The mind big bang: how humans evolved super
The human brain why so big?At present, scientists have begun to decode the brain activebiologicalIncentive.Though we are obsessed with their brain size, but in fact, our wisdom, is always far more than the brain capacity.
It is there, let stand on the mantelpiece, with empty eyes looked at her, with a smile.Because she could not help but to stare back, Josephine Salmons know that it is clearly a skull fossils of extinct baboons.In 1924, Salmons is one of the few anatomy at the university of witwatersrand university of one of the female students.That day she just in a friend Pat Izods home, Izods father in soup town, the town of Taung) near to operate a quarry.The workers in the process of production found a lot of fossils, and the skull is Izods as a souvenir.Salmons told the news to her supervisor Raymond Dart, an anthropologist for brain research is interested in.He was incredible, because before this rarely found this primate fossils in South Africa.If these fossils belonging to soup town, it will be a difficult to measure the treasure.The Salmons bring the skull to the Dart, he confirmed the discovery of Salmons was right: it is the fossil great apes.
Later, Dart set out to make soup town will find the other primate fossils were shipped to him.At the end of that year, when he is ready to go to a friend's wedding,
he received a large trunk, one of the sample to his surprise, almost missed out on a friend's wedding.The sample includes two parts: a normal cranial cavity model (kept the brain contour within the brain fossil model) and a matching facial skull, including the eyes, nose, chin and teeth.The Dart immediately noticed this is fossils of extinct apes, rather than the monkey.From the perspective of the structure of the teeth the anthropoids probably died of about six years old.The combination of the spinal cord and skull joint special, indicates it is a walk upright individuals.And the structure of cranial cavity is larger than non-human animals of the same age group, has also appeared in the surface has the characteristics of the human brain.With further research, Dart decided that this is a modern human ancestors unknown fossil apes - South Africa.
Raymond Dart and soup, children
At first, the scientific community is generally to the discovery of the Dart strongly questioned.If the "tang town kid" (the nickname from the fossil) really
belongs to the ancient human, then he should have a larger brain.His cranium is larger than the same period the gorilla, but no more.Moreover, is generally believed that human ancestors in Asia at that time, instead of Africa.Dart in Nature in 1925 by the "little laughably" illustrations, and about the sample of the sample evidence didn't have much effect.Until in the end, these experts see "soup, children," some similar findings emerged gradually, everyone's attitude began to change slowly.In the 1950 s, anthropologists have acknowledged the "soup town of children" is indeed a apes, and consider the brain size and not as the only standard to judge whether the human.From Florida state university in the human brain evolution have a remarkable contribution to the professor of anthropology at Dean Falk called "tang town kid" "twentieth century ape found in the history of the most important one of a few big discovery."
After tens of years, through continuous excavation and compared with other fossil skull and cranial cavity model, paleontologists have recorded the most dramatic change in human evolution.We may call it the "big bang" mind.Humans, bonobos, chimpanzees in Africa in six to eight million years ago, from their common ancestors created a separate populations.In the next several million years, compared to our ape ancestors and relatives, early hominid brains are not obvious.However, since about 3 million years ago, ancient human brain a startling expansion and development.200000 years ago, our species of homo sapiens appeared in the 200000 years ago, the human brain from the original 350 g to 1300 g.The human brain in the process of the rapid development of the three million, single in the case of brain volume, than primates evolved the ancestors of the big 4 times higher than in 60 million.
Fossil confirmed that the "big bang" mind.But they did not tell us how and why of the human brain can develop so fast so large.Of course, the reason for this rapid development, there are many kinds of explain its theory: the increasing complexity of social network, interaction of collective culture, the use of tools and adapt the severe and changeable weather condition, all this evolutionary pressure as we evolve bigger brains.
Although the possibility is very attractive, but it is extremely difficult to verify.In the past eight years, however, scientists are beginning to answer "how to" extend the human brain, that is to say, cell volume level how to propagate and how humans on the physiology of refactoring the multiplication of the brain to adapt to volume and power consumption."So far everything is speculation, but we finally can in tools help to seek some clues.", an evolutionary biologist at duke university Gregory Wray said."What kind of mutation happened, and how did they happen? For how the process is complex, we are beginning to search for the answer, to form a more profound understanding."
What makes the human brain is unique?
Especially have a scientist changed the way the researchers measured the brain.Compared with traditional measure brain mass or volume as the assessment
method of intelligent, she focused on calculating the components of the brain.Biochemistry of union university in Rio DE janeiroscienceLaboratory, Suzana Herculano - Houzel continue to dissolve the brain into the nucleus (cell genes control room) suspension.Each neuron has a nucleus, by using the fluorescent molecular markers nuclei and measuring dyeing, can get the exact number of brain cells.She will this kind of method is widely used to the mammalian brain, measurement results show that with the long-standing conjecture on the contrary, more large mammalian brain is not always had more neurons, and their distribution is not the same.
