Evolution of Human Brain and Mind

The earliest forms of life on earth are about 3.8 billion years old, compared to its 4.5 billion years age.

Mammals are 3 to 5 million years old. Homo sapiens of today are not more than 1, 00,000 years old,

though hominid line is 3 to 5 million years old. First example of hominid fossils comes from Laetoli in

Tanzania, which belonged to the genus Australopithecus, aged about 3.7 million years.

Australopithecus was a bipedal, small-brained hominid, which later diversified into 2-3 more robustly

built species, as well as probably giving rise to members of our own genus, Homo. It was mainly

confined in the African continent. Fossils of our direct ancestors, classified as Homo come from come

from south-west Ethiopia and adjacent Kenya. This species named Homo habilis, were 2 million years

old and it had a larger brain than Australopithecus. It appeared at approximately the same time as the

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earliest stone tool age. Then came much more modern looking Homo erectus, successor to Homo

habilis, which was 1.5-1.8 million years old. Only after 1.0 m.y.a. do we find that this species of

Homo has spread into Eurasia. Archaic forms of Homo sapiens are variously recognized from Afro-

Eurasian specimens dated to 300 000 years ago.

Phylogeny of Brain

MacLean first attempted to explain the structure of human brain in terms of how it has evolved.

According to him three separate and distinct brains exist, from oldest to more recent. As each brain

evolved, the older brain was retained for its specialized functions, and the new brain simply formed

around it. The human brain, top to bottom, has three parts: the neo-cortex mushrooming out at the top,

the limbic system (below that), and the brain stem (at the base).

The Triune Brain

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From an evolutionary standpoint the oldest part of the brain is called the reptilian brain (R-complex).

Responses like, eating, breathing and the fight or flight occurs here. Many of the body’s systems

respond automatically in order to increase the chance of survival when under attack. The limbic

system, once thought to be associated exclusively with emotion, is now known to process not only

emotional response but also a number of high-level thinking functions, like reaction to a perceived

threat, respond automatically in order to increase the chance of survival when under attack memory.

The neo-cortex, sometimes called the cerebral cortex, is believed by researchers to have grown out of

the limbic system at some time in human evolution. Though not exclusively, the neo-cortex is where

most higher-order and abstract thoughts are processed. The two hemispheres of the neo-cortex also

handle input from our sensory systems, making connections between various stimuli, such as

associating what we see with what we hear. This makes comprehension possible, and is how we make

it all meaningful. This newest part of our brain, the neo-cortex, also attaches feeling and value to

stimuli it receives. When humans learn, the structure and chemistry of nerve cells in the neo-cortex are

changed.

The Three-in-one Master-marvel

The Archipallium, the primitive one is responsible for self preservation. It is there that the mechanisms

of aggression and repetitive behavior are developed. It is there that occur the instinctive reactions of

the so-called reflex arcs and the commands which allow some involuntary actions and the control of

certain visceral functions (cardiac, pulmonary, intestinal, etc), indispensable to the preservation of life.

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The development of the olfactory bulbs and their connections made possible an accurate analysis of

olfactory stimuli and the improvement of answers oriented by odors, such as approach, attack, flight

and mating. Throughout evolution, some of these reptilian functions were lost or minimized (in

humans, the amygdala and the entorhinal cortex are the only limbic structures that connect with the

olfactory system). It is also in the R-complex that started the first manifestations of the phenomena of

ritualism, by means of which the animal tries to define its hierarchic position inside the group and to

establish its own space in the ecological niche. This system commands certain behaviors that are

necessary for the survival of all mammals. It gives rise and modulates specific functions that allow the

animal to distinguish between the agreeable and the disagreeable. Here, some specific affective

functions are developed, such as the one that induces the females to nurse and protect their toddlers,

or the one which induces these animals to develop ludic behaviors (playful moods). Emotions and

feelings, like wrath, fright, passion, love, hate, joy and sadness, are mammalian inventions, originated

in the limbic system. This system is also responsible for some aspects of personal identity and for

important functions related to memory. When the superior mammals arrived on the Earth, the third

cerebral unit, the neopallium or rational brain was finally developed. It is a highly complex net of

neural cells capable of producing a symbolic language, thus enabling man to exercise skillful

intellectual tasks such as reading, writing and performing mathematical calculations. The neopallium

is the great generator of ideas, centre for abstraction and invention.

Functions of Triune Brain

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Three phylogenetically different brains are compressed into one human brain, although

interconnected; each one retained their peculiar types of intelligence, subjectivity, sense of time and

space, memory, mobility and other less specific functions. Fear and intimidation are two main reasons

for downshifting to occur. In the time of crisis, the functioning brain shifts its information processing

from the higher-level thinking regions of the brain, the neocortex and even the limbic system, down

into the brain stem and even into the automatic responses of reflex. Usually we don’t want to

downshift. Downshifting is the last choice. Trouble is, in most of human situations you need your

whole brain involved, especially the neo-cortex, in order to solve these problems as fight or flight

reactions won’t help. One thing you can do is to notice, when your emotions react, and your mind

seems to shift into an automatic mode of response. Being self aware of a downshift gives you the

chance to incorporate your higher level thinking skills in evaluating the situation. Then your whole

brain is in operation; ideas and creativity can flow to help you determine a better way to respond to the

challenge at hand. This enhanced state of being fully engaged and aware is what we call whole brain

activation. Taking in and processing information in many different ways activates the whole brain.

