MAN'S PLACE IN NATURE

OR

NATURE'S PLACE IN MAN

Zoologically, mankind (collective singular) is a member of the phylum Chordata, subphylum Vertebrata, class Mammalia, infraclass Eutheria, order Primates, suborder Anthropoidea, superfamily Hominoidea, family Hominidae, genus Homo, species sapiens.

• Members of the phylum Chordata have 4 distinguishing characteristics:

1. A dorsal notochord

2. A dorsal hollow nerve cord

3. Pharyngeal gill slits

4. A postanal tail

• In addition, members of the subphylum Vertebrata possess an internal skeleton surrounding the brain and spinal cord. The 8 classes of vertebrates include the:

1. Agnatha

2. Placodermi

3. Chondrichthyes

4. Osteichthyes

5. Amphibia

6. Reptilia

7. Aves

8. Mammalia

A. Prototheria -- egg layers

B. Metatheria -- marsupials

C. Eutheria -- placentals

• Major advances of the placental Mammals over the Reptiles include the following adaptations:

1. Viviparous internal development via the placenta

2. Homoiothermy (endothermy = warm-blooded)

3. 4-chambered heart

4. Hair, sebaceous and sweat glands

5. Diaphragm (hence diaphragmatic breathing)

6. Mammary glands

7. Differentiation of the muscles of facial expression

8. Secondary palate

9. Malleus and incus incorporated as ossicles

10. Single dentary - mandible

11. Dentition = heterodont/diphyodont

12. Occipital condyles doubled

13. Limbs rotated (parallel to the sagittal plane)

14. Long bones with epiphyses (fixed period of growth)

15. Increase in brain size/complexity, neopallium, corpus callosum - intelligence!

• Primates are distinguished from other mammalian orders by the possession of:

1. A relatively large and complex brain.

2. An acute visual sense (dominant over olfaction) resulting from the forward rotation of the orbital plane (leading to stereoscopic vision), expansion of the visual cortex of the brain, and separation of the orbital cavity from the temporal fossa by the development of a postorbital bar-wall.

3. Prehensile cheiridia normally enhanced by opposable or pseudo-opposable preaxial digits (pollex/hallux) and expanded distal phalanges for the support of flattened nails (vs. claws) and sensitive tactile pads (marmosets = major exception).

4. A relatively generalized dentition permitting an omnivorous diet with hypertrophied canines for defense and based on a dental formula of 2 / 1 / (2,3,4) / 3.

HOMO SAPIENS may be anatomically defined as follows: Terrestrial bipedal striders with hindlimbs longer than forelimbs; thumb fully opposable and hand capable of both power and precision grips; hallux aligned with other toes (adducted and laterally rotated); foot nonprehensile; brain relatively large and highly fissured; neurocranium more expansive than the viscerocranium; facial skeleton relatively nonprotrusive; DF = 2.1.2.3 x 4 with relatively small canines; relatively hairless.