Genetics and Human Brain Evolution

You are starting to get a bit more strident. If you keep going in that direction you risk crossing a line, moving outside the bounds of polite debate and getting a suspension.Several individuals are trying to do you a favour and point out where you lack knowledge of some basic biology. Do NOT get nasty about it or a suspension will follow.Edited by AdminNosy, : correct author

Hi eggasai, You should bear in mind that brain size is correlated with body size. For this reason, absolute brain volumes are not a very useful comparative measure; rather we would normally want to use a relative measure of brain size which takes into account differences in overall body size. Because when the whole body gets larger, the brain gets larger as well but doesn't necessarily imply evolutionary change specific to the brain.If you take body size into account, it seems to me at least that to have the same size brain as an ape when you are only three feet tall is having a LARGE brain size, not a small one, since apes are aready considered fairly large-brained and they can grow up to six feet.The normal way to take account of body mass is to measure relative brain size as the observed brain size divided by the expected brain size. The expected brain size for any individual based on body size is given by the regression of log brain mass against log body mass. This measure is called the encephalization quotient (EQ). On this scale, a value of 1 means that you have a brain exactly as large as expected based on body mass. A value of two means that you have a brain twice as large as expected based on body mass. A value of 0.5 means that you have a brain half as large as expected, based on body mass. Etc. etc.If you calculate values for the various primates from fossils and extant species, and take the average EQ, you get the following values (mean from both sexes):

Species                           EQ
Homo sapiens (modern)             5.27
Homo sapiens (archaic)            3.87
Homo erectus                      3.27
Homo habilis                      2.73
Homo rudolfiensis                 3.13
Australopithecus boisei           2.14
Australopithecus aethiopicus      2.07
Australopithecus africanus        2.95
Chimpanzee                        1.39
Gorilla                           1.10
Gibbon (multiple species)         1.89-4.64
Guenons (multiple species)        1.45-2.49
Colobus monkey (multiple species) 1.08-1.21

SourceI think this data clearly shows that it is wrong to suggest, on the basis of absolute brain size in Homo habilis versus ape that no trend towards larger brains was present in the early members of the Homo genus.Apes are large animals, and they have large brains in the same way that they have large arms and legs, and large skulls. But gorillas and chimps still have larger brains than we would expect based on body mass (10-40% larger than predicted).The very earliest fossil hominids (Australopithecus) already had brains that were up to 100% larger than we would expect based on their body size, and the early members of the genus Homo had brains up to 227% larger than we would expect.If you look at these encephalizatoin quotients across time, you see a major jump in the Australopithecines, where go from an average kind of brain size to one that is twice as large as expected; then a steady, gradual increase within the Homo genus; followed by a second major jump in the early Homo sapiens, where we go from a species with a brain 3.9 times larger than we would expect based on body size, to a species with a brain 5.3 times larger than we would expect.CheersMickEdited by mick, : corrected a type - changed "200%" to "100%"Edited by mick, : No reason given.

No, it's more than a cliche that scientists use evidence to back up their theories. Creationists however love to ignore evidence and pretend they can keep repeating the same position no matter how much evidence is given that refutes it.I noticed you still did not address the issue:
(Source of picture is 29 Evidences for Macroevolution: Part 1)Showing the intermediate stages - transitionals - still takes the impression of a "giant leap" out of the picture doesn't it?Here is the key to the picture:

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(A) Pan troglodytes, chimpanzee, modern
(B) Australopithecus africanus, STS 5, 2.6 My
(C) Australopithecus africanus, STS 71, 2.5 My
(D) Homo habilis, KNM-ER 1813, 1.9 My
(E) Homo habilis, OH24, 1.8 My
(F) Homo rudolfensis, KNM-ER 1470, 1.8 My
(G) Homo erectus, Dmanisi cranium D2700, 1.75 My
(H) Homo ergaster (early H. erectus), KNM-ER 3733, 1.75 My
(I) Homo heidelbergensis, "Rhodesia man," 300,000 - 125,000 y
(J) Homo sapiens neanderthalensis, La Ferrassie 1, 70,000 y
(K) Homo sapiens neanderthalensis, La Chappelle-aux-Saints, 60,000 y
(L) Homo sapiens neanderthalensis, Le Moustier, 45,000 y
(M) Homo sapiens sapiens, Cro-Magnon I, 30,000 y
(N) Homo sapiens sapiens, modern

