Theory of Evolution

Chapter 15

The History of Evolutionary Thought

 Evolution  The development of new types of organisms

from preexisting types of organisms over time.  Also could be described as a heritable change

in characteristics within a population from one generation to the next

The History of Evolutionary Thought  Darwin’s Ideas

 Used the phrase “descent with modification” to describe the process of evolution

 Every species, living or extinct, must have descended by reproduction from preexisting species and that species must be able to change over time.

Theory of Natural Selection (Darwin) 1. Overproduction

 More offspring are produced than can survive to maturity

2. Genetic Variation  Within a population, individuals have different

traits. Ex: Thick fur  Occasionally, new traits may appear in a

population

Theory of Natural Selection (Darwin) 3. Struggle to Survive

  Individuals must compete with each other   Some variations improve an individuals chances to

reproduce, but some variations reduce this chance. 4. Differential Reproduction

  Organisms with the best adaptations are likely to survive and reproduce

  Through inheritance, the adaptations will become more frequent in the population

Evidence of Evolution

  Fossil – the remains or traces of an organism that died long ago.

  Show that different types of organisms appeared at different times and places on earth.

 Superposition – this principle states that if the rock strata at a location have not been disturbed, the lowest stratum was formed before the strata above it.

 Geologists put together a timeline for the order in which different groups of rocks and fossils were formed.

 The Geologic Time Scale  Relative age – its age compared to that of other

fossils.  Absolute age – more accurate using radiometric

dating  Not all fossils are discovered and not all

remains become fossilized

Distribution of Fossils 1.  Different organisms lived at different times 2.  Today’s organisms are different from those of the past 3.  Fossils found in adjacent layers are more like each

other than fossils found in deeper or higher layers. 4.  By comparing fossils and rocks from around the

planet, we can infer when and where different organisms existed.

5.  Species have differed in a gradual sequence of forms over time.

Transitional Species

  Have features that are intermediate between those of hypothesized ancestors and later descendant species.

  Example – Page 304

Anatomy and Embryology  Homologous structures – anatomical structures

that occur in different species and that originated by heredity from a structure in the most recent common ancestor of the species.

Anatomy and Embryology

  Analogous structures   have closely related

functions but do not derive from the same ancestral structure.

Anatomy and Embryology

  Vestigial structures – seem to serve no function but that resemble structures with functional roles in related organisms.

Anatomy and Embryology  The development of animal embryos is also

evidence of descent with modification

Biological Molecules   Biologists can compare the DNA, RNA, proteins,

and other biological molecules from many different organisms.

  They can then look for similarities and differences among the data for each species

  The greater the number of similarities between any given species, the more closely the species are related through a common ancestor.

Evolution in Action  Convergent Evolution – process by which

different species evolve similar traits.

 Divergent Evolution – process in which the descendants of a single ancestor diversify into species that each fit different parts of the environment.

 Adaptive radiation – sometimes, a new population in a new environment, such as an island, will undergo divergent evolution until the population fills many parts of the environment

Artificial Selection   this process occurs when a human breeder

chooses individuals that will parent the next generation.

Co-evolution  when two or more species have evolved

adaptations to each other’s influence.  Ex: Bacteria and humans – resistance