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This is topic will begin a reading of The Ancestor's Tale. I think we can discuss here the prologue and the Farmer's and Cro-Magnon's Tale, at least.
"we human pilgrims pass only about 40 rendezvous points in all, before we hit the origin of life itself"
40 points of confluence separate homo sapiens from the likely bacterium grandma.
That seems to me to be an astoundingly small number.
I think that's the new understanding, though it's not repeated often enough. We very often here that the 2nd law of thermodynamics dictates how, on the whole, entropy increases, but it's seldom mentioned that in the presence of abundant energy evolution by natural selection can bootstrap pockets of complexity.
Scifi fans might enjoy Greg Egan's short story "Crystal Nights" in which scientists, acknowledging that evolution is the only known mechanism for creating an intelligent organism, set about evolving intelligent life in a computer simulation:
It strikes me as quite amazing as well. I like that Dawkins tells us the approximate number of generations in the past at which rendezvous occurred. Granted a million generations is quite a lot, but it's not an astronomically large figure.
Today's bacteria have essentially evolved from our same common ancestor over the past 3 Gy, enough evolutionary change to stay successfully adapted to the world as it changed over that time.
I try to picture the changes that the genus Homo has undergone in the last couple million years, to envision similar change in all species that are presently alive today.
Part of my trouble I think is that I am trying to apply this concept to the speciation rendezvous's. Those previous individuals prior to the most common ancestor that do not have a descendant in one species may possibly have a descendant in another species.
It may be that this point about the earlier common ancestors is not a significant point. It just so far has confused me.
This is discussed in the first part of the Tasmanian's Tale.
I thought this was a little confusing too and would have benefited from a diagram. I think Dawkins is referring to how it might have looked in the very beginning when life first came into existence. We might imagine a soup of proto-organisms like goop in a giant test tube. Presumably all life arose from a sub-population within the big tube. At this early point, the proto-organisms are either part of those that gave rise to everything we see today (each one of these can be considered our common ancestor), or they are in the groups of proto-organisms that died out leaving no surviving descendents.
Rather than one giant test tube, it could be that life arose in several places on the earth and that our lineage displaced all the others. I find this particularly fascinating. Might we still find remnants of one of the other lineages? Does the current lineage of life preclude it from arising in a different form? If not, why hasn't it bootstrapped itself again over the last 3 billion years?
Some possible reasons that other lineages have not arisen might be that the conditions no longer exist for spontaneous creation of life, the existence of other competing life with a firmer hold on survival, general difficulty in achieving sustainable chain of life.
It seems possible that proto life would have come into existence many times, but only once did it become established. The same forces that bring together the right molecules may almost as quickly destroy them. At some point the right combination formed within a membrane that provided protection from the environment.
It may be difficult to exist as RNA without a protective membrane. Things always seem to point to the cell for the start.
Dawkins though hints at the excitement that would exist around the first new type of life.
That's an interesting idea. We know that microorganisms had a reducing affect for a very long time adding oxygen to the early anaerobic atmosphere. Perhaps anoxic conditions are more favorable. If so, perhaps some of the extreme environments on earth would still be conducive for the process.
It may be difficult to exist as RNA without a protective membrane. . . .
You're familiar with the RNA-world hypothesis? Micelles have been shown to form spontaneously when lipids are added to water, providing a safe haven for fragile RNA molecules. But why aren't the RNA-based progenitors still around? Why did they all give way to DNA-based life? Perhaps there's a sort of platypus-like microorganism waiting to be discovered. We mostly know about bacteria indirectly, by growing colonies in a plate containing some concoction of nutrients. It's thought (at least it was around 10 yrs. ago) that we're capable of growing only a small fraction of the existing bacteria. Maybe some undiscovered variety hails from a completely different lineage, one that stalled at the microorganism phase. Carl Woese had a near-miss when he characterized the Archaeans.
