Biology 2 exam 4

in a hydra, digestion is completed A) intracellularly B) extracellularly C) in the alimentary canal D) in the gastrovascular cavity

A) intracellularly

Which extant chordates are postulated to be most like the earliest chordates in appearance? A) lancelets B) adult tunicates C) amphibians D) chonodrichthyans

A) lancelets

to reproduce, many plants produce seeds--structures containing embryonic offspring along with nutrients inside a tough coat. these offspring develop after being released by the parent plant. to which animal reproductive "strategy" is seed production most comparable? A) oviparous reproduction B) ovoviparous reproduction C) viviparous reproduction D) internal development and ballistic dispersal

A) oviparous reproduction

a trend first observed in the evolution of the earliest tetrapods was A) the appearance of jaws B) feet with digits C) the mineralization of the endoskeleton D) the amniotic egg

B) feet with digits

which of the following is (are) unique to animals? A) the structural carbohydrate, chitin B) nervous system signal conduction and muscular movement C) heterotrophy D) flagellated gametes

B) nervous system signal conduction and muscular movement

which of the following is a characteristic of all chordates at some point during their life? A) jaws B) post-anal tail C) four-chambered heart attack D) vertebrate

B) post-anal tail

whatever its ultimate cause(s), the cambrian explosion is a prime example of? A) mass extinction B) evolutionary stasis C) adaptive radiation D) a large meteor impact

C) adaptive radiation

the process by which digested dietary substances cross cell membranes to be used by the body is known as A) ingestion B) digestion C) hydrolysis D) absorption

D) absoprtion

which structure of the amniotic egg has most closely surrounds the embryo? A) the chorion B) the yolk sac C) the allantois D) the amnion

D) amnion

which of the following would you classify as something other than an animal? A) sponge B) coral C) jellyfish D) choanoflagellate

D) choanoflagellate

You find a new species of worm and want to classify it. Which of the following lines of evidence would allow you to classify the worm as a nematode and not an annelid? A) it is segmented B) it is triploblastic C) it has a coelom D) it sheds its external skeleton to grow

D) it sheds its external skeleton to grow

which tissue type or organ is NOT correctly matched with its germ layer tissue? A nervous-mesoderm B) muscular-mesoderm C) stomach-endoderm D) skin-ectoderm

A) nervous-mesoderm

which structure do sea slugs use to feed on their prey? A) nematocysts B) an incurrent siphon C) a radula D) a mantle cavity

C) a radula

which phylum is characterized by animals that have a segmented body? A) cnidaria B) platyhelminthes C) arthropoda D) mollusca

C) arthropoda

which of these are amniotes? A) amphibians B) fishes C) turtles D) lungfish

C) turtles

which of the following taxonomic groups is the most successful? A) fungi are the most successful, based on their ability to digest cellulose, the most common organic compund on earth B) bony fishes are the most successful, based on their high species diversity (almost as many as all other vertebrates combined) C) mammals are the most successful, based on their complex mode of reproduction D) all extant species are successful, based on their continuing existence

D) all extant species are successful, based on their continuing existence

the presence of a swim bladder allows the typically ray-finned fish to stop swimming and still A) effectively circulate its blood B) use its lateral line system C) use its swim bladder as a respiratory organ D) not sink

D) not sink

if a mammal did not obtain enough iodine in its diet, you might expect A) a decreased ability to produce thyroid hormones B) a decrease in enzyme function C) the animal to have weak bones D) a decrease in muscle function

A) a decreased ability to produce thyroid hormones

a land snail, a clam, and an octopus all share A) a mantle B) a radula C) gills D) distinct cephalization

A) a mantle

bone consists of A) a mixture of hardened collagen and minerals B) chondroitin sulfate secreted by chondrocytes C) many columnar epithelial cells packed together D) hardened fibrous connective tissue

A) a mixture of hardened collagen and minerals

Why do adult urochordates (tunicates) lack notochords, even though larval urochordates have them? Larvae use notochords to _____. A) aid in swimming; adults are sessile and thus no longer propel themselves B) stiffen their bodies; in adults, the notochord, is replaced by a column of bone C) induce tissue differentiation; in adults, tissue is already differentiated D) organize their nervous systems; adults nervous systems are fully developed and do not change

