Events in the Life of Charles Darwin

Lessons from Malthus

"Struggle for existence" involves:

• struggle with environment
• struggle with other species (predator/prey)
• struggle with similar individuals

Any difference, however small, can be an advantage.

Artificial selection as practiced by breeders is a practical model for natural process of selecting fittest individuals.

excerpt from Vestiges....

These facts clearly shew how all the various organic forms of our world are bound up in one--how a fundamental unity pervades and embraces them all, collecting them, from the humblest lichen up to the highest mammifer, in one system, the whole creation of which must have depended upon one law or decree of the Almighty, though it did not all come forth at one time.

It is ... "a struggle for existence," in which the weakest and least perfectly organized must always succumb....
[S]o long as a country remains physically unchanged, the numbers of its animal population cannot materially increase.

If one species does so, some others requiring the same kind of food much diminish in proportion....

[T]hose that die must be the weakest--the very young, the aged, and the diseased,--while those that prolong their existence can only be the most perfect in health and vigour--those who are best able to obtain food regularly, and avoid their numerous enemies....

...Most or perhaps all the variations from the typical form of a species must have some definite effect, however slight, on the habits or capacities of the individuals.

Even a change of colour might, by rendering them more or less distinguishable, affect their safety; a greater or less development of hair might modify their habits....

• animal altruism
 
Can cooperation be an adaptive feature?

• vestigial parts

Why do organisms retain useless organs?

• heat death of the universe

How long can the sun burn at its current rate?

• inheritance of characteristics

How can one individual spawn a new line of organisms?

• Proposed existence of gemmules (from Latin root word for "twinning")
• granules given off by all cells
• some are dormant, others expressed
• contain formula to program the growth of new cells
• travel to, and concentrate in reproductive organs

• Heredity is the passing on of these gemmules.

If new cells inherit patterns from parents, what accounts for variations among offspring?

• Proposed that disturbance in this process:
• environmental changes
• level of competition
• food supply...

• causes variations:
• number of gemmules increased or decreased
• result--ordinary variations
• manifestation--individuality of people

• modification of gemmules themselves
• result--new structures
• manifestation--major change in form and function

• This is the variation that natural selection acts on.