Evidence for Evolution PDF

Natural Selection & Macro-evolution Evolution – the definition ◼ Evolution explains both the immense diversity of living things as well as their commonalities. ◼ Small scale evolution=Micro-evolution (changes in DNA (genetics) in a population from one generation to the next) ◼ Lar...

Natural Selection & Macro-evolution Evolution – the definition ◼ Evolution explains both the immense diversity of living things as well as their commonalities. ◼ Small scale evolution=Micro-evolution (changes in DNA (genetics) in a population from one generation to the next) ◼ Large scale evolution=Macro-evolution (the descent of different species from a common ancestor over many generations ◼ Macro-evolution results from an accumulation of many small genetic changes over time Explaining Evolution… ◼ Evolution is not just change over time, lots of things change over time, but do not evolve ◼ E.g. trees lose leaves in fall & rock formations erode over time ◼ BUT, these are not examples of evolution b/c they don’t involve descent/change through genetic inheritance  Evolution – Common Ancestor ◼ The idea of evolution is that life has history – it has changed over time – and different species share common ancestors ◼ Consider the Animal Kingdom, all animals share some defining characteristic, and have changed over time to best suit their environments  Arriving at the Theory of Evolution Charles Darwin: ◼ Medical student, more interested in botany and insects ◼ Went on 5 year journey on HMS Beagle to study plants & animals in South America ◼ Important discoveries made that lead to his theories of evolution (which he called “descent with modification”)  Charles Darwin ◼ Darwin collected many species of birds & other animals ◼ Noted that different islands in the Galapagos contained birds that all differed slightly from each other, even though the climate & environment were similar ◼ This made him consider the fact that animals may change to better adapt to their surroundings Darwin’s Theory of Evolution by Natural Selection Natural Selection ◼ organisms with traits best suited to their environment are more likely to survive and reproduce ◼ For natural selection to occur, there must be diversity among species 1. There is variation/diversity in traits; e.g. some beetles are green and some are brown 2. Since the environment can’t support unlimited population growth, not all beetles can reproduce to their full potential. Say birds prefer to eat green beetles; few green beetles will survive & reproduce less often than brown beetles 3. Genetics is involved – the surviving brown beetles are more likely to have brown babies because this trait has a genetic basis 4. The more advantageous trait, brown, which allows the beetles to have more babies, becomes more common in the population; eventually all beetles may be brown Factors that Govern Natural Selection ◼ Organisms produce more offspring than can survive, so they compete for limited resources ◼ Individuals of a population vary; this variation is heritable (due to genetics) ◼ Individuals best suited to their local environment survive to reproduce (and pass on their genes for these favorable traits) ◼ Processes for change are slow & gradual  Macro-Evolution ◼ Visible changes in the characteristics of populations/organisms that occur over many generations Evidence for Macro-Evolution: ◼ Anatomy ◼ Embryology ◼ Fossils ◼ Geographic Distribution ◼ Molecular Biology Review of Evidence Anatomy: ◼ Homologous structures – similar structures that are derived from a common ancestor but no longer have the same function. (vertebrate limbs) ❑ The same bone types are found in human, cat, horse, bat, bird, whale forelimbs BUT they are arranged differently for different purposes (see next slide) Homologous Structures Review of Evidence Anatomy: ◼ Analogous structures - structures that may have the same function, but they do not necessarily have the same structure & they are not derived from a common ancestor. (bird & insect wings) ◼ show natural selection – as flight was deemed important for survival Review of Evidence Anatomy: ◼ Vestigial structures – structures present in modern animals that are no longer in use (no current function). They give hints to the evolution of an organism ❑ (forelimb/wing in ostrich but they can no longer fly; pelvic bones in whales but they no longer have hind legs) Vestigial Structures Review of Evidence Embryology: ◼ Similar stages of embryological development are seen in different species ◼ E.g. all vertebrates have tails and gills in early stages of embryonic development ❑ Fish have gills & tails ❑ In humans, gills become eustachian tube (links pharynx to inner ear) & tail becomes coccyx (tail bone) Review of Evidence Geographical Distribution ◼ geographically close environments are more likely to have related species than distant places ◼ isolated regions such as Australia have unique species that are not found anywhere else (marsupials) ◼ islands have species that are similar to nearby continents or other islands, but show slight differences (finches of Galapagos) Review of Evidence Fossils ◼ fossils form when organisms are buried in sediment that becomes rock ◼ They provide evidence that organisms from the past are different from organisms today ◼ depth of fossils indicate age (radioactive dating/carbon dating can be used to more accurately determine age) ◼ recent fossils are most similar to living organisms today, older fossils are more different ◼ fossils appear in chronological order, starting with invertebrates (older) and then vertebrates (fish, amphibians, reptiles, birds, mammals) Review of Evidence – Transitional Fossils ◼ Transitional fossils are organisms that came in between a past version of a species and the current species. ◼ They show intermediate forms of a species as they changed and accumulated adaptations at a slow pace. ◼ e.g. animals with both gills & lungs show link between fish and amphibians (e.g. lobe finned fish/lung fish) ◼ e.g. Archaeopteryx-bird/reptile-had feathers, but claws on wings, teeth, bony tail Archeaopteryx-transitional fossil? appeared to be a bird with dinosaur-like traits. It had wings and feathers, but teeth instead of a beak. Possibly showed how birds evolved from dinosaur ancestors. Fossils provide evidence of descent with modification of different species of organisms Review of Evidence Molecular Biology ◼ All organisms use same genetic code (DNA/RNA) to make amino acids & proteins ◼ comparing DNA can determine how closely related organisms are (study differences in certain coding regions of DNA) ❑ e.g. humans & chimps have 2.5% difference in DNA sequence, humans and lemurs have 42% difference in DNA sequence ❑ all organisms have some proteins in common, e.g. proteins involved in basic functions like respiration (hemoglobin)