Deer Mouse

Peromyscus. P. maniculatus

The Deer Mouse has been acknowledged as one of the quickest-evolving examples of natural section

In a period of only 8000 years the colour of the deer mice has adapted to their environment

What is a Deer Mouse?

A Deer Mouse is a small rodent, more commonly known as a 'field mouse'. They have large bulging eyes, big ears, a bicoloured patterned body and a long tail. They are larger than harvest mice, though they are smaller than a house mouse.

How has the deer mouse evolved?

As the Deer Mouse can live in multiple different environments. The species has evolved to be able to live in one environment and be able to live there without any risk of dying out, due to not being suited to that environment.

Evolving of the deer mouse has included;

- Pigmentation of fur coat in different environments

- Length of the tail

- Markings on the tail

- Size of mouse and feet [ depending upon surroundings (larger in woodlands) ]

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Natural Selection, what is it?

Natural selection has been defined as; the process where organisms that are better adapted to their environment, tend to survive. Therefore produce more offspring.

Evolution, what is it?

Evolution has been defined as; the process by which different kinds of living organisms are believed to have developed from earlier forms during the history of the earth.


Charles Darwin looked at the evolution of certain animals and he linked it together through a simple flow diagram. With this diagram, you can see how natural selection leads to evolution.

How does Natural Selection have and effect on evolution?

Natural Selection can affect evolution in a variety of ways.

i.e; the raw material for natural selection. This in turn leads to evolution.

Natural Selection has enforced evolution upon Deer Mice

Variation of a species

Variation is the differences in organisms of the same species. Such as colour variation.


Colour variation within the deer mouse is dependant upon genetic and environmental factors. Therefore the environment that the deer mouse lives in corresponds to the colouring of the fur. There are two different colours of deer mice, ones with a dark coloured fur, and those with a light coloured fur. The pigmentation changes over a period of time due to the gene/ allele that determines the fur coat colour. With the adaptive allele in the mice, there is still a possibility either the lighter or darker coloured coat allele may still be in the gene. Therefore a lighter coloured mouse in woody lands is possible, as is a darker coloured mouse on sand dunes.


For a Deer Mouse living in sand dunes, their fur coat is more commonly going to be of a lighter colour, as it is the favourable adaptation. The favourable adaption occurs not only in one or two generations, but, hundreds. It has been shown that it has taken as little as 8000 years for a colour adaption to completely occur within this species.


Even though the mouse may have pigmentation that 'blends' in with its environment, there are still predatory avian [i.e. hawks, eagles and owls] and mamialian [i.e. other larger mice, foxes and shrews] animals that can still see the tracks and the animal itself.


As the lighter and darker coloured mice blend into the surrounding environment, they are harder to see. Therefore; the colouration gene is more likely to be carried through generations, increasing the population of to favoured colour of mouse.

Natural selection for coat color in deer mice - Hopi Hoekstra (Harvard/HHMI)

Where do they live?

Deer Mice are commonly found in several locations. Such as;

- California

- Alaska

- Canada

- Central and some coastal areas of Mexico

- South Eastern United States

They are a highly abundant species, taking up to as many as ten per acre.

How often do Deer Mice reproduce?

Deer Mice tend to breed every three- four weeks during the warmer months. Though less frequently during the colder months.

How does high altitudes affect Deer Mice?

As Deer Mice live underneath the ground, the mice living at high altitudes are exposed to cold environments. Therefore; searching for food becomes a life or death situation. Some go above ground, and as it is so cold and they cannot produce sufficient body hear they become hypothermic and are very likely to die. Though, if they don't venture out in search of food and stay underground they starve and die.

So the deer mice living at high altitudes have evolved in body size to withstand colder temperatures. By evolving in size, the deer mouse's organs are closer into the inside of the animals body away from the freezing temperatures, compared to if they were closer to the skin lacking fatty tissue and muscle around the organs.