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Welcome to the discussion group for Making of the Fittest by Sean Carroll. Prompts and posts are student generated. This is a collective effort to engage in discussions that connect the theory of evolution with the biological concepts and themes discussed in our course throughout the year.
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2009
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March
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- Genealogical Trees?
- The Source Of All Variety Is Mutation
- Independent Convergence
- Return to Bouvet Island
- Fitting into the World
- The Evolutionary Arms Race
- Complexity in Fruit Fly Wing Patterns
- Even though Allison is his last name I keep thinki...
- Wisdom Teeth
- Overfishing and the Domino Effect
- DNA Record
- Ruminating Monkeys :D
- Common ancestor
- Speed of evolution
- Sudden change in the sticklebacks
- Fossil Genes
- Are we evolving yet?
- YES we are all mutants...
- The relation between primates and humans
- The organization of life and mutations
- Ultraviolet Rays
- Bighorn Sheep and Unnatural Selection
- Melanic Moths
- Selective Advantage
- Gleevecs
- Senses
- Ice Fish and Hemoglobin
- Heart Size and Metabolism
- Malaria and CF
- Endosymbiosis
- SINES and LINES
- Timeline of Icefish Evolution
- Ultraviolet Vision of Birds
- Fossilization of Human Olfactory Genes
- The Coelacanth
- Hungry Ghosts
- Color Vision
- Preventing Mutations
- DNA decay
- Armor Plates of Stickleback Fish
- Immortal Genes
- Original Triplet
- Bacteria "mix up"
- Preservative force of Natural Selection
- Reproducible Evolution
- Cold Resistant Microtubules
- Fossil Records
- Brains
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- Josh Lewis
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- Katie F
- Kimberly Kenyon
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- kimberly ha
- mitchell gruzmark
No it wasn't evolutionarily necessary for our brain size to increase because intelligence is correlated to brain size, but the brain size does not determine a "genius" or not. Geniuses brains have been measured and studied, and they range in size from 1000cc to 2000cc in modern humans. Our brain size was the size of a chimp's brain, 400 cc, then grew to 1200cc, and now our brain is at 1400 cc. Also, the shape of our brain changed during those million years, because the chimp size brain had no forehead at all which correlates to a smaller brain with less smaller lobes that can't hold as much knowledge.
ReplyDeleteThere is a slight correlation between brain size and body size, which then affects intelligence. However, a larger brain does need more care and feeding, which isn't an advantage. It requires high protein, a proper temperature. Therefore, to increase the size of our brain humans began eating meat. Also, our brain requires a lot of energy in order to function, so humans had to eat more which was not a selective advantage. In addition, humans needed to figure out how to make sure that our brain did not over heat. Our larger brain does allow us to have more "room" for knowledge and better functioning lobes, but it also requires much more work on our part. We have to feed it, rest it, and make sure it is in a proper temperature environment. These such efforts to help the larger brain prosper does in turn require more energy on our part, which could have been used in a different system, like the reproductive system because it is important to survive and reproduce!
(continued from above)
ReplyDeleteThe brain did increase in size through evolutionary history due to the gene that causes microcephaly, a human disorder where brain size is reduced. However may also play a role in brain size evolution. It has been shown that ASPM and microcephalin genes have been under selective pressure during the start of evolution. ASPM codes for a protein that deals with spindle formation in the brain, so changes in ASPM result in an increase of cell division and therefore a larger brain size. Also, it has been tested that Nde1 has caused very small brains, so an increase in this gene would therefore create a larger brain size. In addition, protein evolution could be a key reason for the increase of brain size. It has been shown that protein evolution rates are higher starting from ancestral primates and leading up to humans, so these genes may regulate brain size and therefore increase it.
