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13.21: Introduction to the Evolutionary History of the Animal Kingdom - Biology

13.21: Introduction to the Evolutionary History of the Animal Kingdom - Biology


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Discuss the evolutionary history of the animal kingdom

Many questions regarding the origins and evolutionary history of the animal kingdom continue to be researched and debated, as new fossil and molecular evidence change prevailing theories. Some of these questions include the following: How long have animals existed on Earth? What were the earliest members of the animal kingdom, and what organism was their common ancestor? While animal diversity increased during the Cambrian period of the Paleozoic era, 530 million years ago, modern fossil evidence suggests that primitive animal species existed much earlier.

What You’ll Learn to Do

  • Describe the features that characterized the earliest animals and when they appeared on earth
  • Explain the significance of the Cambrian period for animal evolution and the changes in animal diversity that took place during that time
  • Discuss the implications of mass animal extinctions that have occurred in evolutionary history

Learning Activities

The learning activities for this section include the following:

  • Pre-Cambrian Animal Life
  • The Cambrian Explosion
  • Post-Cambrian Evolution
  • Self Check: The Evolutionary History of the Animal Kingdom

Post-Cambrian Evolution and Mass Extinctions

The periods that followed the Cambrian during the Paleozoic Era are marked by further animal evolution and the emergence of many new orders, families, and species. As animal phyla continued to diversify, new species adapted to new ecological niches. During the Ordovician period, which followed the Cambrian period, plant life first appeared on land. This change allowed formerly aquatic animal species to invade land, feeding directly on plants or decaying vegetation. Continual changes in temperature and moisture throughout the remainder of the Paleozoic Era due to continental plate movements encouraged the development of new adaptations to terrestrial existence in animals, such as limbed appendages in amphibians and epidermal scales in reptiles.

Changes in the environment often create new niches (diversified living spaces) that invite rapid speciation and increased diversity. On the other hand, cataclysmic events, such as volcanic eruptions and meteor strikes that obliterate life, can result in devastating losses of diversity to some clades, yet provide new opportunities for others to “fill in the gaps” and speciate. Such periods of mass extinction (Figure) have occurred repeatedly in the evolutionary record of life, erasing some genetic lines while creating room for others to evolve into the empty niches left behind. The end of the Permian period (and the Paleozoic Era) was marked by the largest mass extinction event in Earth’s history, a loss of an estimated 95 percent of the extant species at that time. Some of the dominant phyla in the world’s oceans, such as the trilobites, disappeared completely. On land, the disappearance of some dominant species of Permian reptiles made it possible for a new line of reptiles to emerge, the dinosaurs. The warm and stable climatic conditions of the ensuing Mesozoic Era promoted an explosive diversification of dinosaurs into every conceivable niche in land, air, and water. Plants, too, radiated into new landscapes and empty niches, creating complex communities of producers and consumers, some of which became very large on the abundant food available.

Another mass extinction event occurred at the end of the Cretaceous period, bringing the Mesozoic Era to an end. Skies darkened and temperatures fell after a large meteor impact and tons of volcanic ash ejected into the atmosphere blocked incoming sunlight. Plants died, herbivores and carnivores starved, and the dinosaurs ceded their dominance of the landscape to the more warm-blooded mammals. In the following Cenozoic Era, mammals radiated into terrestrial and aquatic niches once occupied by dinosaurs, and birds—the warm-blooded direct descendants of one line of the ruling reptiles—became aerial specialists. The appearance and dominance of flowering plants in the Cenozoic Era created new niches for pollinating insects, as well as for birds and mammals. Changes in animal species diversity during the late Cretaceous and early Cenozoic were also promoted by a dramatic shift in Earth’s geography, as continental plates slid over the crust into their current positions, leaving some animal groups isolated on islands and continents, or separated by mountain ranges or inland seas from other competitors. Early in the Cenozoic, new ecosystems appeared, with the evolution of grasses and coral reefs. Late in the Cenozoic, further extinctions followed by speciation occurred during ice ages that covered high latitudes with ice and then retreated, leaving new open spaces for colonization.


13.21: Introduction to the Evolutionary History of the Animal Kingdom - Biology

Figure 1. An artist’s rendition depicts some organisms from the Cambrian period.

