Medical Academy named after S.I. Georgievsky of Vernadsky CFU

(LA-2)
SUPERVISOR- ANNA ZHUKOVA

tend to survive and produce more offspring. The theory of

its action was first fully expounded by Charles Darwin and is now believed to be the main process that brings about evolution.

consider a simplified, hypothetical example. In this example, a group

of mice with heritable variation in fur color (black vs. tan) has just moved into a new area where the rocks are black. This environment features hawks, which like to eat mice and can see the tan ones more easily than the black ones against the black rock.
Because the hawks can see and catch the tan mice more easily, a relatively large fraction of the tan mice are eaten, while a much smaller fraction of the black mice are eaten. If we look at the ratio of black mice to tan mice in the surviving ("not-eaten") group, it will be higher than in the starting population.

new heritable traits, such as fur colors, is random mutation

(changes in DNA sequence). Random mutations that are passed on to offspring typically occur in the germline, or sperm and egg cell lineage, of organisms. Sexual reproduction "mixes and matches" gene variants to make more variation.

traits. Most of this variation is heritable (passed from parent

to offspring).

to produce far more offspring than will survive to produce

offspring of their own.

What are some of the challenges living things must overcome to survive?

chance to survive in their environment. Those that survive will

produce more offspring. This is called natural selection.

individuals with these favorable traits leading to a change in

the average characteristics of a population over time. This is called evolution.

supports each postulate in natural selection
Individuals in a population vary

in their traits

2. Most of this variation is heritable – passed on to offspring

3. More offspring are produced than can survive (due to limited resources such as food)

4. Individuals with advantageous traits are more likely to survive and reproduce

Medium Ground Finch Geospiza fortis

giraffe’s neck became long?

that inhabit the Earth today are different from those that

inhabited it in the past.
Natural selection is one of several processes that can bring about evolution, although it can also promote stability rather than change. It follows that natural selection is not the same thing as evolution.
The four propositions underlying Darwin's theory of evolution through natural selection are: (1) more individuals are produced than can survive; (2) there is therefore a struggle for existence; (3) individuals within a species show variation; and (4) offspring tend to inherit their parents' characters.
The three necessary and sufficient conditions for natural selection to occur are: (1) a struggle for existence; (2) variation; and (3) inheritance.
Endler's experiment with guppies demonstrated that evolution through natural selection can occur in relatively few generations.

Mutation is the ultimate source of variation.

The frequency of a particular character in a particular population may be due to chance events (e.g. the founder effect and/or genetic drift) rather than to natural selection.