And what is his “implied” question?
What do you mean how and why it happened? It’s not really a question anyone can possibly answer. From our perspective changes to genomes are random and certain parts of the genome are under very selection pressure due to the environment. That’s it. There’s not really much that one can necessarily predict beyond rather simple things like Darwin did in predicting there should be some kind of insect that could possibly get pollen from the following flower:
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I agree with the way you put it. I’m not sure what the why question would be about that makes it different from the how question. Surely no intention is required.
Should I take your response to mean that the moderators of this forum are unwilling or unable to locate the article that I wrote previously and post it as part of this discussiob or tell us where to find it?
The most important thing they had was the hollow bones. Hard to tell which had feathers, but it is known this does precede flight. Oh and by the way… new evidence suggests that dinosaurs were warm blooded… or in between… and this whole idea of warm blooded versus cold blooded is a bit misleading anyway. The evolution of flight isn’t all that extraordinary considering it happened at least 3 times… among insects and mammals as well as from the dinosaurs… 4 time if you include flying fish which considering the difficulties involved is perhaps a more extra-ordinary feat than the other cases.
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You don’t have to be a moderator to search but the only thing I could find that you posted was this
Is this what you meant?
Excellent response. There are more groups which fly than you might think: Flying and gliding animals - Wikipedia
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This is what I meant. Thank you for your effort.
A very interesting study published in September, 2014 in Current Biology depicts how dinosaurs made the transition to birds is a long series of changes before they were able to fly. This summary was taken from a report in the National Geographic on the web.
The first step was the development of feathers. It has been suggested that many dinosaurs developed feathers, not for flight, but for warmth. They provide excellent insolation.
The next step was to get smaller and the evidence indicates that these fauna get smaller just as other dinosaurs were getting larger. While there is no clear reason for this, I would suggest that this could be based on warmth also. If the warmth problem was solved by feathers, just as mammals used fur, dinosaurs could get smaller. Gigantism of the Mammoths and the Saber Tooth Tiger is tied to cold.
When dinosaurs became small enough to be supported by their wings in the air they were ready to conquer the air.
Why do birds fly? There is an old saying, “Nature abhors a vacuum.” This means that when there is an imbalance in nature, nature3 seeks to restore that balance.
Let us imagine a world where there is no birds. Billions of insects would exist without any predators to keep them in check. Billions of meals would go uneaten. The God of nature found a natural way to populate an important ecological niche by the creation of birds.
The new study supports the views of George G. Simpson published in 1941 that suggested that “evolutionary innovation can lead to rapid diversification among species exploiting new environmental niches.”
Opening the air as a biological niche in a new way through flight undoubtedly saved bird/dinosaurs from the extinction suffered by other dinosaurs 66 million years ago.
This important example amply proves the power of ecology and the environment to shape and guide evolution through Natural Selection.
The first thing I would do is recognize that for large changes in a population, I would need a lot of genetic diversity. So I’d get my population of rodents as big as I can—hopefully a few million—and then let a thousand or so generations go by, so that lots of variation has time to build. Then I’d introduce selection for the animals that do best in the water, and after we got as much change from the population as we could, if diversity had gotten low again, we could repeat the whole process as many times as we wanted, or until the food ran out.
This is also why comparisons of evolution to human domestication is of limited use. Humans can increase selection pressure, and we could even increase mutation rate, but evolution requires vast populations and numbers of generations in order to get truly dramatic results. Think about the process of creating any truly complex piece of technology: nobody schemes anything up from scratch, you always see generations of ideas and trying different things to see what works.
(Note that rather than rodents, whales evolved from small, primitive ungulates, and their closest living relatives are hippos.)
Matthew @pevaquark, most people know that the dinosaurs went extinct because the climate of the earth grew colder. Are you claiming that this is false? Of course there is some disagreement as to the causes of this change.
However now we know that some descendants of dinosaurs did not go extinct, the avian dinosaurs who became birds. Can you say that the evolutionary changes that they went through were not related the to the ecological changes that killed off the other dinosaurs?
