LLL Innis 2018

TERTIARY AND QUATERNARY CLIMATE CHANGE AND THE

EVOLUTION AND SPREAD OF HUMANS.

Today’s uplifting message!

Last week we saw that a record of

climate change extends back about 4

billion years. It’s a record of

changing sedimentary

environments and the emergence

and evolution of life. The record is

limited until the last 600 million

years; since the Cambrian and the

apparently rapid diversification of life

known as the Cambrian Explosion.

The record of biodiversity through the last 600 million years indicates a logarithmic increase in species through time. However, the increase is not a smooth one. It is interrupted by several mass extinction events at which biodiversity is drastically reduced – the Big Five mass extinctions. The largest occurred at the end of the Permian when perhaps 90% of species went extinction. The latest one, at the Cretaceous-Tertiary (K-T) boundary, had about a 70% loss.

All except the K-T extinction appear to

have been caused by a complicated set of

mechanisms determined by plate

tectonics. At the K-T boundary we can

make a good case for asteroid impact as

the cause.

That boundary is very significant for us.

From that time we see modernization of

the biosphere – the rise of mammals,

insects, birds, flowering plants, etc.

Evolution of animals V= birds, BB= placental

mammals

Evolution of plants and animals after the K-T event .

angiosperms=flowering plants, ungulates=hoofed

animals, macropods= marsupials.

The early Tertiary was warm, but cooled through

the Eocene. By the Pliocene, the world had

significant ice. By the Pleistocene, there were

frequent advances and retreats of ice across

Europe and North America.

The pulse-like ice expansions (glacials)

and contractions (interglacials) seem to

have been driven by Milankovitch

Effects.

As climate cooled, tropical rainforests

contracted and were replaced by

grasslands and deserts in the tropical

zone, and the biomes familiar to us –

prairies, boreal forest, temperate

broadleaved forests - formed. Until then,

much of North America would have been

forested. Until the mid-Tertiary, these

forests extended across the Arctic

archipelago!

Present global

biomes(left) and in

the Eocene

(below)

Tertiary fossil forests

in the Canadian

Arctic.

One order that evolved was the Primate Order. We evolved from these as the family Hominideae, in the genus Homo. Our species? Homo sapiens.

This evolutionary process appears to have been largely driven by the global climatic changes from the mid-Tertiary.

As climate cooled, tropical rainforests contracted and were replaced by grasslands and deserts in the tropical zone. Until the mid-Tertiary, much of the Arctic archipelago had forest cover.

Currently there

are 16 families,

72 genera and

about 350

species of

primate.

Evolution of primates.

Our ancestors, the primates, were once widely

distributed, but they have always been largely

tropical fauna and largely arboreal.

Thus, climatic cooling caused their contraction

into the current tropical zone and the loss of

forest cover stimulated some to become ground

dwellers. This required the exploitation of

different resources so there were morphological

and behavioural changes. The most obvious of

the latter was the development of bipedalism.

Current distribution of primates

Our lineage

Early primate

Ring-tailed lemurs. Lemurs are

confined to Madagascar. Why?

Old and New

World

monkeys.

We share about 96% of our genes

with gorillas

And 98% with chimpanzees

Our African Origins;

Although climatic changes through

the Tertiary were global, the evolution

of hominids/hominins was not . It was

confined to Africa. Was this because

Africa had a suite of environmental

conditions that only allowed our

evolution to occur there or was it

fortuitous?

Why Africa?

(a) increasing aridity and seasonality

leads to major contraction of once

extensive rainforest

(b) expansion of tropical savanna

(c) creation of isolated forest fragments

in a ‘sea’ of savanna

(d) isolation facilitated by uplift and

volcanism in the Rift Valley system

(e) strong seasonality with fire a natural

part of the cycle, and long animal

migrations.

(f) strong coevolutionary associations

between herbivores, carnivores and

scavengers.

Massive environmental changes then triggered life-style and dietary changes in hominids. Obvious consequences included bipedalism and an increase in body (and brain) size.

These responses are evident with both

proto humans and all species of Homo.

The proto humans are usually considered

to be the Australopithecenes. A.

afarensis , Lucy, is the best known of

these. A new genus, Ardipithecus, was

recently recognized. It predates the

Australopithecines.