Although an increase in brain size was not necessary it can be seen as advantageous to us. Looking around at the world filled with animals, such as the cow, that has a brain 1/3 a humans while still outweighing us by 7 times our body weight we can see that a large brain is not a necessity with survival. Yet with a larger brain humans were given an advantage, not by just mere size, but by which lobes were increased in size, such as the cerebellum and neocortex. The cerebellum works with coordination, balance, and most importantly sensory perception, allowing humans to apprehend certain colors, shapes, or ideas, in different ways. This allows for the plethora of ideas and concepts today. Also through the sensory perception we are able to learn and understand through images and meanings allowing our knowledge to grow. The neocortex, the outermost layer of the cerebral hemisphere, is also associated with motor functions and sensory perceptions, but it also plays a key role in reasoning and language. With the increase of the neocortex humans are able to more effectively look into a situation and determine outcomes, whether good or bad and communicate with one another using a more advanced system of communication. These are advantages in allowing humans to manipulate the world to better suit themselves and use the resources of the world to their advantage in not only allowing survival but comfort and luxury as well.
ReplyDelete(continued)
ReplyDeleteWith the addition of the neocortex and cerebellum came new "powers" in the brain. The new structures that were added had the ability to control the structures that had previously been in control. This pyramid of power allows humans to execute actions that would not normally be seen in other organisms. The human brain can override itself, placing itself in danger or even causing death by suicide. No more is it instinct for survival, but these new additions call for new reasoning and choices which can be seen as a downfall or an advantage depending on seeing this as a suicide attempt or the ability to sacrifice oneself in place of millions.
Along with the increase in brain size for the cerebellum and neocortex are their connections with the neuro system of the human body. In such simple organisms as the jellyfish, nerve cells are more spread out while in more complex organisms the neurons are concentrated creating a spinal cord. Also the concentration of these neurons to the brain for humans was shown to shorten the time period in which it takes for signals to be sent to sensory organs in the body. Another factor in the increase of the size of the human brain was in allowing for a higher memory and for the brain to actually learn from actions and to modify itself.
Brain to body size ratio is not the only indicator of intelligence. Smooth brains are less advanced than convoluted brains that can be found in mammals such as dolphins, humans, and. For humans this convolution occurs in the womb after 6 months. Before this 6 month period the fetus has a smooth brain which will then become convoluted in preparation for birth.
In connection to birth this increase in brain size also caused the size of the human head to increase. This meant that mothers needed to have birth while the baby was less mature in order for the head to fit through the narrow pelvic canal. This means that the child is less mature and requires more parental protection for a longer period of time in order to survive. The earlier birth may cause a strain on the child, not being able to fend for itself in the world at such a young age. Yet it can be seen as an advantage as parents must stay with the child for a longer period of time ensuring that the survival rate of children will be higher. It is seen today as animals that practice internal fertilization and internal growth have a higher percentage of parents that care for the children after birth and most of these animals are more evolved than those that practice external fertilization or external growth.
http://www.youramazingbrain.org.uk/Insidebrain/brainevolution.htm
http://faculty.ed.uiuc.edu/g-cziko/wm/05.html
http://www.maropeng.co.za/index.php/exhibition_guide/brain/
Contrary to what Jackie and Kim had said, I actually believe that it was evolutionarily necessary for our brain size to increase dramatically. On an evolutionary stand point, it would seem that natural selection had chose those of our ancestors with larger brain size to survive and reproduce, thereby we can see it must have been advantageous for us to have a larger brain size. I realize that it’s been shown that there may be no correlation between body size and brain size. In a study done by Dr. Paul Grobstein at Haverford University, who specializes in Biology with Concentration in Neural and Behavioral Sciences, he showed that human and mouse ratios (brain size to body weight ratios) are roughly identical and the horse and elephant ratios are also roughly identical. In addition, the ratio small birds are much larger than for humans (Source: http://serendip.brynmawr.edu/bb/kinser/Int3.html). Therefore, along with similar studies, I guess it is suggestive that larger brain size does not directly lead to greater intelligence. However, this does not mean that the gradual growth of our brain size has no evolutionary necessity.