Many questions regarding the origins and evolutionary history of the animal kingdom continue to be researched and debated, as new fossil and molecular evidence change prevailing theories. Some of these questions include the following: How long have animals existed on Earth? What were the earliest members of the animal kingdom, and what organism was their common ancestor? While animal diversity increased during the Cambrian period of the Paleozoic era, 530 million years ago, modern fossil evidence suggests that primitive animal species existed much earlier.


The Cambrian Explosion of Animal Life

The Cambrian period, occurring between approximately 542–488 million years ago, marks the most rapid evolution of new animal phyla and animal diversity in Earth’s history. It is believed that most of the animal phyla in existence today had their origins during this time, often referred to as the Cambrian explosion (Figure). Echinoderms, mollusks, worms, arthropods, and chordates arose during this period. One of the most dominant species during the Cambrian period was the trilobite, an arthropod that was among the first animals to exhibit a sense of vision (Figureabcd).

An artist’s rendition depicts some organisms from the Cambrian period. These fossils (a–d) belong to trilobites, extinct arthropods that appeared in the early Cambrian period, 525 million years ago, and disappeared from the fossil record during a mass extinction at the end of the Permian period, about 250 million years ago.

The cause of the Cambrian explosion is still debated. There are many theories that attempt to answer this question. Environmental changes may have created a more suitable environment for animal life. Examples of these changes include rising atmospheric oxygen levels and large increases in oceanic calcium concentrations that preceded the Cambrian period (Figure). Some scientists believe that an expansive, continental shelf with numerous shallow lagoons or pools provided the necessary living space for larger numbers of different types of animals to co-exist. There is also support for theories that argue that ecological relationships between species, such as changes in the food web, competition for food and space, and predator-prey relationships, were primed to promote a sudden massive coevolution of species. Yet other theories claim genetic and developmental reasons for the Cambrian explosion. The morphological flexibility and complexity of animal development afforded by the evolution of Hox control genes may have provided the necessary opportunities for increases in possible animal morphologies at the time of the Cambrian period. Theories that attempt to explain why the Cambrian explosion happened must be able to provide valid reasons for the massive animal diversification, as well as explain why it happened when it did. There is evidence that both supports and refutes each of the theories described above, and the answer may very well be a combination of these and other theories.

The oxygen concentration in Earth’s atmosphere rose sharply around 300 million years ago.

However, unresolved questions about the animal diversification that took place during the Cambrian period remain. For example, we do not understand how the evolution of so many species occurred in such a short period of time. Was there really an “explosion” of life at this particular time? Some scientists question the validity of the this idea, because there is increasing evidence to suggest that more animal life existed prior to the Cambrian period and that other similar species’ so-called explosions (or radiations) occurred later in history as well. Furthermore, the vast diversification of animal species that appears to have begun during the Cambrian period continued well into the following Ordovician period. Despite some of these arguments, most scientists agree that the Cambrian period marked a time of impressively rapid animal evolution and diversification that is unmatched elsewhere during history.


Materials and Methods

DNA extraction and amplification.

DNA was extracted and amplified from two H. moorei bones (Table S1) as previously described [10] using appropriate ancient DNA techniques. “Modern” toepad tissue (museum specimens) was extracted using Qiagen (Valencia, California, United States) DNeasy tissue extraction kits. Multiple negative extraction and amplification controls were included, to detect contamination. All PCR reactions were conducted as described in [10] using Platinum Taq HiFi (Invitrogen, Carlsbad, California, United States) together with the cyt b and ND2 primers listed in Table S2. Thermal cycling conditions were typically 40 cycles of 95 °C/55–60 °C/68 °C (30–45 s each). Sequences were determined using ABI Big Dye (v.3.1) on an ABI 3100 or 3730 (Applied Biosystems, Foster City, California, United States), according to manufacturer's instructions. Modern samples, and ancient samples subsequent to PCR amplification, were analysed in the Zoology Department, Oxford University. A single Harpagornis bone was sent to an ancient DNA facility at University College London (I. Barnes) for independent replication, where identical sequences were obtained for two cyt b amplifications. Similar cyt b and ND2 tree topologies, in addition to multiple overlapping sequences, make it unlikely that we are detecting a nuclear pseudogene.

Phylogenetic methods.

