Unformatted text preview: Onymacris unguicularis, the head standing beetle Namibia Atlantic ocean • 1 of 350,000 beetle species • Has typical beetle traits: pair of wings; 6 legs; hard exterior • Possesses it’s own unique behavior • Prior example illustrates the features of all life: shared traits; variation; features (adaptations) that allow each species to be suited to their environment; culminates in the diversity of life on earth. • Observe changes in populations of a species over successive generations of breeding & the production of offspring • *Species = describes a population whose members naturally interbreed & produce fertile offspring • Charles Darwin’s explanation for these observations, detailed in The Origin of Species (1859), described evolution as descent with modification [ancestor very different descendant species]
descendants Common ancestor • Evolution can be viewed as a pattern of change by a process consisting of mechanisms that produce change. • Evolution is the unifying theory that explains & connects all of biology. • Before Darwin: merge ideas from ancient Greek philosophy with Christian Doctrine, called “Natural Theology” (1400’s)
– Aristotle’s (300’s B.C.) “scala naturae”; compared the fixed traits of both living & non‐living forms to classify nature from simple to complex forms (“ladder of nature”). – Natural theology: “species are immutable”; they could not change or become extinct, new species could not form; are perfectly designed for their environment.
• Linnaeus: “father” of modern taxonomy; originated binomial nomenclature for naming organisms; cataloged all species & grouped in a nested manner • Darwin later used Linnaeus’ system as support for evolution • Renaissance period (1500’s‐1700’s): emergence of the fields of biogeography, comparative anatomy, and geology challenged the view of a static earth and unchanging life.
– Chief among these was the field of paleontology (study of fossils) and observations on Earth’s geological change. • Mid‐1700s: mapping of geological strata (layering of sedimentary rocks beneath the soil surface) • Formation of fossils
– Remains left in sedimentary rock (formed from sand/mud that settle to bottom of lakes & seas)
New sediment layers cover older ones – Older fossils simpler forms; More recent look similar to modern day forms – Evidence shows progression from earliest unicellular organisms to organisms of today – Shows life has evolved through time – Also shows record of extinction, emergence of new species
Cuvier & catastrophism idea Strata exposed as water level changes & seafloor pushed up • Hutton & Lyell: Earth’s geologic features occur through the cumulative effect of slow, continuous processes (earth’s age> 6000 yrs). *Darwin similarly slow processes produce biological change Jean Baptiste de Lamarck (1744–1829)
• First to propose a mechanism by which organisms undergo change as a result of natural phenomenon :
– Use & Disuse: increased or decreased usage of an organ or body part that leads to an increase in the size of the feature or it may disappear altogether. – Inheritance of acquired characteristics; believed modifications evolved via the use/disuse mechanism could be passed onto offspring. (EX: why giraffes have long necks) • Though not correct, credit Lamarck for proposing:
– That organisms change in response to their environment – That such change can be passed to offspring – That gradual evolutionary change leads to adaptation of an organism to its environment. Darwin’s Voyage: H.M.S. Beagle (1831)
Expedition’s primary mission: to chart the South American coastline. • On trips to the mainland & islands, Darwin made detailed descriptions & illustrations of the flora & fauna, as well as geographical features.
Observed that animals in various S. American habitats resembled each other, but differed from species occupying similar habitats in Europe. Fossils found in a particular region, resembled species currently inhabiting that area. Distribution of species on the Voyage Galapagos Islands. Animals on of the different islands varied slightly in Beagle form; many species resembled those on the nearby mainland. Hypothesized: Galapagos spe‐ cies descended from mainland species; island isolation changed them. Darwin’s Observations
• S. American species resemble each other, but differ from those found in similar habitats on other continents. Nutria of S. America European Beaver • Fossils often resemble organisms that inhabit the same area today. Glyptodont fossils discovered in Argentina, S. America present day descendants are armadillos • Many of Darwin’s observations focused on adaptations: environment‐specific characters that enhance an organism’s survival & reproductive success. • Darwin linked adaptation & origin of new species as closely related processes • An example of this thinking comes from his observation of finches of the Galapagos isles.
– Mainland, opposite the islands: only a couple of finch species – Galapagos isles possessed varying terrain and habitats – Darwin hypothesized Cactus eater. The Seed eater. The mainland species migrated long, sharp beak large ground finch of the cactus to nearby islands; as (Geospiza ground finch magnirostris) species adapted to the (Geospiza varying habitats, new scandens). species evolved. Insect eater. The – This thinking rejects the notion green warbler finch that species are immutable. (Certhidea olivacea). • Field of geology Influences on Darwin – 1600’s‐1800’s (Hutton, Lyell): Earth’s age >6000 yrs due to the slow pace of geological processes (erosion, uplifting, volcanic activity, etc). – Lyell’s Principles of Geology • Artificial selection
– Selective breeding to develop desired varieties of animals & crops. – Plants varieties obtained from wild mustard plant by human‐directed breeding. • Essay of Thomas Malthus
– Human population has the potential to increase faster than the food supply can sustain. Famine, war, & disease maintain population controls. – Darwin adapted idea to nature; he called it the “struggle for existence”. Natural Selection
• Natural selection was Darwin’s proposed process to explain the patterns of evolution. He supported this mechanism through the practice of artificial selection, the ideas of Malthus, and of his own observational experiences of the natural world. • Darwin’s four observations:
• Population members variability among their characteristics • Traits are inherited from parent to offspring • Species are capable of producing more offspring than the environment can support. • Many offspring do not survive due to lack of resources. Darwin’s Inferences from the observations:
• Differential reproductive success: individuals inheriting favorable traits have greater probability of surviving & producing more offspring. • Differential reproductive success leads to accumulation of favorable traits in the population. • Darwin reasoned that natural selection is capable of substantial modification of species over many hundreds of generations. Natural Selection Recap
• Key features of natural selection:
• Populations evolve, not individuals • Only heritable traits matter • Natural selection acts on the phenotype of an organism • Environmental factors determine which traits are favorable or not.
