Human Evolution: Trails from the Past

446 Pages·2007·8.8 MB·English

by  Camilo J. Cela-Conde

Human Evolution
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Human Evolution
Trails from the Past
Camilo J. Cela-Conde and Francisco J. Ayala
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Contents
Preface: Homosapiens,therationalanimal vii
Chapter1 Evolution, genetics,andsystematics 1
1.1 Thetheoryofevolution 1
1.2 Population andevolutionarygenetics 9
1.3 Theclassification oflivingbeings 33
Chapter2 The evolutionofhominoids 44
2.1 Hominoidtaxonomy 44
2.2 EarlyMiocene hominoids 54
2.3 MiddleMiocene:the migrationofapes outofAfrica 61
2.4 LateMiocene:thedivergence ofgreatapes 70
Chapter3 The homininlineage 81
3.1 Theoriginofhominins 81
3.2 Bipedallocomotion 92
Chapter4 MioceneandPliocenegeneraandspecies 106
4.1 Thefirsthominins 106
4.2 Australopithecus 117
Chapter5 Pliocene hominins:SouthAfricaandtheRiftValley 135
5.1 SouthAfricansites 135
5.2 SouthAfricanhominins ofthePliocene 145
5.3 The‘‘gracile’’and‘‘robust’’alternatives inEastAfrica 156
Chapter6 The Pliocenecladogenesis: Paranthropusversus Homo 166
6.1 EvidencefromKoobiFora 166
6.2 Alternativesinthe evolutionofrobustandgracileclades 181
Chapter7 The radiationofHomo 194
7.1 AsianHomoerectus 194
7.2 Theerectusgrade inAfrica 205
Chapter8 Evolutionary characteristics oftheerectusgrade 216
8.1 Culturalpatternsinthemigrationout ofAfrica 216
8.2 Theearliestcultures 228
8.3 HomoinEurope 241
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Chapter9 Thelate-Pleistocene transition 253
9.1 ArchaicHomosapiens 253
9.2 Neanderthals 271
9.3 Molecular data 287
9.4 Theoriginofmodern humans 300
Chapter10 Theuniquenessofbeinghuman 314
10.1 Cultureandmental traitsduring thelatePaleolithic 314
10.2 Theoriginsofsymbolism 326
10.3 Theoriginoflanguage 339
10.4 Theevolutionofmoralbehavior 353
Glossary 367
References 377
Index 419
Homo sapiens
Preface: , the rational
animal
Questions about human nature, about what it is Inthemidstofthedramaticadvancesofcurrent
that makes us distinctively human, have been paleoanthropology,weareawarethatmanyques-
raised since antiquity, at least since the dawn of tionsremainunanswered.Howmanygenera,and
the philosophical way of thinking in Classical which ones, belong to the human lineage? And
Greece, four centuries before the Christian Era. which among the hominid species are our direct
Aristotle, the greatest biologist of antiquity, iden- ancestors?Howdidtheycomeabout?Whatarethe
tifiedhumansfirstandforemostas‘‘animals,’’but critical adaptive events in humankind’s evolu-
he called them ‘‘rational animals’’: the power of tionarysojourn?Whoweretheveryfirstancestors
reason as the distinctive feature that separates us of the human lineage and what were their most
from the rest of the living world. It would be prominent features? And what about the first
only many centuries later, with the publication migrants out of Africa? What lithic tools had they
ofDarwin’stheoryofevolutionbynaturalselection, and how were they modified as they wandered
that an understanding could emerge of why we through other continents? What about the Nean-
sharesomuchofwhatwearewithotheranimals, derthals?WeretheyHomosapiens,membersofour
particularlywiththoseclosesttous,theprimates. species?Didtheyspeak?Didtheyappreciateart?
Oneandahalfcenturiesafterthepublicationof Stepbystepthesequestionswillbeansweredor,
Darwin’s The Origin of Species we know much at least, formulated more precisely. These ques-
about the evolutionary history that brought about tions and the partial answers available are part of
the distinctive features that make us human. thisbook,whichtellsthestoryofhumanevolution
Surely, Darwin would have been pleased by the as it is known today, with as many questions, or
numerousdiscoveriesofhominidancestorsandby more, as there are answers. This is how we must
the progress of knowledge concerning human approach our evolutionary lineage, by exploring
origins. We now know that Darwin’s conjectures with rigor the medley of fossil and archeological
were correct about the fundamental anatomical records, the complexity of the genetic data, and
event in human origins, namely the evolution of takingadvantageofallsortsofavailabletools,con-
