Museo delle Scienze, Trento
Tre giorni per la scuola
25 Settembre 2012
Molti modi di essere umani
Un’ipotesi sulla “doppia nascita” di Homo sapiens
Telmo Pievani
University of Milan Bicocca
[email protected]
Chauvet Cave - 31K
PALEOLITHIC
“REVOLUTION”?
- Punctuated global
innovation?
- Slow trend?
- Gap between anatomically
modern H. sapiens and
cognitively modern H.
sapiens
“The Sorcerer” – Les Trois Frères Cave, 14 K
THE DOUBLE BIRTH OF
MODERN H. SAPIENS
Blombos Cave, 77-75K
Evidence of graduality
Skhul Cave, 100K
(or failed “experiments”?)
First human populations in
Australia
52-40K
Evidence of global rapid innovation?
DEGREES OF EARLY SPECIFICITY IN H. SAPIENS
(200-120K):
TECNOLOGY: low (Middle Paleolithic stone tools, like
Neanderthal)
SOCIAL ORGANIZATION: low (rare significant innovations)
FOX-P2: low (the only two mutations derived, with respect to
chimps, shared with Neanderthal; Krause et alii, 2007, Current Biology, 17, 21,
1908-1912)
HYOID BONE: low (the same in Neanderthal)
THEORY OF MIND: low? (no significant innovations possibly
connected)
------------------A - ANATOMY: high (uniquely derived in the structure of skull
and postcranial skeleton)
B - NEOTENIC TREND: high (re-organization of gene expr.)
C - GENETIC DIVERSITY DISTRIBUTION: high (peculiar)
A
Homo sapiens hidaltu, 160K
* Evolution of language in genus Homo, before H. sapiens
(Di Vincenzo, Manzi, 2012)
B
Smith et alii, “Dental evidence for
ontogenetic differences between modern
humans and Neanderthals”, PNAS, 2010,
107(49): 20923–20928
ONTOGENETIC NEOTENIC TREND
(maximum): dental evidences
and skull development
C
Le differenze genetiche nella nostra specie
sono le più basse di tutti i primati
Albero evolutivo del cromosoma X:
Kaessmann et al. (2001).
Bottleneck events
1
TOBA Eruption? (73 K)
2
(Curtis W. Marean: Ice Age niches)
Pinnacle Point PP13B (195-123K)
3
Multiple bottlenecks?
Bab el-Mandeb Strait
Multiple waves of diffusion
A – Genetic diversity has a maximum
Henn et alii, “Huntergatherer genomic
diversity suggests
a southern African
origin for modern
humans”, PNAS,
March 2011, vol.
108, n. 13.
“African hunter-gatherer populations,
with a maximum in southern Africa,
continue to maintain the highest levels
of genetic diversity in the world”.
B – Genetic diversity decreases with distance from Africa
Ramachandran et alii,
“Support from the
relationship of genetic
and geographic distance
in human populations for
a serial founder effect
originating in Africa”,
PNAS, 2005, 102, n. 44
Li et alii, “Worldwide
Human Relationships
Inferred from GenomeWide Patterns of
Variation”, Science, 2008,
319, 1100-1104.
A SERIAL FOUNDER EFFECT MODEL
(courtesy, Kenneth Kidd, Yale University)
(courtesy, Kenneth Kidd, Yale University)
(courtesy, Kenneth Kidd, Yale University)
(courtesy, Kenneth Kidd, Yale University)
Were we alone?
Terry Harrison , Apes Among
the Tangled Branches of Human
Origins, Science 2010: Vol. 327.
no. 5965, pp. 532 – 534.
Homo di Denisova
Australopithecus
sediba
?
?
The “bushy” tree of
human evolution
?
2011
Story of a finger
40K: five human species (or
“forms”) in the Old World.
Denisova Cave,
April 2010
“Close Encounters of the Prehistoric
Kind”, Science, May 7, 2010
“The long-awaited
sequence of the
Neanderthal genome
suggests that modern
humans and
Neanderthals interbred
tens of thousands of
years ago, perhaps in
the Middle East”
HOMO SAPIENS GLOBALIZATION
Interbreeding with H.
neanderthalensis?
Interbreeding with
Denisova Man?
Neanderthalian symbolic behavior?