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The skull image you used (H)... ... is in the middle of the transitions from Australopithecus africanus to modern human.The fact that there is a clear trend from (B) to (N) in the picture is what evolution predicted - and further predicts that more intermediates will be found to fill in even those "gaps".You haven't addressed the issue of sexual selection that allows faster adaptations for run-away features than for normal features, and the only argument you have is your personal incredulity that what we see in genetics and in fossil evidence could not have happened naturally.Unfortunately for you, nature is not constrainted in any way by your incredulity.Enjoy.

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Join the effort to unravel {AIDS/HIV} {Protenes} and {Cancer} with Team EvC! (click)

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No, it's not. It's hilarously incorrect. An amino acid is any molecule that contains both an amine and a carboxyl functional group. These functional groups are sort of like the pips and sockets on a Lego:in that an amine group in one amino acid is peptide bonded to the carboxyl group of another (via polymerization), forming a polypeptide chain that, after completion, folds into a functional protein shape. 20 such acids are employed in living organisms, and are specified within genes by the three-nucleotide codons that people have been talking about. Egg seems to think that those lists are actually telling him what amino acids are made of, but that's a drastic misunderstanding. The chemical structure of the 20 amino acids necessary for life can be found here: Proteinogenic amino acid - WikipediaAs you can see, no amino acid contains any nucleotides.Amino acids are the essential structural building blocks of proteins. This is such an essential, basic fact of biology that it's staggering that someone could get it so wrong and yet be so sure he's right. I look forward to the rest of his short EvC career with great interest.

So in your alternative universe form of molecular biology what does transfer RNA do?I would highly reccommedn you to read some of the textbooks available on the pubmed bookshelf especially the RNA to protein section of 'Molecular Biology of the Cell' by Alberts et al. This is pure fantasy, Watson and Crick may have worked on the problem but the didn't solve the nature of the genetic code. It was Gamow who proposed that there were codons in mucleotide triplets and Khorana, Holley and Nirenberg who did the first experiments showing what certain particular triplets coded for; work for which they won the nobel prize. Perhaps you are thinking of Crick's work with Sidney Brenner which bears some relation at least to what you are suggesting (Crick et al, 1961). There is an interesting historical review of the several different theories proposed for the gentic code in an American Scientist article (Hayes, 1998)Of course if you have a refeerence for this paper of Watson and Crick's I think now would be the time to provide it. So true, and so amusing. Perhaps you may understand now why the discussions of comparative genomics have stuck. Because it is you who lacks a rudimentary understanding of the principles involved. You obviouly think of yourself as an educated layman but in fact you are just a layman.I really think you should start providing some references for where you are getting your basic information from because either it or your understanding of it is fundamentally wrong.TTFN,WKEdited by Wounded King, : No reason given.Edited by Wounded King, : No reason given.

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I though amino acids make up the basic components of proteins and not code for them.

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Originally I said that a single nucleotide substitution in the protein coding genes could shut down the reading frame. The rest of it is a tangent, this is how the amino acid sequence codes for proteins: The triplet codons make the amino acids. The amino acids in a specific sequence make up the 'code'. My point was that there was no such thing as a coding nucleotide, it's the amino acid seqeunce that determines the protein. Apparently, things are going to be bogged down on semanitcs and basic biology for a while. I was trying to talk about the protein coding genes but instead we are spending all our time on what a protien code is.They think I don't know basic biology, that's the real problem. Edited by eggasai, : transcript errors

