In chapter 2, Shubin describes Sir Richard Owen as a great anatomist that discovered many of the patterns that links the similarities between the species of animals as they have evolved over time. Owen discovered that "All creatures with limbs, whether those limbs are wings, flippers, or hands, have a common design. One bone, the humerus in the arm or the femur in the leg, articulates with two bones, which attach to a series of small blobs, which connect with the fingers or toes" (30). Wings, flippers, and hands all perform different functions that benefit the specific species, yet they all develop from the same basic foundation. What are some of the environmental factors that have caused this evolution of the fin to hand? How come humans have more use for hands with five fingers rather than wings for flying? What are some specific examples of how the variations on bone structure found in the human hand benefits the survival of various species?
(Claire Yao, claire.yao521@gmail.com)
One thing fish almost never have to experience in their lives is gravity, with the exception of when they jump out of the water. A fish’s fins, and the rest of its body, are supported by water. Water is about 800 times denser than air, and at a technical standpoint, a fish’s fins can be 800 times weaker than human bones and still be able to sufficiently move the fish. But, when animals made the transition from water to land, fins were no where close to being able to support an entire body in terms of strength! So when animals made the transition from water to land, stronger appendages were needed in order to support their bodies and fight gravity. A very simple and general environmental factor that could have driven the transition from flimsy fish fin to strong, bony human hand and foot is gravity itself.
ReplyDeleteHumans have hands with five fingers instead of one big appendage like a wing because as the human race developed a larger brain more dexterity and coordination were added to the human arsenal of methods to survive. Let’s face it, if human beings didn’t have five fingers today, or in the past for this matter, almost everything we use to live today wouldn’t exist! Technology would be primitive because intricate circuits and computer chips would be too complicated for an animal with holding-abilities to make. There virtually wouldn’t be any houses! Building a house requires intense manual labor made possible with the use of hands, especially opposable thumbs. Natural selection favored humans that were able to create tools with their hands because the world was becoming filled with animals that competed for food.
There are certain variations in hand structure among the animals that have similar hand structures to humans, such as chimps, monkeys etc., and the variations in hand structure reflect the specific function a hand does to fit the animals lifestyle. For example, primates spend most of their lives in trees of tropical rainforests to get the various abundant fruits for sustenance. Many tree-dwelling primates have hands that have a shorter opposable thumb and longer fingers. Human fingers are naturally straight, but primate fingers are slightly curved (Brittanica Online Encyclopedia). Human fingers are smaller than primate fingers so a more dexterous grip is possible, however primates are much better at grabbing and hanging from things because their long fingers give them more leverage.
Mikey Ling (mikeyling@ymail.com)
The evolution from fin to hands happened because human ancestors moved from water to living in air. Air tension is much less compared to water tension; therefore the use of fins in order to move humans from one place to another is unpractical. Some may look at humans and argue that they go swimming (which is a main purpose of fins), but the truth is that the proportion of time spent in water compared to air is minimal. Also, most organisms that have fins, rarely touch the floor of any body of water and instead float above. Humans, on the other hand, constantly are on the earth and therefore need fingers and toes in order to have balance, climb, have traction, and are able to pick things up.
ReplyDeleteAs far as anatomy goes, humans are not built like birds in order to fly. Birds are light weight and have large muscles for their size. These organisms even have hallow bones in order to be as light as possible. Humans on the other hand, are extremely heavy and would therefore require both ridiculously large wings and muscles. The effort to push the air down hard enough with the wings in order to be able to fly is not humanly possible. (http://www.thegeminigeek.com/why-cant-we-fly-like-birds/). As far as function wise goes, hands are much more helpful for humans than wings would be because of the advancement of our brains. Birds need wings in order to avoid many predators because of their small brains. Humans have very large and functional brains that allow them to create tools and outsmart their predators. Humans need their fingers in order to create these tools and be overall more functional.
The only other creatures that have hands very similar to those of humans are primates. Both humans and primates have opposable thumbs in order grasp things better and do more meticulous activities (like opening a banana). Primates have much smaller thumbs because larger thumbs would, "[get] in the way of the hook-like grasp they need for swinging from the trees" (http://www.ehow.com/about_6137415_human-vs_-primate-hands.html). Another difference between human and primate hands is that humans have more flexible wrists. This may seem like a disadvantage to chimps as they are more limited in activities, but it is actually quite functional for the rest of their less evolved bodies. Since primates still walk using their hands, they would be more likely to get hurt if their wrist was super flexible but the bending of the wrist still gives them many advantages when it comes to climbing and grabbing objects.
Jackie James (jackie.james@comcast.net)
Mikey made a great point by saying that the point of developing hands with fingers instead of a long appendage like a wing is to fight gravity, but aren’t wings to fight gravity also? Weren’t the point of wings for animals to be able to create lift and fight gravity and glide through the air? Well, in fact, I think that when water animals started to move towards the lands, some environmental conditions pressured the land animals to develop wings as a means of surviving. While in one area, the water animal may have developed appendages with hands and fingers simply because that was the best option for them. The theme of evolution is noticeable in the formation of wings because as water animals moved to land, variation between the animals that moved and started to live on land became obvious. Wings were a variable in the new species that arose from water, and because wings were a selective advantage for those animals those animals were able to survive and reproduce better and won the contest of survival of the fittest.
ReplyDeleteOne of the environmental pressures to develop wings could be from the location of food. If the food was located high up in a tree and it was unreachable by the animal, one species could have developed the wing from its fins. Using the tiktaalik as an example, the tiktaalik had shoulders and fins that were able to come up and waddle on land with their fins like a seal. Some of the tiktaalik eventually evolved into land animals that developed wings because the trees on land had a source of food that was an easier access than finding food in water. This selective advantage led to those animals surviving and passing their genes down. As wings became a common structure amongst the animals, some animals adapted even more to bring in feathers. Feathers are “light but very strong, and they are flexible but very tough” (1). Feathers were another selective advantage for specific birds because it was light weight and using in flying. It kept the birds warm during the winter and cool in the summer (1). Evolution kept going throughout the birds because every species of birds we have today has different types of feathers, length of wings, and shape of the wings. The species of birds we see today were the best birds with the best selective advantages to allow them to survive and reproduce.
The development of wings is not only important for birds, but also for nature and ecosystems. Some ways that plants disperse their seeds is by animals. Some seeds attach onto the skin or the body of the bird while others can be dispersed by feces from edible fruits (2). This is beneficial for plants survival as this would bring the seeds of a species wherever the birds go. The theme of interdependence in nature is prevalent with seed dispersal by the help of birds. Some seeds “can sprout better after passing through the digestive tract of certain frugivores” (3). If that’s not enough, the seed’s survival can greatly increase if the seed is brought to a location further away from other seeds because then there will be less competition for resources(3). This makes me think that maybe migration isn’t simply because birds need to move to a better environment during winter. It may be possible that birds unknowingly carried seeds to an area where it excels and when it came back the several seasons later, a food source was made available for them. Even the dispersal of seeds came because birds with wings came from animals from water that evolved to make this possible.
ReplyDelete1. http://wings.avkids.com/Book/Animals/intermediate/birds-01.html
2. Campbell
3. http://www.cnr.uidaho.edu/range556/Appl_BEHAVE/projects/seed_dispersal.html
Benny Jeong
bennyjeong218@gmail.com