1. For your homologous
traits provide the following information:
a. Briefly describe (not
just identify) the two different species that possess the homologous trait.
According to
Introduction to Physical Anthropology, “Structures that are shared by species
on the basis of descent from a common ancestor are called homologies” (Jurmain
et al. 110). What this means is that two species may share a homologous trait passed down from a common ancestor. The two different species that I chose to analyze for this assignment are horses and
turtles. These species possess similarities having to do with the bones that makeup the forelimbs. A horse, a mammal, and a turtle, a reptile, both have
forelimbs that consist of a humerus, radius, ulna, carpals, metacarpals, and
phalanges.
b. Describe the
homologous trait of each species, focusing on the differences in structure and
function of the trait.
Why do these homologous traits exhibit differences between the two
species? Make sure your
explanation is clear and complete.
As previously stated, one will find the same set of bones on the forelimbs of both horses and turtles. However, the forelimbs of these species vary in structure and function. The horse appears to have a more linear shape with regard to its bone structure. When observing its phalanges, a reduction from five digits to one digit can be seen. The reason for this is simply because
the horse requires a strong, weigh bearing limb to support any type of
locomotion. The turtle, on the other hand, appears to have metacarpals and phalanges that are more spread, somewhat resembling a human hand. The shape of a turtle's forelimb ensures propulsion through a rowing motion. The bones in the forelimbs exhibit
differences between the two species in response to adaptation to locomotion.
c. Who was (generally,
not specifically) the common ancestor of these two species and how do you know
that ancestor possessed this homologous trait?
Generally, the horse is considered a mammal while the turtle is known as a reptile. The common ancestor of a mammal and a reptile can be thought of as an amphibian. Early
amphibians are known to have forelimbs of similar structure and function.
d. Provide an image of
each species in this comparison.
2. For your analogous traits provide
the following information:
a. Briefly describe the
two different species that possess the analogous trait.
Analogies are those
similarities in which are based on common function, not taking common ancestry
into consideration. Two different species that possess the analogous trait are
birds and butterflies. These species both have wings; however, each set of
wings has unique attributes. A bird's wings are attached to its shoulder girdle, located below its neck. The composition of a bird's wing consists of bone and muscle cells, covered by feathers. In comparison, a butterfly wing is made up of veins, encased by delicate scales (Understanding Evolution).
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.
When considering wings, a bird has
bones while a butterfly lacks bones. Though there is a difference in composition, these wings serve a similar
function. This analogous trait has allowed a bird and a butterfly to adapt to life in the air. Remarkably, these two different species have
developed their wings independently. As a result, “…their (superficial) similarities
are a product of separate evolutionary responses to roughly similar functional
demands” (Jurmain et al. 110). For a better understanding, these similarities are brought forth by convergent evolution.
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?
Reptiles, ancestors of
birds, do not have wings. An ancestor of butterflies, arthropods, appear to function without wings as well. Due to the fact that these ancestors appear to have
no wings, one can conclude that this trait is analogous. These wings were
developed as a means of living.
d. Provide an image of
each species in this comparison.
Citations
Jurmain, Robert, Lynn
Kilgore, Wenda Trevathan, and Russell L. Ciochon. Introduction to
Physical Anthropology. Belmont, CA: Wadsworth Cengage Learning, 2014.
Print.
Understanding Evolution. 2017. University of California Museum of Paleontology. 22 August 2008 <http://evolution.berkeley.edu/>.