Yes, it is an educated guess, but isn’t that what science is about, guesses confirmed by the observed facts? To say that we cannot know something because of some theory is not science.
That’s not what that means.
Also the average density of the universe is one single proton per cubic meter.
Did you read my posts? Or maybe you did and misunderstood what I was saying which is entirely possible. Because the part right after that I said:
That’s pretty much all someone can possibly answer as to how and why we ended up with birds in the modern sense. That seems to be kind of like you were saying as well though I’m prepared to see several posts on ecology and evolution now.
Incorrect. It is an unsolved mystery and the most well known hypothesis is the Yucatan asteroid impact leaving a layer of iridium all over the place. At least hypotheses like this would explain why they didn’t simply adapt to the climate changes. In other words, there is probably more than one cause and an impact could have been a triggering event for more than one these changes to make a more sudden change which many species were unable to adapt to. It was also likely to have been something of a chain reaction, as the loss of plants and animals starved out those species which depended upon them.
The flying squid were certainly a surprise to me.
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It’s false in a few ways. Most but not all dinos went extinct, during a mass extinction event that eradicated 3/4 of the earth’s species. There is consensus that the era was characterized by dramatic climate change, but “colder” is too simplistic. Overall climate became cooler but is typically characterized as more chaotic and definitely as “disrupted.” More importantly, I think there is substantial support for the position that ecosystem destruction was catastrophic, leading to complete collapse of entire ecosystems. There seems to be debate about whether ecosystems were already stressed, due to some notable but not singularly catastrophic climate swings. (See first paper below.) But conversely, there seems to be consensus that a catastrophic event, namely the Chicxulub impact, triggered the global collapse leading to massive extinction. See the second paper.
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That is interesting. I was taught that flight is made possible because a (partial) vacuum is created when air flows over a wing and air pushing up under the wing to fill that vacuum creates lift.
Now I am generalizing from that concept. Organisms seek food and the more food available the more pressure there is to fill a vacuum created by the lack of predators.
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Could you explain both of these a bit more?
“From our perspective changes are random…” is there another perspective by which these changes are not random?
“Certain parts of the genome are under selection pressure due to the environment…” I’m not sure exactly what you mean by this, specifically?
I’m afraid this is a question begging fallacy. If we assume that flight is the result of unguided evolution, then, yes, we can conclude that it must not be all that extraordinary, since it happened those numerous times.
You’re right that we shouldn’t just assume that. A better way to make the point might be to look at how many existing (or extinct) animal forms are somewhere between flight and not-flight, and you might be surprised at the diversity of gliding creatures in the natural world. Squirrels, fish, squid, lemurs, snakes, lizards, ants, and frogs all have species capable of gliding flight. Looking at all these examples, it becomes not so difficult to posit a gradual transition to powered flight, animals which can flap effectively enough to provide lift through the air rather than “just” a more controlled descent.
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Here is a great summary of what a ‘random mutation’ means done by @T_aquaticus at Peaceful Science- What "Random Mutation" Means in Science - Peaceful Science
There are different types of selection pressure that I was thinking of but the basic idea is the genome changes each generation and these changes will (from our perspective) be random. These changes can be neutral, negative or positive.
Negative selection pressure/purifying selection:
Here is an example shared by @sfmatheson a little while back where some researchers found regions of the genome unaffected by mutation which could indicate they are under purifying selection:
Survival bias, WWII planes, and human genetics
Purifying selection can be defined as:
Purifying selection prevents the change of an amino acid residue at a given position in a multiple alignment, thus favoring an excess of synonymous versus nonsynonymous substitutions.
For reference:
Synonymous vs. nonsynonymous mutations which are briefly discussed here-
Positive selection:
Here’s a neat example of looking for parts of the Dolphin genome that are under positive selection pressure that can help learn what makes a dolphin unique:
Note: I probably made at least one error in a nuanced definition so please let me know if that’s the case.