The Origin of New Species

Transcription

1 The Origin of New Species

2 Introduction If microevolution is small changes in gene frequencies What, then would macroevolution be? And how might that work????

3 The biological species concept emphasizes reproductive isolation In 1942 Ernst Mayr defined species. Can mate and have fertile offspring. Examples??? Same # of chromosomes and the same sequences of genes on them.

4 Species are based on infertility, not physical similarity. For example, these two meadowlarks are different species. But all these folks belong to the same species.. Fig. 24.2

5 2.How can a new species come about? There are two key ingredients to the process of speciation: Reproductive isolation A vacant niche. Then, time to Evolve (by what mechanisms???).

6 Reproductive isolation can occur for many reasons. But very often it is geography. Fig. 24.5

7 1. Geographic barriers can lead to isolation and the origin of new species: Islands are great examples. How about those Grand Canyon squirrels? And marsupials mi 2:00

8 They also require the means to survive - a niche they can fill. Gause s Law, or the Law of Competitive Exclusion: this town s not big enough for the both of us. The less well adapted population will either?

9 So here s how it works: The isolated populations face different selection pressures and have different random mutations occur. Chance may also be involved The result is that their gene pools gradually grow different enough and, voila, they are two different species. Even if reunited, their members can no longer mate and produce fertile offspring.

10 Common ancestor??? adaptive radiation??? divergent evolution??? Fig

11 Items referring to adaptive radiation, convergent evolution, coevolution, or punctuated equilibrium should focus on the concepts rather than on the definition of the terms.

12 Divergent Evolution This is the main pattern we see when we look at the history of life on earth. It is the branching tree pattern of a common ancestor giving rise to different species, orders, kingdoms, etc. Similarities in homologous structures, chemicals like DNA and embryological development all are evidence of evolutionary change with this pattern. Adaptive radiation is divergent evolution that has resulted in the formation of, at the very least, new species. The two terms are almost synonyms.

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14 Convergent Evolution, on the other hand is a pattern we see in which groups which, even though they diverged from a common ancestor in the past, were different from each other at one point in time and then later evolved analagous structures which serve similar functions. Two classic examples: The evolution of a streamlined body shape and fins in sharks (fishes), whales (mammals with dog-like ancestors) and reptiles (swimming dinosaurs with 4-legged, land-living ancestors). The evolution of wings in birds, bats and insects, all from ancestors without wings.

15 Now, just to be confusing, let s look at co-evolution. This is not another pattern, really, like divergent and convergent evolution, this is when two organisms are evolving based on the selection pressures provided by the other. 2 examples: Cheetahs and antelopes have both evolved speed related adaptations as a result of each other s speed. Flowers and their pollinators. Great example. 3:40

16 3. The punctuated equilibrium model has stimulated research on the tempo of speciation Traditional evolutionary trees diagram the diversification of species as a gradual divergence over long spans of time. This assumes that big changes occur because of the accumulation of many small ones - the gradualism model. Like sharks.

17 In the fossil record, many species appear as new forms rather suddenly (in geologic terms), persist essentially unchanged, and then disappear from the fossil record. Darwin noted this when he remarked that species appear to undergo modifications during relatively short periods of their total existence and then remained essentially unchanged. Draw a fossil/rock layers map to show this idea. He could not explain this fossil evidence in his gradualism theory, but we have learned much since then.

18 In the punctuated equilibrium model, the tempo of speciation is not constant. Species undergo most morphological modifications when they first bud from their parent population. After establishing themselves as separate species, they remain static for the vast majority of their existence. Fig b

19 Periods of mass extinction (13:25 with Neil degrasse Tyson) followed by rapid speciation (:30) do exist in the fossil record. Stephan Jay Gould helped pioneer the idea of punctuated equilibrium. Let s watch a bit of video?: The Day the Mesozoic Died

20 How did the dinosaurs become extinct?

21 Under this model, changes may occur rapidly and gradually during the few thousands of generations necessary to establish a unique genetic identity. Species will appear suddenly in rocks of a certain age Stabilizing selection may then operate to maintain the species relatively the same for tens to hundreds of thousand of additional generations until it finally goes extinct. Another neat example of how science keeps adding pieces to the puzzle. FSU link

22 Most evolutionary novelties are modified versions of older structures The Darwinian concept of descent with modification can account for the major morphological transformations of macroevolution. It may be difficult to believe that a complex organ like the human eye could be the product of gradual evolution, rather than a finished design created specially for humans. However, the key to remember is that that eyes do not need to as complicated as the human eye to be useful to an animal.