When talking about the brain, the volume is not absolute.The human brain than the brains of elephants and whales are much smaller.But in the human brain cortex is apparently more neurons than any other animal.
The human brain has a total of 86 billion neurons, including 69 billion neurons in the cerebellum, it is the base of a nerve at the back of the brain, to coordinate the body basic functions and activities;With 16 billion neurons in the cerebral cortex, the brain brain area, produce the most complex mental and inspiration here, such as self consciousness, language, problem solving and abstract thinking ability;There are 1 billion neurons in the brainstem and extend to the kernel of the brain.Elephants, by contrast, the volume of the brain is three times of our brain, there are 251 billion neurons in the cerebellum, to manage the huge trunks, feature-rich, and elephants only 5.6 billion neurons in the brain cortex.If considering the brain capacity or volume alone covers these important differences.
Herculano - Houzel make inference according to their own research: primates evolved a way to can put far more than any other mammal neurons in the cortex.Volume is small compared to the elephant and the whale, apes but their cerebral cortex neurons is much more intensive, there are 9 billion cortical neurons, chimps and gorillas chimpanzees have 6 billion.Of all the great apes, the human brain is the largest, so we have up to 16 billion cerebral cortex neurons.In fact, seems to be a human cortex neurons than that of any other species upon earth."This is the most obvious difference between human and non-human brain", Herculano - Houzel said, all of these are in terms of structure and not just the size.
A high energy consumption of the human brain is also one of its characteristics, although the brain accounts for only two percent of the weight, but the human brain in the resting consumes up to twenty percent of the total energy body.Chimpanzees, by contrast, only half the energy consumption of the brain.Researchers have long wanted to understand how the human body is to adapt and maintain the shearing section.at organs of high energy consumption.In 1995, the anthropologist Leslie Aiello and evolutionary biologist Peter Wheeler, put forward the "energy intensive organization hypothesis (expensive tissue content)" may be able to answer the above questions.Basic logic is clear: the human brain evolution requires metabolic balance.In order to let the brain growth, other organs e. must also atrophy, energy was supposed to flow to the latter, eventually to flow to the former.There is evidence that they obtained data showed that primates have bigger brains and small intestines.
A few years later, the anthropologist Richard Wrangham think the invention of cooking is very important to the evolution of the human brain.Soft after cooking the food than the stiffness of the unprocessed food easier to digest, so the workload of the gastrointestinal tract in order to gain the more calories.Perhaps, cooking is at the cost of the large intestine, and make the brain more powerful.Because chimps are much more stronger than human, other researchers put forward a similar tradeoff between the brain and the muscles.
Overall, these assumptions and modern anatomy observation is convincing, but they are based on millions of years of evolution.In order to determine what has happened, in order to understand allows the brain to the rapid evolution of physiological adaptability, we must further into the body through genes.
The number of neurons in the cerebral cortex is with cortex size change and change?Because the rules of proportion is different, for rodents, cerebral cortex neuron number ten times growth will make its cortical volume growth fifty times.For primates, in contrast, the growth of the number of neurons only can let the same brain cortex volume increased tenfold, this is a more economical and practical.
How to build the brain genes?
About 80 years ago, Wray, and his colleagues began to study influence of glucose as an energy source in the spectrum of genes cell activity.A gene is active in the brain tissue lineage, and the other a gene is the most active in the muscle.If the human brain size need metabolic balance between brain tissue and muscle, so these genes in humans and chimpanzees have different performance.
Wray, and his team from the dead and chimpanzees to collect the brain, muscles and liver tissue, and try to test each sample of gene activity.Cell "express" gene, the first DNA transcription of messenger RNA (mRNA) sequence, then form a chain of amino acids to form proteins.Can be detected according to the change of different mRNA level, the activity of a gene in a particular organization.
In order to measure the relative abundance of different mRNA, Wray team from these organizations to extract a large number of mRNA and enlarge them many times.They found that the human brain tissue of the brain activity of glucose
transporter gene 3.2 times higher than in chimpanzees, and the muscles of the chimpanzee central gene 1.6 times than human active.However, these two genes in the liver tissue of humans and chimps activity.
Given that humans and chimps gene sequence is almost the same, there must be some other reason can explain the behavior of the different between them.Wray, and his colleagues found that the gene regulatory sequence (promote or inhibit the activity of genes DNA fragments) between different, very enlightening.In human muscle and brain glucose transporter gene regulation in the sequence, is more of a cumulative genetic mutations not people think the accident of gene mutation, indicating that these regions had accelerated evolution.In other words, the evolution of the powerful pressure forced the human gene regulatory sequence to reduce the energy supply for muscle in some way, strengthen the energy supply to the brain.Genes to a way of fossil never clarify confirmed energy-intensive organization hypothesis.