ReplyDeleteAs of now, scientists are still not completely sure of why our brain size increased, but there has been some very popular theories. Dr. Grover S. Krantz at Washington University has done several studies that indicate that the expansion was due to a gradual increase in memory requirements. He points that the only physical capability modern humans share that surpasses other land mammals is long range running. This, he postulates, was the main hunting strategy used by early humans, much as it is even today among stone-age cultures. When the climate changed and the early humans had to adapt to savannas the hunting territory increased, and a hunter that had to hunt and return to his family needed better memory (Source: Brain size and hunting ability in earliest man, Krantz). If this was the case, then we can clearly see the selective advantage of being able to remember more information. Furthermore, within the human species, modern studies using MRI have shown that brain size shows substantial and consistent correlation with IQ among adults of the same sex. Some scientists prefer to look at more qualitative variables such to relate the size of measurable regions of known function. For example relating the size of the primary visual cortex to its corresponding functions, that of visual performance (Source: http://www.ncbi.nlm.nih.gov/books/bv.fcgi?rid=neurosci.box.1833). For Further reading, I would really recommend going to this site mentioned above. It’s got some really good information on the common misconceptions of brain size and offers some really detailed studies that explain the details of human evolution, specifically the brain very well.
This example would tie in very well with the theme of evolution, which is change in the genetic material of a population of organisms from one generation to the next. These changes are caused by a combination of three main processes: variation, reproduction, and natural selection. Genes that are passed on to an organism's offspring produce the inherited traits that are the basis of evolution. These traits vary within populations, with organisms showing heritable differences in their traits. When organisms reproduce, their offspring may have new or altered traits. These new traits arise in two main ways: either from mutations in genes, or from the transfer of genes between populations and between species. In species that reproduce sexually, new combinations of genes are also produced by genetic recombination, which can increase variation between organisms. Evolution occurs when these heritable differences become more common or rare in a population. Natural selection, a process causing heritable traits that is helpful for survival and reproduction to become more common in a population, and harmful traits to become more rare. This occurs because individuals with advantageous traits are more likely to reproduce, so that more individuals in the next generation inherit these traits. Over many generations, adaptations occur through a combination of successive, small, random changes in traits, and natural selection of those variants best suited for their environment. This ties in really well with one of Carroll’s most important messages, which is the fact that evolution does not occur over night. He pointed out the common misconception of those who argue against the Theory of Evolution, that sometimes, we as humans may not live to see an evolutionary event occur, but it does prove evolution false. Like Jessica had referred to in the book, Carroll emphasized that it took over 1 MILLION years for this growth of brain size to reach twice its size. In short, Carroll makes a really critical pint that people shouldn’t be quick to disprove the theory of evolution just because they don’t understand the intricacies in this complex cycle of mutation and natural selection.
It was not evolutionarily necessary for our brain size to double because brain size does not correlate to increased intelligence. The ratio of brain weight to body weight does, with higher ratios equating to higher intelligence. More recently evolved animals do have a higher proportion of the brain composed of the cerebral cortex, which important in memory, perceptual awareness, thinking, language, and consciousness. These are evolutionary advantages, and the increased percentage of the cerebral cortex allows for improved language skills.
ReplyDeletePredatory animals have larger brain/body mass ratios than prey animals, an evolutionary advantage that helps them to strategize methods of capturing dinner. Since homo erectus was not much smaller in body size than humans living just last century yet had half the brain mass, the increase in brain size in proportion to body mass made humans more intelligent beings. With increased size came an increased ability to perceive our surroundings. At the very least, an increase in perception would provide an advantage for finding food, a mate, and avoiding enemies, so increased ability to perceive more and more complex surroundings would have been a major evolutionary advantage.
http://faculty.washington.edu/chudler/brainsize.html
http://www.youramazingbrain.org.uk/Insidebrain/brainevolution.htm
http://faculty.ed.uiuc.edu/g-cziko/wm/05.html
continued from above:
ReplyDeleteInstead of our brains increasing, the body/brain mass ratio also implies that humans would have gotten smarter if our brains had stayed the same size but our bodies shrunk. Yet this is not necessarily the case, as it is the increased complexity of our brains that resulted in our increased intelligence. The portion of the human brain that grew the most is the prefrontal cortex, the location of higher cognitive abilities. The brain most likely grew so rapidly because of increased social behavior. The cooperative benefits that resulted would have selected for better communication skills as locations of good could be more easily shared among individuals. The cortical areas of the brain are more flexible, adopting function based on stimulus. Plasticity in the cortex can result in an area of cortex changing its function depending on the frequency and type of tasks that an animal is required to perform in its daily life. Improved performance would have caused the cortical area of the brain to devote itself to more and more complex tasks.
http://www.brainconnection.com/topics/?main=fa/brain-evolution4