Biology Chapters 18 and 19
Terms in this set (38)
Describe the defining characteristics of animals.
bodies composed of multiple eukaryotic cells; ingestion of food (heterotrophic nutrition); absence of cell walls; unique cell junctions; nerve and muscle cells (generally); sexual reproduction and life cycles with unique embryonic stages; unique developmental genes; gametes alone representing the haploid stage of the life cycle
How does evolutionary change often occur? How do starfish relate to evolution?
Evolutionary change often occurs through paedomorphosis. The starfish embryo is bilateral and the common ancestor of starfish and all other deuterosomes is thought to most resemble the larval form of the starfish. Starfish larva are not the common ancestor of chordates because it has been continually evolving since starfish split from the line that would become chordates, but they are most similar among living organisms.
Describe the Cambrian "explosion" of animal diversity and two hypotheses that have been advanced to explain its occurrence.
Toolbox genes like Hox genes got acted upon by natural selection. The explosion represented the culmination of millions of years of evolution during which all the genes evolved to create the body plans, and when the correct selective pressure was placed on the organisms, it was simply a matter of mutations in switches or duplication and modification of existing genes that resulted in the diversity of body forms. Two hypotheses: increasingly complex predator prey relationships drove a diversity of body forms. increased levels of oxygen may have also played a role in enabling later animals with greater metabolic needs.
Explain the differences between a deuterostomes and protostomes.
The fate of the opening formed during gastrulation leads to the developing digestive tract. In protostomes, this opening becomes the mouth, and, in deuterostomes, it becomes the anus. Other differences between the two include the pattern of early cell divisions and the way the coelom forms. The difference in embryonic development between them represent an evolutionary split such that any features that are shared between the two groups beyond being bi-lateral are homologous.
Describe the characteristics of Arthropoda.
protostomes, have an exoskeleton, have a ventral hollow nerve chord and a dorsal digestive tract, jointed appendages, body segmentation- makes it modular meaning that one part can evolve without affecting other modules, develops independently, results in vast number of bug species
Describe the characteristics of Echinodermata.
deuterostomes, embryos are bilateral, see stuff on starfish
Describe the characteristics of Chordata.
deuterostome, dorsal hollow nerve chord and ventral gut, pharyngeal slits, post anal tail, notochord
Explain segmentation and what kind of animals they occur in. Explain implications of this
Arthropods have distinct body segments, each of which is specialized. Because they (especially insects) have an external skeleton, each segment is very modular, meaning each body segment develops independently, modification of how genes and switches of downstream tool box genes can modify the development of each body segment without affecting the other segments. A huge diversity of body forms has resulted because there's much less developmental constraint on body form. Chordates also have distinct body segments. Because they have internal skeletons, development body segments are more integrated and thus do not occur independently, putting more constraints on body form
*** Compare the phylogenetic relationships in Figures 18.4 and 18.15, noting similarities and differences.
In the morphology-based tree, annelids and arthropods are hypothesized to be more closely related to each other than to mollusks, largely based on their segmented bodies. In the molecular-based tree, arthropods are separated from both annelids and mollusks and are placed in the ecdysozoan clade. *** both are chordates but not vertebrates
Explain what we have learned about the evolution of life from the study of velvet worms.
Velvet worms confirm that changes in body form occurred because of changes in gene expression due to gene duplication and modification of switches rather than evolution of new genes. Velvet worms are evolutionarily ancient organisms. *** The same box genes that are present more modern organisms. Only the pattern of gene expression is different, reinforcing the ideas of the cambrian explosion. All genes were in place very early on. evolution rarely invents something new, just modifies an existing structure.
Describe the characteristics of lancelets.
They have all structures to be a chordate. They also have a notochord that goes the length of body and thus don't have a distinct head segment even though they have brains.
*** Describe the characteristics of hagfishes/lampreys.
Have a head because the notochord doesn't continue into the head making it a distinct structure. They are vertebrates *** They have mouths but they are not hinged, so their jaws do not work.
Describe the characteristics of chondrichthyans.
have skeletons made out of cartilage (developmentally cartilage becomes bone, ancestors likely had bone and lost it later in evolution), sharks and rays. They have a hinged jaw that evolved from the anterior most pharyngeal slits which were originally used for filtering food. In humans, the jaw bones make up the inner ear. slits used for gas exchange
***Describe the characteristics of ray-finned fishes.
have swim bladders which is used for holding air so that the fish can remain buoyant (that is homologous with tetrapod lungs), skeleton made of bone
***Describe the characteristics of lobe-finned fishes.
have bones in limbs that match the box expression of tetrapod limbs, swim bladder
Describe the characteristics of amphibians.
became tetrapods (vertebrates with two sets of limbs), still tied to water because they have to fertilize externally
Describe the characteristics of reptiles.
amniotic eggs enable internal fertilization and so reptiles aren't dependent on water for reproduction
Describe the characteristics of mammals.
nurse and care for their young, hair, mammary glands that produce milk
Name and describe the transitional species that occupy the range between fishes and amphibians in evolutionary history.
