Text 6.4. Human Evolution: Primate Ancestors
■ Essential targets:
By the end of this text you should be able to:
● explain the significance of the adaptations of primates to an arboreal mode of life.
Pre-reading
■ With your partner try and answer these two questions. Then see if you were right by quickly scanning the text.
1. Do you agree with the statement that all humans are descendent from a common ancestor?
2. How do modern primates differ from their ancestral primates?
■ Read the given text and make your essential assignments:
The theory of evolution applies just as much to humans as to other organisms. All humans are in the same way related and, in the words of Darwin, are “descended with modification” from a common ancestor. Although our social and technological developments have freed us from many of the effects of natural selection, our present-day physical and behavioural characteristics are rooted in the adaptations of our ancestors. So, by finding out more about our ancestors, we can learn more about ourselves.
Adaptation of primates
T
he classification of humans reflects our evolutionary relationships. About 150-170 million years ago, all mammals were small insectivores rather like the shrews of today. About 75 million years ago some of these insectivores adopted an arboreal (tree-dwelling) mode of life and evolved into lemur-like primates. The adaptations of these ancestral primates to their new tree-living mode of life are thought to have included a short nose, large eyes and prominent ears, long flexible fingers with nail-like claws, and teeth well adapted for eating insects. These features are found in tarsiers (lemur-like primates) living today in Indonesia. Many other features that evolved in ancestral primates as adaptations to an arboreal life have been retained by modern primates.
These features include:
- A prehensile (grasping) limb: the hands (and often the feet) of primates have long and highly mobile digits so that they can grasp the branches of trees. The first digit can oppose the remaining four digits, giving primates a powerful grip. Primates have flattened nails that support pads of sensitive skin on the fingers or toes.
- A mobile forearm: the clavicle (collar bone) and scapula (shoulder blade) are adapted to allow a wide range of movements. Mobile forearms are essential for moving from tree to tree, and for manipulating objects in the hand; for example, to transfer food to the mouth or to bring an object to the eyes for closer examination.
- Well developed stereoscopic vision: the ability to judge distances is essential for leaping from branch to branch. Primates have large, well developed, forward-looking eyes with overlapping fields of view. The development of stereoscopic vision has been associated with a flattening of the face.
- A reduce sense of smell: it is not easy to locate scents through the canopies of trees and primates have a reduced sense of smell and a relatively small nose. Combined with the flattering of the face, a shorter nose is associated with the development of stereoscopic vision, and has allowed the development of facial muscles which play an important part in non-verbal communication.
- An inspecialised digestive system: primates have relatively unspecialised teeth and guts and they can exploit a wide range of food sources. Although some primates have a specialized herbivorous diet, all primate families have some omnivorous members that have a mixed diet.
- A skull modified for upright posture: primates have an upright posture associated with having a forward-looking face. The skull rests on top of the vertebra and has a large opening, the foramen magnum, though which the medulla of the brain emerges and extends downwards as the spinal cord.
- Reduced number of offspring: life in the trees is difficult and dangerous, especially for young animals. Some arboreal animals, such as birds and squirrels, build nests in which the young can be protected until they are old enough to fend for themselves. Primates have adopted another strategy: from birth, the young cling to the mother’s body and only slowly gain independence. Primates produce few young but look after them for a long time: they have a long gestation period a prolonged period of dependency after birth.
- A large brain: an active life in the trees requires precise movements and therefore good muscular coordination, vision, tactile senses, memory, thought, and learning. These processes depend on a large and highly developed brain.
- A social groupings: all primates live to some degree in social groups in
which members cooperate with each other. Complex social behaviour probably stems from the strong pair bond which enables a mother and her young to remain closely together for a long time. Lengthy rearing of a small number of young is most successful when he mother has support from other adults. The continued success of a group of animals depends on the recruitment of young helpers, and so evolves a social interdependency which is the basis of our own human society.
The groups of modern primates
At about the same time as the dinosaurs became extinct, about 65 million years ago, the primitive primates diverged quickly to give rise to two main suborders; the prosimians (meaning “before apes”) and anthropoids (meaning “ape fom”). The prosimians are represented today by lemurs, lorises, and tarsiers, and the anthropoids by monkeys, apes, and humans.
Monkeys are distinguished from apes in having long tails, and the forelimbs are not usually longer than the hindlimbs. They are believed to have evolved from two different groups of lemur-like animals which became isolated when continental drift separated Eurasia from North America. The North American group evolved into New World monkeys which died out in North America but somehow colonised South America. The Eurasia group gave rise to Old World monkeys, from which apes and humans evolved. There are several differences between Old World monkey and New World monkeys which show their separate evolution. For example, the nostrils of monkeys from South America are wide open and far apart, and New World monkeys have a long tail that is prehensile (adapted for grasping branches); the nostrils of monkeys from Africa and Asia are narrow and close together and no old World monkey has a prehensile tail.
