Evolution “Nothing in Biology Makes Sense Except in the Light of Evolution” - Theodosius Dobzhansky Early mysteries of life • Organisms are adapted to their environments in striking ways • Unity of life, shared characteristics Adult dead-leaf moth • Diversity of life Juvenile dead-leaf moth Theory of evolution: Timeline Intellectual climate • Paleontology, study of fossils, by Georges Cuvier ‒ Dissimilar fossils in older stratum ‒ Appearance of new species ‒ Disappearance of old species • James Hutton (geology) – profound changes through cumulative effect of slow but continuous processes • Charles Lyell (geology) – existence of continuous process even today at the same rate Jean Baptist Lamarck • Proposed a mechanism for evolution, ultimately proved incorrect • Lamarck’s mechanism for changes in life over time ‒ use and disuse – parts of body used extensively become larger and stronger and those that are not used deteriorate ‒ inheritance of acquired characteristics – transmit acquired characteristics to offsprings • Suggestive observations ‒ Giraffes tall necks to reach higher heights for food. ‒ Vestigial organs reduce in size over time • Counter observations ‒ Mice tail was cut for 20 generation, yet each generation was born with a tail ‒ ‘Trained’ bonsai tree offspring are of normal size Charles Darwin Darwin’s observations • Plants and animals in temperate regions of South America more closely resembled species living in the South American tropics than species living in temperate regions of Europe • Fossils of ocean organisms were found high in the Andes – connection with geology • Galapagos islands ‒ Many similar but unique species ‒ Related to species from mainland ‒ Hypothesis – colonized by organisms from mainland and later diversified into many species Key ideas • Adaptations – inherited characteristics that enhance survival and reproduction • Natural selection – individuals with favorable adaptations to the immediate environment survive and reproduce at higher rates in comparison to other individuals because of those traits Origin of species • Descent with modification – unity, diversity and suitability to environment • History of life depicted as a tree Persuasive arguments • Artificial selection - modified other species over many generations by selecting and breeding individuals that possess desired traits Persuasive arguments • Natural selection – analogous to artificial selection ‒ Variation of inherited traits across offspring ‒ Abundance of offspring – Thomas Malthus ‒ Better adaptation leads to better reproductive capability ‒ Better survival and reproductive abilities accumulates those favorable traits in the population Persuasive arguments • Adaptation – analogous to artificial selection Mantis camouflage ‒ Advantageous heritable traits can influence both the individual and its offspring’s performance with respect to environmental challenges. ‒ For example, adaptation renders advantage in escaping predators, obtaining food, or tolerating physical conditions. ‒ Such advantages increase the number of offspring that survive and reproduce, and the frequency of such traits in the subsequent generations from the individual. ‒ Natural selection resulting from factors such as predators, lack of food, or adverse physical conditions increase the proportion of these favorable traits in the population. Natural selection • Natural selection is a process in which individuals that have certain heritable traits survive and reproduce at a higher rate than do other individuals because of those traits. • Over time, natural selection can increase the frequency of adaptations that are favorable in a given environment. • If an environment changes, or if individuals move to a new environment, natural selection may result in adaptation to these new conditions, sometimes giving rise to new species. Natural selection • Occurs through interactions between individual organisms and their environment – population evolves and not individuals • Amplify or diminish only those heritable traits that differ among the individuals in a population • A trait that is favorable in one place or time may be useless - or even detrimental - in other places or times Types of Selection • Stabilising selection - Environment is conducive and conditions are favourable. No need for extremes to fight for survival. Normal population growth. • Directional selection - Environment becomes extreme and there is severe selection pressure. Only a specific fraction of the population survive and grow. • Diversifying selection - Due to some reasons, the population splits into two and grow and adapt to the new environments ESSIYER@IITGOA Keys to success – the Darwin way • How did Darwin succeed where many previous evolutionists failed ‒ Creativity – plausible scientific mechanism ‒ Cognitive skills – immaculate logic ‒ Hard work – avalanche of supporting evidence Experimental evidence • Reduction in beak length of Soapberry bug in response to new plant species with easier access to seeds Experimental evidence • Emergence of drug-resistance in pathogens Experimental evidence • Homology – similarity resulting from common ancestry ‒ Phenotype (external) Experimental evidence • Homology – similarity resulting from common ancestry ‒ Phenotype (external) ‒ Genotype (internal/molecular) ‒ “Tree” thinking Experimental evidence • Convergent evolution – independent evolution of similar features in different lineages (analogy) ‒ Homology: common ancestry, but not necessarily similar function ‒ Analogy: shared function, but not common ancestry Experimental evidence • Fossil records ‒ Missing links in evolutionary tree ‒ Supports DNA sequence data Experimental evidence • Biogeography – geographic distribution of species ‒ Testable predictions based on geographical data such as continental drift ‒ Similarity of species in islands to nearest mainland ‒ Even Islands with similar environmental conditions are inhabited by distinct species similar to their respective nearest mainland Evolution continues .... • Case of Peppered Moth (1811-1896) J. W, Tutt, Great Britain ‒ Before 1811, most moth were white very few black ‒ By 1850 there were black moth ‒ By 1890, white moths were outnumbered! • Possible cause: Industrial revolution Testing the theory evolution • Male adult guppies have highly varied color patterns, which attract female guppies • However, the bright colors make the males more conspicuous to predators. • One predator, the killifish, preys on juvenile guppies that have not yet displayed their adult coloration. • What will happen if adult guppies with drab colors were transferred to a pool with only killifish?
