Download Chapter 22 Concepts Key

Chapter 22 (Descent with Modification) Concepts
1.) Who were the major scientists before and during Darwin’s time that influenced the
development of his theory of natural selection and evolution? Describe briefly how they
either refuted or supported Darwin’s ideas.
Aristotle: Greek philosopher who believed life forms were made perfect for their
place in the world and stayed unchanging; developed scala naturae concept
which ranked organisms like rungs on a ladder, increasing in complexity. This
ranking does not support the Darwinian notion of evolutionary change in
organisms.
Linnaeus: Swedish scientist who founded the field of taxonomy which seeks to
organize and classify all living organisms. While Linnaeus’ classification system
follows well with Darwin’s eventual concept of the “Evolutionary Tree of Life”,
Linnaeus himself believed in a divine creation of all living creatures rather than
being directed by an evolutionary force and by their environments.
Cuvier: French geologist who developed concept of catastrophism which sought
to explain new species’ appearance not by gradual change but by abrupt
disruptions which caused old species to be wiped out locally and new species to
fill in their places from other areas. This process does not match with Darwin’s
concept of species adjusting over time to gradual change in their environments.
Hutton and Lyell: Geologists who both supported idea that Earth’s surface
changes slowly from continuous forces and that those forces are still optional
today (e.g. Canyon being “carved” out of landscape by action of rivers). Lyell
developed concept of uniformitarianism which states these mechanisms of
change are constant over time. These geological principles matched well with
Darwin’s idea of slow change in organisms as well over time.
Larmarck: French scientist who was first to attempt an explanation of how
organisms change over time. He proposed a “use and disuse” principle which
suggested that body characteristics that are used more will become more
prominent and those that are not used will become less so. One example would
be working out with weights to make larger muscles. Larmarck proposed
additionally that these “acquired characteristics” (and therefore not inherited)
could be passed on to offspring. Unfortunately, there is no genetic basis for this
type of inheritance for the actual DNA sequence.
Mathus: Economist who contented that much of mankind’s problems such as
disease, famine and war stem from overpopulation and therefore limited
resources. This idea led Darwin to consider the fact that most species produce
more individuals than can survive which drives the concept that only those
individuals best suited for their environment will live to pass on their genes.
2.) What were some of the major observations Darwin made on his voyage on the
HMS Beagle?
Darwin noticed species that were closer geographically were more similar to
each other than comparing species from different areas, such as the tropics
versus temperate areas. His witnessing of an earthquake in South America and
the subsequent change in the geology of the land made him question again the
age of the Earth and how change over time in the Earth’s surface could explain
the movement of fossils from earlier times. The Galapagos Islands off the coast
of South America forced him to further think about the geographic distribution of
species as he noticed different species of birds and other animals between the
different islands and he began to notice the specific adaptations different species
had in their unique environments. These observations made him think more
abou thow species might develop after they had been separated from the
mainland and were able to speciate each island in possibly different ways.
3.) Explain how adaptations and natural selection work together as the driving forces
behind evolution.
Adaptations are inherited characteristics of organisms that enhance their survival
and reproduction in specific environments. Natural selection is a process in
which individuals that have certain inherited traits tend to survive and reproduce
at higher rates than other individuals because of those traits. In a nutshell, the
organisms that are best adapted to their particular environment will be the ones
natural selection will “allow” to live better and reproduce more so therefore the
specific genes that are responsible for the best suited adaptations will be the
ones most likely passed on and be in the next generation. Over time, this leads
to possible changes in the populations as those with the best traits for survival
are more represented in the population. If the environment changes, even very
slowly, over time natural selection will alter which adaptations are the best suited
and this can lead to changes in species, even to the point of a new species
emerging.
4.) What was the signficance of Darwin’s Tree of Life to evolutionary theory?
Darwin thought of the history life best represented as a “tree” with earlier
ancestral organisms situation at the base or trunk of the tree and then new
species branching out so that the tips of the branches indicated the more recent,
modern species. Each fork of the tree represented the mores recent common
ancestor to all organisms branching out from that ancestor. By following the
speciation through the branches of the tree, one can trace how evolution directed
the formation of new species. This evolutionary tree of life matched with
Linneaus’ classification system although Lineaus based his system more on
phyisical resemblances and not evolution.
