And? Would this not be an intermediate brain size between that of a human and a chimp? Because that's bigger than chimp and smaller than modern human. Considering that Homo habilis is the most ancient of the genus Homo I am aware of, I am not surprised by the brain size.
Yea not surprising at all except there is no cause, just an assumed effect.
In one of the areas of the human genome that would have had to change the most, Human Accelerated Region (HAR), we find a gene that has changed the least over just under 400 million years HAR1F. Just after the Cambrian is would have had to emerge de novo, fully formed, fully functional and permanently fixed along broad taxonomic categories. In all the time since it would allow only two substitutions, then, while the DNA around it is being completely overhauled it allows 18 substitutions in a regulatory gene only 118 nucleotides long. The vital function of this gene cannot be overstated:
The most dramatic of these ‘human accelerated regions’, HAR1, is part of a novel RNA gene (HAR1F) that is expressed specifically in Cajal– Retzius neurons in the developing human neocortex from 7 to 19 gestational weeks, a crucial period for cortical neuron specification and migration. HAR1F is co-expressed with reelin, a product of Cajal–Retzius neurons that is of fundamental importance in specifying the six-layer structure of the human cortex. (An RNA gene expressed during cortical development evolved rapidly in humans, Nature 16 August 2006)
This all has to occur after the chimpanzee human split, while our ancestors were contemporaries in equatorial Africa, with none of the selective pressures effecting our ancestral cousins. This is in addition to no less then 60 de novo (brand new) brain related genes with no known molecular mechanism to produce them. Selection can explain the survival of the fittest but the arrival of the fittest requires a cause:
The de novo origin of a new protein-coding gene from non-coding DNA is considered to be a very rare occurrence in genomes. Here we identify 60 new protein-coding genes that originated de novo on the human lineage since divergence from the chimpanzee. The functionality of these genes is supported by both transcriptional and proteomic evidence. RNA– seq data indicate that these genes have their highest expression levels in the cerebral cortex and testes, which might suggest that these genes contribute to phenotypic traits that are unique to humans, such as improved cognitive ability. Our results are inconsistent with the traditional view that the de novo origin of new genes is very rare, thus there should be greater appreciation of the importance of the de novo origination of genes…(De Novo Origin of Human Protein-Coding Genes PLoS 2011)
Whatever you think happened one thing is for sure, random mutations are the worst explanation possible. They cannot produce de novo genes and invariably disrupt functional genes. You can forget about gradual accumulation of, 'slow and gradual accumulation of numerous, slight, yet profitable, variations' (
Darwin). That would require virtual
Ha, what? What do you mean by conserved? I'd say there is a lot more variation in the size of human brains than there is in the size of our hearts. Which, by the way, people can survive being born without quite large portions of brain (not survive well, but survive nevertheless). No one survives missing half a heart. Not to mention the variety of defects associated with the brain. I mean, 18% of the adults in the United States have been diagnosed with some mental disorder or another. Yet, even though heart defects are some of the most common congenital defects people are born with, only about 1% of babies born have them.
-_- the genetic changes that result in our large brains also result in negative consequences, namely our species having a much, much larger chance of brain cancers than other modern apes. This is the result of a broken brain growth control gene. So, our brains actually grow during development at rates a little to close to how fast cancer cells grow. Furthermore, not all mutations in brain related genes result in disorder. One in particular that is becoming more common is one which reduces the number of hours a person requires to get restful sleep. No associations with a lower quality of life, shorter life, or reduced intelligence. However, it is painfully obvious that not all brain gene mutations result in lower intelligence simply by the variation in human intelligence now and the fact that ancient skulls of our species indicate a smaller brain size average than modern ones.
Brain related genes do not respond well to changes. Two dramatic giant leaps that would have had to occur in order of the human brain to have emerged from ape like ancestors SRGAP2, HAR1F. In addition genes involved with the development of language (FOXP2), changes in the musculature of the jaw (MYH16) , and limb and digit specializations (HACNS1).
The ancestral SRGAP2 protein sequence is highly constrained based on our analysis of 10 mammalian lineages. We find only a single amino-acid change between human and mouse and no changes among nonhuman primates within the first nine exons of the SRGAP2 orthologs. This is in stark contrast to the duplicate copies, which diverged from ancestral SRGAP2A less than 4 mya, but have accumulated as many as seven amino-acid replacements compared to one synonymous change. (Human-specific evolution of novel SRGAP2 genes by incomplete segmental duplication Cell May 2012)
What is the problem with 7 amino acid replacements in a highly conserved brain related gene? The only observed effects of changes in this gene in humans is disease and disorder:
- 15,767 individuals reported by Cooper et al. (2011)] for potential copy-number variation. We identified six large (>1 Mbp) copy-number variants (CNVs), including three deletions of the ancestral 1q32.1 region…
- A ten year old child with a history of seizures, attention deficit disorder, and learning disabilities. An MRI of this patient also indicates several brain malformations, including hypoplasia of the posterior body of the corpus callosum…
- Translocation breaking within intron 6 of SRGAP2A was reported in a five-year-old girl diagnosed with West syndrome and exhibiting epileptic seizures, intellectual disability, cortical atrophy, and a thin corpus callosum. (Human-specific evolution of novel SRGAP2 genes by incomplete segmental duplication Cell May 2012)
The search for variation with regard to this vital gene yielded no beneficial effect upon which selection could have acted. The only conceivable way the changes happen is relaxed functional constraint which, unless it emerged from the initial mutation perfectly functional it surly would have killed the host. Mutations are found in children with 'developmental delay and brain malformations, including West Syndrome, agenesis of the corpus callosum, and epileptic encephalopathies'.
