1. Descent With Modification
Chapter 19
Descent With Modification

2. Jean Baptiste Lamarck
Lamarck (1809) proposed a mechanism by which specific adaptations evolve, which included two related principles:
1. Use and disuse: Body organs used extensively to cope with the environment become larger and stronger while those not used deteriorate.
2. Inheritance of acquired characteristics: Modifications an organism acquired during its lifetime could be passed along to its offspring.
Ex: birds’ wings, giraffes’ necks.
Experiments and new knowledge have disproven Lamarck (mice tails experiment)

4. Charles Darwin
Darwin, serving as ship’s naturalist on the H.M.S. Beagle, observed unique species on the South American coast including the Galapagos Islands.
Published On the Origin of Species by Means of Natural Selection in 1859.
Made two major points:
1. Species evolved from ancestral species due to inheritable variations.
2. Natural selection is a mechanism that could result in this evolutionary change.

5. Darwin’s Theory
Natural selection: Due to survival of the fittest, organisms with certain traits survive to reproduce; this results in changes in inherited characteristics of a population over time.
Transmutation: (“descent with modification”) species have descended, with changes, from other species over time.

7. Evidence Presented
Fossil record – shows how organisms on earth have changed over time.
Record has “gaps”; difficulty finding accurate “age”.

9. Evidence Presented cont.
Homologous structures -- organisms have similar structures used for similar purposes.
Did they have a common ancestor?

10. Evidence Presented cont.
Vestigial structures -- organs that serve no purpose, but resemble those found in other organisms.
Scientists are still discovering functions.

11. Evidence Presented cont.
Comparative embryology -- embryos of vertebrates look similar in early stages.
Did they have a common ancestor?
Early sketches were exaggerated.

12. Evidence cont.: Biogeography

13. The New Frontier
Comparative biochemistry --The DNA revolution has disproven and supported some old ideas.
Similar DNA sequences may tell which species are more closely related.

14. More on Natural Selection
Variations in a population arise by chance through mutation and recombination during sexual reproduction.
Darwin’s view of Gradualism :
Life evolved by a gradual accumulation of small changes over vast spans of time.
… Or Punctuated equilibrium (S.J. Gould):
Species have long periods of no change, then short periods of drastic change, due to intense environmental pressure.