Lesson 4 of 6 · Life’s origins and evolution
Life’s origins and evolution
10 minute lesson · 3 checks along the way
Your goal for this lessonDistinguish origin-of-life hypotheses from evolutionary change, and calculate how inherited variants can change in frequency.
Words with a dotted underline open a short definition right here in the lesson.
Two questions with different evidence
The origin of life concerns the transition from nonliving chemistry to systems with the connected capacities of living things. Biological evolution concerns changes in inherited characteristics across generations once reproducing lineages exist. Understanding evolution does not, by itself, supply every chemical step that produced the earliest evolving system. Conversely, uncertainty about that earliest transition does not erase the many independent observations supporting evolution.
Origin research tests how molecules can form, concentrate, interact, store information, and become organized into compartments. RNA can carry information and some RNA molecules catalyze reactions, making RNA-based stages a productive set of hypotheses. Researchers also investigate metabolic networks, membranes, mineral surfaces, and environmental cycles. These possibilities need not be mutually exclusive. Demonstrating one useful reaction in a laboratory is progress, but it is not a complete replay of Earth’s history.
Selection is a population comparison
Natural selection requires heritable differences associated with different reproductive success in a particular environment. A trait’s advantage is conditional: a variant that leaves more descendants under one resource supply may perform poorly after conditions change. Organisms do not have to anticipate a future need for a population to evolve. Mutation, , and exchange of genetic information also affect evolution; selection is not the only process changing populations.
Common ancestry is another historical inference. Shared molecular machinery helps researchers reconstruct relationships among present-day organisms. The , often shortened to LUCA, refers to an inferred ancestral population in the history shared by extant cellular life. It is not automatically the first living system or an unchanged microbe still living today. Reconstructing ancient ancestry and explaining the original emergence of life are related investigations with different limits.
Check 1 of 3
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Work through a decision
Track descendants rather than intentions
Start a fictional population with 90 individuals of inherited type A and 10 of type B. Under a specified environment, each A produces two surviving descendants in the next generation and each B produces three. Ignore migration, mutation, random variation, and resource limits for this one modeled generation. The next generation contains 180 A descendants and 30 B descendants, for a total of 210.
B began at 10/100 = 10 percent and now accounts for 30/210, about 14.3 percent. It increased in frequency while remaining the minority. The model illustrates selection on an existing difference; no individual chose to transform because it needed to improve. Nor does this arithmetic calculate the probability that life originates. Its assumptions already include reproducing types and inherited differences, which are precisely some of the features origin researchers seek to explain.
Population size and inherited fractions
Original instructional population model. Bars share a count scale, so the next generation is 2.1 times as long. The yellow segment rises from 10/100 to 30/210. The stipulated reproduction rates do not explain how living systems first arose.
Open full-size diagram in a new tab: Population size and inherited fractionsCheck 2 of 3
10 pointsUse the reading above. You can try again without losing points.
Test a proposed pathway against its setting
A plausible prebiotic experiment should specify its starting materials, energy inputs, environmental conditions, and products. A reaction may work in concentrated purified chemicals but fail at the dilution or competing chemistry of a proposed natural site. Another process may concentrate ingredients locally. The scientific task is to connect feasible steps and check whether they can occur together, rather than celebrating a single molecule as a complete living system.
and origin conditions may also differ. A habitat able to sustain an already evolved organism need not be the setting where its first arose. Earth’s organisms have changed their environments over time, and modern conditions are not a preserved sample of the early planet. Comparing laboratory models, rocks, and biological ancestry can narrow possibilities while leaving alternatives open. A careful explanation states what an experiment demonstrates and which steps remain unresolved.
Check 3 of 3
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Put it together
Your lesson progress
Each check connects to a part of the story. Complete all 3 to earn your 25-point lesson bonus.
Go to the source
Explore the evidence behind this lesson. These optional readings and videos open in a new tab.
- Read: NASA: origin-of-life laboratory researchExperiments probe components and integrated systems.
- Read: Origin of cellular componentsExplicit research questions about plausible materials and protocells.
- Read: Adaptive evolutionInherited variation and differential reproductive contribution.
- Read: LUCA and the limits of historical reconstructionRead the distinction between common ancestry and the origin of life; particular reconstruction details remain model dependent.