Natural Selection and Adaptation Because the environment is always changing, there is no perfectly-adapted organism. There are three preconditions for natural selection: a. The members of a population have variations that can be passed on. b. Overpopulation = more individuals are produced each generation than the environment can support. c. Some individuals have adaptations that allow them to survive and reproduce better than others

There are two consequences of natural selection. a. An increasing number of individuals in future generations will have the adaptations. b. A population becomes adapted to its local environment.

Natural selection can only use variations that are randomly provided; therefore there is no directedness or anticipation of future needs. Extinction occurs when  previous adaptations are no  longer suitable to a changed  environment.

Organisms Have Variations 1. variations are essential in natural selection (before looked at as imperfections) 2. variation is completely random. 3. New variations can be harmful or helpful. 4. Variations that make adaptation possible are those that are passed on from generation to generation. 5. Darwin could not state the cause of variations because genetics was not yet established.

ORGANISMS DIFFER IN FITNESS FITNESS is a measure of an organism’s reproductive success Reproduction is important for evolution, only those who survive to reproduce, pass on those advantageous genes.

Organisms Become Adapted An adaptation is a trait that helps an organism be more suited to its environment.  2. This is recognizable when unrelated organisms living in a particular environment often display similar characteristics.

Evidence for Evolution Evidence supports common descent. Fossils Evidence Biogeographical Evidence Anatomical Evidence Biochemical Evidence

Evidence for Evolution: Fossil Record Fossil evidence Fossils record the history of life from the past Documents a succession of life forms from the simple to the more complex Sometimes the fossil record is complete enough to show descent from an ancestor Transitional fossils are a common ancestor for two different groups of organisms It allows to trace the descent of organisms

Evidence for Evolution: Biogeographical Distributions of plants and animals across earth Consistent with origin in one locale and then spread to accessible regions Hypothesis that different mix of plants and animals would be expected whenever Geography separates: Continents, islands, seas, mountains, and so on.

Evidence for Evolution: Anatomical Vertebrate forelimbs: Homologous - All contain the same sets of bones in similar ways Yet they are modified extensively to meet various adaptive needs Darwin interpreted this as support for a hypothesis of common descent Embryological development All vertebrate embryos have: A postanal tail and Paired pharyngeal (gill) pouches

The Evidence of Evolution: Anatomical Homologous Structures: Anatomically similar because they are inherited from a common ancestor May be functionally similar or not Analogous Structures: Serve the same function Not constructed similarly Do not share a common ancestor Vestigal Structures: Fully-developed anatomical structures Reduced or obsolete function

Significance of Homologous Structures bird humerus ulna radius metacarpals phalanges bat whale cat horse human

Significance of Developmental Similarities fish O f r o m a i r salamander tortoise chick pharyngeal pouches human postanal tail

Biochemical Evidence Almost all living organisms: Use the same basic biochemical molecules Utilize same DNA triplet code Utilize same 20 amino acids in their proteins DNA base-sequence differences: When very similar, suggest recent common descent When more different, suggest more ancient common descent

Significance of Biochemical Differences yeast moth fish turtle duck pig monkey human 10 20 Number of Amino Acid Differences Compared to Human Cytochrome c 30 Cytochrome c is a small protein that plays an important role in the electron transport chain within mitochondria of all cells 40 50