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BIOLOGY - CLUTCH

CH.23 - EVOLUTION BY NATURAL SELECTION

CONCEPT: DESCENT WITH MODIFICATION

Evolution in the simplest sense is the change in phenotype in a biological population over time.

● Lamarckism – an organism passes on to its offspring traits it acquired during its own lifetime

□ Use and disuse would strengthen and weaken parts of the body, respectively.

EXAMPLE:

● Darwin’s ideas about descent with modification, or evolution:

1. Individuals in a population vary in the traits they posses.

2. Some of these trait differences can be inherited.

3. Every generation only some individuals will survive long enough to reproduce, and some will reproduce more than others.

4. Some individuals survive better and produce more offspring because of certain heritable traits.

● Natural selection – the process by which heritable traits become more or less common in a population based on the

difference in reproductive success between the individuals who have those traits

EXAMPLE:

BIOLOGY - CLUTCH

CH.23 - EVOLUTION BY NATURAL SELECTION

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CONCEPT: DESCENT WITH MODIFICATION

Darwin traveled on the Beagle to the Galapagos Islands, and noticed variation between the finches.

● Fitness – the ability of an organism to survive and reproduce

● Adaptation – trait that is maintained and evolved by natural selection that enhances the fitness of an organism

EXAMPLE:

● Industrial melanism – organisms evolve darker pigmentation due to industrial pollution

EXAMPLE:

● Artificial selection – the process by which humans breed organisms for certain traits

EXAMPLE:

BIOLOGY - CLUTCH

CH.23 - EVOLUTION BY NATURAL SELECTION

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CONCEPT: DESCENT WITH MODIFICATION

● Fossil record – all fossils found on Earth, form when organic tissues are mineralized, provides evidence for evolution

□ The age of fossils is determined using radiometric dating.

□ Fossils can reveal extinct species, though some extant species have fossil remains as well.

● Geologic time scale – a measurement of time that relies on geologic data.

EXAMPLE:

● Convergent evolution – the independent evolution of similar features

□ Analogous structures – have similar function, but independent origins (homoplasy)

● Divergent evolution – accumulation of differences between groups leading to the formation of new species

□ Homologous structures – have shared ancestry (homology)

EXAMPLE:

BIOLOGY - CLUTCH

CH.23 - EVOLUTION BY NATURAL SELECTION

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CONCEPT: DESCENT WITH MODIFICATION

● Transitional feature – a trait that has a form somewhere between the ancestral form and the form of descendants

● Vestigial trait – structure or attribute that has lost ancestral functionality, but is still retained by evolution

● Non-adaptive traits – some traits don’t appear to be adaptive, instead having a neutral or deleterious effect on fitness

EXAMPLE:

● There is no scientific definition for “complexity”, and there is no such thing as “higher order” organisms.

● Evolution is constrained by genetic variation, and what has already evolved.

● Fitness trade-offs – compromises between traits

EXAMPLE:

BIOLOGY - CLUTCH

CH.23 - EVOLUTION BY NATURAL SELECTION

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