11/24/2023 0 Comments Genetic drift and gene flow![]() ![]() Another challenge was a general lack of understanding about how variation is initiated and how inheritance works. One reason for this is that, as we now know, natural selection is only one of the forces of evolution. However, as other researchers began doing what scientists do-testing whether or not the concept of natural selection could consistently account for the variation seen in organisms-they began to find many exceptions. Those individuals with the longest necks would be the most likely to survive to pass on their longer-neck alleles to future generations.Īs noted in Chapter 2, Darwin’s 1859 book On the Origin of Species made a big splash Figure 4.2A The Lamarckian hypothesis: If a short-necked parent often stretched its neck to reach higher branches, each generation of offspring would be born with somewhat longer necks. Rethinking Darwin Figure 4.2B The Modern Synthesis perspective: The ancestral population had a range of variation in neck length. It would take many decades, and many careful scientific experiments to solve the puzzle of evolution. Neither Darwin’s theory of natural selection, nor Mendel’s particulate inheritance were individually sufficient to fully explain all the phenomena being observed in the natural world. When learning about biological sciences today, we always recognize the contributions of Charles Darwin and Gregor Mendel, so it may be surprising to learn that for a time, before we arrived at today’s understanding of genetics and inheritance, both Darwin’s and Mendel’s work fell out of favor. THE MODERN SYNTHESIS Historical Framework This chapter explores the mechanisms by which that amazing transformation occurred and considers some of the crucial scientific experiments that shaped our current understanding of the evolutionary process. Through a wondrous series of mechanisms and events, that first single-celled organism gave rise to the rich diversity of species that fill the lands, seas, and skies of our planet. Looking at the common sequences in modern genomes, we can even make educated guesses about what the genetic sequence of the first organism, or universal ancestor of all living things, would likely have been. In fact, with today’s genetic and genomic technologies, we can now trace genetic lineages, or phylogenies, and determine the relationships between all of today’s living organisms-eukaryotes (animals, plants, fungi, etc.), archaea, and bacteria-on the branches of the phylogenetic tree of life (Figure 4.1). This organism had the potential to reproduce by making copies of itself, just like bacteria, many amoebae, and our own living cells today. What we do know is that a living single-celled organism was present on Earth during the early stages of our planet’s existence. Scientists still study and debate how life came into being and whether it originated on Earth or in some other region of the universe (including some scientists who believe that studying evolution can reveal the complex processes that were set in motion by God or a higher power). ![]() It’s hard for us, with our typical human life spans of less than 100 years, to imagine all the way back, 3.8 billion years ago, to the origins of life. Explain how allele frequencies can be used to study evolution as it happens.Discuss the evolutionary significance of mutation, genetic drift, gene flow, and natural selection. ![]() Identify the forces of evolution and become familiar with examples of each.Define populations and population genetics as well as the methods used to study them.Describe the history and contributions of the Modern Synthesis. ![]()
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