Maximum-likelihood trees for cyt b and ND2 were selected using a heuristic search as implemented in PAUP*4.0b10 [11] under the HKY + Γ4 + I substitution model. The assumption of a molecular clock was tested using a likelihood ratio test in which the χ 2 test statistic was two times the log likelihood difference between clock and non-clock models. For the cyt b tree the assumption of rate constancy was not rejected. Node support was evaluated for 1,000 bootstrap replicates. Bayesian Markov Chain Monte Carlo phylogenies were also generated on the cyt b dataset using BEAST [12] and MrBayes [13] under similar substitution models—the topology of these trees was consistent with Figure 1C and generated posterior support values higher than the bootstrap values.

Using the maximum-likelihood tree in Figure 1C, an independent-contrasts analysis was employed to determine whether correlations existed between phylogenetic position and body mass. Mean live weight estimates were obtained from the literature, and the average mass of H. moorei was estimated from femur length [2]. A test to measure the index of phylogenetic dependence was conducted this measures the degree to which traits vary across taxa (in a phylogeny) in accordance with predictions of a neutral Brownian model according to [14]. The results (not shown) clearly demonstrate that the mass of H. moorei is clearly an “outlier” in the context of the phylogeny presented here.

Hieraaetus systematics.

The type species for the genus Hieraaetus is H. pennatus (Gmelin, 1788) therefore, the taxa grouping strongly with H. pennatus must remain in that genus. The close genetic relationship of H. morphnoides with H. pennatus firmly embeds this species in Hieraaetus. However, the New Guinea subspecies presently recognised as H. morphnoides weiskei is genetically, geographically, and morphologically distinct and warrants species status, which necessitates the new combination Hieraaetus weiskei (Reichenow, 1900). Harpagornis moorei is included in the clade with H. pennatus and H. morphnoides, and hence its generic assignment must reflect that. The name for the extinct Harpagornis moorei of New Zealand should therefore be amended to Hieraaetus moorei (Haast, 1872).


Next Generation Science Standards for this Video

Mitchell Sogin compares the sequence of a gene found in all animals to look for common ancestry. The evidence he finds explains that sponges were the first animals.

Mitchell Sogin finds genetic evidence for the evolution of the animal kingdom, and reconstructs evolutionary history from the first animal—the sponge.

Mitchell Sogin compares the sequence of a gene found in all animals to look for common ancestry.

Mitchell Sogin uses technology to sequence genes and is also familiar with the traits of the animals.

Mitchell Sogin looks at the genes of many different animals.

Mitchell Sogin compares the sequence of a gene found in all animals to look for common ancestry. Fossil evidence had suggested this.


Review Questions

Which of the following periods is the earliest during which animals may have appeared?

  1. Ordovician period
  2. Cambrian period
  3. Ediacaran period
  4. Cryogenian period

What type of data is primarily used to determine the existence and appearance of early animal species?

  1. molecular data
  2. fossil data
  3. morphological data
  4. embryological development data

The time between 542–488 million years ago marks which period?

Until recent discoveries suggested otherwise, animals existing before the Cambrian period were believed to be:

  1. small and ocean-dwelling
  2. small and non-motile
  3. small and soft-bodied
  4. small and radially symmetrical or asymmetrical

Plant life first appeared on land during which of the following periods?

Approximately how many mass extinction events occurred throughout the evolutionary history of animals?


Contents

The history of zoology traces the study of the animal kingdom from ancient to modern times. Prehistoric man needed to study the animals and plants in his environment in order to exploit them and survive. There are cave paintings, engravings and sculptures in France dating back 15,000 years showing bison, horses and deer in carefully rendered detail. Similar images from other parts of the world illustrated mostly the animals hunted for food but also the savage animals. [2]

The Neolithic Revolution, which is characterized by the domestication of animals, continued over the period of Antiquity. Ancient knowledge of wildlife is illustrated by the realistic depictions of wild and domestic animals in the Near East, Mesopotamia and Egypt, including husbandry practices and techniques, hunting and fishing. The invention of writing is reflected in zoology by the presence of animals in Egyptian hieroglyphics. [3]

Although the concept of zoology as a single coherent field arose much later, the zoological sciences emerged from natural history reaching back to the biological works of Aristotle and Galen in the ancient Greco-Roman world. Aristotle, in the fourth century BC, looked at animals as living organisms, studying their structure, development and vital phenomena. He divided them into two groups, animals with blood, equivalent to our concept of vertebrates, and animals without blood (invertebrates). He spent two years on Lesbos, observing and describing the animals and plants, considering the adaptations of different organisms and the function of their parts. [4] Four hundred years later, Roman physician Galen dissected animals to study their anatomy and the function of the different parts, because the dissection of human cadavers was prohibited at the time. [5] This resulted in some of his conclusions being false, but for many centuries it was considered heretical to challenge any of his views, so the study of anatomy stultified. [6]

