Evolution Evolution is the idea that living species are descendants of ancestral species that were different from present-day ones Evolution describes the genetic changes (mutations) in an organism over time

Evolution Organisms are adapted to their environment As descendants of a remote ancestor spread into various habitats over millions and millions of years, they accumulate diverse modifications (adaptations) that fit them to specific ways of life

Evolution Natural variation among individuals is based on heredity (and mutation). These variations enable organisms to become adapted to their environment over time

Natural Selection Natural selection is the process by which favorable, inherited traits become more numerous in future generations of a population of reproducing organisms Over time, natural selection leads to species that are well adapted (highly evolved) to their environments

Natural Selection The concept of natural selection was developed by Charles Darwin; a naturalist who sailed around the world and noted the unique adaptations of animals in many diverse environments (most notably the Galapagos Islands)

The Principles of Natural Selection Variation Some individuals, due to heredity or mutation, possess characteristics which make them better adapted to their environment

The Principles of Natural Selection Inheritance of Traits Best-suited organisms will survive to produce more individuals that share same adaptation

The Principles of Natural Selection Struggle for existence/Competition More offspring are produced than can be supported by resources King Penguin Rookery © Momatiuk - Eastcott/Corbis

“Survival of the Fittest” Organisms are adapted to their environment through natural selection

Population with varied inherited traits 1 Elimination of individuals with certain traits 2 Reproduction of survivors 3 Certain individuals with one particular inherited trait will be eliminated, while others with a different inherited trait will avoid elimination

Let’s look at an example… Normal allele; vulnerable to pesticides Alternate allele; resistant to pesticides Survivors ‘Resistant’ allele passed to next generation

Mechanisms of Evolution Evolution is dependent on genetics Reproductive component – organisms must reproduce Heredity component – offspring must resemble parents (traits passed on to offspring) Variation component – there must be genetic variation among individuals of population genetic variation leads to variation in fitness (the ability to survive and reproduce)

Evolution Remember, evolution is the genetic change in populations over time Individuals do NOT evolve; evolution refers to generation-to-generation changes Evolution does not lead to perfectly-adapted organisms; natural selection results from environmental factors that vary from place to place and from time to time (a trait that is favorable in one situation may be detrimental in another)

Evolution Evolution is a gradual change over time

Evidence for Evolution Fossils!!! – the fossil record (the sequence in which fossils appear in layers of sedimentary rocks) provide some of the strongest evidence of evolution Sedimentary rocks form from sand and mud that settles to the bottom of seas, lakes and swamps; when organisms die, they settle along with the sediments and are preserved as fossils

Evidence for Evolution Allosaurus: 65 mya Seed fern: 150 mya Trilobite: 230 mya

Artificial Selection Artificial selection – the process by which humans have modified other species by selectively breeding for desired traits All dogs are domesticated breeds of the Gray wolf, Canis lupus

Evidence for Evolution Homologous structures – similar characteristics that result from a common ancestry Humerus Radius Ulna Carpals Metacarpals Phalanges Human Cat Whale Bat

Developmental similarities reflect descent from a common ancestor

Evidence for Evolution A prime (and very amusing) example of homologous structures are vestigial organs; remnants of structures that have no apparent function, but served important functions in organism’s ancestors

Evidence for Evolution A good example of homologous structures are vestigial organs; remnants of structures that have no apparent function, but served important functions in organism’s ancestors

Evidence for Evolution Vestigial structures of a whale

Evidence for Evolution In contrast to homologous structures, analogous structures also provide evidence for evolution Analogous structures are structures that share functional similarities, not due to common ancestry Analogous structures arise among unrelated organisms in response to similar needs or similar environmental factors

Analogous Structures Examples: wings of insects and birds; flippers of seals and penguins

Evidence for Evolution Remember, evolution uses the materials and processes that are already available (it fashions adaptations, rather than starting from scratch) Evolution is a tinkerer, not a master engineer (a tinkerer uses tools already there to improve) Adaptations are not perfect Evolution is constant; traits that are helpful for adaptation today may not be so helpful in the future

Evidence for Natural Selection Darwin’s fishes of the Galapagos Islands 14 species of finch; 1 common ancestor (from the mainland); different beaks

Mutations and sexual reproduction are the driving forces of evolution New alleles originate by mutation, a change in the nucleotide sequence of DNA Only mutations in cells that produce gametes can be passed along to offspring Most mutations are harmful, however a mutant allele may improve the adaptation of an individual to its environment and enhance its reproductive success

Mutations and sexual reproduction are the driving forces of evolution Spontaneous mutation rates in animals and plants average ~1 in every 100,000 genes per generation (a slow process) Sexual reproduction provides a means of increasing genetic diversity and variation, creating genetically-distinct individuals with new combinations of alleles (which may enhance adaptation and reproductive success)

Evolution Evolution is a widely accepted scientific theory that describes the observed changes in living things over time Scientists use evolution to explain the great diversity of life, but some dispute its ability to describe the origins of life on Earth

Other theories out there Name Descent with modification? Common ancestor? Extinction? Creation (A) No No No Transformism (B) Yes No No Evolution (C) Yes Yes Yes extinction (A) (B) (C) change change change

Evolution Remember, evolution is an accepted (and well-supported) scientific theory Scientific theories can never be proven (you cannot prove a hypothesis) but can be supported or rejected; must also be testable and falsifiable