A) aid in swimming; adults are sessile and thus no longer propel themselves

what is the probable sequence in which the following animal clades originated, from earliest to most recent? A) bilaterians, deuterostomes, vertebrates, tetrapods, amniotes B) bilaterians, deuterstomes, amniotes, vertebrates, tetrapods C) deuterostomes, bilaterians, amniotes, vertebrates, tetrapods D) deuterostomes, bilaterians, vertebrates, tetrapods, amniotes

A) bilaterians, deuterostomes, vertebrates, tetrapods, amniotes

Cadherin proteins help animals stick (adhere) to each other. Choose which statement about cadherin in cancer cells that are metastasizing (spreading) throughout a patients body is most likely correct. A) cadherin proteins in metastasizing cancer cells are likely to have mutations that make them less "sticky" B) B) cadherin proteins in metastasizing cancer cells are likely to have mutations that make them more "sticky" C) mutations in cadherin proteins are unlikely to affect the metastasizing of cancer cells D) mutations in cadherin proteins accumulate at a constant rate that can be measured by a molecular clock

A) cadherin proteins in metastasizing cancer cells are likely to have mutations that make them less "sticky"

which of these statements, if accurate, would support the claim that the ancestral cnidarians had bilateral symmetry? A) cnidarian larvae possess anterior-posterior, left-right, and dorsal-ventral aspects B) cnidarians have fewer Hox genes than bilaterians C) all cnidarians are acoelomate D) the pressure of collar cells

A) cnidarian larvae posses anterior-posterior, left-right, and dorsal-ventral aspects

What was an early selective advantage of a coelom in animals? A coelom _____. A) contributed to a hydrostatic skeleton, allowing greater range of motion B) was a more efficient digestive system C) allowed cephalization and the formation of a cerebral ganglion D) allowed asexual and sexual reproduction

A) contributed to a hydrostatic skeleton, allowing greater range of motion

The sharp, inch-long thorns of the crown-of-thorns sea star are its spines. These spines, unlike those of most other sea stars, contain a potent toxin. If it were discovered that crown-of- thorns sea stars do not make this toxin themselves, then the most likely alternative would be that this toxin is _____. A) derived from the nematocysts of its prey B) absorbed from the surrounding seawater C) an endotoxin of cellulose-digesting bacteria that inhabit the sea star's digestive glands D) injected into individual thorns by mutualistic corals which live on the aboral surfaces of these sea stars

A) derived from the nematocysts of its prey

which of the following combinations correctly matches a phylum to its description? A) echinodermata--bilateral symmetry as a larva, water vascular system B) nematoda--segmented worms, closed circulatory system C) cnidaria--flatworms, gastrovascular cavity, acoelomate D) platyhelminthes--radial symmetry, polyp, and medusa body forms

A) echinodermata--bilateral symmetry as a larva, water vascular system

What group of mammals have (a) embryos that spend more time feeding through the placenta than the mother's nipples, (b) young that feed on milk, and (c) a prolonged period of maternal care after leaving the placenta? A) eutheria B) marsupiala C) monotremata D) lagomorpha

A) eutheria

which of the following is most likely to be aquatic? A) filter feeder B) mass feeder C) deposit feeder D) fluid feeder

A) filter feeder

sponges A) have larvae that are motile and move via the motion of cillia B) are the simplest diploblastic animals C) have a nerve net but not a central nervous system D) have feeding cells called dinoflagellates

A) have a larvae that are motile and move via the motion of cillia

which of these is least useful in assigning the phylum cycliophora to a clade of animals? A) having a true coelom B) having a body symmetry that permits a U-shaped intestine C) having embryos with spiral cleavage D) lacking ecdysis (molting)

A) having a true coelom as a body cavity

the process of obtaining food is known as ______ and requires specialized feeding mechanisms A) ingestion B) digestion C) absorption C) excretion

A) ingestion

Blood is best classified as connective tissue because A) its cells are separated from each other by an extracellular matrix B) it contains more than one type of cell C) its cells can move from place to place D) it is found within all the organs of the body

A) its cells are separated from each other by an extracellular matrix

if you think of the earthworm body plan as a drinking straw within a pipe, where could you expect to find most of the tissues that developed from endoderm? A) lining the straw B) lining the space between the pipe and the straw C) forming the outside of the pipe D) forming the outside of the straw

