PRESENTATION OF THE ARTICLE: THE NAKED

TRUTHIN SCIENTIFIC AMERICAN

(2012)GABRIEL FIOSSI ASSAGBAMATRIKEL NO: 9027395

TO PROF. WEIHER

CONTENT

• INTRODUCTION• IMPORTANCE OF HAIR (IN GENERAL)• EVOLUTION OF THE HAIR• ADAPTATION OF MAN AND OTHER MAMMALS• AQUATIC APE THEORY• GENETIC EXPLANATIONS• VARIABLES OF HAIRLESSNESS• CONSEQUENCES OF HUMAN HAIRLESSNESS

INTRODUCTION

AMONG PRIMATES, HUMANS ARE UNIQUE IN HAVING NEARLY NAKED SKINMEMBERS OF OUR EXTENDED FAMILY HAVE DENSE COVERING OF HAIR. E.G. MONKEY AND ORANGUTAN AND OTHER MAMMALSHINTS BY FOSSIL RECORDS ABOUT HOW WE TRANSFORMED FROM BEING HAIRY TO NEARLY NAKEDIN ADDITION, EXPLANATION OF ROLE OF NAKED SKIN TO THE RISE OF OTHER CHARACTERISTIC HUMAN TRAITSTO UNDERSTAND, WE OUGHT TO CONSIDER WHY OTHER RELATIVES HAVE COATS

IMPORTANCE OF THE HAIR (GENERAL)

• INSULATION AND PROTECTION• CAMOUFLAGE• RECOGNITION AMONG SAME SPECIES• SOCIAL DISPLAYS, E.G. AGGRESSION OR AGITATIONBUT OTHER MAMMALS HAVE NEARLY SPARSE TO NAKED SKIN• MARINE MAMMALS, E.G. WHALES• UNDERGROUND MAMMALS, E.G. NAKED MOLE RAT• LARGE TERRESTRIAL MAMMALS, E.G. ELEPHANTSBUT FOR HUMANS, NAKEDNESS IS FOR STAYING COOL

ADAPTATION OF MAN AND OTHER MAMMALS

KEEPING COOL IS A BIG PROBLEM FOR MANY MAMMALS, NOT JUST THE GIANT ONES, ESPECIALLY WHEN THEY LIVE IN HOT PLACES AND GENERATE ABUNDANT HEAT FROM PROLONGED WALKING OR RUNNING. THESE ANI MALS MUST CAREFULLY REGULATE THEIR CORE BODY TEMPERATURE BE CAUSE THEIR TISSUES AND ORGANS, SPECIFICALLY THE BRAIN, CAN BE COME DAMAGED BY OVERHEATING.ADAPTATION FOR SOME MAMMALS ARE:• PANTING, E.G. DOGS• BEING ACTIVE IN THE EVENINGS, E.G. CAT SPECIES• OFFLOADING THROUGH BREATHING, E.G. ANTELOPES• SWEATING, E.G. PRIMATES, INCLUDING HUMANS

SWEATING IN FUR COVERED PRIMATES

MAMMALIAN SKIN CONTAIN THREE TYPES OF GLANDS WHICH COMBINE TOGETHER TO CREATE SWEAT. NAMELY, SEBACEOUS, APOCRINE AND ECCRINE.SEBACEOUS AND APOCRINE ARE DOMINANT IN MOST SPECIES NEAR BASE OF THE HAIR FOLLICLES. THEIR SECRETIONS COMBINE TO COAT HAIR WITH AN OILY MIXTURE WHICH HELPS COOL THE ANIMAL BUT IS LIMITED.THE EFFECTIVENESS OF COOL ING DIMINISHES AS AN ANIMAL’S COAT BECOMES WET AND MATTED WITH THIS THICK, OILY SWEAT.THE LOSS OF EFFICIENCY ARISES BECAUSE EVAPORATION OCCURS AT THE SURFACE OF THE FUR, NOT AT THE SURFACE OF THE SKIN ITSELF, THUS IMPEDING THE TRANSFER OF HEATCOMPENSATION IS NORMALLY DONE THROUGH DRINKING OF WATER WHICH MAY NOT BE AVAILABLE.

