Molti modi di essere umani

Un’ipotesi sulla “doppia nascita” di Homo sapiens

Museo delle Scienze, Trento

Tre giorni per la scuola

25 Settembre 2012

Telmo Pievani

University of Milan Bicocca

telmo.pievani@unimib.it

Chauvet Cave - 31K

PALEOLITHIC

“REVOLUTION”?

- Punctuated global innovation?

- Slow trend?

“The Sorcerer” – Les Trois Frères Cave, 14 K

- Gap between anatomically modern H. sapiens and cognitively modern H. sapiens

THE DOUBLE BIRTH OF MODERN H. SAPIENS

Blombos Cave, 77-75K

Evidence of graduality

(or failed “experiments”?)Skhul Cave, 100K

First human populations in Australia52-40K

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)

Smith et alii, “Dental evidence for ontogenetic differences between modern humans and Neanderthals”, PNAS, 2010, 107(49): 20923–20928

B

ONTOGENETIC NEOTENIC TREND (maximum): dental evidences

and skull development

Le differenze genetiche nella nostra specie sono le più basse di tutti i primati

C

Albero evolutivo del cromosoma X: Kaessmann et al. (2001).

Bottleneck events

TOBA Eruption? (73 K)

1

Pinnacle Point PP13B (195-123K)2

(Curtis W. Marean: Ice Age niches)

3

Multiple bottlenecks?

Bab el-Mandeb Strait

Multiple waves of diffusion

Henn et alii, “Hunter-gatherer genomic diversity suggests a southern African origin for modern humans”, PNAS, March 2011, vol. 108, n. 13.

A – Genetic diversity has a maximum

“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 Genome-Wide 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.

Australopithecus sediba

Homo di Denisova

?

2011

??

The “bushy” tree of human evolution

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 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

Thylacoleo carnifex

Smilodon populator

(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)

Howieson’s Poort Culture: 5000 years (65-60K)

?

?

“Ephemeral and punctuated nature of these bursts of

technological and behavioral innovation”

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

“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)

(influencing social networks)

THE FINAL WAVE

Cognitively modern?

More “invasive”?

Neanderthal (70K) H. sapiens (100K) H. sapiens (26K)

(Lieberman, McCarthy, “Tracking the Evolution of Language and Speech”, 2007, www.museum.upenn.edu)

The specificity of our “final wave”

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, 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

Atkinson, Q. D. 2011. Science 332:346-349.

“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)

modernity and ultimately led to our colonization of the

globe”

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.

Atkinson, Q. D. 2011. Science 332:346-349.

Summary of the model for modern human origins and d ispersal from Africa.

First wave Out of Africa

Second wave?

Mellars P PNAS 2006;103:9381-9386

©2006 by National Academy of Sciences

Why?

Second wave?

Third wave Out of Africa

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!