During the post-classical era, Middle Eastern science and medicine was the most advanced in the world, integrating concepts from Ancient Greece, Rome, Mesopotamia and Persia as well as the ancient Indian tradition of Ayurveda, while making numerous advances and innovations. [7] In the 13th century, Albertus Magnus produced commentaries and paraphrases of all Aristotle's works his books on topics like botany, zoology, and minerals included information from ancient sources, but also the results of his own investigations. His general approach was surprisingly modern, and he wrote, "For it is [the task] of natural science not simply to accept what we are told but to inquire into the causes of natural things." [8] An early pioneer was Conrad Gessner, whose monumental 4,500-page encyclopedia of animals, Historia animalium, was published in four volumes between 1551 and 1558. [9]

In Europe, Galen's work on anatomy remained largely unsurpassed and unchallenged up until the 16th century. [10] [11] During the Renaissance and early modern period, zoological thought was revolutionized in Europe by a renewed interest in empiricism and the discovery of many novel organisms. Prominent in this movement were Andreas Vesalius and William Harvey, who used experimentation and careful observation in physiology, and naturalists such as Carl Linnaeus, Jean-Baptiste Lamarck, and Buffon who began to classify the diversity of life and the fossil record, as well as studying the development and behavior of organisms. Antonie van Leeuwenhoek did pioneering work in microscopy and revealed the previously unknown world of microorganisms, laying the groundwork for cell theory. [12] van Leeuwenhoek's observations were endorsed by Robert Hooke all living organisms were composed of one or more cells and could not generate spontaneously. Cell theory provided a new perspective on the fundamental basis of life. [13]

Having previously been the realm of gentlemen naturalists, over the 18th, 19th and 20th centuries, zoology became an increasingly professional scientific discipline. Explorer-naturalists such as Alexander von Humboldt investigated the interaction between organisms and their environment, and the ways this relationship depends on geography, laying the foundations for biogeography, ecology and ethology. Naturalists began to reject essentialism and consider the importance of extinction and the mutability of species. [14]

These developments, as well as the results from embryology and paleontology, were synthesized in the 1859 publication of Charles Darwin's theory of evolution by natural selection in this Darwin placed the theory of organic evolution on a new footing, by explaining the processes by which it can occur, and providing observational evidence that it had done so. [15] Darwin's theory was rapidly accepted by the scientific community and soon became a central axiom of the rapidly developing science of biology. The basis for modern genetics began with the work of Gregor Mendel on peas in 1865, although the significance of his work was not realized at the time. [16]

Darwin gave a new direction to morphology and physiology, by uniting them in a common biological theory: the theory of organic evolution. The result was a reconstruction of the classification of animals upon a genealogical basis, fresh investigation of the development of animals, and early attempts to determine their genetic relationships. The end of the 19th century saw the fall of spontaneous generation and the rise of the germ theory of disease, though the mechanism of inheritance remained a mystery. In the early 20th century, the rediscovery of Mendel's work led to the rapid development of genetics, and by the 1930s the combination of population genetics and natural selection in the modern synthesis created evolutionary biology. [17]

Research in cell biology is interconnected to other fields such as genetics, biochemistry, medical microbiology, immunology, and cytochemistry. With the sequencing of the DNA molecule by Francis Crick and James Watson in 1953, the realm of molecular biology opened up, leading to advances in cell biology, developmental biology and molecular genetics. The study of systematics was transformed as DNA sequencing elucidated the degrees of affinity between different organisms. [18]

Zoology is the branch of science dealing with animals. A species can be defined as the largest group of organisms in which any two individuals of the appropriate sex can produce fertile offspring about 1.5 million species of animal have been described and it has been estimated that as many as 8 million animal species may exist. [19] An early necessity was to identify the organisms and group them according to their characteristics, differences and relationships, and this is the field of the taxonomist. Originally it was thought that species were immutable, but with the arrival of Darwin's theory of evolution, the field of cladistics came into being, studying the relationships between the different groups or clades. Systematics is the study of the diversification of living forms, the evolutionary history of a group is known as its phylogeny, and the relationship between the clades can be shown diagrammatically in a cladogram. [20]

