Conceptual framework

This list of conceptual understandings regarding evolution is aligned across grade levels to help instructors identify age-appropriate learning goals for their students and understand how concepts taught at one grade level lay the groundwork for more sophisticated concepts later on. Access a printable pdf version of this document. To search for teaching materials that address these concepts, visit the teaching guide for your grade level: K-2, 3-5, 6-8, 9-12, or Undergraduate.

The conceptual framework is aligned with the 2012 Framework for K-12 Science Education and the Next Generation Science Standards (NGSS). In the table below, conceptual alignment is indicated by a code that follows each aligned concept. For example, LS4.A indicates correspondence to the Life Sciences core idea “Evidence of common ancestry and diversity” from both the NGSS and the Framework for that grade level, P3 indicates correspondence to “Planning and carrying out investigations,” the third of eight Science and Engineering Practices listed in those documents, and NOS2 indicates correspondence to the second concept outlined in NGSS’s appendix on the nature of science, “Scientific knowledge is based on empirical evidence.” Read more about Understanding Evolution and the NGSS/Framework alignment.

The Understanding Evolution Framework is divided into five strands:
History of life | Evidence of evolution | Mechanisms of evolution | Nature of science | Studying evolution

MECHANISMS OF EVOLUTION
K-2	3-5	6-8	9-12	13-16
				Evolution is often defined as a change in allele frequencies within a population.
				The Hardy-Weinberg equation describes expectations about the gene pool of a population that is not evolving — one that is very large, mates randomly, and does not experience mutation, natural selection, or gene flow.
		Evolution results from natural selection acting upon variation within a population. (LS4.B)	Evolution occurs through multiple mechanisms.	Evolution occurs through multiple mechanisms.
			Evolution results from selection acting upon genetic variation within a population. (LS4.B)	Evolution results from natural selection acting upon genetic variation within a population.
			Evolution results from genetic drift acting upon genetic variation within a population.	Evolution results from genetic drift acting upon genetic variation within a population.
				Evolution results from mutations. Evolution results from gene flow. Evolution results from hybridization.
There is variation within a population. (LS3.A, LS3.B)	There is variation within a population. (LS3.A, LS3.B)	There is variation within a population. (LS3.B)	There is variation within a population. (LS3.B)	Natural selection and genetic drift act on the variation that exists in a population.
		Variation is the result of genetic recombination or mutation. (LS3.A)	Natural selection acts on the variation that exists in a population. (LS4.B, LS4.C)	Life on Earth 3.8 billion years ago consisted of one-celled organisms similar to present-day bacteria.
		The variation that occurs within a population is random.
			Natural selection acts on phenotype as an expression of genotype.	Natural selection acts on phenotype as an expression of genotype.
			The amount of genetic variation within a population may affect the likelihood of survival of the population; the less the available diversity, the less likely the population will be able to survive environmental change.	Phenotype is a product of both genotype and the organism’s interactions with the environment. Variation of a character within a population may be discrete or continuous. Continuous characters are generally influenced by many different genes.
Living things have offspring. (LS3.A)	Offspring inherit many traits from their parents, but are not exactly identical to their parents. (LS3.A, LS3.B)	Offspring inherit many traits from their parents, but are not identical to their parents. (LS3.B)	New heritable traits can result from recombinations of existing genes or from genetic mutations in reproductive cells. (LS3.B)	New heritable traits can result from mutations.
			Mutations are random.	Mutations are random.
Offspring inherit many traits from their parents, but are not exactly the same as their parents. (LS3.A)			Organisms cannot intentionally produce adaptive mutations in response to environmental influences.	Organisms cannot intentionally produce adaptive mutations in response to environmental influences.
Siblings are similar to, but not identical to, one another.			Complex structures may be produced incrementally by the accumulation of smaller useful mutations.	Complex structures may be produced incrementally by the accumulation of smaller advantageous mutations.
	Advantageous features help living things survive. (LS4.B, LS4.C)	Traits that are advantageous often persist in a population. (LS4.B, LS4.C)	Inherited characteristics affect the likelihood of an organism’s survival and reproduction. (LS4.B, LS4.C)	Inherited characteristics affect the likelihood of an organism’s survival and reproduction.
	Depending upon the environment, some living things will survive better than others. (LS4.B, LS4.C)	Individual organisms with advantageous traits are more likely to survive and have offspring. (LS4.B, LS4.C)	Over time, the proportion of individuals with advantageous characteristics may increase (and the proportion with disadvantageous characteristics may decrease) due to their likelihood of surviving and reproducing. (LS4.B, LS4.C)	Over time, the proportion of individuals with advantageous characteristics may increase (and the proportion with disadvantageous characteristics may decrease) due to their likelihood of surviving and reproducing.