Shanidar I e IV
Fumane, 2010
Divje Babe Flute
RECENT EXTINCTION (40-12K)
Same period: extinction of megafaunas
Diprotodon
Smilodon populator
Thylacoleo carnifex
(Zenobia Jacobs and Richard G. Roberts, 2009)
“Two bursts of human
innovation in southern
Africa during the Middle
Stone Age may be linked
to population growth and
early migration off the
continent”
Still Bay points: 1000
years (71-70K)
“Ephemeral and punctuated
nature of these bursts of
technological and behavioral
innovation”
?
Howieson’s Poort Culture:
5000 years (65-60K)
?
Howieson’s Poort
points (attached to
wooden handles).
(Zenobia Jacobs and Richard G. Roberts, 2009)
Sibudu Cave, Still Bay and
Howieson’s Poort cultures
Pulses of demographic
expansions and contractions
(influencing social
networks)
“Our results hint at the possible
role of population expansions in
Africa as a trigger for these
Stone Age innovations, and,
maybe, for early migrations
from Africa about 60K ago”
(according to L3 mt-DNA
haplogroup expansion)
THE FINAL WAVE
Cognitively modern?
More “invasive”?
Neanderthal (70K)
H. sapiens (100K)
(Lieberman, McCarthy, “Tracking the Evolution of
Language and Speech”, 2007, www.museum.upenn.edu)
The specificity of our “final wave”
H. sapiens (26K)
Science 15 April 2011:
Vol. 332 no. 6027 pp. 346-349
DOI: 10.1126/science.1199295
Phonemic Diversity Supports a Serial Founder Effect Model of
Language Expansion from Africa
Quentin D. Atkinson
Human genetic and phenotypic diversity declines with distance from Africa,
as predicted by a serial founder effect in which successive population
bottlenecks during range expansion progressively reduce diversity,
underpinning support for an African origin of modern humans. Recent work
suggests that a similar founder effect may operate on human culture
and language. Here I show that the number of phonemes used in a
global sample of 504 languages is also clinal and fits a serial founder–effect
model of expansion from an inferred origin in Africa. This result, which is not
explained by more recent demographic history, local language diversity, or
statistical non-independence within language families, points to parallel
mechanisms shaping genetic and linguistic diversity and supports an
African origin of modern human languages.
The point of view of phonemes
Atkinson, Q. D. 2011. Science 332:346-349.
The point of view of genes
A connection between language and expansion?
Atkinson, Q. D. 2011. Science 332:346-349.
“Truly modern
language, akin to
languages spoken
today, may thus have
been the key cultural
innovation that
allowed the
emergence of these
and other halmarcks
of behavioral
modernity and
ultimately led to our
colonization of the
globe”
“Language was central to human expansion
across the globe. It was our secret weapon, and
as soon we got language we became a really
dangerous species”
(Mark Pagel, NYT, April 14, 2011)
Atkinson, Q. D. 2011. Science 332:346-349.
Linguistic caveats:
1) It is not proven the unique origin of modern languages;
2) Phonemic diversity is a weak statistical basis because it
varies inside the languages in a wide range of regional
variants (other methodologies needed: ex. regional
variants; ex. units of syntax);
3) Differences between biological evolution and linguistic
evolution.
Summary of the model for modern human origins and dispersal from Africa.
First wave Out
of Africa
Second wave?
Why?
Third wave Out
of Africa
Mellars P PNAS 2006;103:9381-9386
©2006 by National Academy of Sciences
AN “EXAPTIVE” HYPOTHESIS
(updated from I. Tattersall, “Human Origins: Out of Africa”, PNAS, 2009, 106, 16018)
A - (enabling equipment or “exaptive” potential – 200K)
ANATOMIC INNOVATION (a tall African species)
NEOTENIC TREND (reorganization of gene expression; new neural substrate;
influences on social organization and language)
B - (punctuated bursts of cultural innovation – 80-60K)
EARLIEST EVIDENCES OF SYMBOLIC BEHAVIOR, IN AFRICA
CLIMATE INSTABILITY (pulses of demographic expansions and contractions)
COMPLETE EVOLUTION OF THE VOCAL TRAIT (enabling articulated language)
C - (cultural stimulus and rapid diffusion – 60-50K)
ORIGIN OF MODERN COMPLEX LANGUAGE IN AFRICA
DEMIC (L3 HAPLOGROUP) AND CULTURAL DIFFUSION: THE FINAL WAVE
THANKS!