– Change in environment may give rise to new species
Spore cloud Heritable variation Adaptation Overproduction The Darwinian View of Life
• “Descent with Modification”
– All life forms descended from an ancestral form which lived long ago. – Descendants of this ancestor accumulated diverse modifications based on the environments they inhabited; passed onto offspring. – Mechanism of this process natural selection – Resulting modifications due to natural selection adaptations. • Darwin viewed life’s history as a tree, branches emerging from a common root (trunk): Evolutionary history of elephants
“Root” of tree: ancestor of all elephants extinct species Sketch from Darwin’s Notebook Branch forks: ancestor to all branches emanating from fork Branch tips: current living species Evidence for Evolution
• In the 150 yrs since the Origin of Species, count‐ less experiments have documented evolutionary patterns and the processes by which it occurs:
– Direct observations of evolutionary change – Fossil record – Homologies:
• Comparative anatomy • Molecular evidence: DNA, RNA, & protein sequences • Embryology – Biogeography Direct Observation of Evolutionary Change
• Predators influence the adaptations of their prey; prey that are better at predator avoidance likelier to survive & reproduce • Natural selection of guppy coloration due to intense predation:
Female guppy (attracted to bright colored males) Two selective pressures at work what is the effect on male coloration? male guppy Bright # males In separate pools, the pike‐cichlid feeds on bright colored adults (drab‐colored adults favored) Predators (tend to Drab Drab Low High prefer bright colored predation guppies) Among guppy predators, the killifish feeds on drab‐colored juveniles (bright colored adults favored) Transplant drab‐colored adults to killifish‐only pool: what is the affect of natural selection on transplanted adults? • Results among transplants: bright colored males selected for; offspring (descendants) more brightly colored: – Results show change in predator type influenced variation in color pattern of prey species brighter color patterns favored; an observed evolutionary change due to natural selection. • Key points regarding natural selection:
– Natural selection did not “create” a bright color pattern among guppies, rather it is an editing process. – Natural selection depends on time & place Fossil Evidence Reveals Whale Evolution
Mesonychid 50 mya Balaenoptera (present day blue whale) Ambulocetus Millions of years Rodhocetus Basilosaurus 38 mya Fossil Evidence Reveals Evolutionary Change
• Fossils document the emergence of new groups of organisms. • Example: appearance of cetaceans 50‐60 mya (mammalian order of whales, dolphins) • Prior to this, mammals were terrestrial; fossil evidence shows progression of terrestrial ancestor transitioning to life in the sea. • Comparison of transitional forms reveals changes in bone structures; indicates adaptations to the aqueous environment.
– Ankle bone of fossil forms links cetaceans to artiodactyls (hippos, deers, camels, etc) 50 mya 47 mya 40 mya • Fossils can be dated to reveal pat‐ terns of evolution; i.e., the order in which different groups evolved. 25 mya Analysis of Similarities Among Organisms Reveals Homologies
• Homologous structures
– Characteristic among related species that is inherited from a common ancestor; are similar structurally, but differ in function. – Comparison of limb bones in mammals reveals an underlying similar bone structure, but each are adaptations for different functions. Represent modifications from a common ancestor. • Vestigial structures
– Remnants of functional structures once present & functional in ancestral organisms; lost during evolutionary development. – Example: vestigial pelvic & hind limb bones in modern whales
Vestigial hind legs of python • Embryological homologies: homologous features present in developmental stages not seen in comparison of adult forms. • This example shows similarity in development among different vertebrates. • Molecular homologies: The “genetic language” (DNA, RNA) of life is universal
– Comparisons of DNA, RNA sequences also yield homologies, and thus evolutionary relationships among organisms. • Evolutionary trees: represent patterns of descent from common ancestors; constructed from comparisons of anatomical & DNA sequence data
Evolutionary tree of lungfishes & tetrapods Ancestor of all members here
Tetrapod ancestor; all descendants have 4 limbs Amnion ancestor; all descen‐ dants produce amnion layer around embryo (note: amphibians do not). Trees form a nested pattern; smaller groupings within larger ones. Convergent Evolution
• The appearance of similar characteristics in distantly related groups occurs through convergent evolution.
– Such characteristics would have evolved independently under similar environmental selection pressures. • Australian sugar glider & N. American flying squirrel evolved from different mammalian lines and developed flying ability independently. • Similar structures that form between distantly related groups are termed homoplastic (or analagous); similar in function, different in structure. • Other example of homoplastic structures: bird wing & insect wing, or bat wing & bird wing Biogeography
• Study of past & present geographic distribution of life; many factors influenced this distribution:
– Continental drift: slow movement of Earth’s continents; original, single supercontinent (Pangaea) split apart 240 mya – Evolution of new species due to movement of, the splitting of, & isolation of populations due to continental drift & related geologic processes of mountain formation, volcanic activity, etc. 240 mya 120 mya 60 mya today • Island effect: islands often possess many endemic species (found only there) due to isolation; have species closely related to species from nearest mainland. Summary
• Pre‐Darwinian views of life • Influences on Darwin • Mechanism of Evolution: natural selection
– Observations & inferences: genetic variation, overproduction, growth limitation, & differential reproductive success. – Natural selection & Adaptations • Evidence for evolution
– Direct observation, fossil record, homologies, biogeography, etc. ...
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- Spring '08
- Darwin, Darwin's finches, new species, Warbler Finch