Last year, Japan's Okinawa institute of science and technology of computational biologist Kasia Bozek published a similar study, metabolism were studied from different angles.Bozek but watch gene expression, and her colleagues also analyzed the levels of metabolites, including sugar, different of small molecules such as nucleic acids and neurotransmitters.Many metabolites are necessary for metabolic or production.Different organs have different metabolic pathways, depending on what to do and how much energy is needed.To sum up, a close relative species organ metabolite levels is more similar than distantly related species, for example, Bozek found that is very similar to humans and chimps renal metabolic pathways.But based on the typical evolution rate, chimps and the human brain metabolite levels four times higher than thought;The muscle metabolites level seven times higher than expected.Bozek said. "so even if the gene level difference, the metabolic level can make a big difference, it is not just two or three mutations, your brain suddenly became bigger."
Subsequently, Bozek and his colleagues identified 42 people, including college basketball players and professional climber, in strength tests against chimpanzees and monkeys.All primates must carry weight pull a sliding shelves to yourself.In terms of volume and weight, chimpanzees and monkeys is double that of human beings.Not sure why, but it may be because they deliver more energy for muscle, thus making the primate Cousins muscle strength more than us.Bozek said, "compared with other primates, we lost muscle power supply to the brain more energy. But that doesn't mean our muscles naturally weaker, but simply because the metabolism of different."
At the same time, Wary consulted his colleagues at duke university, embryonic brain development expert Debra Silver, then begin a pioneering experiment.They not only to find out our brain evolution related gene mutations, and these mutations into mice genome, and observations.Silver said, "this is never tried."
First they scan human evolution speed area (the human accelerated regions, HARs) gene database, the regulation of DNA sequence is similar in all vertebrates, but mutations in humans.They decided to put emphasis on HARE5 gene, the gene seems to control the brain development.Different from chimpanzees, the human HARE5 gene consists of 16 DNA sequence.Silver and Wary HARE5 gene replication of chimpanzees to a group of mice, by contrast, another group of mice reproduce the human HARE5, then they looked at how the brain of the mouse embryos development.
Go through nine days of growth, mouse embryos to begin to form the cerebral cortex (closely related to the most complex mental function of the brain corrugated surface).In 10 days, were human HARE5 gene in the brain is more active than chimpanzees, at the end of the day, the mice implanted with human gene brain volume, 12% larger than transplantation orangutans.Further experiments showed that HARE5 genes will some embryonic brain cell division and proliferation of time reduced from 12 hours to 9 hours.The mice with human HARE5 gene brain, to produce new neurons.
"Ten years ago would have been conducted the study, but at that time, we haven't finished the whole genome sequencing," Silver said, "this is really exciting."But she also stressed that to complete answers to how the human brain mutations, also need a lot of research."We can't just rely on one or two genetic mutations to explain the whole brain. It is absolutely wrong. We could obtain the evolution rules of some aspects of many small changes."
Wray, agrees: "is not only one or two genetic mutations, snap! Your brain rapid evolution. As our change of between humans and chimpanzees have more understanding, we realize that this is the outcome of combined action of many genes, each gene has its own contribution. We have got the doorways. The evolution of the brain is so obscure and subtle."
The brain and body
Although the expansion of the human brain has always been a mystery, but its importance has never been questioned.Researchers again and again will be much higher than other animals human wisdom, due to the evolution of the brain.The recent research on the whale and the elephant suggests that large size isn't everything, but it is also an important aspect.We have more than the ape cortical neurons, not because of our brain neuron density is bigger, but because we are able to evolve enough brain, to accommodate all those extra cells.
However, too obsessed with their own brain is dangerous.Yes, need a more intelligent neurons of the brain, but only this is not enough.Imagine what will happen if dolphins have hands.Dolphins are very clever.They have proved to have self awareness, collaboration and the ability to plan, and preliminary language and
grammar.But compared with the great apes, they manipulate ability is insufficient for raw materials, their ability to severely limit.Because they are only the fin, the dolphins will never be able to enter the Stone Age.
Also, we know that chimps and bonobos can understand human language, even can use the touch screen to make some simple sentences, but they track will be able to make clear different syllables.Instead, some birds of track structure, can make them perfect mimic human speech, but a bird's brain is too small, unable to grasp the complex syntax.
No matter the degree of the development of the human brain, or how much we need to provide energy, if there is no suitable body that it would be useless.Three important adaptive evolution in particular, is closely related to the improvement of our overall intelligence: upright can make us free hands to create tools, use of fire and hunting;Our hands to the flexibility of far more than any other animals;Proper channels that we can speak and sing.Human wisdom, not only by the evolution of a certain organ, no matter how big is it.The evolution of the different organ in our body, the effect of brought together by chance, to promote the development of wisdom.Although we are still obsessed with the size of his own brain, but in fact, our wisdom, is always far more than the brain capacity.