February 2017 update: add bit on Cameron Smith's book.
From page 138 of my copy of Stephen Jay Gould's Full House: The Spread of Excellence from Plato to Darwin.
- All organisms tend to produce more offspring than can possibly survive.
- Offspring vary among themselves, and are not carbon copies of an immutable type.
- At least some of this variation is passed down by inheritance to future generations. Consequently,
- If many offspring must die, and individuals in all species vary among themselves, then on average (as a statistical statement, and not in every case), survivors will tend to be those individuals with variations that are fortuitously best suited to changing local environments. Since heredity exists, the offspring of survivors will tend to resemble their successful parents. The accumulation of these favorable variants through time will produce evolutionary change.
Cameron M. Smith makes the same point even quicker (57 words) on page 22 of The Fact of Evolution:
Evolution is a word we use to characterize the unintended consequences of three independent facts of the nature world:
- The fact that lifeforms have offspring (replication)
- The fact that offspring are not identical (variation)
- The fact that some offspring pass more of their genes on to the next generation than do other offspring (selection)
Pretty simple, and yet only 40% of US residents think humans are subject to the process.