"In the struggle for survival, the fittest win out at the expense
of their rivals because they succeed in adapting themselves best to their
environment." - Charles Darwin
1 1. Explain the concept of natural selection using the snails as an example.
Individuals in a population differ from
each other. Some individuals will have characteristics that make them well
adapted to their environment whereas others will have characteristics that make
them less adapted to their environment. The better adapted individuals are the
ones that are more likely to survive and produce offspring while the less
adapted ones are more likely to die. This is called natural selection. Natural
selection results in the better adapted individuals to pass on their
characteristics to more offspring as the lesser adapted ones are more likely to
die before they reproduce. Over time, this result accumulates and a new
generation is created with the favourable characteristics that make this
species better adapted to its environment. Natural selection has lead to the
species evolving. The one of land-snails species, Cepaea nemoralis, for
instance shows a clear example of a process of natural selection as seen in the
casual relationship between their different characteristics within their own
population and their overall geological distribution. These land snails vary in
shell color and patterns, ranging from brown, pink and yellow where the brown
and pink shelled snails are the darker snails and also ranging from unbranded to
unbranded patter with the branded pattern with several distinct lines. These
different colored and pattern shells may seem trivial but they play a
significant role in the chances of survival. Genetics are what determine the
color and the patterns of the shells, where the dominant genotype, like its
name, is the dominant one and thus represents the organism’s phenotype. Like
wise, the dominant characteristics of a snail are supportive of the snail’s
survival and thus they were past down. Although some may claim that the causes
of evolution may be arbitrary, there is actually nothing random about natural
selection. It’s just simple algorithm: the more likely you are to survive, the
more likely your genes are advantageous and the more likely your genes will be
passed own. In the case of the snails, both the abiotic factors like the
environment, climate and temperature affecting the distribution of brown/pink
snails and yellow snails and biotic factors such as the snails’ predators are
what determined its survival. There are evidence that pointed out that the
darker shelled (brown and pink) snails are, the more likely they will survive
in Northern Europe rather than in Southern Europe, where climate and
temperature are much warmer due to its ability to absorb solar radiation more
effectively in comparison to that of the lighter shelled snails. The less
absorption of solar radiation propels the snails with yellow shells to thrive
better in environments with higher temperature in places such as the Southern
Europe because unlike the brown/pink shelled snails, the yellow snails are less
likely to be overheated and died off. In colder areas, the brown and
pink-shelled snails thrive because of their ability to trap scarce heat to warm
them up. In addition, the environment and the other organisms living within the
environment in which the snails live also affect the chance of survival. Yellow
snails are noticeable in woodlands when compared to brown and pink snails.
Thus, they are often fed in this area. However, the brown/pink snails are
easily distinguished in grasslands and therefore are frequently predated in
those areas. The same characteristic, in this case the shell color, can be a
double-edged sword: it can either benefit you or harm you. This is simply
natural selection.
2. Research another
case of natural selection in action. Write a summary of this research
(1-2 paragraphs). Site your source(s) at the end of the summary.
The cases of natural selection in action are right in front of us. In reality, these cases are actually us, human beings. Are humans
still evolving? The simple answer is yes, even if the changes are not obvious.
Experts believe that about 9 percent of our genes are undergoing rapid
evolution as we speak. The genes most affected by natural selection are those
involving the immune system, sexual reproduction and sensory perception.
Lactose intolerance is one example of natural selection. We are the only
species that doesn't become lactose intolerant as we grow up. This case of
natural selection in action can be supported by a case study by Sabeti in 2006.
The domestication of plants and animals roughly 10,000 years ago
profoundly changed human diets, and it gave those individuals who could best
digest the new foods a selective advantage. The best understood of these adaptations is lactose tolerance.
The ability to digest lactose, a sugar found in milk, usually
disappears before adulthood in mammals, and the same is true in most human
populations. However, for some people, including a large fraction of
individuals of European descent, the ability to break down lactose persists
because of a mutation in the lactase gene (LCT). This suggests that the allele became common in Europe because of increased nutrition from cow's milk,
which became available after the domestication of cattle. This hypothesis by
Sabeti and colleagues was later eventually confirmed by Todd Bersaglieri and
his colleagues, who demonstrated that the lactase persistence allele is common
in Europeans (nearly 80% of people of European descent carry this allele), and
it has evidence of a selective sweep spanning roughly 1 million base pairs (1 megabase). Indeed, lactose tolerance is one of the strongest
signals of selection seen anywhere in the genome. Sarah Tishkoff and colleagues
subsequently found a distinct LCT mutation also conferring lactose tolerance,
in this case in African pastoralist populations, suggesting the action of convergent
evolution.
Let me ask you one last question. Are you lactose intolerant? Well, many people are. In fact, the ability
to digest lactose may be an example of adaptive evolution in the human lineage.
3. Explain the relationship between evolution, ecology and genetics.
Ecology is the study of the distribution of
living organisms and their relationships to each other. Evolution involves the
changes that take place as new species come about. The ecology of an
ecosystem changes as the biological diversity changes. For example, during the Jurassic period, the ecosystem
involved large reptiles as the dominant animals. However, as the ecology
changes overtime, the mammals evolve and the dinosaur eggs are destroyed,
altering the population dynamics.
In order for evolution to work, a mechanism that keeps trait discrete
must exist. Genetics describes the pattern of inheritance. In order for
evolution to work, a mechanism that keeps trait discrete must exist. Genetics
describes the pattern of inheritance. A mutation is a change in DNA, the
hereditary material of life. An organism’s DNA affects how it looks, how it
behaves, and its physiology. So a change in an organism’s DNA can cause changes
in all aspects of its life. Mutations are truly essential to evolution as they
are the raw material of genetic variation. If the mutation made is beneficial
to the organisms, the mutated genes will be passed on to the next generation.
Without mutation, evolution could not occur.