Part of the conditions for creation of life might also be vast numbers of interactions. Perhaps we might think that vast numbers could be achieved with vast time, say 3 Gy or so, but maybe not. It may take vast numbers in the current time of ample extreme conditions
Plus one of the most significant conditions for the creation of life might be the absence of competition. Life is fragile. Incipient life probably more so.
Perhaps life started many times. And of those many times, it took hold on Eath just once. Among those vast numbers of opportunity, only once. And that was without competition from a superior pre-existing form.
The non sex DNA haplotypes have older date for the most recent common ancestor, in the 500 Kya range. mtDNA and Y-DNA are from the 140 Kya range. That date is consistent with the dating of Mitochondrial Eve.
Dawkins indicates that there is nothing special about our current Eve. As various blocks of descendants die out, the date for Mitochondrial Eve will advance. Our current Eve will lose her place of eminence.
What is the significance of the persistence of older haplotypes?
It will also be interesting to see what done on a continuing basis with the distinction between genetic and individual heritage. It seems likely to me that such a distinction will not be continued as a main point in subsequent chapters.
Dates derived from molecular evidence are notoriously tricky since they have to assume a certain rate of DNA mutation, which is known to vary considerably (mtDNA, due to its close proximity to reactive radicals mutates 5-10 times more quickly).
An old haplotype would generally be assumed to be evolutionarily restrictive in some way, such that alternative alleles were selected against. The lab I worked in specialized in mitochondrial medicine, and I worked on systems used to assess the the likely contribution of a given DNA variant to a disease phenotype. If a variant caused a change to a very old haplotype, one that we share with distantly related species for example, that was an indication of trouble.
Life may have been brought to Earth in our case, but of course that does not answer the question about life's origins.
A related question that I have asked before is how would the discovery of other life forms impact our survival - what is the chance that a microorganism from another world bring new disease to our world?
Your point about old haplotypes is helpful. I was trying to think how a significant section of DNA might avoid some type of recombination over such a long period. Luck? Especially strong bonds? Close proximity - but if all the genes are close then it could not be especially long, could it?
Your point is that alleles in these haplotypes have heavy selection pressure against their survival? So these DNA section likely experience normal recombination, but typically the genotypes with these sections recombined do not survive?
I'm constantly surprised how we oxygen breathers have - however remotely - ancestors to whom oxygen was toxic and who mostly died out. Is it too fanciful to imagine a future, long after the direst outcome of climate change for example, when perhaps methane is the dominant atmospheric component, and oxygen breathers have died out to be replaced by methane breathers?
But perhaps I'm speculating outside the scope of this conversation? If so, please tell me so, and I will withdraw to less rarified climes!
Life may have been brought to Earth in our case, but of course that does not answer the question about life's origins.
True, but it greatly expands the possibilities. One of the astrobiology seminars discussed the chemistry that occurs on asteroids in deep space. Though cold, they heat up momentarily due to collisions. The things produced are similar to those in the famous Miller–Urey experiment.
A related question that I have asked before is how would the discovery of other life forms impact our survival - what is the chance that a microorganism from another world bring new disease to our world.
I'm not an immunologist, but I know the general rule of thumb for infectious diseases. Largely, they are host-specific, so it seems quite likely that an alien microorganism would be benign. But who knows what form it might take. Perhaps it has a novel way attacking carbon molecules in general. And when an infectious disease does "jump species" it's often quite deadly (e.g. HIV).
Certain haplotypes do ride along unchanged over time simply by being in very close proximity to a region that's under strong selective pressure, but generally the longer the region of DNA the more likely it is to undergo a recombination event (mtDNA doesn't go through meiotic recombination).
Your point is that alleles in these haplotypes have heavy selection pressure against their survival?
Selection pressure works both ways, i.e. for or against survival. In the clinical I worked in, we were attempting to identify newly acquired variants that were deleterious. Seeing a variant, especially one not found in close relatives, that exists within a highly conserved region of DNA is a smoking gun.