			Populations, not individuals, evolve.
			Traits that confer an advantage may persist in the population and are called adaptations. (LS4.B, LS4.C)	Traits that confer an advantage may persist in the population and are called adaptations.
				Complex traits can arise through the cooption of another trait.
		The number of offspring that survive to reproduce successfully is limited by environmental factors. (LS4.B, LS4.C)	The number of offspring that survive to reproduce successfully is limited by environmental factors. (LS4.B, LS4.C)	The number of offspring that survive to reproduce successfully is limited by environmental factors.
		Organisms with similar requirements may compete with one another for limited resources.	Depending on environmental conditions, inherited characteristics may be advantageous, neutral, or detrimental.	Depending on environmental conditions, inherited characteristics may be advantageous, neutral, or detrimental.
	Environmental changes may affect an organism’s ability to survive. (LS4.B, LS4.C, LS4.D)	Environmental changes may provide opportunities that can influence natural selection. (LS4.B, LS4.C)	Environmental changes may provide opportunities that can influence natural selection. (LS4.B, LS4.C)
				Natural selection can act on the variation in a population in different ways.
				Natural selection may favor individuals with one extreme value for a trait, shifting the average value of that trait in one direction over the course of many generations. Selection favoring an extreme trait value reduces genetic variation in a population. Natural selection may favor individuals with traits at each extreme of the range for that trait. Selection favoring individuals with traits at each extreme of a range maintains genetic variation in a population. Natural selection may favor individuals with an intermediate value for a trait. Selection favoring an intermediate value for a trait reduces genetic variation in a population. Natural selection sometimes favors heterozygotes over homozygotes at a locus. Heterozygote advantage preserves genetic variation at that locus (i.e., within the population, it maintains multiple alleles at that locus). Natural selection sometimes favors rare traits and acts against those that become too common in a population. Frequency-dependent selection preserves genetic variation in a population.
				Sexual selection occurs when selection acts on characteristics that affect the ability of individuals to obtain mates.
				Sexual selection can lead to physical and behavioral differences between the sexes.
			Fitness is reproductive success — the number of viable offspring produced by an individual in comparison to other individuals in a population/species.	An individual’s fitness (or relative fitness) is the contribution that individual makes to the gene pool of the next generation relative to other individuals in the population.
				An organism’s fitness depends on both its survival and its reproduction.
			Fitness is often measured using proxies like mass, number of matings, and survival because it is difficult to measure reproductive success directly.	Fitness is often measured using proxies like mass, number of matings, and survival because it is difficult to measure reproductive success.
				Natural selection is capable of acting at multiple hierarchical levels: on genes, on cells, on individuals, on populations, on species, and on larger clades.
			Random factors can affect the survival of individuals and of populations.	Random factors can affect the survival of individuals and of populations.
				Smaller populations are more strongly affected by genetic drift than are larger populations. Genetic drift can cause loss of genetic variation in a population.Founder effects occur when a population is founded from a small number of individuals. Founder effects can affect the genetic makeup of a newly started population (and reduce its genetic variation) through sampling error. Bottlenecks occur when a population’s size is greatly reduced. Bottlenecks can affect the genetic makeup of a population (and reduce its genetic variation) through sampling error.
				A species is often defined as a group of individuals that actually or potentially interbreed in nature.
				There are many definitions of species.
			Speciation is the splitting of one ancestral lineage into two or more descendant lineages.	Speciation is the splitting of one ancestral lineage into two or more descendant lineages.
			Speciation is often the result of geographic isolation.	Speciation is often the result of geographic isolation.
				Speciation can also occur without geographic isolation.
			Speciation requires reproductive isolation.	Speciation requires reproductive isolation.
				Reproductive isolation can occur through mechanisms that prevent fertilization from occurring. Reproductive isolation can also occur through mechanisms that act after fertilization, when a fertilized egg (or the individual resulting from that egg) has low fitness.
			Occupying new environments can provide new selection pressures and new opportunities, leading to speciation. (LS4.C)	Occupying new environments can provide new selection pressures and new opportunities, leading to speciation.
				Occasionally offspring, known as hybrids, result from matings between distinct species or between distinct parental forms.
				Some hybrids have increased fitness relative to their parents. Some hybrids have decreased fitness relative to their parents.
			Evolution does not consist of progress in any particular direction.	Evolution does not consist of progress in any particular direction.

