Lecture 4-2 早期人类演化与环境

1.1. Savanna hypothesis ( 稀树草原理论 )

1.2. Variability selection hypothesis ( 变化选择学说 )

1.3. Woodland-mosaic hypothesis ( 镶嵌理论 )

一、人类起源和演化理论

1.1. Savanna hypothesis

Savanna 理论认为，在中新世晚期 (5-8 Ma), 由于全球气候变干、变冷，非洲的森林变得稀疏

这种干冷的气候导致东非的某一种 ape 从生活在西非的茂密森林中的 ape 家族分离出来

此后，东非的这些 ape 不得不适应这里干旱、开阔的 savanna 环境，这种环境有利于陆生环境中生物的进化

为了获取食物、抵御敌害，这些分离出来的 ape可能形成较大的社会群体－导致语言的形成？？

草原生活的挑战可能促进早期人类开始制造和使用工具，以便捡拾其他大型动物剩落的食物 (scavenging meat from the kills of predators).

食肉是早期人类演化的重要阶段，可以增强人类的智力 (mental abilities), 增加人类的脑容量 (the development of larger brains)

Savanna 理论的不足

西非的 Chad 发现南方古猿

非洲的 open savanna 出现的时间比人类出现要早 , 并且是在 2Ma

以后才广泛分布

Chad 位于东非裂谷以西 2500 km 的西非 , 发现了南方古猿的下颌骨 , 可能属于 A. afarensis.

(Brunet et al., 1995, Nature)

意义：南方古猿可能生活在整个非洲大陆的广大地区，而不仅在南非、东非；当时东非与西非的环境并非截然不同 .

Biochronology:3-3.5 Ma

Turnover-pulse hypothesis• Ecosystems periodically experience significant disruption

s, these in turn result in mass extinctions. Extinctions in t

urn hurt specialists more than generalists, where the gen

eralists will in turn thrive within the environment by utilizi

ng new environmental opportunities, or by moving elsew

here in diaspora to take advantage of other environment

s

• The specialists will experience more extinctions, and a

"pulse" of positive and random speciation within their gr

oups

• These two events lead to more specialists in isolated areas whe

reas the generalists will become more spread out

• well known example is the 2.5 million year event, in which a mass fluctuation of temperature occurred 2.5 million years BP, causing a rapid burst of speciation

• It was during this event, so the hypothesis states, that many species attempted to move from their now uninhabitable habitats and later developed different adaptations in their new environments, evolving into different species

• Evidence of the hypothesis points to the conc

urrent split in Australopithecus afarensis, and

Paranthropus robustus which developed sepa

rate traits in separate regions around the sam

e time.

• Counter-evidence points to the presence of

Homo habilis and the lack of evidence that wo

uld support significant mutations occurring wit

hin that species in that same time frame.

1.2. Variability selection hypothesis

变化选择 (VS) 理论认为，早期的南方古猿经历许多环境变化，最终生活在各种生态环境中 (a range of habitats) ，包括 forests 、 open-canopy woodlands, 以及 savannas ，他们逐渐适应了各种环境 .

VS 理论强调 climatic variability 的长期变化特点，例如偏离平均气候状态的幅度和持续时间以及对动物的环境适应、自然选择和进化过程的影响

It states that dramatic and frequent climate changes drove adaptations that enabled individuals to cope with a wide range of environmental conditions. These frequent climate changes thus drove hominins to evolve ways to better adapt to a variable environment.

(Potts, 1998, Evol. Anthropol.)

27Ma以来每百万年内氧同位素变率

(Potts, 1996)

VS 理论认为，生物进化和新物种形成主要发生在气候变化明显、幅度最大的时期 .

非洲和亚洲实例

(Trauth et al., 2005, Science)

Ethiopia, Kenya, Tanzania 的湖泊演化记录表明，东非与早期人类有关的湖泊的发育和全球气候变化相关 .例如， 2.6Ma ，北半球冰盖形成， Turkana 湖发育，最早的石器出现； 1.8Ma ， Walker 环流形成，直立人出现； 1Ma ，中更新世气候转型，直立人地理大扩张

南海 13C高值事件 Wang et al(2004)

毛乌素沙漠阶性扩张Ding et al.(2002)

•CLP C4植被阶段性扩张 An et al (2005)•~1 Ma青藏高原曾显著隆升 Sun (2000)