A) lining the straw

As animals have evolved large body size, they have also evolved adaptations to improve exchange of energy and materials with the environment. For example, in many larger organisms, evolution has favored lungs and a digestive tract with ________. A) more branching or folds B) increased thickness C) larger cells D) decreased blood supply

A) more branching or folds

The nematocysts of sea slugs should be most effective at protecting individual sea slugs from predation if the predators A) remove small bites of flesh from sea slugs and have long-term memory B) remove small bites of flesh from sea slugs and have no long-term memory C) consume entire sea slugs in one gulp and have no long-term memory D) consume entire sea slugs in one gulp and have long-term memory

A) remove small bites of flesh from sea slugs and have long-term memory

cardiac muscle cells are both A) striated and interconnected by intercalated disk B) smooth and under voluntary control C) its cells can move from place to place D) smooth and under involuntary control

A) striated and interconnected by intercalated disk

What is believed to be the most significant result of the evolution of the amniotic egg? A) tetrapods are no longer tied to the water for reproduction B) tetrapods can now function with just lungs C) newborns are much less dependent on their parents D) embryos are protected from predators

A) tetrapods are no longer tied to the water for reproudction

which of the following T. adhaerens traits is different from all other known animals? A) T. adhaerens is multicellular B) T. adhaerens lacks muscle and nerve cells C) T. adhaerens has cillia D) T. adhaerens lacks cell walls

B) T. adhaerens lacks muscle and nerve cells

An advantage of a complete digestive system over a gastrovascular cavity is that the complete system A) excludes the need for extracellular digestion B) allows for specialized regions with specialized functions C) allows extensive branching D) facilitates intracellular digestion

B) allows for specialized regions with specialized functions

In terms of food capture, which sponge cell is most similar to the cnidocyte of a cnidarian? A) amoebocyte B) choanocyte C) epidermal cell D) pore cell

B) choanocyte

jaw first occurred in which extant group of fishes? A) lampreys B) chondrichthyans C) ray-finned fishes D) placoderms

B) chondricthyans

A researcher is trying to construct a molecular-based phylogeny of the entire animal kingdom. Assuming that none of the following genes are absolutely conserved, which of the following would be the best choice on which to base the phylogeny? A) genes involved in chitin synthesis B) collagen genes C) genes involved in directing segmentation development D) genes involved in eye-lens synthesis

B) collagen genes

Lysine is an essential amino acid for animals. If an animal did not consume lysine in its diet, you might expect that the animal ________. A) would make lysine from other amino acids B) could not effectively make many necessary proteins C) was a carnivore D) would be very healthy

B) could not effectively make many necessary proteins

Much of the coordination of vertebrate body functions via chemical signals is accomplished by the _____. A) respiratory system B) endocrine system C) integumentary system D) excretory system

B) endocrine system

while looking at some seawater through your microscope, you spot the egg of an unknown animal. which of the following tests could you use to determine whether the developing organism is a protostome or deuterostome? see whether the embryo A) develops germ layers B) exhibits spiral cleavage or radial cleavage C) develops a blastospore D) develops an archenteron

B) exhibits spiral cleavage or radial cleavage

the water vascular system of echinoderms A) functions as a circulatory system that distributes nutrients to body cells B) functions in locomotion and feeding C) is bilateral in organization, even though the adult animal is not bilaterally symmetrical D) is analogous to the gastrovascular cavity of flatworms

B) functions in locomotion and feeding

which of these, if discovered among cycliophorans, would cause the most confusion concerning our current understanding of cycliophoran taxonomy? A) if the cilliated feeding ring is a lophophore B) if embryos are diploblastic C) if the body cavity is actually a pseudocoelom D) if the organism show little apparent cephalization

B) if embryos are diploblastic

You find what you believe is a new species of animal. Which of the following characteristics would enable you to argue that it is more closely related to a flatworm than it is to a roundworm? A) it is a suspension feeder B) it has no coelom C) it is shaped like a worm D) it has a mouth and an anus

B) it has no coelom

While sampling marine plankton in a lab, a student encounters large numbers of fertilized eggs. The student rears some of the eggs in the laboratory for further study and finds that the blastopore becomes the mouth. The embryo develops into a trochophore larva and eventually has a true coelom. These eggs probably belonged to a(n) A) echinoderm B) mollusk C) nematode D) arthropod