Although someone who made a scientific study of animals would historically have described themselves as a zoologist, the term has come to refer to those who deal with individual animals, with others describing themselves more specifically as physiologists, ethologists, evolutionary biologists, ecologists, pharmacologists, endocrinologists or parasitologists. [21]

Although the study of animal life is ancient, its scientific incarnation is relatively modern. This mirrors the transition from natural history to biology at the start of the 19th century. Since Hunter and Cuvier, comparative anatomical study has been associated with morphography, shaping the modern areas of zoological investigation: anatomy, physiology, histology, embryology, teratology and ethology. [22] Modern zoology first arose in German and British universities. In Britain, Thomas Henry Huxley was a prominent figure. His ideas were centered on the morphology of animals. Many consider him the greatest comparative anatomist of the latter half of the 19th century. Similar to Hunter, his courses were composed of lectures and laboratory practical classes in contrast to the previous format of lectures only.

Gradually zoology expanded beyond Huxley's comparative anatomy to include the following sub-disciplines:

Classification Edit

Scientific classification in zoology, is a method by which zoologists group and categorize organisms by biological type, such as genus or species. Biological classification is a form of scientific taxonomy. Modern biological classification has its root in the work of Carl Linnaeus, who grouped species according to shared physical characteristics. These groupings have since been revised to improve consistency with the Darwinian principle of common descent. Molecular phylogenetics, which uses nucleic acid sequence as data, has driven many recent revisions and is likely to continue to do so. Biological classification belongs to the science of zoological systematics. [23]

Many scientists now consider the five-kingdom system outdated. Modern alternative classification systems generally start with the three-domain system: Archaea (originally Archaebacteria) Bacteria (originally Eubacteria) Eukaryota (including protists, fungi, plants, and animals) [24] These domains reflect whether the cells have nuclei or not, as well as differences in the chemical composition of the cell exteriors. [24]

Further, each kingdom is broken down recursively until each species is separately classified. The order is: Domain kingdom phylum class order family genus species. The scientific name of an organism is generated from its genus and species. For example, humans are listed as Homo sapiens. Homo is the genus, and sapiens the specific epithet, both of them combined make up the species name. When writing the scientific name of an organism, it is proper to capitalize the first letter in the genus and put all of the specific epithet in lowercase. Additionally, the entire term may be italicized or underlined. [25]

The dominant classification system is called the Linnaean taxonomy. It includes ranks and binomial nomenclature. The classification, taxonomy, and nomenclature of zoological organisms is administered by the International Code of Zoological Nomenclature. A merging draft, BioCode, was published in 1997 in an attempt to standardize nomenclature, but has yet to be formally adopted. [26]

Vertebrate and invertebrate zoology Edit

Vertebrate zoology is the biological discipline that consists of the study of vertebrate animals, that is animals with a backbone, such as fish, amphibians, reptiles, birds and mammals. The various taxonomically oriented disciplines such as mammalogy, biological anthropology, herpetology, ornithology, ichthyology identify and classify species and study the structures and mechanisms specific to those groups. The rest of the animal kingdom is dealt with by invertebrate zoology, a vast and very diverse group of animals that includes sponges, echinoderms, tunicates, worms, molluscs, arthropods and many other phyla, but single-celled organisms or protists are not usually included. [27]

Structural zoology Edit

Cell biology studies the structural and physiological properties of cells, including their behavior, interactions, and environment. This is done on both the microscopic and molecular levels, for single-celled organisms such as bacteria as well as the specialized cells in multicellular organisms such as humans. Understanding the structure and function of cells is fundamental to all of the biological sciences. The similarities and differences between cell types are particularly relevant to molecular biology.

Anatomy considers the forms of macroscopic structures such as organs and organ systems. [28] It focuses on how organs and organ systems work together in the bodies of humans and animals, in addition to how they work independently. Anatomy and cell biology are two studies that are closely related, and can be categorized under "structural" studies. Comparative anatomy is the study of similarities and differences in the anatomy of different groups. It is closely related to evolutionary biology and phylogeny (the evolution of species). [29]

Physiology Edit

Physiology studies the mechanical, physical, and biochemical processes of living organisms by attempting to understand how all of the structures function as a whole. The theme of "structure to function" is central to biology. Physiological studies have traditionally been divided into plant physiology and animal physiology, but some principles of physiology are universal, no matter what particular organism is being studied. For example, what is learned about the physiology of yeast cells can also apply to human cells. The field of animal physiology extends the tools and methods of human physiology to non-human species. Physiology studies how for example nervous, immune, endocrine, respiratory, and circulatory systems, function and interact. [30]

Developmental biology Edit

Developmental biology is the study of the processes by which animals and plants reproduce and grow. The discipline includes the study of embryonic development, cellular differentiation, regeneration, asexual reproduction, metamorphosis, and the growth and differentiation of stem cells in the adult organism. [31] Development of both animals and plants is further considered in the articles on evolution, population genetics, heredity, genetic variability, Mendelian inheritance, and reproduction.

