Basis Of The Evolution

The Basis of Evolution “There is grandeur in this view of life, with its several powers, having been originally breathed into a few forms or into one; and that, whilst this planet has gone cycling on according to the fixed law of gravity, from so simple a beginning endless forms most beautiful and most wonderful have been, and are being, evolved.” -- Charles Darwin

What’s the Big Idea? • Descent with Modification – organisms are altered through descent from an ancestor that lived in the remote past • Environments change • Species change

Lecture 1-19 (HHMI)

19.3

Sirenia (Manatees Hyracoidea (Hyraxes) and relatives)

Barytherium

Mammuthus

Stegodon Platybelodon

Mammut

Deinotherium

Elephas Loxodonta maximus africana (Africa) (Asia)

Moeritherium

Millions of years ago

Years ago

• Descent with Modification is like a tree with multiple branching points from a common trunk to the tips of the youngest twigs that represent the diversity of living organisms Loxodonta cyclotis (Africa)

Homology • Homology – Is the study of similar structures in different species due to their ancestry

19.5

Anatomical Homologies • Homologous structures are anatomical similarities that represent variations of a structure that was present in a common ancestor

19.5

Human

Cat

Whale

Bat

• Homology in embryology (study of development) – Reveals additional anatomical similarities not visible in adult organisms

Pharyngeal pouches

Post-anal tail

Chick embryo

19.5

Human embryo

Vestigial organs – Are remnants of structures that served important functions in the organism’s ancestors

Letter c in the picture indicates the undeveloped hind

19.5

legs of a baleen whale.

• Genetic homologies – Are generally reflected in their molecules, their genes, and their gene products Species

Percent of Amino Acids That Are Identical to the Amino Acids in a Human Hemoglobin Polypeptide 100%

Human Rhesus monkey

95%

Mouse

87%

Chicken

69%

Frog

19.5

Lamprey

54%

14%

Gene sequence conservation in hemoglobin Coding

Coding

Coding

INTRON

• • • • •

Human Chimp Rat Mouse Chicken

EXONS 19.5

Genome Browser

What’s the Big Idea? • Natural Selection – “The preservation of favorable variations and the rejection of injurious variations I call Natural Selection” -- Charles Darwin

19.1-3

What’s needed for Natural Selection? • Variation – differing characteristics • Adaptation - characteristics that offer a survival/reproductive advantage • Selection – favoring or rejection of certain characteristics • Time – TIME (thousands/millions of years) Lecture 1-26 (HHMI)

19.1

• Observation #1: Many more offspring are produced than survive for each species • Observation #2: Nonetheless, populations tend to be stable in size • Observation #3: Populations of species have limited resources • Inference #1: There is a struggle for existence among individuals of a population, with only a fraction of their 19.4 offspring surviving

• Observation #4: Members of a population vary extensively in their characteristics • Observation #5: Much of this variation is heritable

19.4

• Inference #2: Survival depends in part on inherited traits. Individuals whose inherited traits give them a high probability of surviving and reproducing are likely to leave more offspring than other individuals.

• Inference #3: This unequal ability of individuals to survive and reproduce will lead to a gradual change in a population, with favorable characteristics becoming more common (natural selection). 19.4

Artificial Selection • Human (not nature) directed • Demonstrates that selecting variations can alter form over time

19.6