Gene may be the key to evolution of larger human brain. Genetic scientists have identified a gene that

appears to have played a role in the expansion of the human brain's cerebral cortex – a hallmark of the

evolution of humans from other primates. By comparing the gene's sequence in a range of primates,

including humans, as well as non-primate mammals, the scientists found evidence that the pressure of

natural selection accelerated changes in the gene, particularly in the primate lineage leading to

humans. Lahn and associates, in their work, have looked at evolution of a large number of genes, and

in the vast number of cases, they saw only weak signatures of adaptive changes. So, they were quite

surprised to see that this one gene shows such strong and unambiguous signatures of adaptive

evolution – more so than most other genes they have studied. By contrast, the researchers' analyses of

the Abnormal Spindle-like Microcephaly Associated (ASPM) gene in the more primitive monkeys and

in cows, sheep, cats, dogs, mice and rats, showed no accelerated evolutionary change. The fact that

they saw this accelerated evolution of ASPM specifically in the primate lineage leading to humans, and

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not in these other mammals, makes a good case that the human lineage is special. According to them,

among the next steps in his research will be to understand how ASPM functions in the brain. Studies

by Walsh and others hint that the protein produced by the gene mediate it.

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. 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. These

time windows are extraordinarily short in evolutionary terms, indicating that the new versions of the

genes were subject to very intense natural selection pressure that drove up their frequencies in a very

brief period of time. 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, the group found that the developmental genes showed much higher rates of

change than the housekeeping genes.

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. A rough calculation has been

made 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.

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Evolution of human brain is a great event and hence a tedious process. It's clear that human evolution

did not occur in one fell swoop, 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. 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, that is the most exciting part of evolution of human

brain.

Quite surprisingly, modern intelligence stayed unutilized till date. In the last 3-4 million years brain

volume within the hominid lineage has increased from less than 400 ml to roughly 1400 ml. Overall

conclusion is that 'essentially modern intelligence was achieved 300,000 years ago' by which time, as

you will recall, brain sizes were within the modern range. Around 300,000 years ago, our human

ancestors were communicating vocally, had achieved the characteristic level of modern human

intelligence, and controlled all this with a brain that had been fundamentally human in its organization

for a long time, and which was now within the modern range for human brain size. But the

archaeological record indicates that humans were not doing anything much different than they had

been doing over the previous million years or so until relatively recently.

Findings suggest that evolution of human brain is still underway. "People have this sense that as 21st

century humans we've gotten as high as we're going to go," said Greg Wray, director of Duke

University's Center for Evolutionary Genomics. "But we're not played out as a species. We're still

evolving and these studies are a pretty good example of that." Their studies indicate the trend that the

defining characteristic of human evolution - the growth of brain size and complexity - is likely, still

going on. "Meanwhile, our environment and the skills we need to survive in it, are changing faster

than we ever imagined," Lahn said. "I would expect the human brain, which has done well by us, so

far, will continue to adapt to these changes.” Their analyses focused on detecting sequence changes in

two genes – microcephalin and abnormal spindle-like microcephaly associated (ASPM) gene – across

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different human populations. In humans, mutations in either of these genes can render the gene

nonfunctional and cause microcephaly – a condition in which the brain does not develop to a normal

size. The human brain will likely continue to evolve under the pressure of natural selection, speculates

Lahn. "What we can say is that our findings provide evidence, that the human brain, the most

important organ, that distinguishes our species, is evolutionarily plastic.” The current version of

Microcephalin appeared about 37,000 years ago, and now occurs in about 70 percent of the present

human population, while that of ASPM emerged about 5,800 years ago, and now shows up in

approximately 30 percent of today's humans, according to the team's analysis. Each variant apparently

emerged concurrently with cultural advances in human populations. The appearance of the

Microcephalin variant occurred roughly at the same time as the emergence of such traits as art and

music, religious practices and sophisticated tool-making techniques. The emergence of the ASPM

variant first appeared at about the same time as the spread of agriculture, settled cities, and the first

record of written language, the study indicates.

There are major problems involved in saying anything with certainty about the evolution of human

behaviour: mainly a lack of direct evidence. Behaviour does not fossilize. Neither, do brains. And

then, evolution of brain chemistry needs to be understood, which is even more difficult. Noradrenalin

is the basic neurotransmitter for fight or flight. Serotonin, the neurotransmitter is one example of an

ancient biochemical control system. It is found in neurons in roughly the same location of every

vertebrate brain, suggesting the system's presence in the first chordates, 500 million years ago. The

serotonin-containing neurons project throughout the brain, profoundly influencing nearly every brain

process through over 14 different types of serotonin receptors. Among the behaviors affected by

serotonin are the male dominance hierarchy in vervet monkeys and the risk of violent death by

accidents or suicide in humans, which is linked with low serotonin activity. The dopamine system

could have been offered as an equally interesting example of an ancient neuromodulatory system.

Dopamine-containing neurons are important for predicting future rewards (essential for all animals)

and for the mechanisms underlying addictive behaviors.

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With scientific understanding we are in a position to propose that mind is no more an enigma and

consciousness no more supernatural. The human brain is the most complex living structure on this

planet and therefore the ultimate goal of biological research. There are no strong reasons of the belief

that its structure and function will never be understood, or that its composition is something more than

molecules and cells. Once understood, mind and behaviour will be far more important for future

human well-being, than various technological advances which are much more frequently discussed in

the media or else where. The various problems in brain function in both young and old will be

understood and effective treatments developed. The origins of crime and anti-social behaviour will be

revealed and definite intervention would be possible.

So, the saga of evolution continues and so does our adventurous journey of understanding brain

mechanisms.

Devashish Konar MD Consultant PsychiatristMental Health Care CentreBurdwan & Kolkata

M: 09434009113 / 09732221712

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