Human evolution: the year 2010 in review (Part 1)

That’s some good-looking gombo, cher!

gumbo
Creative Commons License photo credit: Southern Foodways Alliance

This blog contribution aims to be like a good Louisiana seafood gumbo: thick, hearty, spicy, and made up all kinds of finger-licking ingredients (pun intended). There will be some French, which would be apropos, some Latin as well, and all kinds of discoveries related to human origins, as they transpired this past year. I will follow up with a second part in a week or two with an observation and a comment.

In an earlier blog, “A pinky’s promise,” I wrote about the incredible discovery that was made early in 2010 when DNA analysis was performed on one small finger bone retrieved from a cave in Southern Siberia. The bone dated to a period (50,000 to 30,000 years ago) when all scientists assumed that the only living humans were either Homo sapiens sapiens or Neanderthals (perhaps we should now be saying Homo sapiens neanderthalensis, but I am getting ahead of the game). This first assumption proved to be wrong.

Entrance to the Denisova Cave
Creative Commons License photo credit:ЧуваевНиколай

In 2008, DNA analysis carried out on a single finger bone revealed that there was a third species of human walking the earth at that time. Toward the end of 2010, this view was corroborated by additional DNA analysis of a few teeth that were found in the same Denisova cave. The Max Planck Institute in Leipzig announced that these so-called “Denisovans” represent a new species.
More interesting still, some of their DNA is still around: the “Denisovans” interbred with the ancestors of Melanesians. This implies that at one point, this third species was quite widespread in Asia. If these conclusions hold up, the lesson we should take away from this breakthrough is that every little scrap of evidence counts when studying human origins, even a single tooth, or a finger bone. I wonder how many single finger bones or teeth have been overlooked in the past, or are still awaiting re-discovery in a museum drawer somewhere.

Neanderthals were also in the news this past year. For years, researchers have been vexed by questions such as “Who were these people?”, “Where did they come from?”, “What made them extinct?” and last but not least “Is there a little bit of Neanderthal in (some of) us?”

With regard to the last question, also discussed in earlier blogs, the way in which we answer that question will result in a different scientific (read: Latin) nomenclature for Neanderthal. Allow for the possibility of interbreeding between Homo sapiens and Neanderthals and also agree that their offspring was fertile, i.e., they successfully reproduced, then you would have to refer to Neanderthals as Homo sapiens neanderthalensis. If you disagree with this idea, and think it was unlikely these two populations interbred, or that their offspring was not capable of producing fertile offspring, then you would have to refer to Neanderthals as Homo neanderthalensis. This classifies them as a species separate from modern humans; by definition, species cannot interbreed and produce fertile offspring.

Man
A Happy Neanderthal
Creative Commons License photo credit: erix!

The latter way of thinking was long popular among paleoanthropologists. Now the pendulum is swinging the other way. Scientists at the institute decoded the Neanderthal genome and compared it with that of modern humans. The result? In their words: “By comparing that genome with those of various present day humans, the team concluded that about 1 percent to 4 percent of the genome of non-Africans today is derived from Neanderthals.”  In people speak: up to 4% of a European’s genetic makeup could be inherited from the Neanderthal lineage, now extinct.

Before you check for hair on your knuckles, thank (or blame) a single finger bone and a few teeth, as well as the staff at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany for all this.

Lest we all (well, at least those of us of European descent) break out in hives and run for the nearest hills, scientists were quick to add: “[T]he Neanderthal DNA does not seem to have played a great role in human evolution.”

Certainly, 1 to 4% overlap in genetic makeup is not very much, but it is a whole lot more than we were willing to consider just a year ago. Differences between Homo sapiens sapiens and Homo sapiens neanderthalensis remain significant. The overall physical appearance of a modern human is very different from that of a Neanderthal. In terms of behavior, and cognitive abilities, the two subspecies also appear to be a world apart, never mind they shared portions of our planet.

Comparing Neanderthals and modern humans
One of the areas in which there were both similarities and differences was diet. These insights also came out this past year.  Did you know that Neanderthals ate their veggies? And that they liked to cook them as well? Perhaps you did. However, did you also know that they were not averse from eating each other?

Check back next week to see more on this, when Dirk discusses teeth, DNA, and his own conclusions to 2010 in review.

Neanderthal Controversy

As mentioned in a previous post, the question of whether or not Neanderthalers were able to have offspring continues to be hotly debated by scientists. Depending on the answer given, we would have to classify Neanderthalers either as people like us, or people very different from us. Of course, proponents of both of these statements claim they have evidence to back up their very different positions.

Those who suggest that there was interbreeding between our ancestors (Homo sapiens sapiens) and Neanderthalers would label Neanderthal bones as belonging to Homo sapiens neanderthalensis.

With this label, the word “Neanderthalensis” appears in the third position of the nomenclature, which refers to the level of sub-species. This implies that the differences between us and Neanderthalers are so small that they are contained within the range of variation one would expect to find within a species (in other words, we are related to Neanderthals on a sub-species level, rather than being classified as two different species.)

According to this interpretation, the ability to interbreed with modern humans might have also spelled doom for the Neanderthals. But if the two species interbred, why don’t we see the “typical Neanderthal look” today?

As time went by and interbreeding between our ancestors and Neanderthalers continued, the thinking goes that the Neanderthalers’ genetic contribution to each new generation became ever smaller. Eventually, this percentage became so small that all people began to look like humans rather than a Neanderthal individual.

Scientists refer to this scenario as genetic swamping. If this is what happened, it would be possible for the two species to have interbred over many generations, while also explaining why the influence of Neanderthaler genes can’t be seen by the naked eye. A child burial uncovered in Portugal is seen as evidence that “admixture between the two groups must have been significant, at least in such cul-de-sacs as the Iberian Peninsula,” providing more support for this position.

Others disagree and suggest that we use the nomenclature Homo neanderthalensis.

Here the term “neanderthalensis” is in the second position of the nomenclature, referring to the species. This is a scientist’s way to say that the difference between humans and Neanderthalers is at the much more significant species level. This has an important implication: according to these proponents, Neanderthal populations and Homo sapiens populations could not have produced fertile offspring.

Of the two positions just outlined, most scientists prefer the second one and refer to DNA analysis for support. DNA analysis of Neanderthal bones has been undertaken for a while. A comparison of Neanderthal DNA against modern human DNA suggests that there are enough genetic differences to warrant labeling them as a separate species.

Most scientists, therefore, prefer seeing “Homo neanderthalensis” in the scientific literature. Since interbreeding and subsequent genetic swamping cannot occur in this scenario, the disappearance of the Neanderthalers is blamed on outright genocide practiced by our ancestors, or greater hunting skills on the part of the newcomers.

Extinction doesn’t mean failure

What the fossil record clearly shows is that the life forms that existed millions of years ago were successful in their own right. They lived and reproduced in numbers large enough to maintain their species over incredibly long periods of time. The term “half-evolved” therefore does not accurately represent these fossil life forms.

We should not fall into the trap of considering early hominids as half-baked versions of the final perfect version seen in our times. We would do better to consider these earlier versions as successful adaptations to the conditions that were prevalent at that time.

Consider Lucy. She and the other members of the species Australopithecus afarensis were successful survivors over a period of 600,000 years, as evidenced by a collection of fossils representing about 300 different Australopithecine individuals.

Nothing half-evolved here. These Australopithecines were very successful over a period of time about three times as long as our own species, Homo sapiens sapiens, has been around.

If we are willing to consider Lucy half-evolved, then what epithet would apply to us?