Big Idea 1: The Process of Evolution Drives the Diversity and Unity of Life


Evolution is a change in the genetic makeup of a population over time, with natural selection its major driving mechanism. Darwin’s theory, which is supported by evidence from many scientific disciplines, states that inheritable variations occur in individuals in a population. Due to competition for limited resources, individuals with more favorable variations or phenotypes are more likely to survive and produce more offspring, thus passing traits to future generations.

In addition to the process of natural selection, naturally occurring catastrophic and human induced events as well as random environmental changes can result in alteration
in the gene pools of populations. Small populations are especially sensitive to these forces. A diverse gene pool is vital for the survival of species because environmental conditions change. Mutations in DNA and recombinations during meiosis are sources of variation. Human-directed processes also result in new genes and combinations of alleles that confer new phenotypes. Mathematical approaches are used to calculate changes in allele frequency, providing evidence for the occurrence of evolution in a population.

Scientific evidence supports the idea that both speciation and extinction have occurred throughout Earth’s history and that life continues to evolve within a changing
environment, thus explaining the diversity of life. New species arise when two populations diverge from a common ancestor and become reproductively isolated. Shared conserved core processes and genomic analysis support the idea that all organisms — Archaea, Bacteria, and Eukarya, both extant and extinct — are linked by lines of descent from common ancestry. Elements that are conserved across all three domains are DNA and RNA as carriers of genetic information, a universal genetic code and many metabolic pathways. Phylogenetic trees graphically model evolutionary history and “descent with modification.” However, some organisms and viruses are able to transfer genetic information horizontally.

The process of evolution explains the diversity and unity of life, but an explanation about the origin of life is less clear. Experimental models support the idea that chemical and physical processes on primitive Earth could have produced complex molecules and very simple cells. Under laboratory conditions, complex polymers and self-replicating molecules can assemble spontaneously; thus, the first genetic material may not have been DNA, but short sequences of self-replicating RNA that may have served as templates for polypeptide synthesis. Protobiontic formation was most likely followed by the evolution of several primitive groups of bacteria that used various means of obtaining energy. Mutually beneficial associations among ancient bacteria are thought to have given rise to eukaryotic cells.


Enduring understanding 1.A: Change in the genetic makeup of a population over time is evolution.

Essential knowledge 1.A.1: Natural selection is a major mechanism of evolution.
Essential knowledge 1.A.4: Biological evolution is supported by scientific evidence from many disciplines, including mathematics.




Chapter 22 Presentation-Descent with Modification: A Darwinian View of Life

Enduring understanding 1.A: Change in the genetic makeup of a population over time is evolution.
Enduring understanding 3.C: The processing of genetic information is imperfect and is a source of genetic variation.
Enduring understanding 4.C: Naturally occurring diversity among and between components within biological systems affects interactions with the environment.


Essential knowledge 1.A.1: Natural selection is a major mechanism of evolution.
Essential knowledge 1.A.2: Natural selection acts on phenotypic variations in populations.
Essential knowledge 1.A.3: Evolutionary change is also driven by random processes.

Essential knowledge 3.C.1: Changes in genotype can result in changes in phenotype.
Essential knowledge 4.C.3: The level of variation in a population affects population dynamics.
Essential knowledge 4.C.4: The diversity of species within an ecosystem may influence the stability of the ecosystem.





Chapter 23 Presentation-The Evolution of Populations

Enduring understanding 1.C: Life continues to evolve within a changing environment.
Enduring understanding 2.E: Many biological processes involved in growth, reproduction and dynamic homeostasis include temporal regulation and coordination.

Essential knowledge 1.C.1: Speciation and extinction have occurred throughout the Earth’s history.
Essential knowledge 1.C.2: Speciation may occur when two populations become reproductively isolated from each other.
Essential knowledge 1.C.3: Populations of organisms continue to evolve.
Essential knowledge 2.E.2: Timing and coordination of physiological events are regulated by multiple mechanisms.




Chapter 24 Presentation-The Origin of Species

Enduring understanding 1.A: Change in the genetic makeup of a population over time is evolution.
Enduring understanding 1.B: Organisms are linked by lines of descent from common ancestry.

Enduring understanding 1.C: Life continues to evolve within a changing environment.
Enduring understanding 1.D: The origin of living systems is explained by natural processes.
Enduring understanding 2.E: Many biological processes involved in growth, reproduction and dynamic homeostasis include temporal regulation and coordination.
Enduring understanding 4.B: Competition and cooperation are important aspects of biological systems.

Essential knowledge 1.A.4: Biological evolution is supported by scientific
evidence from many disciplines, including mathematics.
Essential knowledge 1.A.4: Biological evolution is supported by scientific evidence from many disciplines, including mathematics.
Essential knowledge 1.B.1: Organisms share many conserved core processes and features that evolved and are widely distributed among organisms today.
Essential knowledge 1.C.1: Speciation and extinction have occurred throughout the Earth’s history.

Essential knowledge 1.D.1: There are several hypotheses about the natural origin of life on Earth, each with supporting scientific evidence.
Essential knowledge 2.E.1: Timing and coordination of specific events are necessary for the normal development of an organism, and these events are regulated by a variety of mechanisms.
Essential knowledge 4.B.3: Interactions between and within populations influence patterns of species distribution and abundance.




Chapter 25 Presentation-The History of Life on Earth

Enduring understanding 1.B: Organisms are linked by lines of descent from common ancestry.
Enduring understanding 1.D: The origin of living systems is explained by natural processes.

Essential knowledge 1.B.2: Phylogenetic trees and cladograms are graphical representations (models) of evolutionary history that can be tested.
Essential knowledge 1.D.2: Scientific evidence from many different disciplines supports models of the origin of life.




Chapter 26 Presentation-Phylogeny and the Tree of Life



Endosymbiotic Theory