Analogy & Homology

Week 3 - Analogy & Homology Blog Post

1. For your homologus traits provide the following information (25pts):

a. Briefly describe the two different species that possess the homologus trait. (5 pts)

Humans and Cats both carry a homologous trait of possessing phalange bones.

b. Describe the homologus trait of each species, focusing on the differences in structure and function of the trait. Why do these homologus traits exhibit differences between the two species? Make sure your explanation is clear and complete. (10 pts)

Human phalanges are located in a person’s two hands and two feet. They are most commonly known as fingers and toes. Fingers are used for an infinite number of things varying from typing, to pushing buttons, to pinching, etc. Toes are a vital body part that assists a person by providing balance.

Cat phalanges are located in all four cat’s paws. They are most commonly known as toes. A cat’s two front paws have five toes while the two back paws have only four toes. Toes, like in humans, provide a balance assist a cat with balance along with grip and support (i.e. when they climb).

So, while the phalange bones in a human are essential for balance (toes) and manipulating other objects (fingers), the phalange bone in a cat is solely essential for balance (toes).

c. Who was (generally, not specifically) the common ancestor of these two species and how do you know that ancestor possessed this homologus trait? (5 pts)

Boreoeutherian is the common ancestor between cats and humans. 

d. Provide an image of each species in this comparison. (5 pts)

2. For your analogous traits provide the following information (25pts):

a. Briefly describe the two different species that possess the analogous trait. (5 pts)

Flies and birds have wings as an analogous trait.

b. Describe the analogous trait of each species, focusing on the similarities in structure and function of the trait. Clearly explain why these analogous traits exhibit similarities between the two species. (10 pts)

Flies have a pair of fully developed wings on the thorax and a second pair of wings that are used primarily for balance.

The main function of a bird wing is to propel the animal in flight so it can travel to wherever necessary and also provides warmth and protection for their offspring.

c. All pairs of organisms share some common ancestor if you go back far enough in time. Could the common ancestor of these two species have possessed this analogous trait? How do we know these traits are analogous and not genetically related from common descent? (5 pts)

Coelurosaurian theropods is the common ancestor of flies ad birds.

d. Provide an image of each species in this comparison.(5 pts)

      Bird Wing

Fly Wing

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Charles Lyell's Influence on Charles Darwin

Charles Lyell is not only considered the founder of modern geology but he is also the most influential individual at the time of Charles Darwin’s development of his natural selection theory.

 Lyell brought forward the concept of “deep time” (Gould, 1987) which made all scientists look at a wider range of geographic history when establishing new theories. That concept alone helped Darwin reach all eight of the basic processes he stated were the explanation of evolution. Natural selection, as we’ve been told, is the key to evolution. Without the concept of “deep time” Darwin, along with other scientists, would not have thought of evaluating different species over time and made it possible to form theories like, “Individuals who possess favorable variations or traits have an advantage over those who don’t” (Jurmain 38).  That statement comes straight from one of Darwin’s explanation of evolution. Now, those individuals who have the favorable traits are more likely to survive as opposed to the individuals who don’t have those traits. This means, over time the individuals without the favorable traits are likely to be extinct since their low survival rate lowers their chance to sexually reproduce. For example, in Ecuador, the hummingbirds with longer bills in an environment with tall flowers were most favorable. On the other hand, the humming birds with shorter bills were not favorable. That meant the longer billed hummingbirds were able to sexually reproduce just fine whereas the shorter billed hummingbirds were most likely not going to survive long enough to reproduce and over time that meant there would only be long billed hummingbirds in that area. (PBS Video: How Does Evolution Really Work?) Like I stated above, without Lyell’s concept of “deep time”, Darwin, and other scientists, would not have been able to conduct studies to conclude natural selection occurs in species because they would not have been looking at the progression of a species trait over its entire known existence.

Darwin was hesitant to publish his book Origin of Species because during that time many people came to associate evolution with atheism and political subversion (Jurmain 34). Evolutionary ideas made people strongly believe if the ideas were accepted “the church would crash, the moral fabric of society would be torn apart, and civilized man would return to savagery” (Desmond and Moore, 1991, p.34). Basically, accepting the idea of evolution meant Darwin would be going against the church’s strong belief that God created the Earth and all living species on it and the majority, if not all, of society was accustomed to siding with the church’s belief.