Q&A With Lee Berger on Human Evolution

The Sunday Times has an interview with Lee Berger about human evolution, in advance of his new book, co-written with John Hawks, Almost Human: The Astonishing Tale of Homo naledi and the Discovery That Changed Our Human Story. As was reported earlier, the original fossils were undated but appeared to be reflective of an early stage in the development of Homo. This idea was shattered when new dates were derived.  As I wrote at the time:

Homo naledi, however, was missing a date—until recently. Nearly everyone in the scientific community thought that the date of the Homo naledi fossils, when calculated, would fall within the same general time period as other primitive early Homo remains. We were wrong. The radiometric dates—recorded using several methods carried out at different laboratories—yielded almost identical ages of between 236 and 300 thousand years before the present (BP). This was an order of magnitude younger than we expected. To say we were surprised would be an understatement.

Interestingly, the interviewer asks no important questions about Homo naledi or the Dinaledi Star cave, itself.  Amid all of the sturm und drang of his tortuous relationships with Ron Clarke and Philip Tobias (✟ 2012), there is one interesting question about human evolution in general:

Throughout the final chapters of the book you often mention how much there still is to learn about Homo naledi and that it’s very likely that there are more early hominim species which are yet to be discovered. The skeletal material you recently came across in the Lesedi Chamber shares similarities with Homo naledi and adds to this statement. What can/does this new discovery tell us about human evolution in Africa?

I think the clear picture that has come from both the discovery of Australopithecus sediba and Homo naledi is that the story of human evolution is not a simple, linear, straightforward one but that ours is a complex history. Naledi and sediba show us that there is more to be found – it’s clear that we don’t really know their ancestral history and the few fossils of other species found across Africa don’t help us much with interpreting where they fit in our family tree – and that’s exciting. We currently are back in the Dinaledi and Lesedi Chambers and making new discoveries – particularly exciting is we seem to have strong evidence that Homo naledi did indeed come down the narrow chute the way our “underground astronauts” come – and that is wonderful and hard to explain – but it’s exciting!

This has been a contentious issue: whether or not the fossil remains were “placed” there or were brought in by scavengers. What is also not clear is if the book was published before the new dates became available, or not.  I will have to buy the book to find that out.  While the rest of the interview is a tad unsubstantive, it is interesting.

How Will Climate Change Affect Human Evolution?

Gizmodo asked a number of scholars how they thought AGW will affect human evolution.  Some of the answers were interesting. Biological anthropologist John Hawks wrote:

I’ll be honest — the degree of climate change we are talking about in the next couple of centuries, which is on the order of several degrees Celsius, is by and large going to make the temperate regions of the world more similar in temperature to tropical Africa, where all our ancestors originated. We’re effectively terraforming the world to be more like our origins. The effects on humans are much more social and economic than evolutionary.

To the extent we see evolution, it will be changes in plant and animal species. Some will change the timing of their lives, some will invade new areas where they couldn’t adapt before, and many will become extinct — especially those today locked into small “reserves” that will undergo local climate shifts faster than they can adapt. And of course we will exert our own selection and genetic engineering upon our crops and domesticated animals to suit the changing climate.

Biological anthropologist Chris Stringer wrote:

The pace of change is likely to be too fast and dramatic for us to evolve physically to meet the challenges of a much warmer world. Any changes would have to come from cultural or social accommodation to the new situations – if that proves possible.

I think it is still way to early to tell how the earth will respond to anthropogenic changes in climate. If you will recall, only fifteen years ago, people were talking about global cooling.

Denisova Update

John Hawks does not think that the recent data from the paper by Skoglund and Jakobsson holds up under scrutiny. He cites striking discrepancies between the analysis presented by these two with a paper that came out by Reich et al. (http://dx.doi.org/10.1016/j.ajhg.2011.09.005) called “Denisova admixture and the first modern human dispersals into southeast Asia and oceania.” Their salient finding is that there were very few Denisovan markers in mainland Asian populations.

Hawks suggests that the reason the two papers differ so greatly is that in the paper by Skoglund and Jakobsson, the analysis is picking up only slight differences in gene frequencies between populations, and that, while there is hybridization and migration into the area by Denisovans, it is small in amount. He writes:

We aren't very far from a more definitive answer of this question, as the data continue to accumulate every day. What I find interesting is the way that models can generate these 1% differences in ancestry proportions, depending on sampling and the pattern of migration assumed to have happened in the past. Two estimates that differ by less than a percent are not really different. This paper provides the suggestion of a more widespread Denisovan legacy, and I accept that as a possibility.

It is clear that there was some interbreeding between these populations. How much remains to be seen.

Hat tip to Paul Pavao.
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Population Growth Spurring Evolution?

The Daily Galaxy is reporting on some work by John Hawks at U of Wisconsin, Madison on the rate of evolutionary change in humans. They write:

A team led by University of Wisconsin-Madison anthropologist John Hawks estimated that positive selection just in the past 5,000 years alone -- datihttp://www.blogger.com/img/blank.gifng back to the Stone Age -- has occurred at a rate roughly 100 times higher than any other period of human evolution. Many of the new genetic adjustments are occurring around changes in the human diet brought on by the advent of agriculture, and resistance to epidemic diseases that became major killers after the growth of human civilizations.

"In evolutionary terms, cultures that grow slowly are at a disadvantage, but the massive growth of human populations has led to far more genetic mutations," says Hawks. "And every mutation that is advantageous to people has a chance of being selected and driven toward fixation. What we are catching is an exceptional time."

The first caveat to this is that evolutionary biologists have discovered time and time again that small populations undergo evolution faster than larger ones because traits get expressed with a greater degree of frequency, hence the concept of founder effect. In larger populations, genetic load increases and the population bears more selectively disadvantageous traits.

The other caveat is that, as one goes back in time, genetic evidence gets scantier and scantier to the point where we really don't know exactly how fast evolution was happening in some populations, in part because we don't have all the fossil data. I think there is merit in what Hawks is trying to show but the above two concerns need to be addressed.