What is Evolution? What is Evolution?

EVOLUTION: the process of change over time Evolution is the idea that new species develop from earlier species by accumulated changes. This is also referred to as “descent with modification”.

Evolution is NOT… It is NOT a fact...it's a theory: a well supported testable explanation of something that occurred in the natural world.

Lamarck's Hypothesis: Inheritance of Acquired Characteristics 1. “Acquired Characteristics”: Through use and/or non-use, those features needed for survival are developed in each individual. 2. Inheritance: Those characteristics developed (“acquired”) by individuals are passed on to their offspring, who can continue that development. 3. New Species: Eventually, over many generations, enough differences have developed that we can say we have a new species.

Darwin's Hypothesis: Natural Selection 1.Overproduction: There are more offspring produced than will survive and reproduce 2. “Survival of the fittest” (not necessarily the strongest): Those with more adaptive traits tend to survive longer and/or produce the most offspring; these are the “naturally selected”.

Natural selection is based on 4 facts: 1.Organisms produce more offspring than can survive. 2.There is variation among offspring. 3.There are limited resources (not enough food, water, space, etc. for everyone). 4.The organisms best fit to their environment will survive and the others will not.

Organisms produce more offspring than can survive. §Example: A frog can lay 200 eggs, yet not all eggs will survive to become adult frogs.

Quick Comparison LAMARCKDARWIN 1.Environment changes thus creating a “need” to change. 2. Development of new features, “in order to survive.” or “so that one can survive.” 3.Newly acquired traits somehow get passed down to offspring. 4. New species form, eventually 1.Variations of inheritable features which already normally exist. 2.Environment “screens out” (or SELECTS) features contributing to survival, and tends to eliminate the others 3. Those with traits which help survive and have more offspring, who inherit those traits. 4.New species form, eventually

Evidence of Evolution -- Fossils!! §Fossils are preserved remnants or impressions left by an organism that lived in the past. §Usually, the deeper down the fossil is, the older it is.

Evidence of Evolution -- Embryology! §It is believed that all vertebrates evolved from a common ancestor. The genetic information that guides their development is nearly the same. §That's why scientists can learn about human development by studying other organisms-- including zebrafish.

Evidence of Evolution -- Anatomical/Physiological Similarities §Notice how there are similar bones and similar structures in humans, birds and whales! l Can you tell which is the bird and which is the whale?

Divergent Evolution §formation of two new species from common ancestor. (The two species are said to have diverged from the same ancestor.) aka. Adaptive Radiation

Structural homology TurtleHumanHorse BirdBat Seal Humerus Radius and ulna Carpals Metacarpals Phalanges Figure 21.2a Divergent Evolution – Homologous structures

Convergent Evolution §different groups evolve similarly because live in same environment (analagous structures) Sticky tongue Not a lot of teeth Rugged stomach Big salivary glands

Convergent evolution and analogous structures

Vestigial Organs organ that serves no useful function over generations, they reduce in size

Adaptations! Inherited characteristic that increase an organism’s chance of survival §Why are most animals in the artic white? l So they blend in with the snow and avoid being seen! §Why do sharks have such sharp teeth? l It allows them to catch their prey! §Why do elephants have such big ears? l To let heat escape their bodies so they can l stay cool!

Results of Evolution -- Speciation!! §Speciation is the process that creates new species! §A species is a group of organisms that can naturally interbreed and produce fertile offspring. §The Liger--the offspring of a tiger and a lion. §Tigers and lions are still considered separate species, because although they can produce offspring, the offspring is not fertile.

Speciation 2 processes by which this can occur: Anagenesis is the accumulation of heritable traits in a population, that transforms that population into a new species. Cladogenesis is branching evolution, in which a new species arises as a branch from the evolutionary tree (cladogram). The original species still exists. This process is the source of biological diversity.

Modes of Speciation 1. Allopatric speciation- geographically separate ranges; new species evolve 2. Sympatric speciation- geographically overlapping populations; chromosomal changes and nonrandom mating reduce gene flow.

Allopatric speciation of squirrels in the Grand Canyon

Polar Bear and Grizzly Bears territories are overlapping (due to global warming) causing these 2 species to mate and produce offspring who can reproduce.

How are species reproductively isolated? §Prezygotic barriers barriers that prevent mating §Postzygotic barriers barriers that operate after mating occurs

Prezygotic barriers 1. Habitat isolation - Two species live in the same area, but occupy different habitats

2. Behavioral isolation - Signals that attract mates are often unique to a species. (e.g., different species of fireflies flash different patterns)

3. Temporal isolation - Two species breed at different times of the day or during different seasons.

4. Mechanical isolation -Closely related species attempt to mate, but are anatomically incompatible. -(Example: flowering plants with pollination barriers; some plants are specific with respect to the insect pollinator, often occurs with butterflies/moths)

5. Gametic isolation - Gametes cannot recognize each other. (Example: fertilization of fish eggs, chemical signals between sperm and egg allows sperm to “recognize” the correct egg)

From speciation to macroevolution: How then do we get from the mechanism of speciation to evolution on a grand scale; i.e., macroevolution? Two models: -The Gradualism model - change is gradual - The Punctuated Equilibrium model - rapid change occurs

Speciation tempo

Why is genetic & biochemical variation important? variation no variation EXTINCTION!! global warming survival

Extinction! §Extinction occurs when there are no members of a species left alive.