Evidence that human brain evolution was a special event

[Antiquarian]

Genes that control the size and complexity of the brain have undergone much more rapid evolution in humans than in non-human primates or other mammals, according to a new study by Howard Hughes Medical Institute researchers.

The accelerated evolution of these genes in the human lineage was apparently driven by strong selection. In the ancestors of humans, having bigger and more complex brains appears to have carried a particularly large advantage, much more so than for other mammals. These traits allowed individuals with "better brains" to leave behind more descendants. As a result, genetic mutations that produced bigger and more complex brains spread in the population very quickly. This led ultimately to a dramatic "speeding up" of evolution in genes controlling brain size and complexity.

"People in many fields, including evolutionary biology, anthropology and sociology, have long debated whether the evolution of the human brain was a special event," said senior author Bruce Lahn of the Howard Hughes Medical Institute at the University of Chicago. "I believe that our study settles this question by showing that it was."

Lahn and his colleagues reported their data in a research article published in the December 29, 2004, issue of the journal Cell.

The researchers focused their study on 214 brain-related genes, that is, genes involved in controlling brain development and function. They examined how the DNA sequences of these genes changed over evolutionary time in four species: humans, macaque monkeys, rats, and mice. Humans and macaques shared a common ancestor 20-25 million years ago, whereas rats and mice are separated by 16-23 million years of evolution. All four species shared a common ancestor about 80 million years ago.

Humans have extraordinarily large and complex brains, even when compared with macaques and other non-human primates. The human brain is several times larger than that of the macaque -- even after correcting for body size -- and "it is far more complicated in terms of structure," said Lahn.

For each gene, Lahn and his colleagues counted the number of changes in the DNA sequence that altered the protein produced by the gene. They then obtained the rate of evolution for that gene by scaling the number of DNA changes to the amount of evolutionary time taken to make those changes.

By this measure, brain-related genes evolved much faster in humans and macaques than in mice and rats. In addition, the rate of evolution has been far greater in the lineage leading to humans than in the lineage leading to macaques.

This accelerated rate of evolution is consistent with the presence of selective forces in the human lineage that strongly favored larger and more complex brains. "The human lineage appears to have been subjected to very different selective regimes compared to most other lineages," said Lahn. "Selection for greater intelligence and hence larger and more complex brains is far more intense during human evolution than during the evolution of other mammals."

To further examine the role of selection in the evolution of brain-related genes, Lahn and his colleagues divided these genes into two groups. One group contained genes involved in the development of the brain during embryonic, fetal and infancy stages. The other group consisted of genes involved in "housekeeping" functions of the brain necessary for neural cells to live and function. If intensified selection indeed drove the dramatic changes in the size and organization of the brain, the developmental genes would be expected to change faster than the housekeeping genes during human evolution. Sure enough, Lahn's group found that the developmental genes showed much higher rate of change than the housekeeping genes.

In addition to uncovering the overall trend that brain-related genes -- particularly those involved in brain development -- evolved significantly faster in the human lineage, the study also uncovered two dozen "outlier" genes that might have made important contributions to the evolution of the human brain. These outlier genes were identified by virtue of the fact that their rate of change is especially accelerated in the human lineage, far more so than the other genes examined in the study. Strikingly, most of these outlier genes are involved in controlling either the overall size or the behavioral output of the brain -- aspects of the brain that have changed the most during human evolution.

According to graduate student Eric Vallender, a coauthor of the article, it is entirely possible by chance that that two or three of these outlier genes might be involved in controlling brain size or behavior. "But we see a lot more than a couple -- more like 17 out of the two dozen outliers," he said. Thus, according to Lahn, genes controlling the overall size and behavioral output of the brain are perhaps places of the genome where nature has done the most amount of tinkering in the process of creating the powerful brain that humans possess today.

There is "no question" that Lahn's group has uncovered evidence of selection, said Ajit Varki of the University of California, San Diego. Furthermore, by choosing to look at specific genes, Lahn and his colleagues have demonstrated "that the candidate gene approach is alive and well," said Varki. "They have found lots of interesting things."

One of the study's major surprises is the relatively large number of genes that have contributed to human brain evolution. "For a long time, people have debated about the genetic underpinning of human brain evolution," said Lahn. "Is it a few mutations in a few genes, a lot of mutations in a few genes, or a lot of mutations in a lot of genes? The answer appears to be a lot of mutations in a lot of genes. We've done a rough calculation that the evolution of the human brain probably involves hundreds if not thousands of mutations in perhaps hundreds or thousands of genes -- and even that is a conservative estimate."

