No - your hand is moving well before you consciously realize exactly what happened. Survival instinct is built within us all to do exactly the things necessary to keep us out off harms way as much as is possible via these types of inherent maneuvers.
Actually...
From - Collias, N.E. (1964) The evolution of nests and nest-building in birds. American Zoologist 4:175-190.
Ability of birds to maintain a high constant body temperature no doubt developed gradually, probably coincident with the evolution of the ability to fly. Even today there are a a few birds that are known to pass into a state of torpidity under certain conditions, and their body temperature falls dramatically (Barthalomew, Howell, and Cade, 1957). If birds passed into a torpid state during cool nights of the breeding season, they could scarcely incubate their eggs effectively. During the transitional period of early avian evolution, when temperature regulation mechanisms were being perfected, some birds probably continued to bury their eggs, leaving incubation to the sun or to decaying vegetation after the reptilian fashion, and as megapodes do among living birds today. The probably low nocturnal body temperature of ancestral birds is an argument in favor of the idea that in an early stage of avian evolution, incubation of eggs may have depended in part or wholly upon some source of heat other than that furnished by the parental body.
From - Collias, N.E. (1964) The evolution of nests and nest-building in birds. American Zoologist 4:175-190.
Some more stuff...
From - Collias, N.E. (1997). On the origin and evolution of nest building by passerine birds. The condor 99:253-270.
Hole nests in general are safer and fledge more young than do nests not in holes (reviewed by Collias and Collias 1984, Skutch 1985). Cavity nesting gives shelter from the weather, helps ameliorate temperature fluctuations, and conserves energy (Kendeigh 1961).
Hole nests in the ground protect from wind chill. In Patagonia, ground-tyrants (Muscisaxicola, Tyrannidae) escape cold winds by nesting in tunnels underground, a clear case of convergent evolution with the miners, Geositta (Johnson and Goodall 1967) and earthcreepers, Upucerthia (Narosky et al. 1987). These tunnels are often placed in slopes or banks giving some protection from rain or floods.
Nests in the ground may be less vulernable to predators than nests on the surface of the ground, as shown by controlled field experiments with artificial nests (Martin 1987). Quail eggs in a wicker basket lined with leaves and placed on the surface of the ground in an Arizona forest had a significantly higher predation rate than similar artificial nests buried with the rim even with the ground and partially covered with dead leaves, or eggs simply placed in a hole in the ground.
Hole nests in the ground protect from wind chill. In Patagonia, ground-tyrants (Muscisaxicola, Tyrannidae) escape cold winds by nesting in tunnels underground, a clear case of convergent evolution with the miners, Geositta (Johnson and Goodall 1967) and earthcreepers, Upucerthia (Narosky et al. 1987). These tunnels are often placed in slopes or banks giving some protection from rain or floods.
Nests in the ground may be less vulernable to predators than nests on the surface of the ground, as shown by controlled field experiments with artificial nests (Martin 1987). Quail eggs in a wicker basket lined with leaves and placed on the surface of the ground in an Arizona forest had a significantly higher predation rate than similar artificial nests buried with the rim even with the ground and partially covered with dead leaves, or eggs simply placed in a hole in the ground.
From - Collias, N.E. (1997). On the origin and evolution of nest building by passerine birds. The condor 99:253-270.
Basically, there's tons of primary literature on this stuff. Go to your local university and start reading it. 
I'm not sure why birds' nests in particular stumped you. I for one believe in evolution from the physical only perspective, but I believe this mind-boggling thing called life would never have come about through just the forces understood by current science. I see a hierarchy of nature spirits fostering the process. Without their involvement with this planet, I believe the earth would look like every other planet or moon we can see; just endless mineral formations without a trace of life.
Oh dear god.
Birds nests? You couldn't think of an evolutionary advantage to taking care of helpless young?
