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Plant Biology - Evolution

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    Study Guide Plant Biology – Evolution 1. Darwin's Theory of Evolution 1.1 What Is Evolution? Evolution is how living populations change over long periods of time. These changes happen as organisms respond to their environment. The instructions for these changes are stored in DNA and passed from parents to offspring. Over millions of years, this pr ocess has led from very simple life forms to the wide variety of complex organisms we see today. The idea of evolution is closely connected to Charles Darwin and his explanation of natural selection . When combined with modern genetics, Darwin’s ideas form the foundation of today’s theory of evolution. 1.2 Darwin’s Big Ideas About Life In his book On the Origin of Species , Darwin explained how life changes over time. When we simplify his ideas and include what scientists know today, his main points are: • All living things likely came from one or a few very simple organisms. • New species do not appear suddenly. They slowly develop from existing species. • Organisms compete with each other for limited resources. • Those that are less well adapted to their environment are more likely to die out (extinction). • The fossil record has gaps, which explains why we do not always see clear transitional forms. These ideas set the stage for understanding why evolution happens. 1.3 Why Does Evolution Occur? Darwin noticed several important patterns in nature: • Organisms produce more offspring than can survive. • Populations usually stay about the same size because food, space, and other resources are limited.

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    Study Guide • Individuals within a population are not identical — they show variation. • Those with traits that help them survive are more likely to live long enough to reproduce. • When these individuals reproduce, they pass their helpful traits to the next generation. Over time, these small advantages add up, leading to noticeable changes in a population. 1.4 Natural Selection Explained Darwin compared natural selection to artificial selection , which is when humans selectively breed plants or animals for certain traits. The key difference is the “selector”: • In artificial selection, humans choose which traits are passed on. • In natural selection, the environment does the selecting. Natural selection works very slowly. Changes happen over many generations, not overnight. This slow pace made sense to Darwin because geologists had recently discovered that Earth was much older than people once believed. This gave natural selection enough time to cause major changes in life forms. 1.5 The Missing Piece: Inheritance One major challenge for Darwin was explaining how helpful traits were passed down. In the 1800s, many scientists believed in the “blending theory of inheritance,” which suggested offspring were just an average of their parents. This idea did not explain how useful traits could remain strong over generati ons. The problem was solved with the work of Gregor Mendel and the discovery of genetics. Scientists learned that traits are passed on as distinct units (genes), not blended together. This discovery completed Darwin’s theory by explaining how favorable traits are preserved and spread. Summary Darwin’s theory of evolution explains how life changes over time through natural selection. With the later discovery of genetics, scientists gained a clear understanding of how these changes are passed from one generation to the next. Together, these ideas help us understand the diversity of life on Earth today.

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