You prove them right when you say things as ignorant as "amino acid sequence codes for proteins".I mean you can't even seem to read your diagram right. That sequence of amino acids down there at the bottom? That's the protein. I mean it's even labeled "growing protein chain."Nucleotides arranged in triplet codons specify amino acids in sequence; amino acids condensed together with peptide bonds (amine to carboxyl) form proteins. No, they don't. They specify amino acids, via the mechanism of tRNA. Amino acids are produced at other places in the cell, or aren't produced at all - they're provided by the diet of the organism. (That's why there's 9 essential amino acids that, as a human, you're required to injest from food. Your cells are unable to produce them de novo.) You could only shut down the reading frame if a substitution turned a amino-specifying codon into a stop codon. Barring that, which is fairly unlikely, the reading frame continutes. A deletion or an addition can shift the frame by one base, but those mutations are counteracting - an insertion later in the sequence can restore a reading frame shifted by an earlier deletion, and vice-versa. No. The nucleotides (A,G,C,T) make up the code. The amino acids they code for make up the protein. Amino acids are the fundamental structural units of proteins, when they're joined together (amine to carboxyl) with peptide bonds. Folding polypeptide chains produce the spacially-determined active sites that allow proteins to catalyze chemistry within the cell. Until your misunderstandings are corrected, debate is impossible. We can't have a debate with you until you know what you're talking about. No, no thanks are necessary - it's our pleasure to educate you.Edited by crashfrog, : No reason given.

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Several individuals are trying to do you a favour and point out where you lack knowledge of some basic biology. Do NOT get nasty about it or a suspension will follow.

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No problem, I'm actually enjoying the basic biology primer.

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You should bear in mind that brain size is correlated with body size. For this reason, absolute brain volumes are not a very useful comparative measure; rather we would normally want to use a relative measure of brain size which takes into account differences in overall body size. Because when the whole body gets larger, the brain gets larger as well but doesn't necessarily imply evolutionary change specific to the brain.

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Still the cranial capacity becomes central to the definition Hominids based on the cerebral rubicon. Cranial capacity is the most distictive feature of the genus Homo, the various definitions within that genus reflect this basic concept.

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If you take body size into account, it seems to me at least that to have the same size brain as an ape when you are only three feet tall is having a LARGE brain size, not a small one, since apes are aready considered fairly large-brained and they can grow up to six feet.

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Gorillas stand pretty tall but their cranial capacity still isn't as big as a chimpanzees, who stand about 3 foot tall. The cerbreal rubicon has long been that main morphological traits that distinquishes hominids from apes. It has become increasingly clear to me that the not all of the hominids belong in the genus Homo. Cranial capacity still marks a clear line of demarkation.

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If you calculate values for the various primates from fossils and extant species, and take the average EQ, you get the following values (mean from both sexes)

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Dimomorphic variance also translates into cranial capacity differences. Hablines generally range from 510cc to 775cc and besides bipedal frames they are clearly knuckle dragging apes.

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I think this data clearly shows that it is wrong to suggest, on the basis of absolute brain size in Homo habilis versus ape that no trend towards larger brains was present in the early members of the Homo genus.

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The trend in the early hominids suggests to me that the trend in ape lineages was a decrease in absolute brain size. Every ape skull dug up in Africa from prehistory is automatically put in human lineage. There should be a concerted effort to determine ape lineage but the need for transitionals takes preferance.

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If you look at these encephalizatoin quotients across time, you see a major jump in the Australopithecines, where go from an average kind of brain size to one that is twice as large as expected; then a steady, gradual increase within the Homo genus; followed by a second major jump in the early Homo sapiens, where we go from a species with a brain 3.9 times larger than we would expect based on body size, to a species with a brain 5.3 times larger than we would expect.

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What we really have for the Austropithecenes is fragmentary peicemeal compositions. There is no genuine absolute brain/body size ratios. With the habilines they are well below the cranial capacity for humans and in some cases for the Homo genus. What you are looking at in ape lineages is a decrease in cranial capacity and a loss of bepediality. That's why this gets so convoluted, too often they are automatically considered human ancestors rather then ape.

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If you look at these encephalizatoin quotients across time, you see a major jump in the Australopithecines, where go from an average kind of brain size to one that is twice as large as expected; then a steady, gradual increase within the Homo genus; followed by a second major jump in the early Homo sapiens, where we go from a species with a brain 3.9 times larger than we would expect based on body size, to a species with a brain 5.3 times larger than we would expect.