B) mollusk

You find a multi-legged animal in your garden and want to determine if it is a centipede or a millipede. You take the animal to a university where a myriapodologist quickly tells you that you have found a centipede. Which of the following may have allowed her to make this distinction? A) the presence of body segments B) poisonous claws C) egg-laying D) molting

B) poisonous claws

Food moves along the digestive tract as the result of contractions by A) cardiac muscle B) smooth muscle C) striated muscle D) skeletal muscle

B) smooth muscle

Chordate pharyngeal slits appear to have functioned first as A) the digestive systems opening B) suspension-feeding devices C) components of the jaw D) sites of respiration

B) suspension-feeding devices

birds are descended from species that laid eggs in water. it could be that embryos of birds still develop in water because A) the shell keeps the embryo from drying out B) the amnion encases each embryo in water C) the chorion, allantois, and yolk sac provide embryos with nutrients and waste disposal D) the amnion protect the embryo in the same way that a seed coat protects plant embryos of flowering plants

B) the amnion encases each embryo in water

An example of a properly functioning homeostatic control system is seen when A) the core body temperature of a runner rises gradually from 37 degrees C to 45 degrees C B) the kidneys excrete salt into the urine when dietary salt levels rise C) a blood cell shrinks when placed in a solution of salt and water D) the blood pressure increases in response to an increases in blood volume

B) the kidneys excrete salt into the urine when dietary salt levels rise

Suppose a researcher for a pest-control company developed a chemical that inhibited the development of an embryonic mosquito's endodermal cells. Which of the following would be a likely mechanism by which this pesticide works? A) the mosquito would develop a weakened exoskeleton that would make it vulnerable to trauma B)the mosquito would have trouble with respiration and circulation, due to impaired muscle function D) the mosquito wouldn't be affected at all

B) the mosquito would have trouble digesting food, due to impaired gut function

It is believed that the coelacanths and lungfish represent a crucial link between other fishes and tetrapods. What is the major feature in these fish in support of this hypothesis? A) like amphibians, they are tied to the water for reproduction B) their fins have skeletal and muscular structures similar to amphibian limbs C) they have highly evolved nervous and circulatory system D) they have lungs and are able to breathe air when water is scarce

B) their fins have skeletal and muscular structures similar to amphibian limbs

Fat digestion yields fatty acids and glycerol, whereas protein digestion yields amino acids; both digestive processes A) are catalyzed by the same enzyme B) use water molecules when breaking bonds (hydrolysis) C) require the presence of hydrochloric acid to lower pH D) require adenosine triphophate (ATP) as an energy source

B) use water molecules when breaking bonds

Arrange these groups in order from most inclusive (most general) to least inclusive (most specific). 1. lobe-fins 2. amphibians 3. gnathostomes 4. osteichthyans 5. tetrapods A) 4, 3, 1, 5, 2 B) 4, 3, 2, 5, 1 C) 3, 4, 1, 5, 2 D) 3, 4, 5, 1, 2

C) 3, 4, 1 , 5, 2

which characteristic is shared by cnidarians and flatworms? A) dorsoventrally flattened bodies B) radial symmetry C) a digestive system with a single opening D) a distinct lead

C) a digestive system with a single opening

interestitial fluid is A) the internal environment inside animal cells B) identical to blood in comparison C) a site of exchange between blood and body cells D) found only in the lumen of the small intestine

C) a site of exchange between blood and body cells

In many animals, fat is stored in specialized cells in the ________. A) bone B) muscle C) adipose tissue D) blood

C) adipose tissue

Suppose, while out camping in a forest, you found a chordate with a long, slender, limbless body slithering across the ground near your tent. This critter could be _____. A) a lamprey B) a mammal C) an amphibian D) a skate

C) an amphibian

soon after the coelom begins to form, a researcher injects a dye into the coelom of a deuterostome embryo. initially, the dye should be able to flow directly into the A) blastopore B) blastocoel C) archenteron D) pseudocoelom

C) archenteron

which of the following are the only extant animals that descended directly from dinosaurs? A) lizards B) crocodiles C) birds D) tuataras

C) birds

The fact that choanoflagellates and collar cells of sponges resemble each other supports the inference that A) choanoflagellates are animals B) choanoflagellates are more closely related to sponges than they are to protists C) choanoflagellates and sponges are sister groups D) choanoflagellates and sponges evolved similar cell structures through convergent evolution

