The Theory of Evolution Unit

What do YOU think the word Evolution means? Evolution = the process of biological change by which Earth’s present day species come to differ from their ancestors - slow process over many many many years

How could Evolution lead to this? Star-nosed mole

What sorts of modifications are obvious in the star-nosed mole? Feelers on snout, poor eyesight, prominent claws How do such traits arise in the first place? Mutations

Star-nosed mole How did star-nosed moles come to look like this? Mutations can be passed from one generation to the next

Star-nosed mole What other factors have been at work over the generations to cause the moles to have the features they do? Its environment, other organisms that compete for the same food, its prey

Charles Darwin

Darwin’s Journey Left in 1831 for a five-year journey aboard the HMS Beagle

Darwin’s Journey

Charles Darwin did most of his research on the Galapagos Islands did most of his research on the Galapagos Islands

Charles Darwin - collected 13 similar but separate species of finches - collected 13 similar but separate species of finches - each had a distinct type of beak for feeding - overwhelming similarities showed they shared a common ancestor

Charles Darwin

- - observations led Darwin to the idea of an adaptation = a feature that allows an organism to better survive in its environment - can lead to genetic change in a population over time

What are the star-nosed moles adaptations? Star-nosed mole

Natural Selection Natural Selection = the process by which organisms best suited (or have more beneficial adaptations) produce more offspring than other organisms - in nature, characteristics are selected only if they give an advantage to the organism in the environment

Natural Selection (cont) Natural selection occurs only if there is both (1) variation in the genetic information between organisms in a population and (2) variation in the expression of that genetic information — that is, trait variation — that leads to differences in performance among individuals.

Natural Selection (cont) The traits that positively affect survival are more likely to be reproduced, and thus are more common in the population. Leads to an increase in the proportion of individuals in future generations that have the trait and to a decrease in the proportion of individuals that do not.

Natural Selection - a population is the smallest unit in which evolution can occur - bell curve = a graph that illustrates that most members of a population show the average form a given measurable trait - only a few individuals will show the extremes of a trait

Bell Curve

Types of Natural Selection 1) Stabilizing Selection = individuals with the average form of a trait have higher fitness - the most common kind of selection - results in very similar appearance of a species

Stabilizing Selection

Types of Natural Selection (cont) 2) Directional Selection = individuals with the more extreme form of a trait have greater fitness than the average form

Directional Selection

Types of Natural Selection (cont) 3) Disruptive Selection = individuals with either extreme variation of a trait have greater fitness than individuals with the average form

Disruptive Selection

Types of Natural Selection (cont) 4) Sexual Selection = females tend to chose the males they mate with based on certain traits - the genes of successful reproducers, rather than those of merely successful survivors, are amplified through natural selection

Sexual Selection

Natural Selection (cont) Changes in the physical environment, (whether naturally occurring or human induced) have thus contributed to: 1) the expansion of some species

Natural Selection (cont) 2) the emergence of new distinct species as populations diverge under different conditions ex: geographical isolation ex: geographical isolation

Geographical Isolation

Natural Selection (cont) 3) the decline — and sometimes the extinction — of some species Species become extinct because they can no longer survive and reproduce in their altered environment. Cannot adjust to change that is too fast or drastic, the opportunity for the species’ evolution is lost.

Extinction of the Dinosaurs

Evidence of Evolution 1) Fossils - shows change over time

Evidence of Evolution Evidence of Evolution (cont) 2) DNA Sequences - DNA sequences vary among species, but there are many overlaps

Evidence of Evolution Evidence of Evolution (cont) 3) Embryology - similar features of embryos in very different organisms suggest evolution from a distant common ancestor

Embryology

Evidence of Evolution Evidence of Evolution (cont) 4) Anatomy Homologous Structures = features similar in structure but have different functions ex) forelimbs of a human, cat, whale, and bat - indicates they share a common ancestor ancestor

Homologous Structures

Evidence of Evolution Evidence of Evolution (cont) Vestigial Structures = structures that are found in an organism but are not useful to them - were useful to a common ancestor - ex) human tailbone, appendix, wings of an ostrich, pelvic bones in whales

Vestigial Structures

Basic Definition of Evolution = Earth’s present day species developed from earlier, distinctly different species through the process of natural selection