Charles Darwin Theory of Evolution as a Mechanistic

Charles Darwin: Theory of Evolution as a Mechanistic Process JRMGUCE 2009

Charles Darwin: Theory of Evolution as a Mechanistic Process • • Darwin’s Idea of Common Descent Darwin’s Idea of Multiplication of Species Darwin’s Idea of Gradualism Darwin’s Idea of Natural Selection

Darwin’s Idea of Common Descent • Descent with modification A. K. A EVOLUTION • common ancestor/prototype • Accumulated diverse modifications or adaptations

The finches posed questions to Darwin: Did they descend from one mainland ancestor, did islands allow isolated populations to evolve independently, and could present-day species have resulted from changes occurring in each isolated population? ? ?

Darwin’s Idea of Common Descent • Life history is like a tree • Common trunk: multiple branching and rebranching • Common ancestor in each fork of branching • lineage of common descent • Extinct species

TAXONOMY: Tree of Life Carolus Linnaeus - Species are fixed - Ordered the great diversity of organisms into “groups subordinate to groups” Kingdom Phylum Class Order Family Genus species

Reflected the genealogy of the tree of life

Darwin’s Idea of Multiplication of Species • species either split into or bud off other species • geographical isolation of a founder species. Founder effect. The frequency of the a allele is low in the initial population, but a small subset, in which one individual is Aa, is removed from the large population and founds a new population. The frequency of a is markedly higher in this new population, due to its relatively high frequency in the founders

Darwin’s Idea of Multiplication of Species • different ecological niches provide different ways of living • different plants and animals come to fill different niches with different shapes and behaviors

Darwin’s Idea of Gradualism • changes through the gradual change of population rather than the sudden production of new individuals • species arise: • Through gradual accumulation of adaptations to a different environment

e. g. Darwin’s finches ADAPTIVE RADIATION

• Rapid evolution may arise: • • Isolation of small population Migration of small group in a new environment Through mass extinction Because of geological barriers

Darwin’s Idea of Natural Selection • Compared processes in nature with artificial selection • Developed a scientific hypothesis to explain how evolution occurs • Struggle for existence (Malthus) • Members of each species compete regularly to obtain food and living space and other necessities in life • Central to his Theory of Evolution

Survival of the Fittest * key factor in the struggle for existence * Fitness -ability to survive and reproduce -result of adaptation -central to the process of evolution by natural selection

• LOW FITNESS » Either DIE or LEAVE FEW OFFSPRINGS • HIGH FITNESS LEVEL – many OFFSPRINGS • referred to as: NATURAL SELECTION • accumulation of changes that differentiate groups from one another, such that a new species may arise

DARWIN’s MISSING INGREDIENT Darwin did not understand the genetic basis for variation – variations – mutations – genetic recombination – mutation as a raw material for evolution

OTHER THINGS TO BE CONSIDERED • Natural vs. Artificial selection • Importance of population in evolution • smallest unit that can evolve • Natural selection acts on individuals but INDIVIDUALS DO NOT EVOLVE

Darwinian View of LIFE • Diverse forms have arisen – DESCENT WITH MODIFICATION FROM ANCESTRAL SPECIES » Biological diversity • Mechanism of modification – NATURAL SELECTION

Patterns of Evolution • Mass extinction • 99% of the species ever lived are now extinct • wiped out whole ecological systems* • Cretaceous extinction » Large asteroid struck the earth • Can be caused by eruptions of many large volcanoes (Permian and Cretaceous) , changing of positions of continents and changing of sea levels

Patterns of Evolution • Adaptive Radiation • single species or small group of species has evolved into several different forms that live in different ways • Ex. Darwin’s Finches Dinosaurs Mammals

Patterns of Evolution • Convergent Evolution • unrelated organisms come to resemble one another • Natural selection may mold different body structures » structures tend to function the same way and look similar • Analogous structures » same look and function » Different embryonic origin

Patterns of Evolution Coevolution two species evolve in response to the changes in each other over time Ex. Fig trees and wasps

Patterns of Evolution • Developmental Genes and Body Plans • Hox genes

Process of Speciation • Species • group of organisms that can interbreed and produce a fertile offspring • Share a common gene pool • As new species evolve populations become reproductively isolated from each other • Reproductive isolation » Can be: Behavioral, Geographical and Temporal

Process of Speciation • Behavioral isolation • Capable of interbreeeding but has different courtship rituals or behavior • Geographical isolation • Two populations are separated by geographic barriers • Acted by natural selection • Ex. Abert and Kaibab Squirrels

Process of Speciation

Process of Speciation

DIANE DODD’s Experiment