Download Comparing Scenarios of Evolution

Comparing Scenarios of Evolution
Which scenario sounds like an explanation that Darwin might give? Why?
Scenario B. It contains elements of Darwin’s natural selection process, including:
1) inheritable variations, 2) an environmental change, and 3) survival and
reproduction of those with traits enabling survival in the changing environment.
No mention of “need” nor individual efforts to make physical changes “in order to
survive.”
Which scenario is NOT an explanation that Darwin would give?
Scenario A. The ideas expressed in scenario A have a few core components
that make it different than what Darwin would propose. For example,
1) environmental change creates “need” for individuals to change
2) by individual effort, physical changes are produced
3) newly acquired physical changes somehow become genetic and heritable, and
are therefore passed on to offspring
This explanation is consistent with another evolutionary scientist’s view on
evolution. The scientist was Jean-Baptiste Lamarck. Lamarck ‘s theory became
known as the “Theory of Acquired Traits”. While Lamarck agreed with the notion
of evolution, his explanation about how organisms change over time did not
produce supporting evidence (unlike Darwin). As a result, people often will just
refer to his ideas as a hypothesis.
Notice how a Lamarckian explanation is different than that of Darwin’s. He is
suggesting that the environmental changes created the necessity for individuals
to change during their lifetime and through effort physical changes could occur.
In other words, individuals that were most successful with “willing” their way to
survive, had the ability to pass on these lifetime acquired traits to their offspring.
Unfortunately, Lamarck couldn’t provide any explanation of how these newly
acquired traits could arise during the lifetime of an organism and then somehow
be transferred to the offspring.
Darwin, on the other hand, got support for his theory because of the
advancements scientists made in heredity and DNA. Darwin always began his
explanation by referring to a spectrum of variations that existed within a
population of individuals. The organisms that had a variation that was best
suited to a changing environment were more likely to reproduce and pass these
variations along to start the next generation. We know now that different
variations come about because of random changes in the DNA (eg. mutation).
Different mutations can give rise to different alleles, and when these alleles are in
different combinations, they can give rise to a range of traits.
Eg. Incomplete dominance
RR – red flowers
Rr- pink flowers
rr – white flowers
Inherent to present day Darwinian theory is that whatever gives rise to the
variation is a random process. Certainly, organisms don’t choose when to
mutate their DNA. It just happens unknowingly. However, once these variations
arise, the environment selects for a particular form of a trait (non-random
process).