It is nothing short of spectacular that so many mutations in so many genes were acquired during the mere 20-25 million years of time in the evolutionary lineage leading to humans, according to Lahn. This means that selection has worked "extra-hard" during human evolution to create the powerful brain that exists in humans.

Varki points out that several major events in recent human evolution may reflect the action of strong selective forces, including the appearance of the genus Homo about 2 million years ago, a major expansion of the brain beginning about a half million years ago, and the appearance of anatomically modern humans about 150,000 years ago. "It's clear that human evolution did not occur in one fell swoop," he said, "which makes sense, given that the brain is such a complex organ."

Lahn further speculated that the strong selection for better brains may still be ongoing in the present-day human populations. Why the human lineage experienced such intensified selection for better brains but not other species is an open question. Lahn believes that answers to this important question will come not just from the biological sciences but from the social sciences as well. It is perhaps the complex social structures and cultural behaviors unique in human ancestors that fueled the rapid evolution of the brain. "This paper is going to open up lots of discussion," Lahn said. "We have to start thinking about how social structures and cultural behaviors in the lineage leading to humans differed from that in other lineages, and how such differences have powered human evolution in a unique manner. To me, that is the most exciting part of this paper."

[Amedeo]

Very interesting information! (Please provide some reference link, whenever possible.)

The evolution of the brain is certainly a fascinating subject, but is it a special event? It appears special when it is viewed againt contemporary primates [non-human primates]. The funny thing about evolution is that for a set of some animal species, there is a set of lower animals such that both sets have a common ancestor. This means that at some point of time, species X bifurcated into two branches: some members evolved [mutations went on], while other members remained practically stagnant. To be sure, a non-evolving branch may have died out. So, for example, I personally do not know whether our amoebas have stagnant sisters, or.... our amoebas are the stagnant offsprings of organisms, a branch of which evolved into something higher than amoebas. (If animal life started a half billion years ago -- for the sake of argument -- then all existing animals, possibly man included, are the stagnant residues of evolution.) If Homo sapiens has been around for 300,000 years, the other primates are twice or more older; they belong to a prior state of evolution and continue to possess a lower brain development.

People used to consider the human races as stages of evolutionary development, for they considered races in terms of external appearence, but complexion differences are present also within sub-human species; in particular, monkeys come in different races and even have black, red, or yellow hair [fur]. If human races are defined by physiognomy [facial bone structure and skin texture] and surface colorations, then we even find that populations may display diverse combinations of these factors.

If we think for a moment of populations along the 40th meridian, in the course of time, we see people of the Negroid race south of Ethiopia and spreading through Africa; Araboid people [usually never classified as a race]
in Ethiopia and Saudi Arabia, and Caucasoid people south of Mt. Caucasus (Mesopotamia and thereabout). Those who spread toward the West will be called Mediterranids, and those who spread in a north-westerly direction will be called Alpines and Nordics. The racial complexions match the climatic conditions in which all of these people lived for thousands of years.

As it is clear even today, the brains of the different human races are alike.
The brains have much in common with the brain of primates. What do brains do? They are the chiefs or lords of the soma [the somatic system of the organism], controlling and regulating the functions of the organs etc. At the same time, all sensory information is processed by the brain (for instance, to correlate hunger urges and picking of suitable foods), and motor activity is performed. The brain is an electric power-house (which is yet to be studied) and integrates both undulatory and mechanical effects from outside, and electric stimuli from within.

The "biological life" of the human brain is better in man than in primates, as somatic structures developed in human which hardly exist in primates. Thus, man is capable of great dexterity, while he has lost much of the instinctive sense and could not individually survive. What is special or superior in man's evolution pertains to both the cerebral system and the somatic system: the larynx, the central organ of speech. A great change occurred in man: concetualization moved from the visual to the auditory field. The electro-physics of the "mind/brain" is yet to begin.

All the human races have speech. Indeed, each race in its early and isolated phase developed its own language, technology, and religion. Some of the African languages, Arabic, Sumerian, and some European languages (such as Basque and Etruscan-and-company) have connections with the oldest languages of the human races. There are more than residues in the ancient European language which, at a certain point, acquired an Indo-European linguistic baggage.