bipedalism, and about the place, Africa, where ceptualandtechnical,whichmaycastsomelighton
humanity came about. We also know the time the understanding of our origins. We must for-
when our lineage separated from the chimpanzee mulate testable theories and explore the empirical
lineage, some 7millionyears ago. Scientists are observationsthatcorroborateorfalsifythem.
currently hard and fast at work, chromosome by The resulting panorama will not be simple, but
chromosome, and nucleotide by nucleotide, seek- need not be confusing. If we are rational beings,
ing to ascertain the features of our genetic code wemayaswelluseourpowersofrationalitytothe
thatmakeusdifferentfrom,aswellasverysimilar maximum extent possible as we seek to discover
to,oursimianrelatives.Further,workisunderway the history of our own evolution.
todeciphertheDNAofourclosestfossilrelatives, Camilo J. Cela-Conde
the Neanderthals. Francisco J. Ayala
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CHAPTER 1
Evolution, genetics, and systematics
(1200–1280) and his student Thomas Aquinas
1.1 The theory of evolution
(1224–1274). Aquinas concluded, after detailed
All organisms are related by descent from com- discussion, that the development of living crea-
mon ancestors. Humans and other mammals des- tures, such as maggots and flies, from nonliving
cend from shrewlike creatures that lived more matter, such as decaying meat, was not incom-
than 150millionyears ago (Ma); mammals, birds, patible with Christian faith or philosophy. But he
reptiles, amphibians, andfishes share asancestors leftittoothers(toscientists,incurrentparlance)to
aquatic worms that lived 600Ma; and all plants determine whether this actually happened.
and animals derive from bacteria-like micro- The first broad theory of evolution was pro-
organismsthatoriginatedmorethan3billionyears posed by the French naturalist Jean-Baptist de
ago. Biological evolution is a process of descent Monet, chevalier de Lamarck (1744–1829). In his
with modification. The process consists of two Philosophiezoologique(1809;translatedasZoological
components. Lineages of organisms change Philosophy), Lamarck held the enlightened view,
through the generations (anagenesis or phyletic shared by the intellectuals of his age, that living
evolution); diversity arises because the lineages organisms represent a progression, with humans
that descend from common ancestors diverge asthehighestform.Lamarck’stheoryofevolution
through time (cladogenesis or lineage splitting, the assertsthatorganismsevolvethrougheonsoftime
process by which new species arise). from lower to higher forms, a process still going
Humancultureshaveadvancedexplanationsfor on, always culminating in human beings. The
the origin of the world and of humans and other remote ancestors of humans were worms and
creatures. Traditional Judaism and Christianity other inferior creatures, which gradually evolved
explain the origin of living beings and their into more and more advanced organisms, ultim-
adaptationstolifeintheirenvironments—legsand ately humans.
wings, gills and lungs, leaves and flowers—as the The inheritance of acquired characters is the
handiwork of the Creator. Myths proposing that theory most often associated with Lamarck’s
different kinds of organisms can be transformed name. Yet this theory was actually a subsidiary
one into another are found in diverse cultures constructofhistheoryofevolution:thatevolution
sinceantiquity.Amongthephilosophersofancient isacontinuousprocesssothattoday’swormswill
Greece,Anaximanderproposedthatanimalscould yield humans as their remote descendants. As
metamorphose from one kind into another, and animals become adapted to their environments
Empedoclesspeculatedthatorganismsweremade through their habits, modifications occur by
up of various combinations of preexisting parts. ‘‘use and disuse.’’ Use of an organ or structure
The notion that organisms may change by reinforcesit;disuseleadstoobliteration.Thechar-
natural processes was considered, usually inci- acteristicsacquiredbyuseanddisuse,accordingto
dentally, as a possibility by Christian scholars Lamarck, would be inherited. This assumption
of the Middle Ages, such as Albertus Magnus that would later be called the inheritance of
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