Homo sapiens: Ecological and demographic change agents; or just in the wrong place at the wrong time?

Sprinkled throughout his book Sapiens, Yuval Noah Hariri provides data showing ecological and demographic changes occurring simultaneously with mankind's expansion around the world. I bring that data together into a single space in this post.

Yuval states that it is a dirty little secret that other Homo species existed on the planet simultaneously with Homo sapiens; and the figure below illustrates that fact. According to the DNA data in the figure below, a proto -Homo sapiens branch grew off the Homo heidelbergensis base and flowered into full Homo sapiens around 325,000 years ago.

Interbreeding between archaic and modern humans
(Source: wikipedia.org)

The chart shows a number of Homo species existing simultaneously with Homo sapiens. It further shows that, with the exception of Homo naledi and Homo erectus, all of these species interbred with Homo sapiens either in Southern Africa or Eurasia. It shows that all Homo species, except Homo sapiens, terminated between 300,000 and 25,000 years ago.

Homo solensis, Homo florensis and a newly identified Neanderthal-Denisovan hybrid species, all of whom have gone extinct, are not shown on the chart.

But these human species are not alone.

Ecological Impact
About 70,000 years ago Sapiens began looking at, and thinking about, the world around them differently. Yuval calls this the Cognitive Revolution. This new cognition resulted in the technologies, organizational skills, and vision that allowed Sapiens to break out of Asia and settle the wider world.

Yuval points to the colonization of Australia as one of the most important events in human history (akin to the Columbus and Apollo 11 journeys). It was the first time that a large terrestrial mammal had crossed from "Afro-Asia" to Australia. It was also the first time that humans had climbed to the top of the food chain on any landmass. It was not too good for the fauna (as shown in the below table).

Table 1. Sapiens impact on selected megafauna populations

Region/Country	First Entry (yrs ago)	Megafauna at First Entry	Megafauna at Period End	Period Duration	Comments
Australia	45,000	24 species	1	A few thousand years	Large number of smaller species also disappeared
North America	16,000	47 species	13	2,000 yrs	Thousands of smaller species of animals, birds, and insects also disappeared
South America	N/A	60 species	10	N/A	ditto
Wrangel Island (Arctic Ocean)	4000	N/A	0	Short
Madagascar	1500	2	0	Short	Elephant Bird and Giant Lemur
New Zealand	800	N/A	Majority extinct	200	As well as 60% of all birds

Table compiled from information sprinkled throughout Sapiens.

According to Yuval, "The first wave of Sapiens colonisation was one of the biggest ecological disasters to befall the animal kingdom":

• 70,000 years ago, the planet was home to approximately 200 genera of large animals weighing 100 pounds or more
• That number had declined to 100 by the beginning of the Agricultural Revolution (12,000 years ago)

Yuval: "Homo sapiens drove to extinction about half of the planet's big beasts long before humans invented the wheel, writing, or iron tools."

Yuval places faunal extinction into three waves:

• First wave -- occurred during the Cognitive Revolution
• Second wave -- occurred during the Agricultural Revolution
• Third wave -- driven by today's industrial activity (e.g., whales being killed by ships).

And the signatures of the first and second waves are eerily similar:

1. Rich and varied population of large animals; no trace of humans
2. Sapiens appear, as evidenced by artifacts
3. Men and women occupy center stage; most large animals, and many smaller ones, extinct.

Demographic Impact
The earlier chart shows that Homo sapiens tried to break out (unsuccessfully) of East Africa on two prior occasions -- 250,000 and 100,000 years ago -- before the successful exit approximately 80,000 years ago. Homo sapiens encountered Eurasia-based Homo species at this time.

The archaeological record shows that Homo solensis became extinct approximately 50,000 years ago -- as did Homo denisova -- while the Neanderthals died out 30,000 years ago. Homo florensis exited  12,000 years ago. Yuval offers two options for their disappearance: (i) Sapiens drove them to extinction through competition or (ii) genocide. Our most recent experiences on Explorer-contact with existing populations may prove to be illustrative as to the fate of those extinct populations.

North and South America were unknown to Eurasia prior to Columbus' first voyage in 1492 (and it took a while to figure out that this was a "new world," rather than a part of Asia) but within 121 years, 90% of the region's populace had died out (see Table 2).

Table 2. Demographic impacts of Old World contact with New

Region/Country	Peoples	Contact Point	Impact	Period	Comments
Caribbean Islands	Caribs, Arawaks, etc.	Columbus (1492)	Most of native population wiped out	21 years	Replaced with African slaves
Americas	Inca, Aztec, Maya, etc.	Cortez landing at Vera Cruz (1519)	90% population reduction	100 years	Unfamiliar diseases
Australia and New Zealand	Aborigines and Maoris	Cook’s 1771 expedition	Native populations declined by 90%	100 years	Replaced by Europeans
Tasmania	Palawa	ditto	From between 3,000 – 15,000 in 1803 to 400 in 1835	32 years

Table compiled from information sprinkled throughout Sapiens.

Prior to Columbus' arrival, the indigenous population in the Americas numbered around 60 million but wars, famine, and diseases -- against which the locals had no defense -- dropped the population down to 6 million 100 years later. According to a recent study published in Quartenary Science Reviews, the deaths occurred on such a large scale that they led to the "little Ice Age," an era of global cooling between the 16th and mid-19th century.

According to the researchers, large areas of farmland was abandoned as a result of the die-offs. This land was reclaimed by trees and flora which sucked enough carbon dioxide out of the atmosphere that the average temperature dropped by 0.15 degrees Celsius.

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The human role in new world human population die-offs is clear but the jury is still out on other Homo species and megafauna. Archaeological evidence shows that we hunted megafauna but the question as to whether we hunted them to extinction has not been answered fully to everyone's satisfaction.

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