In 1758, Carloius Linnaeus placed man in the order primates, which includes a number of Eutherian Mammals. Primate, in Latin ‘Premees” literally means one who is first – in order of time, rank and importance. All primates share certain general characteristics and there are certain evolutionary trends, which are unique to this order.
In general the primates have the following characteristics:
- i) Presence of nails on digits instead of claws.
- ii) Only one pair of thoracicalfy placed mammary glands.
- iii) Prehensile hands and feet, which are, used as grasping organs.
- iv) Well-developed clanicle.
- v) Bony orbit completely enclosed at the back.
- vi) Free mobility of digits.
- vii) Opposability of at least one first digit to the remaining digits.
- viii) Well-marked power grip and pressure grip.
- ix) Orbits are directed forwarded instead of to the side.
- x) Cerebral hemispheres of the brain are enlarged.
Since man has all these characteristics he is included under the order primates.
The Unique characteristics of Primates:
- a) Ability to rotate fore arm in or out, up or down and stretching of legs to a much greater extent than other mammals.
- b) Primates depend more upon their eyes than upon their noses.
- c) There is progressive reduction of the snout or muzzle.
- d) There is increased perfection of the visual appartus with the development of binocular vision.
- e) Increased refinement of hands and feet as grasping organ.
- f) Retention of the primitive mammalian pentadactylism (five fingers and five toes),
- g) Presence of very sensitive tactile pads on fingers and toes which show high degree of mobility.
- h) They possess highly dev eloped and convoluted (well-folded) brain provided with much wrinkled cortex. A high brain-to-body ratio is the specific characteristic feature of primates.
- i) The olfactory centre of the brain is characterized by marked degree in size proportionate.
- j) There is an increased eye-hand coordination and mammal dexterity.
- k) The male primates have pendulous penis.
- L) Teeth are specially meant for mixed diet. The simple cusp pattern and the molar teeth is retained.
- m) The sexual cycle of the female varies from a single ovulation per year to as many as twelve per year.
- n) Females have a tendency to bear only one baby at a time multiple births are rare.
- o) The gestation period has been lengthened.
- p) Thenatural life span has been markedly increased.
- q) There is simple type of stomach.
- r) Primates are not characterized by seasonal sex behavior; they have a year round fertility.
- s) Primate infants have prolonged physical and emotional dependence on their mothers.
- t) Primates have developed an increasing ability for adaptation to diversified ecological conditions.
- u) Primates are the most social of all the mammalian groups.
- v) Growth and maturation period have been longer compared to other animal groups.
- w) The primates are of varied sizes; they range from the very small sized microcebus to the huge sized Gorillas.
- x) There is a progressive development of trunckal uprightness, which leads to the facultative bi-pedalism.
- y) The vocalization pattern and social behavioral activities like grooming, infant care and vigilance have acquired conspicuous complexity.
Since man possesses all the above characteristics to a greater or lesser extent he is inclined in the order Primate. As a primate, man’s most significant characteristic is his increased ability to adjust himself to varying environmental conditions rather than to specific environments. Thus, man stands as a unique one among the primates.
Recent Advances:
Genomic Similarity:
- For example, humans share approximately 98-99% of their DNA with chimpanzees, our closest living relatives. This high degree of genetic similarity indicates a recent common ancestry.
Chromosome Structures:
- Human and primate chromosomes exhibit structural similarities. For instance, humans have 23 pairs of chromosomes, while chimpanzees, gorillas, and orangutans have 24 pairs. The difference is due to a fusion event in human ancestry where two ancestral ape chromosomes fused end-to-end to form human chromosome 2. This fusion is evidenced by the presence of vestigial telomere sequences at the fusion site and an inactivated centromere.
Shared Genetic Sequences:
- Specific genes and sequences are highly conserved across primate species. Genes involved in fundamental biological processes, such as those regulating development, metabolism, and neural function, show remarkable similarity. For example, the FOXP2 gene, involved in speech and language, is nearly identical in humans and other primates, although humans have two unique amino acid changes that are thought to play a role in our advanced language abilities.
Mitochondrial DNA (mtDNA) and Y Chromosome Studies:
- These studies show that humans and other primates share recent common ancestors. The patterns of variation in mtDNA and Y chromosome sequences among primate species are consistent with the evolutionary tree constructed from nuclear DNA evidence.