Adaptation Evolution: The golden Thread Adaptation - Process where species acquire* traits that allow them to survive in their environments. Limited range of physiological modifications. Inheritance of specific genetic traits allowing a species to live in a particular environment. Population-level phenomenon, not the individual. *Over evolutionary time, not the lifespan of an individual. Evolution The idea that living things evolved over time had been around a long time Lamarck published on evolution the year Darwin was born (1809) It was the mechanisms proposed to explain this process that changed over time Lamarck s use and disuse, inheritance of acquired characteristics ideas What is evolution? People have understood that things evolve for 1000 s of years but how does it happen? What are the tools used by scientists to understand evolutionary time? Formation of sedimentary rock and deposition of fossils from different time periods 1. Fossil record 2. Comparative anatomy 3. Comparative embryology 4. Molecular biology 5. Biogeography 1
Strata of sedimentary rock at the Grand Canyon Fossils of trilobites Figure 25.1 A gallery of fossils Radiometric Dating Radiometric dating is a technique used to date materials based on a knowledge of the decay rates of naturally occurring isotopes, Most Common: Carbon-14 K-Ag Radiometric dating Carbon Dating 2
Carbon-14 decay A transitional fossil linking past and present Comparative Anatomy: Homologous Structures Biogeography: Convergent Evolution Descent with modification 3
Molecular Relationships Table 22.1 Molecular Data and the Evolutionary Relationships of Vertebrates Evidence from biogeographical studies: Figure 22.16 The evolution of fruit fly (Drosophila) species on the Hawaiian archipelago Comparative Embryology: Ontogeny recapitulates phylogeny - the appearance of ancestral structures in the embryos of modern descendants (Haeckel) The Odyssey of Life Evolution: The golden Thread 4
Chuck in 1859, the year The Origin of Species was published The Voyage of HMS Beagle The historical context of Darwin s life and ideas Artificial selection: cattle breeders of ancient Africa Canines- Canis familiaris Artificial selection: diverse vegetables derived from wild mustard "Yo quiero Artificial Selection The scientific name for broccoli, Brassica oleracea, is also shared by cabbage, Chinese cabbage, cauliflower, collards, Brussels sprouts, kale, kohlrabi, and tronchuda kale, and many others!. 5
Darwin s work put forward two main ideas: The concept of evolution, meaning that the diversity of species on the earth today arose by decent and modification of existing species That natural selection was the cause of adaptive evolution, i.e., that the modification of existing species results from the interaction between an individual s genetic makeup and the environment leading to differential rates of survival and reproduction. Darwin s main observations and conclusions Darwin s Natural Selection Observation 1- Overproduction Most populations have the potential to produce many more offspring than the environment can support with food, space, resources Therefore: There is a struggle for existence among individuals, only a fraction survive. Observation 2- Individual Variation Individuals vary in their characteristics, much of this variation is heritable, Therefore: there is differential reproduction success between individuals. Those best suited leave a larger share of offspring. Darwin s main points as published 1859 in: The Origin of Species by Means of Natural Selection: Organisms arise by descent and modification of existing species Natural selection acts on individuals as the modifying force The result is changes in the makeup of the population All organisms living today are the consequences of the environmental conditions faced by their ancestors Organisms appear well adapted to current conditions because these resemble the conditions in which they evolved. The theory does not predict perfect adaptation, it is not purposeful; rather, using random variation as the raw material, organisms evolve to match their environment by being the fittest available, the fittest yet, not the best imaginable. Darwin s Observations and Inferences Variation in populations Evolution of insecticide resistance in insect populations 6
Tolerance Limits Galápagos finches Review table on page 119 in book Finches from one island Mechanisms of Microevolution Non-random mating Small population sizes Genetic Drift Bottleneck Events Founder Effect (migration effects) Natural Selection Sexual selection Genetic drift Bottleneck Effect Examples? 7
Founder effect Few individuals colonize an island, lake, or some other isolated habitat Darwin s Finches Three General Outcomes of Natural Selection Disadvantage of sex Sexual selection and the evolution of male appearance Male peacock 8
Gradualism vs. Punctuated Equilibrium What does evolution look like? Macroevolution Mass Extinctions Speciation Other trends in populations / traits Mass Extinctions Have been many, 5-7 major ones. Permian extinction (286-248 mya)=95% of marine species extinct. The great dying K-T extinction (Cretaceous-Tertiary)=85% of species extinct. Many other things that can cause extinctions: Glaciations Volcanoes** and effects of gasses Low O2 in Ocean Land mass movement Patterns of Evolution The cone of increasing diversity vs. the model of decimation and diversification Decimation and Diversification 9