23 We have also discovered genes (HOX genes) that act as master switches that turn on and off whole sets of other genes to cause big changes such as in development. Mutations in these genes can cause big changes very quickly.

24 Critique this picture

25 SC.912.L.15.10: Identify basic trends in hominid evolution from early ancestors six million years ago to modern humans, including brain size, Jaw size, language, and manufacture of tools.

26 Video selections Great Transitions is best if time (20 min.). It has don Johansen, etc. with hip and hand and skull comparisons. Great Transformations is shorter (8 min.) and has some of same Johansen clips. You Inner Monkey is also good but longer than both others.

27 1. Primate evolution provides a context for understanding human origins Primates are monkeys, lemurs, tarsiers and apes (including us!). Compared to other mammals Most primates have hands and feet adapted for grasping. Relative to other mammals, they have large brains and short jaws. They have flat nails on their digits, rather than narrow claws. Primates also have relatively well-developed parental care and relatively complex social behavior.

28 The oldest known anthropoid fossils, from about 45 million years ago, support the hypothesis that tarsiers are the prosimians most closed related to anthropoids. Fig

29 The earliest primates were probably tree dwellers, shaped by natural selection for arboreal (tree) life. The grasping hands and feet of primates are adaptations for hanging on to tree branches. The thumb is relatively mobile and separate from the fingers in all primates, but a fully opposable thumb is found only in anthropoid primates. The unique dexterity of humans, aided by distinctive bone structure at the thumb base, represents descent with modification from ancestral hands adapted for life in the trees. Copyright 2002 Pearson Education, Inc.,

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31 Other primate features also originated as adaptations for tree dwelling. The overlapping fields of vision of the two eyes (binocular vision) enhance depth perception, an obvious advantage when brachiating (tree climbing). Excellent hand-eye coordination is also important for arboreal maneuvering.

32 2. Humanity is one very young twig on the vertebrate tree In the continuity of life spanning over 3.5 billion years, humans and apes have shared ancestry for all but the last few million years. Paleoanthropology is the study of human origins and evolution. Paleoanthropology focuses on the tiny fraction of geologic time during which humans and chimpanzees diverged from a common ancestor.

33 Paleoanthropology has a checkered history with many misconceptions about human evolution generated during the early part of the twentieth century that still persist in the minds of the general public, long after these myths have been debunked by fossil discoveries. First, our ancestors were not chimpanzees or any other modern apes. Chimpanzees and humans represent two divergent branches of the hominoid tree that evolved around 7 million years ago from a common ancestor that was neither a chimpanzee nor a human.

34 Secondly, human evolution did not occur as a ladder with a series of steps leading directly from an ancestral hominoid to Homo sapiens. If human evolution is a parade, then many splinter groups traveled down dead ends and several different human species coexisted. Human phylogeny is more like a multibranched bush with our species as the tip of the only surviving twig.

35 SC.912.L.15.10: Identify basic trends in hominid evolution from early ancestors six million years ago to modern humans, including brain size, Jaw size, language, and manufacture of tools.

36 Items will not require memorization of the names of specific human fossils or the names of the different hominid species. Items will not require memorization of the names of specific human fossils or the names of the different hominid species.

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38 Third, the various human characteristics, such as upright posture and an enlarged brain, did not evolve in unison. Bipedalism was first. Our pedigree includes ancestors who walked upright but had brains much less developed than ours, suggesting that upright walking (bipedalism) set the stage for the evolution of larger brains. After dismissing some of the folklore on human evolution, we must admit that many questions about our own ancestry remains.

39 Human evolution is marked by the evolution of several major features. Brain Size. Based on skull measurements, researchers have estimated that brain size in hominoids tripled over the past 6 million years. It increased from about cm 3 in hominoids (and similar to modern chimpanzees) to about 1,300 cm 3 in modern humans. Jaw Shape. Our hominoid ancestors had longer jaws - prognathic jaws - than those of modern humans. This resulted in a flatter face with more pronounced chins.

40 Paedomorphogenesis, or Neoteny Neoteny is the maintenance of juvenile characteristics into the adult stage, not uncommon in the animal kingdom. Humans are bipedal, neotenous apes, best seen in skull structure comparisons.