Not really. All the ingredients of life are available on Earth so there's nothing to be gained by invoking chemicals from space.
If it is different there would be much to learn about what it means to be alive.
If it is similar, then the question arises in my mind whether we have the same seeding (such as panspermia ideas) or whether we have arisen with separately with similar chemistry (suggesting that life may have limited paths through which to develop).
fossils that suggest the speech areas of the brain enlarged about 2 million years ago
skeletons that suggest a lack of capacity for precision breathing
the speech allele in the FOXP2 gene
even, the idea that the language is related to the Great Leap of the Cro Magnon man
Does anyone know of any new developments in the question of the dating of the development of speech?
Interesting videos. I may enroll into the astrobiology class. You can enroll in the classes and just audit and download the lesson videos. Watching them at some later point when supposedly there is more time. :)
I am just starting on rendezvous 1 with our cousins the chimps. I may post here a question about brain size and the ideas that Dawkins posted about dividing lines and how gradual evolution necessarily is.
The astrobiology course was not accepting new enrollment. I think enrollment was closed after the first quiz deadline. I did register for the next offering TBA.
I know a bit about the controversies surrounding the rate of evolution.
I think itunesU, and similar projects, are a world-changing endeavor that haven't been widely recognized. Now, anyone in the world with an internet connection can get an MIT education (at least they can see the lectures) for free. I'd expect that the value of a diploma will gradually be replaced by the value of knowing.
This is my second read of Ancestor's Tale. And I would like to get a handle on the concepts he discusses, as well as an image of the concestors themselves.
I mentioned the points made about brain size and the incremental changes that accumulate to develop into speciation - the difficulty of drawing the line. It is just at some point two extremes of a spectrum are enough different.
Brain size is discusses with its own significance, but also as illustrative of principles with wider applicability, such as accomodating different sizes (3/4 rule), incremental changes and dividing lines, and co-evolution of traits including matching function and form.
This evolution thing is wonderfully intricate.
No, I just joined in with the conversation - I don't even know what the Ancestor's Tale course is, even. As for 'concestor', you've got me there!
It is not a course, but a book.
The talk about a course is just side chatter about some online courses I am doing on Coursera. One of which though coincidently is on evolution.
concestor is a word coined by Dawkins for the book - it means something like a common ancestor species identified or projected which is shared by multiple modern species.
The idea in the book is that we read tales from various common ancestors, concestors, which lead to the one concestor of all life on Earth.
Species has always been a fuzzy term. Biologists use it pragmatically to denote a group that are likely to couple together to produce viable offspring. Note that two species might be biologically capable of producing offspring, only they normally wouldn't have the opportunity because of physical, temporal, or behavioral separation. Over time they diverge more and more until the offspring are no longer viable or they can't mate at all.
The paragraph beginning 'Suppose and elephant sized animal" through the next 3 or 4 paragraphs.
It is apparently a common correlation factor for comparing different scales among plants and animals. In this tale is focuses on brain size compared to body size.
The graph on p84 shows H sapiens brain 6x larger than expected.
The trend for the genus is ever increasing brain size, which of course suggests that in another few million years the genus will have even larger brains. Not an new idea but one very clearly seen and explained in that graph.
Not really. Evolution doesn't have momentum and the evolutionary pressures today are much different than they were a million years ago so I imagine that the trend could very well have veered to a different course.
Haven't had any reading time the last couple of days, but I listened to Brian Cox discuss the origins of life on the BBC's Discover Wildlife podcast.
I wonder if anyone else is reading along. I have been somewhat slowed by some of the courses - I am taking the evolution course, and also a calculus and a philosophy course. I had some midterm exams this week. And now there is an electromagnetism course starting today.
But I have read through the Gibbons concestor.
The question of bipedality vs tree living in that concestor is very interesting. Just how distinguishing for early humans was bipedality.