Evolutionary biology Edit

Evolutionary biology is the subfield of biology that studies the evolutionary processes (natural selection, common descent, speciation) that produced the diversity of life on Earth. Evolutionary research is concerned with the origin and descent of species, as well as their change over time, and includes scientists from many taxonomically oriented disciplines. For example, it generally involves scientists who have special training in particular organisms such as mammalogy, ornithology, herpetology, or entomology, but use those organisms as systems to answer general questions about evolution. [32]

Evolutionary biology is partly based on paleontology, which uses the fossil record to answer questions about the mode and tempo of evolution, [33] and partly on the developments in areas such as population genetics [34] and evolutionary theory. Following the development of DNA fingerprinting techniques in the late 20th century, the application of these techniques in zoology has increased the understanding of animal populations. [35] In the 1980s, developmental biology re-entered evolutionary biology from its initial exclusion from the modern synthesis through the study of evolutionary developmental biology. Related fields often considered part of evolutionary biology are phylogenetics, systematics, and taxonomy. [36]

Ethology Edit

Ethology is the scientific and objective study of animal behavior under natural conditions, [37] as opposed to behaviourism, which focuses on behavioral response studies in a laboratory setting. Ethologists have been particularly concerned with the evolution of behavior and the understanding of behavior in terms of the theory of natural selection. In one sense, the first modern ethologist was Charles Darwin, whose book, The Expression of the Emotions in Man and Animals, influenced many future ethologists. [38]

A subfield of ethology is behavioral ecology which attempts to answer Nikolaas Tinbergen's four questions with regard to animal behavior: what are the proximate causes of the behaviour, the developmental history of the organism, the survival value and phylogeny of the behavior? [39] Another area of study is animal cognition, which uses laboratory experiments and carefully controlled field studies to investigate an animal's intelligence and learning. [40]

Biogeography Edit

Biogeography studies the spatial distribution of organisms on the Earth, [41] focusing on topics like plate tectonics, climate change, dispersal and migration, and cladistics. It is an integrative field of study, uniting concepts and information from evolutionary biology, taxonomy, ecology, physical geography, geology, paleontology and climatology. [42] The origin of this field of study is widely accredited to Alfred Russel Wallace, a British biologist who had some of his work jointly published with Charles Darwin. [43]

Molecular biology Edit

Molecular biology studies the common genetic and developmental mechanisms of animals and plants, attempting to answer the questions regarding the mechanisms of genetic inheritance and the structure of the gene. In 1953, James Watson and Francis Crick described the structure of DNA and the interactions within the molecule, and this publication jump-started research into molecular biology and increased interest in the subject. [44] While researchers practice techniques specific to molecular biology, it is common to combine these with methods from genetics and biochemistry. Much of molecular biology is quantitative, and recently a significant amount of work has been done using computer science techniques such as bioinformatics and computational biology. Molecular genetics, the study of gene structure and function, has been among the most prominent sub-fields of molecular biology since the early 2000s. Other branches of biology are informed by molecular biology, by either directly studying the interactions of molecules in their own right such as in cell biology and developmental biology, or indirectly, where molecular techniques are used to infer historical attributes of populations or species, as in fields in evolutionary biology such as population genetics and phylogenetics. There is also a long tradition of studying biomolecules "from the ground up", or molecularly, in biophysics. [45]


Link to Learning

Watch the following video to learn more about the mass extinctions.

Mass extinctions have occurred repeatedly over geological time.


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Tangled Bank distinguishes itself amongst a heady group of recent publications as a masterpiece of science writing, publishing, instruction, and as a reference book. It has immediately become one of the books in my library that I most treasure.

