English for

4.2 Reading Resource #2
: Variation and Adaptation 
Natural selection can occur only when there is variation or difference between individuals in a 
population. Importantly, these differences must have a genetic basis; otherwise, selection will not result in 
change in the following generation. This is significant because variation among individuals can be caused by 
non-genetic factors such as better nutrition rather than different genes. A population's genetic diversity is 
derived primarily from two sources: mutation and sexual reproduction. The ultimate source of new s or new 
genetic variation in any population is mutation, a change in DNA. A person with a mutated gene may exhibit 
a different trait than the rest of the population. This, however, is not always the case. A mutation can have one 
of three outcomes on the organisms’ appearance (or phenotype): 
➢
A mutation can change the phenotype of an organism, giving it less fitness—a lower chance 
of survival, resulting in fewer offspring. 
➢
A mutation may produce a phenotype with a beneficial effect on fitness. 
➢
Many mutations, called neutral mutations, will have no effect on fitness. 
Mutations can also have a wide range of effects on the fitness of the organism that expresses them in 
their phenotype, from minor to major. When two parents reproduce, unique combinations of s assemble to 
produce unique genotypes and, consequently, phenotypes in each of the offspring. 
An adaptation
is a heritable trait that aids an organism's survival and reproduction in its current 
environment. An adaptation is a “match” of the organism to the environment. Adaptation to an environment 
comes about when a change in the range of genetic variation occurs over time that increases or maintains the 
match of the population with its environment. The variations in finch beaks shifted from generation to 
generation providing adaptation to food availability. 
35
Fowler, S.,Roush, R. & Wise, J. (2017) 
Concepts in Biology, 
Chapter 11, -Pp.
250-251 
OpenStax, 
https://openstax.org/details/books/concepts-biology
,  

---

96 
Whether or not a trait is favorable depends on the environment at the time. The same traits do not 
always have the same relative benefit or disadvantage because environmental conditions can change. For 
example, finches with large bills were benefited in one climate, while small bills were a disadvantage; in a 
different climate, the relationship reversed.