NATURE OF SCIENCE
K-2	3-5	6-8	9-12	13-16
	Science deals with the natural world and natural explanations. (NOS8)	Science focuses on natural phenomena and processes. (NOS8)	Science focuses on natural phenomena and processes.	Science focuses on natural phenomena and processes.
Scientific ideas may change based on what we observe and experience. (NOS3)	Scientific ideas may change with new evidence. (NOS3)	Scientific knowledge is open to question and revision as we come up with new ideas and discover new evidence. (P6, NOS3)	Scientific knowledge is open to question and revision as we come up with new ideas and discover new evidence. (P4, P6, NOS3)	Scientific knowledge is open to question and revision as we come up with new ideas and discover new evidence.
We learn about the natural world using our senses and extensions of our senses. (P3, P4, P6)	Scientists base their ideas on evidence from the natural world. (P3, P6, P7, NOS8)	A hallmark of science is exposing ideas to testing. (P3, P4, P6, P7)	A hallmark of science is exposing ideas to testing. (P3, P4, P6, P7)	A hallmark of science is exposing ideas to testing.
		Scientists test their ideas using multiple lines of evidence.	Scientists test their ideas using multiple lines of evidence. (P6, NOS2)	Scientists test their ideas using multiple lines of evidence.
		Scientists use multiple research methods (experiments, observations, comparisons, and modeling) to collect evidence. (P2, P3, P4, NOS1)	Scientists use multiple research methods (experiments, observational research, comparative research, and modeling) to collect data. (P2, P3, P4, NOS1)	Scientists use multiple research methods (experiments, observational research, comparative research, and modeling) to collect data.
		Scientists can test ideas about events and processes long past, very distant, and not directly observable.	Scientists can test ideas about events and processes long past, very distant, and not directly observable.	Scientists can test ideas about events and processes long past, very distant, and not directly observable.
			Scientists may explore many different hypotheses to explain their observations. (P7)	Scientists may explore many different hypotheses to explain their observations.
	The real process of science is complex, iterative, and can take many different paths.	The real process of science is complex, iterative, and can take many different paths.	The real process of science is complex, iterative, and can take many different paths.	The real process of science is complex, iterative, and can take many different paths.
				Scientific findings and evidence inspire new questions and shape the directions of future scientific research.
		Accepted scientific theories are not tenuous; they must survive rigorous testing and be supported by multiple lines of evidence to be accepted. (NOS4)	Accepted scientific theories are not tenuous; they must survive rigorous testing and be supported by multiple lines of evidence to be accepted. (NOS2, NOS4)	Accepted scientific theories are not tenuous; they must survive rigorous testing and be supported by multiple lines of evidence to be accepted.
Science is a human endeavor. (NOS7)	Science is a human endeavor. (NOS7)	Science is a human endeavor. (NOS7)	Science is a human endeavor. (NOS7)	Science is a human endeavor.
			Authentic scientific controversy and debate within the community contribute to scientific progress. (P7)	Authentic scientific controversy and debate within the community contribute to scientific progress.