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The austrophithecines average slightly above that of a modern ape. The overall brain size did not double from the Austropithecines to the habilines. Homo habilis had a cranial capacity below 600cc while the austropithecines has a cranial capacity about 400cc. The cranial capacity does not actually make a signifigant jump until Homo habilis where it goes from under 600cc to close to 1000cc.What needs to be understood is that the austropithecines and hablines are actually a mixture of gorilla and chimpanzee ancestors. The human ancestors are actually the Homo erectus fossils.

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You prove them right when you say things as ignorant as "amino acid sequence codes for proteins".

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The amino acid seqeunce is the code the proteins are translated from in the ribosome.

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I mean you can't even seem to read your diagram right. That sequence of amino acids down there at the bottom? That's the protein. I mean it's even labeled "growing protein chain."

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I don't know what you think the problem is here but amino acids are translated into proteins. The amino acids determine the protien chain but they have to be translated into proteins, that is about as basic as it gets.

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No, they don't. They specify amino acids, via the mechanism of tRNA. Amino acids are produced at other places in the cell, or aren't produced at all - they're provided by the diet of the organism. (That's why there's 9 essential amino acids that, as a human, you're required to injest from food. Your cells are unable to produce them de novo.)

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Yes they do, the amino acid is defined by the triplet codons, remove a condon and you got nucletides.

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No. The nucleotides (A,G,C,T) make up the code. The amino acids they code for make up the protein. Amino acids are the fundamental structural units of proteins, when they're joined together (amine to carboxyl) with peptide bonds. Folding polypeptide chains produce the spacially-determined active sites that allow proteins to catalyze chemistry within the cell.

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No, the nucleotides make the triplet codons of the amino acids. Nucletides don't code anything in and of themselves and your spliting semantical hairs. This is twice you tried to contradict me and then elaborated from there on a tangent.

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Until your misunderstandings are corrected, debate is impossible. We can't have a debate with you until you know what you're talking about. No, no thanks are necessary - it's our pleasure to educate you.

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That's kind of funny, most of the basic biology we are discussing could be covered in one post. I don't know if conflating the basic biology is just a rethorical tactic or you actually believe what your saying.This all started with the misconception that a nucleotide has some intrinsic coding quality. I mentioned in passing that a single nucleotide substitution could get the reading frame shut down. I was contradicted and told that every coding nucleotide has at least one reading frame. Terms like; reading frame, coding sequence and protein sequence are just expressions. The basic principle was summed up as DNA-transcription-RNA-translation (aka the central dogma of biology)A debate is impossible because no one seem cognizant of this ubiquitious principle in biology. Basic errors are actually being made not because of my misunderstanding but an attempt to correct and contradict me.The original point was that the protein coding genes show differences at an amino acid sequence level. One regulatory gene 118 nucleotides long has diverges from chimpanzees by 18 nucleotides. The same regulatory gene when comparing chimps to chickens has 2 substitutions which represents 310 million years. When this point couldn't be answered the discusssion was derailed with this...basic biology debate.Edited by eggasai, : transcript errors having a deleterious affect in the alphanumeric word codeing sequences. You know...typos.

Care to show where this happened? I see where Mick said... A sequence of nucleotides is not a single nucleotide.TTFN,WK

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No, it's more than a cliche that scientists use evidence to back up their theories. Creationists however love to ignore evidence and pretend they can keep repeating the same position no matter how much evidence is given that refutes it.

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The Talk Origins shelf of skulls gives the illusion of a gradual anagenesis of the human skull. Homo habils had a cranial capacity just over 500cc while the Austropithecines are thought to have averaged above 400cc. The period from at least 5 mya until under 2 mya represents a prolonged period of stasis with about a 200cc variance not counting dimorphic variables. Homo habilis was most likely contemporary with Turkana Boy or only seperated by a couple of hundred thousands years. Turkana Boy weighs in at a cranial capacity above 900cc and Homo erectus cranial capacity remains static for at least 1 million years.Now, if you would like to take a walk through the shelf of skulls I would be delighted to debunk this optical illusion with substantive details. By the way, Homo rudolfensis was originally dated 3 million years old and only moved because Homo habilis was 200cc smaller. The dates assigned are obviously bogus but given what you listed, this one is a no brainer (LOL I'm so punny ). Everything from A to F is an ape, everything from G to you and me are humans.What Talk Origins fails to clarify is that the human brain is three times that of a chimpanzee.