41 Bipedal Posture. Based on fossil skeletons, it is clear that our hominoid ancestors walked on all four limbs when on the ground, like modern apes. The evolution of bipedalism- upright posture and twolegged walking - is associated with key skeletal changes seen in early hominid fossils. Position of the foramen magnum (where your backbone connects to your skull) is more centered in humans so the heads sits on top of the spine. Feet with arches and a non-opposable big toe Longer, stronger legs/leg bones Larger muscles on legs gluts, hamstrings, quads, gastrocnemius Wider pelvis, knees close together for support S-curve in lumbar spine to support weight above

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43 Cultural evolution events: Tool making (wood, bone and metal) Language Organized hunting and gathering Agriculture Industrial revolution Commerce and technology

44 The various pre-homo hominids are classified in the genus Australopithecus ( southern ape ) and are known as australopithecines. The first australopithecine, A. africanus, was discovered in 1924 by Raymond Dart in a quarry in South Africa. From this and other skeletons, A. africanus probably walked fully erect and had humanlike hands and teeth. However, the brain was only about one-third the size of a modern human s brain.

45 In 1974, a new fossil, about 40% complete, was discovered in the Afar region of Ethiopia. This fossil, nicknamed Lucy, was described as a new species, A. afarensis. These were considered to be our direct ancestors, but are no longer It appears they evolved into other Australopithecines, like africanus, but that they became extinct.

46 Based on this fossil and other discoveries, this species had a brain the size of a chimpanzee, a prognathic (bigger) jaw, longer arms (for some level of arboreal locomotion), and sexual dimorphism more apelike than human. However, the pelvis and skull bones and fossil tracks showed that A. afarensis walked bipedally. Fig

47 In the past few years, paleoanthropologists have found hominid species that predate A. afarensis. An older fossil that is unambiguously more human than ape is Australopithecus anamensis, which lived over 4 million years ago. Other fossils of putative hominids go back 6 million years, closer to the ape-human split that molecular systematists estimate occurred about 5-7 million years ago. News flash 2009 the oldest widely agreed upon direct ancestor is now called Ardipithecus ramidus, found in Ethiopia and dating back to 4.4 million years ago, a full million years older than Lucy.

48 The earliest fossils that anthropologists place in our genus, Homo, are classified as Homo habilis. These fossils range in age from 2.5 to 1.6 million years old. This species had less human-like jaws and larger brains (about cm 3 ) than australopithecines. In some cases, anthropologists have found sharp stone tools with these fossils, indicating that some hominids had started to use their brains and hands to fashion tools. These, however, were NOT our direct ancestors.

49 Homo erectus was the first hominid species to migrate out of Africa, colonizing Asia and Europe. They lived from about 1.8 million to 500,000 years ago. Fossils from Asia are known by such names as Beijing man and Java Man. In Europe, H. erectus gave rise to the humans known as Neanderthals. Compared to H. habilis, H. erectus was taller, had a larger brain (averaging about 1,100 cm 3 ), and had about the same level of sexual dimorphism as modern humans.

50 The other hypothesis, the Out of Africa or replacement hypothesis, argues that all Homo sapiens throughout the world evolved from a second major migration out of Africa that occurred about 100,000 years ago. This migration completely replaced all the regional populations of Homo derived from the first hominid migrations. Fig b

51 2010 update new DNA sequence studies strongly indicate some hybridization between Neanderthals and Homo sapiens. It always changes!! 2011 update a newly found group called Denisovans also appear to have interbred with us. This info comes from DNA found in a fingertip fossil! Depending on your ancestry, you may have varying amounts of modern human, Neanderthal and Denisovan DNA. Will we continue to evolve?

52 Here are the traits the EOC may ask you about This is what separates modern humans like us from our ancestors: Larger brain Smaller, shorter jaws Language Complex tool manufacture

53 Fossil evidence suggests that a number of members of one fish species from an ancient lake in Death Valley, California, became several isolated species. Of the following, which best explains the cause of the speciation? A. episodic isolation B. temporal isolation C. geographic isolation D. behavioral isolation

54 A species of finch has been studied on one of the geographically isolated Galapagos Islands for many years. Since the island is small, the lineage of every bird for several generations is known. This allows a family tree of each bird to be developed. Some family groups have survived and others have died out. The groups that survive probably have A. Interbred with other species B. Been attacked by more predators C. Found new places on the island to live D. Inherited some advantageous variations