■ Glossary of essential terms for you to know
№
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English term
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Russian equivalent
|
1
|
to descend
|
происходить
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2
|
common
|
общий
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3
|
behaviour
|
поведение
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4
|
to be rooted in
|
корнями уходит в…
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5
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adaptation
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адаптация, приспособление
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6
|
ancestor
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предок
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7
|
to find out
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выяснить, обнаружить
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8
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to retain
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сохранять
|
9
|
relationship
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взаимосвязь, родство
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10
|
mammal
|
млекопитающее животное
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11
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insectivores
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насекомоядное животное
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12
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shrew
|
землеройка
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13
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arboreal
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древесный
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14
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mode
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способ
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15
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prominent
|
заметный
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16
|
finger
|
палец руки
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17
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toe
|
палец ноги
|
18
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claw
|
коготь
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19
|
nail
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ноготь
|
20
|
flexible
|
гибкий
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21
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to reduce
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уменьшать
|
22
|
well adapted
|
хорошо приспособленный
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23
|
insects
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насекомые
|
24
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feature
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черта, особенность
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25
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prehensile (syn. grasping)
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хватательный
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26
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limb
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конечность
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27
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digit
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палец (руки или ноги)
|
28
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branch
|
ветка
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29
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grip
|
схватывание
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30
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to flatten
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выравнивать
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31
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to support
|
поддерживать
|
32
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sensitive
|
чувствительный
|
33
|
skin
|
кожа
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34
|
forearm
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предплечье
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35
|
clavicle
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ключица
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36
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scapula
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лопатка
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37
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essential
|
необходимый
|
38
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to transfer
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перемещать
|
39
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vision
|
зрение
|
40
|
to leap
|
прыгать
|
41
|
scent
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запах
|
41
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guts
|
кишки
|
42
|
omnivorous
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всеядный
|
43
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skull
|
череп
|
44
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upright
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вертикальный
|
45
|
posture
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положение
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46
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vertebra
|
позвонок
|
47
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spinal cord
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спинной мозг
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48
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to reduce
|
уменьшать
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49
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nest
|
гнездо
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50
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to fend
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давать отпор
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51
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brain
|
мозг
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52
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tactile senses
|
чувства осязания
|
53
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bond
|
связь
|
54
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forelimb
|
передняя конечность
|
55
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hindlimb
|
задняя конечность
|
56
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nostril
|
ноздря
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57
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tail
|
хвост
|
■ Your Essential Assignments
I. Quick check:
1. Primates evolved as a group adapted to an arboreal mode of life. Briefly explain the importance of the following adaptions:
a. reduced sense of smell
b. opposable thumb
c. small, single uterus
d. flexible pectoral girdle.
II. Fill in the missing words:
Term (verb)
|
Noun
|
Adjective
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reflect
|
.......
|
.......
|
adapt
|
.......
|
.......
|
grasp
|
.......
|
.......
|
depend
|
.......
|
.......
|
support
|
.......
|
.......
|
extinguish
|
.......
|
.......
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separate
|
…….
|
……
|
III. Use monolingual English dictionary and write down what could the words given below mean:
vision, limb, adaptation, modern, independence.
IV. Match these words with their definitions:
1
|
primate
|
A.
|
an animal that eats both meat plants
|
2
|
modern
|
B.
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the smell of a particular animal or person that some other animals, for example dogs, can follow
|
3
|
insectivore
|
C.
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able to move easily
|
4
|
mammal
|
D.
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an animal is very like a human
|
5
|
omnivore
|
E.
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the bones of person’s or animal’s head
|
6
|
brain
|
F.
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a creature that eats insects for food
|
7.
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scent
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G.
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connected with trees or living in trees
|
8.
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mode
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H.
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time belonging to the present time
|
9.
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ape
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I.
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the organ inside your head that controls how you think, feel and move
|
10
|
mobile
|
J.
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one of the class of animals that drinks milk from its mother’s body when it is young
|
11
|
digestion
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K.
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a member of the group of mammals that includes humans and monkeys
|
12.
|
arboreal
|
L.
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a large monkey without a tail, or with a very short tail
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13.
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skull
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M.
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concerning human society and its organization, or the quality of people’s lives
|
14.
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social
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N.
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a particular way or style of behaving, living or doing something
|
15.
|
anthropoid
|
O.