SWEATING IN HUMANS

HUMANS HAVE AN EXTRAORDINARY AMOUNT OF ECCRINE GLANDS: 2 MILLION TO 5 MILLION PRODUCING UPTO 12 LITERS OF THIN WATERY SWEATECCRINE GLANDS DO NOT CLUSTER NEAR HAIR FOLLICLES; INSTEAD THEY RE SIDE RELATIVELY CLOSE TO THE SURFACE OF THE SKIN AND DISCHARGE SWEAT THROUGH TINY PORES

AQUATIC APE THEORY

THE AQUATIC APE THEORY (AAT) POSITS THAT HUMANS WENT THROUGH AN AQUATIC PHASE IN THEIR EVOLUTION (5 MILLION TO 7 MILLION YEARS AGO) – PROPOSED BY SIR ALISTER HARDY IN 1960 AND SUPPORTED LATER BY ELAINE MORGANEVIDENCE OF THIS AQUATIC PHASE, MORGAN ARGUES, COMES FROM SEVERAL ANATOMICAL FEATURES HUMANS SHARE WITH AQUATIC AND SEMIAQUATIC MAMMALS BUT NOT WITH SAVANNA MAMMALS. THE TRAITS ARE BARE SKIN, LESS APOCRINE GLANDS AND FAT DEPOSITS UNDER THE SKIN.UNTENABLE FOR THREE REASONS:• NO CONNECTION BETWEEN AMOUNT OF HAIR AND ENVIRONMENT• FOSSIL RECORDS ON WATERY HABITATS (CROCODILES)• FOSSIL RECORDS ON HUMANS SHOWING TERRESTRIAL LIFESTYLE ALL THROUGH

EVOLUTION OF HUMAN HAIRLESSNESS

TRANSFORMATION BEGUN WITH CLIMATE CHANGE, AROUND 3 MILLION YEARS, EARTH HAD A PHASE OF GLOBAL COOLING HAVING A DRYING EFFECT IN EAST AND CENTRAL AFRICA WHERE HUMAN ANCESTORS LIVED.CHANGING ENVIRONMENT FROM WOODED TO SAVANNA GRASSLANDS. MAKING FRUITS, TUBERS, AND SEEDS WHICH AUSTRALOPITHECINES DEPENDS ON MORE SCARCER DUE TO LESS RAINFALL AND SEASONAL AVAILABILITYADAPTATION BROUGHT ABOUT MORE ACTIVE LIFESTYLE AND INCORPORATION OF MEAT INTO DIET. (STONE TOOLS AND BUTCHERED ANIMAL BONES AROUND 2.6 MILLION YEARS)ACTIVE LIFESTYLE MEANT MORE HEAT PRODUCTION BY THE BODY FROM PROLONGED WALKING AND RUNNING SO NEED TO LOSE HAIR AND OTHER ADAPTATION IN BODY SIZE AND PROPORTION

AUSTRALOPITHECINES HOMO ERGASTER

GENETIC EXPLANATIONS

EXAMINATION OF THE MC1R GENE WHICH IS RESPONSIBLE FOR SKIN PIGMENTATION. SPECIFIC GENE VARIANT IN AFRICANS AS OLD AS 1.2 MILLION YEARS AGO.EARLY HUMANS ASSUMED TO HAVE PINKISH SKIN COVERED BY BLACK SUN SHIELDING HAIR MUCH LIKE CHIMPANZEES.SO THE REASON FOR DARK PIGMENTATION AND EVOLUTIONARY FOLLOW UP FOR LOSS OF HAIRCOMPARISONS BETWEEN HUMANS AND CHIMPS DNA (99% SIMILARITY)

VARIABLES OF HAIRLESSNESS

• REASON FOR HAIR IN ARMPITS AND GROIN (PHEROMONES AND LUBRICATION)• REASON FOR HAIR ON HEAD SHIELD AGAINST EXTRA HEATDENSE HAIR ON THE HEAD CREATES A BARRIER LAYER OF AIR BETWEEN THE SWEATING SCALP AND THE HOT SURFACE OF THE HAIR. THUS, ON A HOT, SUNNY DAY THE HAIR ABSORBS THE HEAT WHILE THE BARRIER LAYER OF AIR REMAINS COOLER, ALLOWING SWEAT ON THE SCALP TO EVAPORATE INTO THAT LAYER OF AIR.HYPOTHESIS ON VARIABLES IS ATTRIBUTED TO SEXUAL SELECTION

CONSEQUENCES OF HAIRLESSNESS• BIGGER BRAIN : COMPARISON BETWEEN AUSTRALOPITHECINES AND HOMO ERECTUS

AND HOMO SAPIENS

• LOSS OF CAMOUFLAGE ABILITIES• LOSS OF SHOW OF AGITATION• EVOLVING OF FACIAL EXPRESSIONS AND BODY POSTURES TO COMMUNICATE• DEVELOPMENT OF LANGUAGE TO SPEAK OUR MINDS