Guide to Evo 101 and Digging Data

Alignment with the Next Generation Science Standards

Understanding Evolution

Conceptual framework

Teach

Learn

HISTORY OF LIFE
K-2	3-5	6-8	9-12	13-16
Life has been on Earth a long time.	Life has been on Earth for billions of years.	Biological evolution accounts for diversity over long periods of time.	Biological evolution accounts for diversity over long periods of time. (LS4.A, LS4.D)	Biological evolution accounts for diversity over long periods of time. (LS4.A, LS4.D)
Life forms have changed over time.	Life forms have changed over time. (LS4.A)	Through billions of years of evolution, life forms have continued to diversify in a branching pattern, from single-celled ancestors to the diversity of life on Earth today.	Through billions of years of evolution, life forms have continued to diversify in a branching pattern, from single-celled ancestors to the diversity of life on Earth today.	Through billions of years of evolution, life forms have continued to diversify in a branching pattern, from single-celled ancestors to the diversity of life on Earth today.
	Many forms of life in the past were different from living things today. (LS4.A)	Life forms of the past were in some ways very different from living forms of today, but in other ways very similar. (LS4.A)	Life forms of the past were in some ways very different from living forms of today, but in other ways very similar. (LS4.A)	Life forms of the past were in some ways very different from living forms of today, but in other ways very similar.
	Many forms of life in the past were similar to present-day living things. (LS4.A)			Evolution is still continuing today.
				Humans directly impact biodiversity, which may then impact future evolutionary potential.
	Present-day life forms are related to past life forms. (LS4.A)	Present-day life forms are descended from past life forms; all life is related. (LS4.A)	Present-day species evolved from earlier species; the relatedness of organisms is the result of common ancestry. (LS4.A)	Present-day species evolved from earlier species; the relatedness of organisms is the result of common ancestry.
			Life on Earth 3.8 billion years ago consisted of one-celled organisms similar to present-day bacteria.	Life on Earth 3.8 billion years ago consisted of one-celled organisms similar to present-day bacteria.
			There is evidence of eukaryotes in the fossil record from about one billion years ago; some were the precursors of multicellular organisms.	There is evidence of eukaryotes in the fossil record from about one billion years ago; some were the precursors of multicellular organisms.
			The early evolutionary process of eukaryotes included the merging of prokaryote cells.	The early evolutionary process of eukaryotes included the merging of prokaryote cells.
		Geological change and biological evolution are linked.	Geological change and biological evolution are linked.	Geological change and biological evolution are linked.
		Tectonic plate movement has affected the distribution and evolution of living things. (ESS1.C)	Tectonic plate movement has affected the evolution and distribution of living things. (ESS1.C)	Tectonic plate movement has affected the evolution and distribution of living things.
		Living things have had a major influence on the composition of the atmosphere and on the surface of the planet.	Living things have had a major influence on the composition of the atmosphere and on the surface of the planet. (ESS2.E)	Living things have had a major influence on the composition of the atmosphere and on the surface of the planet.
Most species that once lived on Earth have gone extinct. (LS4.A)	Most species that once lived on Earth have gone extinct. (LS4.A)	Most species that once lived on Earth have gone extinct. (LS4.A)	During the course of evolution, only a small percentage of species have survived until today.	During the course of evolution, only a small percentage of species have survived until today.
		Background extinctions are a normal occurrence.	Background extinctions are a normal occurrence.	Background extinctions are a normal occurrence.
			Rates of extinction vary.	Rates of extinction vary.
		Mass extinctions occur.	Mass extinctions occur.	Mass extinctions occur.
		Extinction can result from environmental change.	Extinction can result from environmental change.	Extinction can result from environmental change.
				Human influence may be causing a modern mass extinction.
		Extinction can stimulate evolution by opening up resources.	Extinctions may create opportunities for further evolution in other lineages to occur.	Extinctions may create opportunities for further evolution in other lineages to occur.
			Rates of evolution vary.	Rates of evolution vary.
			Rates of speciation vary.	Rates of speciation vary.
			Evolutionary change can sometimes happen rapidly.	Evolutionary change can sometimes happen rapidly.
			Some lineages remain relatively unchanged for long periods of time.	Some lineages remain relatively unchanged for long periods of time.
			Biological evolution has been and can be influenced by interactions with the rest of the Solar System.	Biological evolution has been and can be influenced by interactions with the rest of the Solar System.
			At least one mass extinction on planet Earth has been definitively linked to an asteroid impact.	At least one mass extinction on planet Earth has been definitively linked to an asteroid impact.
			The raw materials and conditions for life and evolution that arose on Earth are the result of complex cosmic interactions and likely also exist elsewhere in the universe.	The raw materials and conditions for life and evolution that arose on Earth are the result of complex cosmic interactions and likely also exist elsewhere in the universe.

