Biology 1202B Lecture Notes - Lecture 4: Directional Selection, Speciation, Microevolution

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23 Aug 2016

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Darwin called the process of humans selecting the characteristics they wanted in the offspring by choosing parents with those traits artificial selection (eg. found in dog breeding) Through thomas malthus"s book, darwin realized individuals within a population compete for limited resources. Natural selection individuals with certain traits leave more offspring than individuals without those traits do. Natural selection favours adaptive traits (hereditary characteristics that make organisms more likely to survive and reproduce a given set of environmental conditions. By favouring individuals that are well-adapted to the environment in which they live, natural selection can change the population over time. Natural selection changes nonmorphologic characteristics of population. Also realised natural selection could be reason for differences between populations and the production of new species. Since many characteristics affect survival and reproduction, natural selection would cause the population to become more different over time, referred to as evolutionary divergence. 17. 3e impact of the theory of evolution by natural selection.

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Excerpt from âOn the Tendency of Species to form Varieties; and on the Perpetuation of Varieties and Species by Natural Means of Selection,â by Charles Darwin [Read July 1st, 1858].

To give an imaginary example from changes in progress on an
island:âlet the organisation of a canine animal which preyed
chiefly on rabbits, but sometimes on hares, become slightly plastic;
let these same changes cause the number of rabbits very slowly to
decrease, and the number of hares to increase; the effect of this
would be that the fox or dog would be driven to try to catch more
hares: his organisation, however, being slightly plastic, those
individuals with the lightest forms, longest limbs, and best eyesight,
let the difference be ever so small, would be slightly favoured, and
would tend to live longer, and to survive during that time of the year
when food was scarcest; they would also rear more young, which
would tend to inherit these slight peculiarities. The less fleet ones
would be rigidly destroyed. I can see no more reason to doubt that
these causes in a thousand generations would produce a marked
effect, and adapt the form of the fox or dog to the catching of hares
instead of rabbits, ... So would it be with plants under similar
circumstances. If the number of individuals of a species with plumed
seeds could be increased by greater powers of dissemination within
its own area (that is, if the check to increase fell chiefly on the seeds), those seeds which were provided with ever so little more down, would in the long run be most disseminated; hence a greater number of seeds thus formed would germinate, and would tend to produce plants inheriting the slightly better-adapted down.

Questions: 2 examples must be provided for each question

DarwinâNatural Selection

Species:

What trait varies within the species?

What is the selective pressure? (In other words, what causes some individuals to produce more offspring than others?)

How would the population change over time?

Excerpt from âOn the Tendency of Species to form Varieties; and on the Perpetuation of Varieties and Species by Natural Means of Selection,â by Charles Darwin [Read July 1st, 1858]. To give an imaginary example from changes in progress on an island:âlet the organisation of a canine animal which preyed chiefly on rabbits, but sometimes on hares, become slightly plastic; let these same changes cause the number of rabbits very slowly to decrease, and the number of hares to increase; the effect of this would be that the fox or dog would be driven to try to catch more hares: his organisation, however, being slightly plastic, those individuals with the lightest forms, longest limbs, and best eyesight, let the difference be ever so small, would be slightly favoured, and would tend to live longer, and to survive during that time of the year when food was scarcest; they would also rear more young, which would tend to inherit these slight peculiarities. The less fleet ones would be rigidly destroyed. I can see no more reason to doubt that these causes in a thousand generations would produce a marked effect, and adapt the form of the fox or dog to the catching of hares instead of rabbits, ... So would it be with plants under similar circumstances. If the number of individuals of a species with plumed seeds could be increased by greater powers of dissemination within its own area (that is, if the check to increase fell chiefly on the seeds), those seeds which were provided with ever so little more down, would in the long run be most disseminated; hence a greater number of seeds thus formed would germinate, and would tend to produce plants inheriting the slightly better-adapted down.

2 examples must be provided for each question. One for each species.

DarwinâNatural Selection

Questions:

What are the two Species? What trait varies within the species?

What is the selective pressure? (In other words, what causes some individuals to produce more offspring than others?)

How would the population change over time?

Biology 1202B Lecture Notes - Lecture 4: Directional Selection, Speciation, Microevolution

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