东亚区域环境变化事件与已发现的早期人类遗址相关

1.3. Woodland-mosaic hypothesis

镶嵌理论认为，早期的南方古猿生活在草原和森林镶嵌的环境中，这种环境提供了“地上”和“树上”两种生活环境

地上生活 (ground feeding) 有利于向直立行走进化

2.1 晚新生代全球气候特征

2.2 早期人类演化与环境变化

2. 早期人类演化与环境变化

2.1. 晚新生代全球气候特征

深海氧同位素

地球气候从新生代早期的 温室期向晚新生代的冰室期演化－－ Global long-term cooling climate

Modified Zachos et al., 2001Modified Zachos et al., 2001

来自全球 40余个 DSDP和ODP钻孔的深海沉积底栖有孔虫壳体氧同位素记录

Courtesy of Sun JMCourtesy of Sun JM

Asian & African climate

monsoonal-arid environments

long-term drying

第四纪气候的特点：叠加在变干、变冷趋势上的冰期－间冰期旋回

Asian Climate

Marine sediment record of SSTs at South Atlantic ODP Site 1084

African climate

(deMenocal, 2004, EPSL)

2.2. 早期人类演化与环境变化

人猿分离 : 5-8 Ma <> 构造气候事件

最早的石器 : 2.6-2.5 Ma <> 北极冰盖形成

H. erectus 的出现 ; 走出非洲 : 1.8 Ma <> C4 expansion (increased drying)

直立人地理大扩张 1.2-0.8 Ma <> MPT

• 构造气候事件 岩石圈水平运动 ( 海道的关闭 ) 岩石圈垂直运动 (高原隆升 )

• Global climate change Drying 亚洲和非洲干旱化

• Orbital forcing 中更新世气候转型事件 (MPT)

北大西洋 Fe-Mn crust 的 Nd同位素。

Note the marked change near 3 to 5 Ma, which some attribute to a change in North Atlantic ocean circulation and others to a change in the source Nd, associated with increased glacial erosion since 3 Ma.

After Molnar (2008, Paleoceanography). After Molnar (2008, Paleoceanography). Data from O’Nions et al. [1998, open circData from O’Nions et al. [1998, open circles] and Burton et al. [1999, closed circleles] and Burton et al. [1999, closed circles].s].

巴拿马地峡关闭巴拿马地峡关闭 : 3-4 Ma: 3-4 Ma

干旱化发展的原因：干旱化发展的原因：

(1) (1) 巴拿马地峡关闭巴拿马地峡关闭 (3-4 Ma) (3-4 Ma) favored early Pliocene warming favored early Pliocene warming of the Northern Hemisphere of the Northern Hemisphere increasing Asian aridificationincreasing Asian aridification

(2) (2) 青藏高原隆升 青藏高原隆升 (~3.6 Ma)(~3.6 Ma)

西峰红粘土孢粉：亚洲内陆上新世干旱化增强 西峰红粘土孢粉：亚洲内陆上新世干旱化增强

(Wang Luo et al., 2006, Palaeo-3)(Wang Luo et al., 2006, Palaeo-3)

Closing of the Indonesian seaway as a precursor to east African aridification around 3~4 Ma ago

印尼海道关闭印尼海道关闭 (3-4 Ma)(3-4 Ma)切断来自南太平洋的暖水团切断来自南太平洋的暖水团印度洋印度洋 SSTSST降低降低东非降水减少东非降水减少 (( 干旱化干旱化 ))

(Cane & Molnar, 2001, Nature)(Cane & Molnar, 2001, Nature)

东非古环境

(Cane & Molnar, 2001, Nature)(Cane & Molnar, 2001, Nature)

北太平洋粉尘记录

亚洲内陆干旱化

(Rea et al., 1998, (Rea et al., 1998, PA)PA)

(a) 地磁 (b) 旧石器或 (c) 靖边黄土岩石磁学 (d) 靖边黄土粒度 (e) 全球氧同位素集成极性年表 早期人类遗址

年龄

(M

a)

马梁

东谷坨，岑家湾公王岭飞梁西侯度半山小长梁，大长梁

马圈沟 -I

马圈沟 -II马圈沟 -III

冰期干旱化增

强间冰期干旱化增

强

2.5

2.4

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2.1

2

1.9

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1.1

1

0.9

0.8

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0.05 0.15

SIR M 1 0 0 m T /SIR M

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1 8 O / o /o o

100 50 0

> 63 m (% )

J

O

BM

L 2 (~0 .2 M a)

L 7 (~0 .7 M a)

L 14 (~1 .2 M a)

KSR

P

CM

P. B. deMenocal, EPSL 220, 3-24 (2004)

Summary diagram of important paleoclimatic and hominid evolution events during the Pliocene-Pleistocene

A. K. Behrensmeyer, Science 311, 476-478 (2006)

Marine and land records showing paleoclimatic trends during human evolution

结论：环境变化是早期人类演化的重要驱动力

适宜的气候和环境条件只是适合早期人类的生存，而气候和生态环境的多变性与不稳定性是促进人类进化的重要因素