2009 was a great year for students and supporters of science, especially those that study evolution given it's the 150th anniversary of Charles Darwin's 1st edition of The Origin Of Species: 150th Anniversary Edition . The year was celebrated partly by several practicing scientists publishing excellent books about evolution directed towards the general reader, nearly all of which were complementary rather than redundant. Having read seven books covering evolution this year, and several that were published just prior to 2009, it's my position that Tangled Bank stands above the rest of the herd, in spite the others also being very worthy of consideration.

Not only is Tangled Bank a great book on evolution on your first read, but it is structured in a way that allows it be used as an extremely valuable reference source. At 9.75 inches tall by 5.5 inches wide, it's large enough to provide ample space on its pages which are filled with beautiful color illustrations, color photos, and other color graphics that greatly help reinforce the subject matter. The quality of the cover and the paper is also first rate so it should be able to sustain a long usable life.

While Tangled Bank is being described as a textbook, it's important to distinguish how Tangled Bank is different from the stereotypical textbook. Tangled Bank does not include quizzes, exercises, or tests instead it can be identified as a textbook based on the structure of the subject material and framing, which is instructive rather than argumentative or a narrative like some of the other evolution books published recently. Each chapter of Tangled Bank ends with a "To Sum Up" page that presents a bullet point list to both help reinforce the objective of the chapter's instruction and help in future reference searches. While most textbooks of this quality can cost as much as $150, Amazon's current price of $40, or even the list price of $60 make this a true bargain given how many years I predict this book will be able to provide value, even as the rate of discoveries increases over time.

In addition Mr. Zimmer provides an excellent reference section categorized by both chapter and subject matter. Nearly all of Mr. Zimmer's references are either peer-reviewed articles generally accepted by the scientific community, or books popular with the scientific community that report on multiple peer-reviewed articles in a certain topical area germane to the chapter Zimmer covers. One reason Mr. Zimmer is an outstanding journalist is his intellectual honesty, where he is careful to report and distinguish between where science is confident in its explanations and where there is either controversy or a lack of confidence.

I would distinguish the closest competitor to what Mr. Zimmer does in Tangled Bank for the general reader to Richard Dawkins' The Greatest Show on Earth: The Evidence for Evolution (aka TGSOE) as follows. TGSOE is like a semester of seminars with a brilliant retired biologist with a wide command of the subject matter but also susceptible to frequent soliloquies that are often tangential, personal to the point it veers from what science understands or peer-accepts (where in the latter case Dawkins' is careful to note) and often illuminating but also sacrifices scientific findings for Dawkins personal reflections. Many of Dr. Dawkins' personal ruminations do serve to reinforce either the subject matter, scientific methodology, or are illuminative on how some research scientists think. However some of his reflections actually supplant what practicing scientists doing research are discovering with Dawkins' own non-fact based speculations, e.g., probability of life on other planets and how it could differ from life on earth.

Tangled Bank on the other hand is a more comprehensive self-guided tutorial of evolution. It's far more ambitious in terms of covering more topics within the relevant scientific disciplines and the format of instructional text coupled to far more graphics guarantees the reader will have a much better understanding of the theory of evolution than they would from books primarily focused on text alone (though Dawkins book does provide some nice color photos). I would argue that given Jerry Coyne's Why Evolution Is True provides a far more compelling and concise argument for the evidence of evolution than TGSOE Tangled Bank makes TGSOE an unnecessary purchase.

While the Tangled Bank's subtitle states, "An Introduction to Evolution", it's my opinion that very few readers would not greatly benefit from owning and perusing this book even if their job is germane to some aspect of the life sciences and they've formally trained in the life sciences through the undergrad level or gone to med school. While it's true that Mr. Zimmer only introduces the topics he covers by chapter rather than drilling down into the 200-level or beyond on any of the topics, the theory of evolution covers a broad cross-section of scientific disciplines and Mr. Zimmer covers nearly all of them. So while someone whose studied developmental biology or cell biology might not learn much on those topics as they're covered here, I think they'd still benefit from Mr. Zimmer's excellent chapters covering radiations and extinctions, the evolution of behavior, or other topics tangential to their field of expertise or subjects studied years ago given Zimmer's ample reporting of recent findings. I've been studying evolution now for thirty-plus years and I either learned quite a bit about topics I'd previously covered, or was re-introduced to subjects with a plethora of additional findings since I last studied the topic.

This is truly a masterpiece of textbook publishing for the general reader.


Watch the video: Animal Classification. Evolution. Biology. FuseSchool (May 2022).