And the range for chimps is 282-500 cc with an average of 384 cc. How can you not realize that the brains of Lucy's species are generally bigger than those of chimpanzees? Not that it matters in terms of being a transitional species. Also, why assume that brain size didn't skyrocket due to just a small number of genes, when one of the biggest reasons for the large brain size of our species is due to a broken brain growth control gene? One gene change can lead to drastic results, there's no reason for this trait to have a smooth, gradual transistion.
Lucy had a chimpanzee size brain, as did the Taung child, in fact she was kind of smaller then average. Speaking of transitionals I noticed you don't have much of a taste for Paranthropos right where you would expect a hominid fossil, a period covering a million years and it's just an ape transitional. Curious, very curious indeed, especially considering our primate cousins are virtually unrepresented in the fossil record.
Due to drastic fluxuations in environmental conditions from 800,000-200,000 years ago, the selective pressures to having better mental faculties to adapt to the environment increased drastically. Also, did you ignore Homo erectus on purpose? Because the brain size of that species was 900 cc on average, which is definitely between chimp and human.
Ok I'm not buying that scientists know as much about the weather 800,000 years ago. I'm really not going to buy the proposition that you can just insert natural selection every time you are missing an actual molecular cause.
Comparative Genomics should have ended, or at least challenged, Darwinian evolution by now but it is exalted above all skepticism. The a priori assumption of universal common descent is immutable in modern philosophies of natural history. The reason they are not questioned isn't the weight of the evidence, indicating chimpanzee-human common ancestry, but the animosity toward anything remotely theistic being suggested as a cause:
Idols of the Theater are those which are due to sophistry and false learning. These idols are built up in the field of theology, philosophy, and science, and because they are defended by learned groups are accepted without question by the masses. When false philosophies have been cultivated and have attained a wide sphere of dominion in the world of the intellect they are no longer questioned. False superstructures are raised on false foundations, and in the end systems barren of merit parade their grandeur on the stage of the world. (Novum Organum)
This grand theatrical production has been performing for over a century now, it's history littered with fabrication. Perhaps the longest running demonstration was easily the Piltdown fraud. The Piltdown Hoax was the flagship transitional of Darwinism for nearly half a century and it was a hoax. A skull taken from a mass grave site used during the Black Plague matched up with an orangutan jawbone. Even Louis Leakey, the famous paleontologist, had said that jaw didn’t belong with that skull so people knew, long before it was exposed, that Piltdown was contrived.
Leakey mentions the Piltdown skull in his book 'Adam's Ancestors':
'If the lower jaw really belongs to the same individual as the skull, then the Piltdown man is unique in all humanity. . . It is tempting to argue that the skull, on the one hand, and the jaw, on the other, do not belong to the same creature. Indeed a number of anatomists maintain that the skull and jaw cannot belong to the same individual and they see in the jaw and canine tooth evidence of a contemporary anthropoid ape.'
He referred to the whole affair as an enigma: In
By the Evidence he says 'I admit . . . that I was foolish enough never to dream, even for a moment, that the true explanation lay in a deliberate forgery.' (
Leakey and Piltdown)
The problem was that there was nothing to replace it as a transitional from ape to man. Concurrent with the prominence of the Piltdown fossil Raymond Dart had reported on the skull of an ape that had filled with lime creating an endocast or a model of what the brain would have looked like. Everyone considered it a chimpanzee child since it’s cranial capacity was just over 400cc but with the demise of Piltdown, a new icon was needed in the Darwinian theater of the mind. Raymond Dart suggests to Louis Leakey that a small brained human ancestor might have been responsible for some of the supposed tools the Leaky family was finding in Africa. The myth of the stone age ape man was born.
The Scottish anthropologist Sir Arthur Keith had built his long and distinguished career on the Piltdown fossil. When it was exposed it sent Darwinians scrambling, Arthur Keith had always rejected the Taung Child (Raymond Dart’s discovery) a chimpanzee child. Rightfully so since it’s small even for a modern chimpanzee. Keith would eventually apologized to Dart and Leakey would take his suggested name for the stone age ape man, Homo habilis, but there was a very real problem. The skull was too small to be considered a human ancestor, this impasse became known as the Cerebral Rubicon and Leakey’s solution was to simply ignore the cranial capacity.
Ever notice that there are no Chimpanzee ancestors in the fossil record? That’s because every time a gracial (smooth) skull, that is dug up in Asian or Africa they are automatically one of our ancestors.
"Sir Arthur Keith, one of the leading proponents of Piltdown Man, was particularly instrumental in shaping Louis's thinking. "Sir Arthur Keith was very much Louis's father in science" noted Frida. Brilliant, yet modest and unassuming, Keith was regarded at the time of Piltdown's discovery as England's most eminent anatomist and an authority on human ancestry...a one man court of appeal for physical anthropologists from around the world....and his opinion that assured Piltdown a place on every drawing of humankinds family tree." (Ancestral Passions, Virginia Morell)
Come on Sarah, you can do better then that.
