James Farley
Underwood
11/24/07
D5
Log 5-Déjà Vu: How and Why Evolution Repeats Itself
Synopsis:
1. How do we know that Howler Monkeys developed trichromatic color vision independently from “old world” monkeys and why is this significant?
The
Howler is known to have an incredible sense of trichromatic sight. The question
posed is whether the Howler inherited this trait from a common ancestor or
whether the trait developed independently over time in the genetic sequence. According
to evolutionary theory the characteristics of the Howler, in relation to “old
world” monkeys, came “at a different time in and entirely independent series of
events” (Carroll 140). In addition, the food source of the Howler is more
similar to “old world” trichromatic species than any other “new world” species
of monkey. The determining factor of evidence for independent evolution of
trichromatic color vision lies in the fact that the Howler holds “a higher
proportion of fossilized olfactory receptor genes than all of its closest
relatives in the
2. What is meant by “convergent evolution”? What are some examples (note: examples should be restricted to those sited in the chapter)? Why is this significant?
Convergent evolution aims to find
similar links between species across the globe in order to draw conclusions as
to the cause of adaption and loss/gain of similar traits and characteristics
noted in various species. The believed theory of “convergent evolution” is the
that “the widespread occurrence is compelling evidence that, given a set of
similar conditions, species often find similar ‘solutions’ for adapting to
these conditions” (Carroll 141). In short, similar adaption occurs to differing
species as a result of natural/environmental causes.
Real-life
examples of convergent evolution include “the evolution of new pancreatic
enzyme in ruminants, the evolution of antifreeze in cold-water fish, and the
loss of galactose pathway genes in yeast” (Carroll 141). The conceptual study of
“convergent evolution” is significant because it is essential to the
comprehensive understanding of the effect of environment on the adaptive
process and the rate at which they occur within species.
3. What is meant by “the relaxation of natural selection”? What are some examples?
Relaxation of natural selection is the process by which genes that are of no advantageous use to survival in the particular environment of a species are slowly lost to decay and eventually erased from the genetic sequence over time. Fish living in caves have lost their sight and color due to habitation in the dark environment. Blue geese and white geese vary also due to difference in environment. In this case of feather color, the white geese live in a colder environment than the blue geese. The color variation of light and dark colored rock pocket mice enables them to survive against predators of the desert environment. The cave fish, geese, and mice are all excellent examples of “relaxation of natural selection”.
4. What are the clues indicating that
Fish located in the genetic tree of descent have no close relation to each other. The orders are differentiated. Therefore, indication that the trait of antifreeze evolved from ancestral capability is highly unlikely. In addition to this compelling evidence, “freezing of the North Atlantic and North Pacific oceans occurred much more recently, about 2.5 million years ago, indicating that the driving force for evolution of antifreeze was separate from the Southern Ocean” (Carroll 152). There is no genetic evidence suggesting that the digestive enzyme gene was a source for the development of the antifreeze adaption. The coding for the antifreeze trait is manufactured in an entirely different process of “threoninie-alanine-alanine or threonine-proline-alanine in multiple tracts, which are separated by the sequence leucine-isoleucine-phenylalanine” (Caroll 152). Thus, it is believed that the Artic and Antarctic fish evolved antifreeze independently.
5. Why does evolution repeat itself? How does evolution reproduce itself?
Evolution repeats itself based on the key ingredients of chance, time and selection. According to evolution, variation is based on the random order of genetic sequencing found within the species. Evolutionary theory also suggests that these sequences are random by chance. Over time the “chance” of sequencing produces a notable variation within the species. In order for any significant effect to last as a result of change, chance, time and selection must all be involved.
6. For any new mutation, what are the three possible fates? Under what conditions is each fate realized?
A mutation “may be actively preserved, actively rejected, or may be neutral and ignored by selection” (Caroll 160). If a mutation is actively preserved, then it is successfully passed down from generation to generation over time. If a mutation is actively rejected, then it becomes a fossilized gene. If a mutation is neutral, then it is passed down genetically but has no positive or negative advantage to the survival of the species. Each fate is realized under chance, time and selection. Conditions of favoring each fate depend widely upon the conditions of the environment.
7. From the section Chance: “identical or equivalent mutations will arise repeatedly by chance,” explain somewhat carefully just where that number 750 years comes from. That is, explain how one can estimate that about once in 750 years a herring gull chick will be born able to see UV light.
The number 750 is the amount of years at which “the serine-to-cysteine switch will arise” (Caroll 157). This means that every 750 years, a herring gull chick will be born able to see UV light. Based on the genetic variation and probability, scientists can make an approximate measurement as to when the switch will occur in UV vision. It is necessary to use chance and probability to accurately note and document the reoccurrence and variation of change in a population. Without documentation, trends and similarities in variation would be lost. By studying data through probability, a scientist could take any information he/she collects and predict the pattern of chance through the occurrence of adaption in offspring.