About 2.6 MYBP the first species of Homo

(H. habilis) appeared, then H. erectus.

Bipedalism; Bipedalism may be seen as a

response to changing lifestyle; from

being arboreal to a life on the ground.

Benefits – increasing mobility,

increasing travel range, arms no

longer required for locomotion,

height gain, tool preparation,

thermoregulation, etc.

Changes from knuckle-walking to

full bipedalism

Increasing Size;

Increasing size was associated with broadened dietary niche, increased home range, increased mobility, change in scavenging activities, increase in thermoregulatory efficiency, increased longevity, slower reproductive rates, increasing brain size and complexity, increasing sociality.

Increasing

brain size and

complexity

Is there a correlation between

brain size and environmental

stress?

Humans appear to be confined

to Africa until the exodus of

Homo erectus about 1.7

million years ago.

In the light of recent

discoveries, what happened

after that is becoming more

murky than it was.

Some wrenches in the works;

The Jebel Irhoud site in Morocco –H.

sapiens here at 300,000 YBP ?

The Misliya site in Israel – 200,000

YBP ?

H. erectus sites in Britain – 1 MYBP?

Happisburgh site, Norfolk, UK

Our global diaspora.

Two main models have been proposed to explain the spread of humans around the globe;

1. The Out of Africa Model – by which human evolved in Africa then spread to other parts of the world (twice!).

2. The Multiregional Model – initial spread by H. erectus, then regional evolution of various strains of H. sapiens.

Both models propose an initial migration by Homo erectus around 1.7 million years ago, but they differ with what ensues.

The Out of Africa model is the most popular, but on the basis of recent discoveries, it appears to be far too simple and may also require rethinking of H. sapiens’ origins.

Homo erectus and the first

Out of Africa exodus.

H. sapiens already Out of Africa?

A second exodus and

interbreeding with H. erectus?

Consolidation and further

expansion?

The later migrations

So modern humans evolved earlier than

previously thought.

‘Where’ is now not obvious.

They spread probably at least 100,000

years earlier than previous estimates.

There were probably several exoduses.

They interbred with species evolved from

the much earlier Homo erectus

movement out of Africa.

The role of climate?

Climate provides an envelope in which

biota evolve, exist and expire.

Changing climate undoubtedly

constrained the evolution of hominins,

their geography and their global

expansion.

Much of that evolution took place during

the ice advances and retreats of the

Quaternary.

Glacial advances shaped their movements.

Ice impeded movement in Europe and determined dispersal routes in North America.

At full glacials, sea level was 120 m below current levels. The resulting land connections facilitated dispersal from Africa, across the Near East ,through southeast Asia to Australia and from Siberia into Alaska (Beringia).

Sea level at maximum glaciation –

120 m below current sea level.

Beringia and

human entry to

the Americas.

Late Pleistocene megafaunal

extinctions

The early migrations did not seem to cause any obvious environmental impacts, but the later ones (to Australia and the Americas ) are marked by a massive die off of large animals (megafauna). In North and South America, 75-80% of big animals became extinct. In Australia, over 80%.

North American Megafauna

Australian Megafauna

The coincidence of these extinctions with the arrival of humans on those continents suggests an anthropogenic cause, but the events occurred in times of rapid and large climatic shift. Climatic change is likely to have been at least a contributing factor.

Extinction of Irish Elk and Mammoth

in Eurasia

Pattern of Extinction in North

America

Cave Art – Lascaux, France.

Australian

aboriginal rock art.

How could small populations

with limited technology

eliminate large numbers of big

animals?

Why didn’t the extinction of

large animals happen in Africa

and Eurasia?

So, the first major environmental impact

of humans may have been the mass

extinction event in the Late

Pleistocene/Early Holocene.

It’s also from this time that we have the

first evidence of plant and animal

domestication.

Domestication brought food surpluses,

allowed population increase,

urbanization, stratification of society –

the emergence of civilization.

We were going to look at plant

and animal domestication and

its consequences next week,

but because of scheduling

issues it will wait until Feb. 16.

Instead, we’ll talk about El Nino

(ENSO) and its impacts on past

and present societies.