Jean Baptiste Lamarck (1744-1829): • Noted fossils resembled living species • Suggests fossils were ancestors of living species • Features had modified over time in response to changing climates & geography • Called this modification, “Transformational evolution” Lamarck’s Theory of the Inheritance of Acquired Characteristics • Living things make adjustments to their environment during their lifetime that can be passed down to their offspring, making the offspring, better adapted to the environment Based on Use/Disuse of Body Parts • Some organs or body parts may be used more than others during process of adaptation • Those “used” more are enhanced • Those “not used” are reduced • Believed these physical changes could be passed down from one generation to the next Significance of Larmarck’s Theory • Recognized crucial relationship between living things and the environment • Modern genetic research tells us genes can be influenced by the environment & changes in genes CAN be passed on to offspring (The Epigenome) Significance of Larmarck’s Theory • Recognized crucial relationship between living things and the environment • Modern genetic research tells us genes can be influenced by the environment & changes in gene function/expression CAN be passed on to offspring (The Epigenome) Charles Darwin (1809-1882) • British naturalist • First studied medicine, then ministry for Church of England • 5 year voyage around the world on the H.M.S. Beagle as naturalist • Observations from Galapagos Islands critical to formulation of theory “The Most Powerful Idea in Science”: Evolution by Natural Selection • Developed by Charles Darwin and Alfred Russell Wallace Pre-Darwin • Is the cornerstone of modern evolutionary theory because it explains how biological change & adaptation occurs NATURAL SELECTION Darwin & Wallace recognized that variation in populations already existed This variation (genetic diversity) provided the “raw material” for natural selection: – some individuals have traits that give them an advantage to surviving Any change in the environment can lead to an advantage for some individuals & disadvantage for others If selective pressure acts against or upon these differences, you get natural selection Natural Selection in a Nutshell Natural selection is the process by which NATURE (i.e. the environment), selects better adapted individuals for more successful reproduction Variation----Selection-----Variation-----Selection Lamarck vs. Darwin Lamarck: Variation when needed Darwin: Variation already present How does this lead to diversity of species? • Over long periods of time, successful variations/traits accumulate such that later populations may become distinct (physically, behaviorally) from ancestral ones What defines a population? • A group of individuals that: – is reproductively isolated (of the same species) – occupies a specific area Natural selection operates on or “selects” individuals, but it is the population that evolves Diversity of species, cont. • If no interbreeding (sharing of genes) occurs, they may eventually become separate species • Populations are adaptable & can change over time in response to changing environments Diversification of species, cont. • Geographical isolation can fuel speciation as populations respond to different selective pressures (different environmental circumstances that influence reproductive success) • Sexual selection also affects the process of natural selection; female preference for specific male qualities In Sum • Natural selection is a process of elimination – “Survival of the fittest”: to be “fit” means to possess certain characteristics that increase the probability of survival & reproductive success • Natural selection is essentially, the differential reproductive success of individuals in a population, mediated by the environment • End result is adaptation • May result in new species developing, but not always Peppered Moths: Natural selection in action • Common variety of moth is spotted gray (peppered) – Also a dark colored moth of same species (less common) • Peppered moth better camouflaged when resting on lichen-covered trees; dark moths more visible to predators, are eaten more frequently (producing fewer offspring than light colored moths) Peppered Moths, cont. • Coal dust from factories kills lichen on trees and turns the bark a dark gray • Light gray (peppered) moths are more visible; dark gray moths better camouflaged • Dark gray variety increase in number, light gray population declines Peppered Moths, cont. • Pollution control enables lichen to grow back on trees • Peppered moths once again better camouflaged, darker variety declines • Natural Selection Short Pesticide resistance among beetles The “–isms” and “schisms” of Darwin’s Theory “schisms” Implies a “belief system,” like 1. Seemed to contradict Hinduism, absolutism, etc. religious explanations Ideas associated with Nat. Sel. 2. Led to Eugenics movement, used to explain & justify social including the Holocaust; differences (Social Darwinism) Darwin never used term or “survival of the fittest” – “survival of fittest” Not Darwin’s doing 3. Process of evolution Darwinism used synonyincludes much more than mously with “Evolution” Darwin ever explained or Darwin’s name & ideas used understood (in 19th century) by others to advance their 4. Darwin would never have own agendas supported those agendas “-isms” 1. 2. 3. 4. What Evolution & Natural Selection ARE NOT: • Evolution means that organisms are “progressing” or getting better. What it IS: • Natural selection does weed out individuals that are unfit in a particular environment • What’s “good” or “better” in one place or time, may not be in another • Fitness (reproductive success) is linked to the environment not progress Example: Chimps are chimps because the features they have are perfectly adapted to their environment & niche Misconception: Natural Selection involves organisms “trying” to adapt Adaptation doesn’t involve “trying” • Nat. Sel. leads to adaptation • Stems from variation (genetic diversity) in the population (no two individuals are exactly alike) • Some individuals will have genes (characteristics) that will enhance its chances of survival, and others won’t Misconception: Evolution means that life has changed “by chance” • There is an element of chance (mutations, genetic processes, movement of populations, etc.) and of luck • Selection of/for specific traits is not random • Nat. Sel. favors characteristics that confer an advantage to survival, thereby increasing the frequency of that trait in the population to keep it adapted to its environment