From the Reproduction & Development Unit, it is shown that all organisms tend to have a very similar embryonic stage in which development looks alike for many organisms. Yet is the the type of species and environment that helps turn on and off genes at certain times to determine whether cells will become wings or arms and other variations of body parts. It is interesting to see in some organisms how temperature determines gender, yellow skin remains permanently blackened, and it becomes "a classic example of gene-environmental interaction" (193). How is it beneficial for the organism to survive and reproduce with such adaptations? Also, how do these adaptations relate to that of humans? (Such as with the taxi drivers and their ability to memorize maps.) For example, why can't humans affect gender like reptiles that need a different temperature?
(Diana Liao - dianaliao3@gmail.com)
The observations noted on page 30 in The Genius in All of Us are due to evolution. Evolution is “the theory that groups of organisms change with passage of time, mainly as a result of natural selection, so that descendants differ morphologically and physiologically from their ancestors” (http://necsi.edu/projects/evolution/cover/evolution_cover.html). For example, one observation is that “young yellow-skinned grasshoppers became permanently black skinned for camouflage if exposed to a blackened (burnt) environment at a certain age” (30). Since this characteristic is a selective advantage, natural selection has caused adaptation and evolution to occur. It’s a selective advantage since it increases the grasshopper’s chances of survival and reproduction. By turning black, the grasshopper is camouflaged by the blackened environment. This helps protect it from predators by reducing the chances of being seen. On the other hand, humans don’t have this adaptation because for humans, it isn’t a selective advantage. Through knowledge and technology, humans have risen to the top of the food chain. Blending into the environment wouldn’t increase chances of survival and reproduction since humans can just use technology, such as guns, to defend from predators.
ReplyDeleteAnother observation is that “the temperature surrounding turtle and crocodile eggs determined their gender” (30). This characteristic is called temperature-dependent sex determination (TSD) and it’s “where sex differentiation is dependent on the specific temperature at which the eggs are incubated” (http://scholarship.rollins.edu/cgi/viewcontent.cgi?article=1011&context=rurj). Currently, the evolutionary significance of TSD seen in reptiles is unknown. Yet many hypotheses believe that TSD is an evolutionary adaptation and somehow increases chances of survival and reproduction (though exactly how is still being researched). This is based on studies that “have revealed that TSD does produce sex-ratios and selective fitness advantages in a variety of ways in different species” (http://scholarship.rollins.edu/cgi/viewcontent.cgi?article=1011&context=rurj). Sex-ratios are important to the survival of a population, since an imbalanced ratio of males and females often reduces the rate of reproduction and affects population stability. Also, selective fitness advantages increases the chances of survival and reproduction of an individual. Therefore, TSD appear to be an evolutionary adaptation in reptiles yet it doesn’t exist in humans. Again TSD doesn’t exist in humans probably because for humans, it isn’t a selective advantage. Reptiles are ectothermic (cold-blooded). Their internal temperatures are similar to the temperature of the environment; therefore, temperature of the environment is a significant factor in reptiles’ chances of survival and reproduction. On the other hand, humans are endothermic (warm-blooded). Homeostasis maintains a stable internal temperature regardless of the temperature of the environment and helps humans survive in hot as well as cold environments. Therefore, temperature of the environment doesn’t affect humans’ chances of survival and reproduction as much. Also technology, such as air-conditioning and heating, has allowed the survival of humans to be less dependent on temperature.
Christine Zhao (c_zhao@ymail.com)
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ReplyDeleteHumans also have unique adaptations, such as taxi drivers and their ability to memorize maps. Development is an ongoing process that, as shown by the G X E model, is constantly affected by environmental factors. British neurologist Eleanor Maguire discovered that “in contrast with non-cabbies, experienced taxi drivers had a greatly enlarged posterior hippocampus – that part of the brain that specializes in recalling spatial representations” and “the longer the driving career, the larger the posterior hippocampus”(35). This development in the posterior hippocampus is an adaptation that helps taxi drivers do their jobs. It reveals the “plasticity” of the human brain, created by genes but molded by environmental factors.
These adaptations connect back to the capacity of learning in animals. For example, the taxi drivers increased their spatial learning, “the establishment of a memory that reflects the environment’s spatial structure” (Campbell 1126). Like wasps that locate their nest by learning its position relative to visible landmarks, taxi drivers learn to locate a place by learning its position relative to landmarks or streets. Also, the adaptations seen in grasshoppers and reptiles are similar to the behavior imprinting. Like imprinting, these adaptations have a sensitive period (critical period), “a limited developmental phase when certain behaviors can be learned” (Campbell 1126). For imprinting animals, the imprinting stimulus causes changes during the sensitive period that affect the animals for the rest of their lives and is often a selective advantage. For example, in greylag geese, the imprinting stimulus is a nearby object moving away from the young. This usually allows the young geese to imprint and learn from their mother. Similarly, in grasshoppers or reptiles, the “imprinting stimulus” (color of environment or temperature) causes changes in the development of the organisms during their sensitive periods that affect them for the rest of their lives and often act as selective advantages.
Christine Zhao (c_zhao@ymail.com)