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the process of digesting food
|
V. Find English equivalents to the following word combinations:
№
|
Russian term
|
English equivalent
|
1.
|
в некоторой степени
|
|
2.
|
физические и поведенческие характеристики
|
|
3.
|
хватать ветки деревьев
|
|
4.
|
нежная кожа на пальцах руки или ноги
|
|
5.
|
подвижное предплечье
|
|
6.
|
подносить предмет к глазам для внимательного изучения
|
|
7.
|
хорошо развитое зрение
|
|
8.
|
пищеварительная система
|
|
9.
|
смешанная диета
|
|
10.
|
большой и высоко развитый мозг
|
|
11.
|
передние и задние конечности
|
|
12.
|
несколько различий
|
|
13.
|
хватательный хвост
|
|
VI. Give Russian equivalents to the following English terms:
№
|
English term
|
Russian equivalent
|
1
|
descended with modifications from a common ancestor
|
|
2
|
arboreal mode of life
|
|
3
|
ancestral primates
|
|
4
|
well adapted for eating insects
|
|
5
|
a prehensile limb
|
|
6
|
to allow a wide range of movements
|
|
7
|
to transfer food to the mouth
|
|
8
|
to locate scents
|
|
9
|
upright posture
|
|
10
|
spinal cord
|
|
11
|
a prolonged period of dependency after birth
|
|
12
|
precise movements
|
|
13
|
social grouping
|
|
14
|
complex social behaviour
|
|
VII. Find synonyms among the pool of words:
Pool of words
|
Synonyms
|
1)1.descend /2.grip /3.grasp /4.originate
|
|
2)1.digit/2.bond/3.scent/4.finger/5.link/6.smell /7.toe
|
|
3)1.feature /2. limb /3.characteristic /4. arm /5. leg
|
|
4)1.primitive /2.independence /3. freedom /4. ancient
|
|
VIII. Answer the following questions. Use all information given before:
What has freed us from many of the effects of natural selection?
2. What does “arboreal mode of life” mean?
3. What features did ancestral primates have?
4. What features have been retained by modern primates?
5. What are the two main groups of modern primates?
6. How are monkeys distinguished from apes?
IX. Match the sentence halves. Make complete sentences:
1.
|
Although our social and technological developments have freed us from many of the effects of natural selection,
|
A.
|
can be protected until they are old enough to fend for themselves.
|
2.
|
About 75 million years ago some of these insectivores adopted an arboreal
|
B.
|
and for manipulating objects in the hand.
|
3.
|
Primates have flattened nails that support pads
|
C.
|
(tree-dwelling) mode of life and evolved into lemur-like primates.
|
4.
|
Mobile forearms are essential for moving from tree to tree,
|
D.
|
and they can exploit a wide range of food sources.
|
5.
|
The development of stereoscopic vision has been associated
|
E.
|
our present-day physical and behavioural characteristics are rooted in the adaptations of our ancestors.
|
6.
|
Primates have relatively unspecialized teeth and guts
|
F.
|
of sensitive skin on the fingers or toes.
|
7.
|
Some arboreal animals, such as birds and squirrels, build nests in which the young
|
G.
|
the prosimians (meaning “before apes”) and anthropoids (meaning “ape fom”).
|
8.
|
The primitive primates diverged quickly to give rise to two main suborders;
|
H.
|
with a flattening of the face.
|
X. Read and translate the short text without any dictionary:
Fact of life:
Lemurs are cat-like primates that live exclusively in the tropical rainforests of Madagascar. It is thought that ancestral lemurs became isolated on the island about 50 million years ago and gradually diversified into 40 species. Lemurs have retained numerous primitive characteristics while at the same time developing many features in parallel with monkeys and apes that evolved on the mainland. During this evolution, body mass gradually increased (the ancestral species was very small) which corresponds with a shift away from mainly nocturnal (night-time) activity to diurnal (day-time) activity. This evolutionary trend is also seen among the monkeys and apes. Primitive lemur species are small nocturnal animals that spend nearly all their time climbing and leaping in trees, living mainly on insects. Several other species of lemur (including Lemur catta) live on the ground. These more advanced lemurs evolved to live in social groups, associated with their becoming diurnal.The young grow up within a troop and much time is spent learning the skills of life, individuals cooperate within the group to gather (fruit and leaves as well as insects) and avoid predators. However, none of the lemurs have the manual dexterity or intelligence of apes and monkeys.
XI. Food for thought:
Suggest how stereoscopic vision evolved by natural selection in arboreal primates.
Biology Jokes
Biology and humor, as most students know, don`t usually go hand in hand. It`s always nice, however, to step back and take a humorous look at biology. Below is a listing of biology terms and their possible meanings. Remember this is just for fun!
Humorous Biology Definitions
Antibody not in favor of anybody.
Amphibian someone who tells lies.
Aphotic doesn`t like to take pictures.
Axon the name of a gas station.
B cell prison cell block.
Biogeography where I live.
Blood pressure persistent relatives.
Fauna likes (as in I am fauna you)
Fertilize very big lies.
Homeostasis stays at home.
Interferon to get in the way.
Microbodies short people.
Node past tense of know.
Organelle a small musical instrument.
Seed past tense of see.
Remember this is just for fun!
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