Few populations today are predominantly of one race. Whether mostly pure or hybrid, the members of a race are not all mentally equal. A given population has a common or general intelligence, but then some individuals stand out: they conceive, excogitate, invent, create. The brains some of individuals develop or progress beyond the others. So, there is no strict correlation between racial somatic traits and a superior mind, otherwise all the members of one race would be mentally equal.

No bio-physical studies of genial minds exist. At any rate, geniality is not something that can be tested: One does not produce a philosophical treatise, a poem, a music composition, a strategic plan of production, a discovery of nature, a gemetrical demonstration, etc., on demand -- even if the tester knew enought to formulate the questions. A genial mind is known from what it accomplished as a matter of fact.

We can look at the geniality of races in terms of the civilizations they have created. The Caucasoids stand out in terms of the quantity and the quality of their accomplishments. Consider the following civizations, which would take hundreds of pages to just summarize:

-- The Sumerian civilization. (Agriculture, urbanization, transportation, writing, mathematics, astronomy, etc.)
-- The Hellenic civilization -- the extent and depths of which remain unsurpassed.
-- The Etrusco-Graeco-Roman civilization (inclusive of the distinctive creation of the institution of the republic and of jurisprudence). [Civis rei publicae --> civil; civility; civilization.]
-- The Italian Renaissance civilization.
-- The European Recontrivance civilization (beginning in the 17th century).

[Amedeo]

Language: In the primordial Age of Homo Sapiens

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From:
http://www.perceptions.couk.com/equal2.txt


ON THE ORIGIN OF THE SPEECHES

Genetics is about natural selection, say the English. No,
it's about language, the pioneering Italian, Luigi Luca
Cavalli-Sforza tells Steve Connor --

20 October 2000

Something like 99 per cent of human history occurred
before the invention of writing and the start of our
cultural heritage.
..........

Fifty years ago, he wanted to know whether natural
selection was really the sole factor driving human
evolution or whether another, random element, called
"genetic drift", was also important.

...........

He first set about collecting samples of blood from each
village to record the frequency of the three main blood
groups - groups A, B and O. Since the early part of the
20th century, geneticists had known that different
populations from around the world had different
proportions of the three blood groups for no apparent
or obvious reason. Cavalli-Sforza thought this difference
might, at least in part, be the result of random drift,
something that Fisher, in his brilliant mathematical
analysis, had dismissed.

............
It is not that the research downgraded the importance of
natural selection, just that it demonstrated there were
other elements to human evolution which had a more
random, non-selective basis. "I have now reanalysed the
data and I am convinced that, for one of the three blood
groups we studied, there was some variation on top that
was due to natural selection. We now know that the
ABO blood groups are subject to selection of various
kinds," he says.

..........

The relative frequency of the genes determining the
blood groups of modern Europeans clearly shows, for
instance, a pattern of early migration from the Middle
East to north-west Europe. Most scientists now accept
that this must represent the movement of the earliest
neolithic farmers about 10,000 years ago. From the
physical remains of early human settlements,
anthropologists know that it took several thousand years
for farming technology to spread from the fertile
crescent of the Middle East to the most westerly
margins of Spain, the British Isles and Scandinavia. The
language of the genes tells this story.

Cavalli-Sforza can lay claim to another radical insight
into human prehistory in the way that he has combined
genetics with linguistics. He saw very early on that genes
and languages have many things in common. They pass
from one generation to the next, they suffer "mutations"
that change them over time, and that a small, isolated
population is likely to share many of the same genes, as
well as the same mother tongue.

.............. Cavalli-Sforza saw that linguistics
offers another route to cross-checking the predictions
made from population genetics. Both could be used to
unravel the story of the many mass migrations that must
have taken place in human prehistory.

"Language is the central thing that makes us human. It
would not be possible to have modern language without
thinking in the way that we do. We all think in the same
way and we can all learn to speak with equal skills in
any language," Cavalli-Sforza says.

............
Each of the many thousands of modern languages owes
its existence to the development of an early
proto-modern tongue some 50,000 years ago, he says.

It was this, and the further development of stone
technology and the invention of boat-building, that led to
the most important migration in history - from our
African homeland and across the four continents to
become the most widely distributed species on the
planet.

..............
From "The Independent" - an English broadsheet

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