adaptation and evolution of populations

biological evolution

Many changes in the genetic makeup of a species may accumulate over time, especially if the environment is changing. Eventually the descendants will be very different from their ancestors and may become a whole new species. Changes in the genetic makeup of a species over time are known as biological evolution.

natural selection

The mechanism for evolution is natural selection. Traits become more or less common in a population depending on whether they are beneficial or harmful. An example of evolution by natural selection can be found in the deer mouse, species Peromyscus maniculatus. In Nebraska this mouse is typically brown, but after glaciers carried lighter sand over the darker soil in the Sand Hills, predators could more easily spot the dark mice. Natural selection favored the light mice, and over time, the population became light colored. An explanation of how adaptations de- velop. Click image to the left or use the URL below. URL:



The characteristics of an organism that help it to survive in a given environment are called adaptations. Adaptations are traits that an organism inherits from its parents. Within a population of organisms are genes coding for a certain number of traits. For example, a human population may have genes for eyes that are blue, green, hazel, or brown, but as far as we know, not purple or lime green. Adaptations develop when certain variations or differences in a population help some members survive better than others (Figure 1.1). The variation may already exist within the population, but often the variation comes from a mutation, or a random change in an organisms genes. Some mutations are harmful and the organism dies; in that case, the variation will not remain in the population. Many mutations are neutral and remain in the population. If the environment changes, the mutation may be beneficial and it may help the organism adapt to the environment. The organisms that survive pass this favorable trait on to their offspring.

instructional diagrams

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a mutation can be:

a) beneficial

b) harmful

c) neutral

-->  d) any of the above

if a region has brown sand and the mice are all brown, if a white mouse is born it

a) means that there is a gene or genes for white fur in the population.

b) probably will not survive to reproduce.

c) will be favored if white sand blows in and covers the brown sand.

-->  d) all of the above.

changes in genetic makeup of species over time is known as biological evolution.

-->  a) true

b) false

the mechanism for evolution is natural selection.

-->  a) true

b) false

a mutation that is harmful, may become beneficial if

a) the population changes.

-->  b) the environment changes.

c) the genetic makeup of the population changes.

d) none of these.

in nebraska, natural selection favors deer mice that

a) contrast with the color of the soil where they live.

b) are able to see over short grass.

-->  c) match the color of the soil where they live.

d) none of these

an organism is most likely to evolve if its

-->  a) environment is changing.

b) environment is stable.

c) ancestors experienced a lot of mutations.

d) current individuals experience a lot of mutations.

all the genetic variation that a population will have exists within it.

a) true

-->  b) false

changes in the genetic makeup of a population may result in

a) a new species.

b) a beneficial adaptation.

c) a new variety or subspecies.

-->  d) all of the above.

diagram questions

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