8. From the section Selection: “their fate …will be determined by the conditions of selections upon the traits they affect,” explain why the mutations at bases 270, 260, and 269 all coded for either violet vision or UV vision in a large number of species of birds. That is, of the 9 possible mutations starting with AGC [what are those 9?], why is it that the 2 of the 9 mutations that produce either violet or UV vision are what we see but the other 7 are not seen?
It could be possible that violet or UV vision is becoming a fossilized gene. If it was not to the bird’s advantage for survival, the bird’s genetic sequence might alter to inhibit the ability to produce proteins for violet and UV vision. Change in temperature, climate and weather are all environmental factors which effect the way a species lives, breathes, and copes with its environment. Through the “relaxation of natural selection”, it is also possible that the species may have lost genes which it did not need to survive. It is possible that the 7 of the 9 mutations are a result of “relaxation of natural selection”. The UV and violet light capabilities can either be positive or negative based on the environment in which the bird inhabits. Evolutionary theory best sums the process of mutation up as, “not a matter of ‘waiting’ for a new mutation, but the preferential increase or decrease of alternative forms in response to changes in the conditions” (Caroll 163) According to theoretical analysis chance, time and selection will tell.
9. Because species often occupy multiple habitats, a mutation may be favored in some locales and selected against or ignored in others. This results in species being variable in many traits across their range. Is this variation an evolutionary advantage? Why or why not?
Mutations can either have advantageous, disadvantageous, or neutral side-effects. The environment determines what it is suitable and what is unsuitable for a species to live in. An organism living in more than one environment possesses traits and advantages gained from a multi-habitat lifestyle. Multiple environmental advantages have proven to be more than beneficial for the species. By sharing an advantage in one or both environments, the species carries traits that are a bonus to survival.
Take Away Idea:
I enjoyed learning about different instances concerning the repetition of adaption in similar and different organisms around the world. I always thought there was some relation to different species in one area of the world adapting in the same way as another species in another area of the world, especially when they both shared similar environments. I also learned that selection of various traits creates a trade-off dilemma. For example, a snake or a deer may have an impeccable sense of hearing but may lack in visual capability. Where one trait lacks, another makes up for it as an advantage for survival.
Most Challenging
Concepts:
Everything was very straightforward and easy to read in the chapter. The concepts and examples given enabled me to visualize and put a face to science. The only concept I did have trouble with was the cause of UV and violet vision. I understood why the mutations occurred but I did not understand if UV and violet vision were advantageous or disadvantageous. I also wasn’t sure if the absence of violet and UV in the 7 of 9 mutations was a byproduct of “relaxation of natural selection”.
Aesthetic Awareness:
Aesthetic Awareness is extremely important to science. Without good observation skills, visible trends of various traits would not have been noticed unless first observed with the naked eye. The ice fish, cave fish, and desert mice were all noted to have something unique about them by first looking at their appearance and questioning how it came to be. The book enabled me to gain a greater understanding through visualizing a picture of the organism in my mind that would not have been possible otherwise without the author’s appreciation for aesthetic awareness. Without good observation skills, no individual can even begin to scientifically deduce the cause and effects of today’s world without aesthetically scratching the surface to life’s innovational beauties.
Critical Thinking:
Understanding the world around us is so essential to realizing mankind’s place amongst so many other living things. Critical Thinking enabled both the author and I to broaden our mental horizons in order to begin to understand why our world is the way it is and how it came to be. The deductions and claims that the author made in the text answered many of my questions. The claim of convergent evolution satisfied some of my own “personal hunches” that I had pertaining to adaption of unrelated species in similar environments. Critically Thinking about relationships of living organisms and the environments they inhabit helped me draw connections that I had otherwise not seen previously before I had read this chapter.
Connection:
I always enjoyed class discussions pertaining to adaption and how an organism or individual is fit through adaptation to survive in their environment. Reading Chapter 6 really put things into perspective. In class, I remember learning about birds with different feet and beaks and how the differences enabled them to live in different environments and live on specific food sources. This fascinated me. Once I read about the adaptive process and similar adaptations of different species in similar environments (convergent evolution), my personal hypothesis pertaining to the subject was confirmed. I had the same ideas lack of evidence to back it up. Now that I have evidence, I am thrilled!
Vocabulary:
Convergent evolution- different species in similar environments have similar adaptations in order to survive in their environments
Relaxation of natural selection- when a specific genetic trait is lost to decay due to the fact that it serves no substantial purpose as an adaptive advantage to survival in the environment it lives in
Serine or cysteine- gene sequences which code for UV and violet sight capability
Key Concepts:
Chance as key ingredient to adaptation- evolutionary theory states that chance is essential to determining the “random” genetic sequence of variation
Time as a key ingredient to adaptation- time is needed in order to see substantial evidence of variation and adaption in a population
Selection as a key ingredient to adaptation- the desirable/advantageous genetic traits are passed on to the offspring, which changes the population as a whole over time
Bibliography
The Making of the Fittest: DNA and the Ultimate Forensic Record of Evolution by Sean Carroll, W.W. Norton; Reprint edition (September 10, 2007)