Construct an explanation of how new understandings of Earth's history, the emergence of new species from pre-existing species, and our understanding of genetics have influenced our understanding of biology (GSE SB6.a).

What this topic is asking

Standard SB6.a asks you to construct an explanation of how three developments shaped modern biology: a new understanding of Earth's history (that the planet is very old and has changed over time), the idea that new species arise from pre-existing species, and the later science of genetics. For the Georgia Milestones Biology EOC you need the story of how the theory of evolution was built: what Darwin proposed, why Lamarck's idea was wrong, and how deep time and genes turned a powerful idea into the foundation of biology. Items test the reasoning, not just dates.

Descent with modification: Darwin's big idea

Before Darwin, the common view was that species were fixed and unchanging. Darwin gathered evidence (most famously the variation among finches and tortoises across the Galapagos Islands) pointing to a different conclusion: species are related through common ancestors and change over time. His explanation, published in 1859, was natural selection, and it remains the core of the theory the EOC tests.

The logic Darwin laid out has a few linked parts:

• Populations show variation, and more offspring are produced than can survive.
• Individuals with traits that suit the environment survive and reproduce more (they have higher fitness).
• Those traits are inherited, so they become more common in later generations.
• Over long time, this gradual change produces adaptation and, eventually, new species.

Why a new view of Earth's history mattered

Darwin's idea needed time, vast amounts of it. In the same era, geologists argued that Earth is extremely old and that its features formed by slow, gradual processes still acting today (rivers carving valleys, sediment forming rock layers). This deep-time view was essential: gradual change by natural selection only produces today's diversity if there have been hundreds of millions of years for it to act. A young, fixed Earth leaves no room for evolution; an ancient, changing Earth makes it possible. The fossil record in old rock layers also showed that life has changed over time, supporting the idea that species are not fixed.

Lamarck: a wrong idea that still taught something

Lamarck was right that species change over time but wrong about the mechanism. Why Lamarck was wrong is a frequent EOC point: only heritable variation can be selected and inherited, exactly what genetics later confirmed.

How genetics completed the theory

Darwin had a problem he could not solve: he did not know where variation came from or how traits were inherited. The science of genetics, developed after his death, supplied both answers:

• Mutation is the ultimate source of new variation, creating new alleles.
• Traits are inherited as discrete alleles (not blended away), shuffled by meiosis and sexual reproduction.

Combining natural selection with genetics produced the modern theory of evolution, in which evolution is a change in allele frequencies in a population over generations. Genetics did not overturn Darwin; it strengthened him by supplying the missing mechanism, which is why the EOC frames evolution in terms of genes and alleles.

Try this

Q1. State Darwin's mechanism for how species change over time, and name the scientist whose competing idea (inheritance of acquired characteristics) was later shown to be wrong. [2 points]

• Cue. Darwin's mechanism is natural selection (heritable favorable traits become more common because their owners survive and reproduce more); the competing, incorrect idea was Lamarck's inheritance of acquired characteristics.

Q2. Explain why a very old, gradually changing Earth was important to Darwin's theory. [2 points]

• Cue. Natural selection produces today's diversity only with vast time; a very old Earth (deep time) provides the hundreds of millions of years needed for gradual change, while a young, fixed Earth would not.