Anthropology Mini Essays

Lecture #9 — Principles of Classification and Macroevolution Today’s Questions? • What is the biological continuum? • How are species classified? • Why do closely related species sometimes look very different? • Why do distantly related species sometimes look similar? • What is a species? How do new species evolve? The Biological Continuum • Understanding the human place in the biological world – Vertebrate Evolution – Mammalian Evolution – Primate Evolution – Human Evolution Classification • Taxonomy — the science of classification – Ordering organisms into hierarchical categories based on evolutionary relationships – Closely related species share more traits than distantly related species Principles of Classification • Classified based on similarities • Similarities must reflect evolutionary relationships • Tetrapods – Four -limbed vertebrates – Vertebrate forelimbs • Similarity due to common descent Mammalian Radiation • Cenozoic — Age of Mammals – Birds and Mammals replaced reptiles as the dominant land -living vertebrates • Monotremes – Egg -laying Mammals • Marsupials – Pouched Mammals • Placentals Common Descent, Adaptive Radiation, and Homology Common Descent, Adaptive Radiation, and Homology • The mammalian forelimb demonstrates adaptive radiation and is an example of a homology – adaptive radiation — the rapid expansion and diversification of life forms into new ecological niches; occupation of different ecological niches by closely related species – homology — a structure shared through descent from a common ancestor Common Descent, Adaptive Radiation, and Homology Common Descent, Adaptive Radiation, and Homology • Mammals first evolved about 200mya but during the Cenozoic they began to spread out on land and fill new ecological niches that had been occupied by dinosaurs – In each of these new ecological niches, closely related species diverged from one another as they adapted to their new environment Common Descent, Adaptive Radiation, and Homology Common Descent, Adaptive Radiation, and Homology • All mammals living today are descended from a common ancestor (explains the similarities among mammalian forelimbs); but as they diverged and adapted to different ecological niches ( adaptive radiation ) their forelimbs diverged to adapt to new functions – All mammals have the same forelimb bones (scapula, humerus , radius, ulna, metacarpals, carpals, phalanges) but they are shaped and arranged differently based on species -specific adaptations. Common Function, Homoplasy , Convergent Evolution, and Analogy Common Function, Homoplasy , Convergent Evolution, and Analogy • Convergent evolution — the evolution of similar characteristics in distantly related species as a result of adaptation to similar ecological pressures – Closely related species that share similar features often share them because of common ancestry, however, sometimes distantly related species appear to share similar features but these are not the result of common ancestry – Rather they emerge as a result of adaptation to similar strategies or ecological niches •  SHARE FUNCTION rather than origin Common Function, Homoplasy , Convergent Evolution, and Analogy Common Function, Homoplasy , Convergent Evolution, and Analogy • When two distantly related species share similar adaptations, we call those analogies — the features are shared because they have the same function, they evolved independently as a response to similar selection pressures, as an adaptation to a similar environment rather than due to common ancestry – Wings of various species are an example Common Function, Homoplasy , Convergent Evolution, and Analogy http://cas.bellarmine.edu/tietjen/Evolution/Charley/Converge36.gif Common Function, Homoplasy , Convergent Evolution, and Analogy • Placental and marsupial mammals are another good example of this – Marsupials split from the placental mammals about 100mya • Marsupial and placental mice exploit basically the same resources in similar environments and, evolutionarily, they have converged on similar solutions to their ecological problems – homoplasy — the separate, independent evolutionary development of similar characteristics in different groups of organisms Common Function, Homoplasy , Convergent Evolution, and Analogy Canis lupus — the Alaskan Grey Wolf Placental Mammal Thylacinus cynocephalus — the Tasmanian Wolf Marsupial Mammal The LAST Tasmanian Wolf in Captivity — 1933 Extinct in the Wild Common Function, Homoplasy , Convergent Evolution, and Analogy Odocoileus virginianus — the Whitetail Deer Placental Mammal Macropus rufus — the Red Kangaroo Marsupial Mammal Constructing Classification • Evolutionary Systematics – Tracing presumed relationships through homologous characteristics • Cladistics – Tracing presumed relationships through derived characteristics • Homologous or Derived? Choosing Traits Choosing Traits • When classifying organisms, we need to be sure we choose biologically meaningful traits. That is, we have to choose traits that reflect evolutionary relationships. • On the previous slide, what are the different ways those organisms could be grouped based on similarities? • Which are biologically meaningful? Ancestral Traits — Both Vertebrates Vertebrates with Feathers Are Birds Vertebrates with Fur Are Mammals Fur is a Derived Trait Common Ancestry http://biology.unm.edu/ccouncil/Biology_203/Images/Phylogeny/lifecladogram.gifa Phylogenetic Trees Biological Species Concept • Group of individuals that are: – Capable of producing fertile offspring with each other – Reproductively isolated from other such groups • Speciation — the process by which a new species evolves from an earlier species The Genus Pan Photo by Me Photo by Kyleb Wild Adapted from de Waal and Lanting 1997 Allopatric Speciation Modes of Evolutionary Change Punctuated Equilibrium Gradualism Macroevolution Evolution and Geological Time Scale  3.5 bya Life on Earth Begins Macroevolution Evolution and Geological Time Scale 500 mya Vertebrates Macroevolution Evolution and Geological Time Scale 130 mya Placental Mammals 60 mya Primates 20 mya Apes 5 mya Hominins 200,000 ya Modern Homo sapiens