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... is in the middle of the transitions from Australopithecus africanus to modern human.

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Then you should be able to tell me both the species, cranial capacity and speciman catalogue ID. I say it's either ape or human, what is your criteria for determining it is a transitional?

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You haven't addressed the issue of sexual selection that allows faster adaptations for run-away features than for normal features, and the only argument you have is your personal incredulity that what we see in genetics and in fossil evidence could not have happened naturally.

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On the contrary, I have the Chimpanzee Genome Consortioums conclusion that natural selection was not a factor in the evolution of humans from the last common ancestor of chimps and humans. I have the selective coefficients from the divergance between human and chimpanzee genomes. I have the comparative anatomy of contemporary chimanzee and human morphological traits to use as a based line. Finally I have the divergance of the respective genomes and the observed mutation rate for hominids, the fixation rate and the deleterious effects of mutations on protein coding and functional genes.I am far from incredulous and I'm immune to these Darwinian rethorical devices. The discussion can focus on circular arguements over semantical hair spliting but I'm not chasing it.I have an idea, why don't you guys just correct the errors in one anothers posts and I'll jump back into the discussion when your done.Edited by eggasai, : I wanted to rephrase something

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A sequence of nucleotides is not a single nucleotide.

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Like I said, let me know when you guys are interested in discussing genetics and the human brain.

No, amino acids are condensed into proteins via peptide bonding. That's the problem here - you don't seem to understand what amino acids are. Amino acids don't have any codons. Codons specify amino acids via the mechanism of tRNA, but amino acids are not made out of codons or nucleotides. Amino acids do not contain nucelotides. The definitive characteristic of an amino acid is that it possesses an amine group at one end and a carboxyl group at the other. Amine and carboxyl groups are complimentary and so two amino acids can combine via a condesative reaction to form a peptide bond between them. This doesn't make a lick of sense. If you remove a codon, you simply remove an amino acid from the protein product of the gene. You don't suddenly "get nucleotides", whatever that means, because nucleotides have been there all along - that's what DNA is made from, nucleotides.Try and repeat it after me: genes have codons. Codons are made of nucleotides. Codons specify amino acid sequences. Amino acids connected in sequence form a protein.It's really not that difficult. Can you explain the problem you're having with this concept? There's nothing semantic about what we're talking about. You continue to assert that proteins are encoded in amino acids, and this is patently false. Amino acids are not molecules of sequence storage; that's what nucleotides do. Amino acids are structural molecules - they're the structural components of proteins. Indeed. This is such a basic principle, which you're so quick to rattle off, that it's amazing to the rest of us that you don't apparently have any idea what it means.Let me walk you through the process. DNA is transcripted into mRNA, a single-stranded nucleotide sequence that is passed off to the ribosome. At the ribosome, each set of three nucleotides (called a codon) is matched to the complimentary nucleotide sequence (the anticodon) on an aminoacylated (or "charged") tRNA molecule. When the tRNA lines up on the RNA, the tRNA's amino acid binds to the carboxyl group of the elongating polypeptide chain. The deaminoacylated tRNA is released, and the ribosome moves three nucleotides down the mRNA, where the process (called "elongation") is repeated until the entire protein unit has been generated.It's almost impossible to believe that you could be getting it so wrong and yet be so determined that you're right. It's possible we're simply miscommunicating here, but absolutely none of the descriptions of the process you've offered bear any resemblance to how proteins are actually stored and expressed from genetic material.

I think some terminology is getting in the way here.Just so you understand my issue.For someone to say "hydrogen and oxygen code for, or are translated into , water" sounds a bit arkward. No?Edited by iceage, : No reason given.