C) choanoflagellates and sponges are sister groups

in figure 33.3 which two main clades branch from the most recent common ancestor of the eumetazoans? A) porifera and cnidaria B) lophotrochozoa and ecdysozoa C) cnidaria and bilateria D) deuterostomia and bilateria

C) cnidaria and bilateria

Ticks are parasites that obtain nutrients by ingesting blood from a host animal. Ticks would be classified as ________. A) filter feeders B) substrate feeders C) fluid feeders D) bulk feeders

C) fluid feeders

arthropod exoskeletons and mollusc shells both A) completely replace the hydrostatic skeleton B) are secreted by the mantle C) help retain moisture in terrestrial habitats D) are comprised of the polysaccharide chitin

C) help retain moisture in terrestrial habitats

the body's automatic tendency to maintain a constant and optimal internal environment is termed as A) balanced equilibrium B) physiological chance C) homeostasis D) static equilibrium

C) homeostasis

fossils of the earliest tetrapods should A) show evidence of internal fertilization B) show evidence of having produced shelled eggs C) indicate limited adaptation to life on land D) feature the earliest indications of the appearance of jaws

C) indicate limited adaptation of life on land

How did the evolution of the jaw contribute to diversification of early vertebrate lineages? A) it allowed for smaller body size B) it was the first stage in development of a bony skull C) it made additional food sources available D) it increased the surface area for respiration and feeding

C) it made additional food sources available

you have before you a living organism, which you examine carefully. which of the following should convince you that the organism is acoelomate? A) it is triploblastic B) it has bilateral symmetry C) is possesses sensory structures at its anterior end D) muscular activity of its digestive system distorts the body wall

C) it possesses sensory structures at its anterior end

Which shark structure is closest in function to a swim bladder full of gas? A)its lateral line system B) its spiral valve C) its liver D) its gills

C) its liver

Primate evolution and behavior, such as hunting skills, have been directed in part by the development of depth perception. What anatomical change made depth perception possible? A) a larger brain B) the formation of compound eyes C) location of the eyes at the front of the head D) diurnal activity

C) location of the eyes at the front of the head

guppies are a common aquarium fish. they have internal fertilization, and females give birth to young that can swim immediately. which of the following statements is correct? A) most fish reproduce like guppies B) guppies reproduce by producing swimming young because they are related to marsupials C) most fish reproduce by laying eggs D) most fish produce amniote eggs

C) most fish reproduce by laying eggs

The heartworms that can accumulate within the hearts of dogs and other mammals have a pseudocoelom, an alimentary canal, and an outer covering that is occasionally shed. To which phylum does the heartworm belong? A) platyhelminthes B) arthropoda C) nematoda D) annelida

C) nematoda

muscle cells are organized to perform specific types of contractions within a tissue. which of the following is a characteristic of smooth muscle? A) many cells fused together B) intercalated disk C) spindle-shaped cells with a single nucleus D) striations with sacromeres

C) spindle-shaped cells with a single nucleus

Among mammals, it is generally true that A) all types of foods begin their enzymatic digestion in the mouth. B) after leaving the oral cavity, the bolus enters the larynx. C) the epiglottis prevents swallowed food from entering the trachea. D) the esophagus is a key source of digestive enzymes. E) the trachea leads to the esophagus and then to the stomach.

C) the epiglottis prevents swallowed food from entering the trachea.

Penguins, seals, and tuna have body forms that permit rapid swimming, because A) all share a recent common ancestor B) all of their bodies have been compressed since birth by intensive underwater pressures C) the shape is a convergent evolutionary solution, which reduces drag while swimming D) this is the only shape that will allow them to maintain a constant body temperature in water

C) the shape is a convergent evolutionary solution, which reduces drag while swimming

which of these statements accurately describes a similarity between sharks and ray-finned fishes? A) they are equally able to exchange gases with the environment while stationary B) they are highly maneuverable due to their flexibility C) they have a lateral line that is sensitive to vibrations D) a swim bladder helps control buoyancy

C) they have a lateral line that is sensitive to vibrations

Examine the digestive system structures in the figure. the agents that help emulsify fats are produced in location A) 1 B) 3 C) 8 D) 9