Tiktaalik was a transitional species between fish and amphibians. It had eyes on top, fins with three sets of bones, one long bone, two skinny bones, lots of little bones. lobed fin fish like paddle fish similar to common ancestor with tiktaalik. lung fish are lobed fin fish and use swim bladder like a lung. The fossil record for the transition from fish to tetrapod demonstrates that many of the tetrapod features evolved prior to becoming terrestrial organisms.
Distinguish between monotremes, marsupials, and placental mammals.
monotremes-egg laying mammal (duck-billed platypus
marsupials- short gestation (kangaroo)
placental mammals- long gestation (humans)
Compare the three main groups of living primates.
Lemurs, lorises, and tarsiers= primates bc have basica primate characteristics of joints that are flexible for climbing trees and swinging on branches, hands that are flexible for climbing trees and swimming
Anthropoids (monkey and apes) have opposable thumb. New World and Old World monkeys split. New World Monkeys have prehensile tails. Apes split from old world monkeys. Apes don't have tails. Chimpanzees and bonobos are most closely related to apes but we didn't evolve from chimps, we share our most recent common ancestor with them.
Describe the evidence that suggests that hominids didn't evolve in a straight line leading directly to our species.
There were many different branches in the human family tree. All hominids evolved in Africa. Each branch followed its own evolutionary path such that each developed a mosaic of characteristics some appearing more or less humanlike. It's difficult to know which were in the direct human line too because they coexisted and continued to exist after more modern hominids appeared. There is no "missing link as would be predicted by a gradualism pace of evolution where all features evolved at the same time, and so a halfway point fossil would need to be found. Nothing halfway between. The bottom evolved first before the top, which remained almost completely ape.
Describe the evidence that suggests when upright posture and large brains first evolved in humans.
To be a hominid, a mammal must be bipedal as evidence by a magnum foramen located beneath the skull. Also typically has reduced canine teeth which in other primates are used for intimidating others and so indicates a more cooperative social structure. Early hominid skeletons had pelvis shapes that were more similar to modern humans than to chimps but still had brains the same size as chimps. Bi=pedal walking evolved to get to more dispersed food patches because it is a very efficient form of locomotion.
Describe the evolution of larger brain size in hominins.
Brain size didn't begin to evolve until climate became variable. Increased brain size adaptation is thus to become adaptable to constantly changing environments. Increased use of tools enabled hominids to not be as dependent on jaws for processing food and obtaining nutrients and thus jaw muscles reduced in size, making room for bigger brains. Selected for bigger brains (relative to body size) and more complex brains (more interconnectedness of brain regions( for better tool making (anticipate flaws in stone) and tool use (more refined tools and throwing spears).
Describe the relationships between Neanderthals and modern humans. Describe the evidence that suggests that all modern humans share a common ancestor that lived 160,000-200,000 years ago.
Neanderthals and humans both evolved in Africa but Neanderthals migrated to Europe first. Humans followed and outcompeted/interbred with Neanderthals leading to Neanderthals extinction. Humans were hunter/gatherers so ate a wider variety of foods. Humans had smaller stature and so didn't have as hight energy demands as Neanderthals did.
Describe the unusual characteristics of the newly discovered Homo floresiensis.
Many different waves of hominids left Africa. Fossil evidence shows that other hominid species could have persisted until as recently as 13 TYA
What happened as humans left Africa? Are humans still evolving?
Huge bottleneck that reduced population of humans to between 2 and 10 thousand. As a result humans have very little genetic diversity as compared to other primates. Lack of genetic diversity helps explain why we haven't split into multiple species, also that we completely fill our nice. Humans are still evolving as evidenced by "hitchhiker" genes onto genes related to immunity to diseases.
List the characteristics that arthropods have in common.
Segmentation, exoskeleton, specialized jointed appendages
What four features do we share with invertebrate chordates, such as lancelets?
Human embryos and invertebrate chordates all have (1) a dorsal, hollow nerve cord, (2) a notochord, (3) pharyngeal slits; and (4) a post-anal tail
Researchers found the velvet worms and arthropods share the same set of homeotic genes. What conclusion did they draw from this result?
the evolution of diverse arthropod body segment types wasn't the result of new genes in arthropods
From what structure might the swim bladder of ray-finned fishes have evolved?
simple lungs of an ancestral species
In what ways are amphibians not completely adapted for terrestrial life?
Their eggs are not well protected against dehydration; many species have an aquatic larval form; their skin is not waterproof and must remain moist to permit gas exchange.
To which mammalian order do we belong? What are the three main groups of this order?
1. lorises, pottos, and lemurs
How can paleoanthropologists conclude that a species was bipedal based on only a fossil skull?
by the location of the opening where the spinal chord exits the skull
What types of evidence indicate that Homo sapiens originated in Africa?
fossils and analyses of mitochondrial DNA and chromosomal DNA
What characteristics prompted the discoverers of the "hobbit" to classify it in the genus Homo?
Humanlike skull characteristics and the apparent use of stone tools
What is the distinction between larva and adult stages?
Larva isn't capable of sexual reproduction but adults are.
What implications does the exoskeleton have for arthropods?
As the arthropod grows, it must periodically shed its old exoskeleton and secrete a larger one, a complex process called molting. This means that they cannot grow beyond a certain size without the exoskeleton crushing them. Must go through soft shell phase.