EVIDENCE OF EVOLUTION
K-2	3-5	6-8	9-12	13-16
Today there are many diverse forms of life. (LS4.D)	Life is very diverse. (LS4.D)	The patterns of life’s diversity through time provide evidence of evolution. (LS4.A)	The patterns of life’s diversity through time provide evidence of evolution.	The patterns of life’s diversity through time provide evidence of evolution.
				Evolution can sometimes be directly observed.
Plants and animals have features that allow them to live in various environments. (LS4.C)	There is a fit between organisms and their environments, though not always a perfect fit. (LS4.C)	An organism’s features reflect its evolutionary history.	An organism’s features reflect its evolutionary history.	An organism’s features reflect its evolutionary history.
Form is linked to function.	Form is linked to function.	There is a fit between organisms and their environments, though not always a perfect fit. (LS4.C)	There is a fit between organisms and their environments, though not always a perfect fit. (LS4.C)	There is a fit between organisms and their environments, though not always a perfect fit.
		There is a fit between the form of a trait and its function, though not always a perfect fit.	There is a fit between the form of a trait and its function, though not always a perfect fit. Some traits of organisms are not adaptive.	There is a fit between the form of a trait and its function, though not always a perfect fit. Some traits of organisms are not adaptive.
		Some traits of organisms are not adaptive.	Some traits of organisms are not adaptive.Features sometimes acquire new functions through natural selection.	Some traits of organisms are not adaptive.Features sometimes acquire new functions through natural selection.
Fossils provide evidence of past life.	Fossils provide evidence of past life. (LS4.A)	Fossils provide evidence of past life. (LS4.A)	The fossil record provides evidence for evolution.	The fossil record provides evidence for evolution.
			The fossil record documents the biodiversity of the past.	The fossil record documents the biodiversity of the past.
		The fossil record contains organisms with transitional features.	The fossil record contains organisms with transitional features.	The fossil record contains organisms with transitional features.The fossil record
			The fossil record documents patterns of extinction and the appearance of new forms.	The fossil record documents patterns of extinction and the appearance of new forms.
		The sequence of forms in the fossil record is reflected in the sequence of the rock layers in which they are found and indicates the order in which they evolved. (LS4.A)	The sequence of forms in the fossil record is reflected in the sequence of the rock layers in which they are found and indicates the order in which they evolved.	The sequence of forms in the fossil record is reflected in the sequence of the rock layers in which they are found and indicates the order in which they evolved.
			Radiometric dating can often be used to determine the age of fossils.	Radiometric dating can often be used to determine the age of fossils.
Living things are alike in some ways and different in other ways.	There are similarities and differences among fossils and living organisms. (LS4.A)	There are similarities and differences among fossils and living organisms. (LS4.A)	There are similarities and differences among fossils and living organisms.	There are similarities and differences among fossils and living organisms.
		All life forms share fundamental similarities. (LS4.A)	Similarities among existing organisms provide evidence for evolution. (LS4.A)	Similarities among existing organisms (including morphological, developmental, and molecular similarities) reflect common ancestry and provide evidence for evolution.
		Anatomical similarities of living things reflect common ancestry. (LS4.A)	Anatomical similarities of living things reflect common ancestry. (LS4.A)
		There are similarities in the cell function of all organisms.	There are similarities in the cell function of all organisms. (LS4.A)
		All life forms use the same basic DNA building blocks.	All life forms use the same basic DNA building blocks. (LS4.A)
			Developmental similarities of living things often reflect their relatedness. (LS4.A)
		Not all similar traits are homologous; some are the result of convergent evolution.	Not all similar traits are homologous; some are the result of convergent evolution.	Not all similar traits are homologous; some are the result of convergent evolution.
				The geographic distribution of species often reflects how geologic change has influenced lineage splitting.
	Selective breeding can produce offspring with new traits.	Artificial selection provides a model for natural selection. (LS4.B)	Artificial selection provides a model for natural selection.	Artificial selection provides a model for natural selection.
		People selectively breed domesticated plants and animals to produce offspring with preferred characteristics. (LS4.B)	People selectively breed domesticated plants and animals to produce offspring with preferred characteristics.	People selectively breed domesticated plants and animals to produce offspring with preferred characteristics.

Conceptual Framework

Footer

Connect

Teach

Learn