D) 9

the increase in plant species diversity allowed which of the following events? A) the evolution of complete metamorphosis in insects B) the evolution of flight in insects C) invasion of marine habitats by insects D) a massive increase in species diversity of insects

D) a massive increase in species diversity of insects

which of the following organisms would you expect to have the largest surface-area-to-volume ratio? A) a mollusk B) an annelid C) an arthropod D) a platyhelminth

D) a platyhelminth

which of the following characteristics is shared by a hagfish and a lamprey? A) a rasping tongue B) paired fins C) jaws D) well-developed notochord

D) a well developed notochord

a terrestrial animal species is discovered with the following larval characteristics: exoskeleton. system of tubes for gas exchange, and modified segmentation. a knowledgeable zoologist should predict that the adults of this species would also feature A) eight legs B) two pairs of antennae C) a sessile lifestyle D) an open circulatory system

D) an open circulatory system

which of the following statements comparing symmetry in sessile and swimming animals is most probable? A) radial symmetry is more advantageous for active swimming than is bilateral symmetry B) radial symmetry occurs most frequently in animals that catch their prey by rapid swimming C)bilateral symmetry allowed animals to evolve nerves D) bilateral symmetric animals can be streamlined for swimming, but radially symmetric animals cannot

D) bilateral symmetric animals can be streamlined for swimming, but radially symmetric animals cannot

What would be the best anatomical feature to look for to distinguish a gastropod from a chiton? A) presence of a muscular foot B) presence of a rasp-like feeding structure C) production of eggs D) dorsal plates

D) dorsal plates

which of the following characteristics evolved independently in mammals and birds? A) amniotic eggs B) jaws C) bone D) endothermy

D) endothermy

Most of the exchange surfaces of multicellular animals are lined with A) connective tissue B) smooth muscle cells C) neural tissue D) epithelial tissue

D) epithelial tissue

Animals that migrate great distances would obtain the greatest energetic benefit of storing chemical energy as A) proteins B) minerals C) carbohydrates D) fats

D) fats

Compared to insects with incomplete metamorphosis, insects with complete metamorphosis A) grow more slowly in size B) use a greater variety of food resources C) have slower population growth rates D) have better abilities to escape from metamorphosis

D) have better abilities to escape from predators

which organ system is responsible for protection against injury, infection, and dehydration? A) reproductive system B) excretory system C) skeletal system D) integumentary system

D) integumentary system

what do animals ranging from corals to monkeys have in common? A) a mouth and an anus B) number of embryonic tissue layers C) some type of body symmetry D) presence of Hox genes

D) presence of Hox genes

connective tissue typically have A) little space between the membranes of adjacent cells B) the ability to transmit electrochemical impulses C) the ability to shorten upon stimulation D) relatively few cells and a large amount of extracellular matrix

D) relatively few cells and a large amount of extracellular matrix

Why do skates and rays have flattened bodies, while sharks are torpedo shaped? A) sharks are more closely related to the tube-like lampreys than are skates and rays B) skates and rays need enlarged pectoral fins to help them stay level in turbulent water, while sharks do not C) skates and rays exchange gases across their skin and thus require a high surface-area-to-volume ratio, while sharks do not D) Sharks are streamlined for active swimming at mid-depths, while skates move about mostly on the ocean bed

D) sharks are streamlined for active swimming at mid-depths, while skates move about mostly on the ocean bed

in the digestive system, peristalsis is A) a process of fat emulsification in the small intestine B) voluntary control of the rectal sphincters regulating defecation C) the transport of nutrients to the liver through the hepatic portal vessel D) smooth muscle contractions that move food along the esophagus

D) smooth muscle contractions that move food along the esophagus

one should expect to find cillia associated with the feeding apparatus of A) annelids B) coral animals C) tapeworms D) sponges

D) sponges

what do all deuterostomes have in common? A) adults are bilaterally symmetrical B) embryos have pharyngeal pouches that may or may not form gill slits C) all have a spinal column D) the spore (blastopore) formed during gastrulation becomes the anus

D) the spore (blastospore) formed during gastrulation becomes the anus

which of the following statements about human evolution is correct? A) modern humans are the only human species to have evolved on earth B) human ancestors were virtually identical to extant chimpanzees C) human evolution has occurred within an unbranched lineage D) the upright posture and enlarged brain of humans evolved seperately

D) the upright posture and enlarged brain of humans evolved seperately