Survival of the Fittest

http://www.britannica.com/EBchecked/topic/533148/selection#ref75077

TITLE: animal behaviour
SECTION: Darwin’s influence

The individuals that are best equipped to survive and reproduce perpetuate the highest frequency of genes to descendant populations. This is the principle known colloquially as “survival of the fittest,” where fitness denotes an individual’s overall ability to pass copies of his genes on to successive generations.

biological principles

• TITLE: selection (biology)

The theory of evolution by natural selection was proposed by Charles Darwin and Alfred Russel Wallace in 1858. They argued that species with useful adaptations to the environment are more likely to survive and produce progeny than are those with less useful adaptations, thereby increasing the frequency with which useful adaptations occur over the generations. 

TITLE: biology
SECTION: Evolution

In his theory of natural selection, which is discussed in greater detail later, Charles Darwin suggested that “survival of the fittest” was the basis for organic evolution (the modification of living things with time). Evolution itself is a biological phenomenon common to all living things, even though it has led to their differences.

• TITLE: biology, philosophy of
  SECTION: Natural selection
  What the thesis of natural selection, or survival of the fittest, really claims, according to Darwinians, is not that the fittest always survive but that, on average, the more fit (or the fittest) are more successful in survival and reproduction than the less fit (or unfit). Another way of putting this is to say that the fit have a greater propensity toward successful survival and reproduction.