5.) How does variation in a population and differential survival rate contribute to
evolution?
Darwin realized that in order for natural selection to take place, organisms
needed to be genetically different from each other or at the very least, there
needed to be the potential for genetic variation. We know now much of that
variation comes from possibility of mixing DNA during events such as crossing
over during meiosis or random mutations but in the end, whatever the cause of
the variation, there are genetic differences between organisms in populations.
Species are not just clones of each other with identical DNA. Once there is
genetic difference, that may cause some organisms to survive better than others
and therefore their genomes passed on more frequently to more offspring. The
second part, the differential survival rate, is important because it sets up the
pressure for some organisms to survive and others not to survive. Organisms
generally produce more offspring than can possibly survive based on the
available resources such as food or shelter. That forces those that have a better
chance at surviving—whether having better skills at finding the limited resources
or somehow ensuring that their offspring survive while others don’t, will be
selected for. If there was always plenty of resources, all organisms, regardless of
their adaptations would pass on their genes and therefore natural selection
would not have a driving force.
6.) Discuss how antibiotic resistant bacterial species is evidence of evolution.
A common misconception about evolution is that you can not study the process
over a shorter time frame so you need to depend on fossil evidence and other
data that is not as direct as watching evolution happen more quickly. However
when you study species such as bacteria that can reproduce very quickly and
therefore go through many more generations in a relatively short period of time,
scientists can witness evolution “first hand” so to speak. In the case of antibiotic
resistance in bacteria such as MRSA, what we are seeing is the ability of some
bacteria to have a natural resistent to the antibiotics that would normally kill
them. Let’s say for the sake of argument, the original population of bacteria has
1 million cells and 999,999 of them died with exposed to an antibiotic. But just
one of those bacterial cells had a random mutation that made it not be effected by
the antibiotic for some reason so it lived. It will therefore pass on its genes to its
offspring and they would also survive if they also have this “resistence gene”.
Even if other populations of bacteria nearby did not have the gene to protect
them and therefore also died with exposure, over time (and with bacteria, that
time scale is rapidly sped up since they can reproduce so quickly and in vast
quantities), many of the bacterial cells in the population could end up having the
resistence to the antibiotic.
7.) What is the significance of homology and vestigial structures in evolutionary theory?
Homology is the existence of certain traits between species is evidence that
those species had a common ancestor. The classic example is the forelimb of
mammals. All mammals share a common arrangement of bones from their
shoulder region to the tips of their digits. The basic structure is all the same
whether you are a human or a whale so the theory is some common ancestor had
that arrangement of bones. But evolution over time has allowed for the bones to
have different functions that were driven by the different environments the
mammals lived it. So for humans, the forelimb is used for carrying as humans
evolved on land and the need to carry tools or weapons or other human activity
strengthened the selection for arms to function in that way. For a whale, who is
not lifting anything, the forelimb evolved into a more effective “paddle” to help it
swim through the water better. When you look at the eventual structures being
very similar in all these types of mammals, it is less likely they all evolved
independently and more likely they evolved from a common ancestor. Vestigial
structures are anatomical features that serve no current day purpose to an
organism for its survival. Typically these structures once had a function in an
earlier ancestor of an organism but that function was lost over time. Other
organisms that share a common ancestor may or may not have lost the function
so the structures may be still functional in current times.
8.) What is convergent evolution and how does it relate to evolutionary theory?
Convergent evolution occurs when 2 or more species that do NOT share a recent
common ancestor each evolve the same particular trait in response to their
shared type of environment or ecological niche. For example, the protein that
codes for “antifreeze” in the blood of aquatic fish that live in the Artic and
Antarctic both evolved independently and did not come from a common ancestor.
The fact such a trait evolved twice lends credibility to the fact it is a trait that is
well matched to the cold environments in both locations and this adaptation
gives organisms that possess it a selective advantage.