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We and the monkeys

The Director of the Max Planck Institute of Evolutionary Anthropology researches what makes us different from the chimpanzee

One of the Directors of the Max Planck Institute of Evolutionary Anthropology in Leipzig, Germany, Dr. Svante Pääbo is among the most important and influential genomic research scientists. From a multi-disciplinary vocation, this 45 year-old Swede with shy manners also studied the history of science, Egyptology and Russian during his graduate years, before becoming a reference in the area of biology and evolutionary genetics. Some of his recent work, that compared fragments of human DNA to other species, created a huge impact. In 1997, studies by a team under his command proved, in a definite manner, that the human being did not descend from the Neanderthal man, a species of humanoid extinct close to 30,000 years.

When he was in Brazil at the end of March to participate in the Brazilian International Genome Conference, Pääbo spoke about the research being done at the Max Planck Institute which is comparing human DNA to that of the chimpanzee (Pan troglodytes), the animal species whose genetic material most resembles that of the Homo sapiens.

Even without having on hand the completely sequenced genome of this primate, the project is surrounded by uncertainties and without a finishing date and complete funding, the scientists estimate that the order of the nucleotides (bases) present in the DNA of man and the chimpanzee is identical in close to 99% of the cases. In constructive terms, therefore, only 1% of the genetic human coding seems to be distinct from the genome of this monkey. For Pääbo, nonetheless, what makes us human, and not chimpanzees, is not only this small fraction of DNA not shared with the primates closest to us, but above all, the unique form peculiar to Homo sapiens, of the use of the common genes of the two species.

In an experiment conducted at the Max Planck Institute, the researcher analyzed the pattern of the expression of 20,000 genes, two thirds of our total, in the blood and in the tissues of the brain and the liver of man and of the chimpanzee. Significant differences in the manner of using these genes were found only in the brain tissue. For this reason, evolutionary biology believes that this organ will be the depository of the secrets that make us human. To develop this theory and, eventually, to prove it, Pääbo would like the sequencing of the genome of the chimpanzee to be taken forward as fast as possible. “The slowness of the scientific community in giving support to the idea of a genome project of the chimpanzee perhaps is explained by a subconscious discomfort in the face of what could come from these comparisons” says the Swedish researcher in an exclusive interview with the journalist Marcos Pivetta.

From the genetic point of view, is it not possible to say what has made us humans and not monkeys?
Not yet. We need to sequence the chimpanzee’s genome which will have to be studied from a functional perspective, so we can know how many of its genes are used and how they are used. The ideal would be to carry out this type of analysis during the process of the development of a chimpanzee, which perhaps might not be possible. I would like to study the expression of the genes during the development of the brain of one of these animals. It is possible that, at the end of the research to which I am referring, we will never have a complete understanding of all of the process that makes us human, but we could have some idea of the fundamentals of this process. We could have some notion of the first steps, of the genetic pre-requisites that make us different from all of the other species. Meanwhile, we cannot forget that the human condition, besides depending on the genetic part, is also linked to cultural and social factors. There are lots of things which turn us into humans: morphology, how we are from the point of view of appearance, language and other cognitive abilities which are not very well defined. I would be glad if during my lifetime one or two of these things were disclosed. Primatology, nevertheless, shows us that many of the supposed absolute differences between a man and a chimpanzee are, in truth, distinctions of grades.

How can you explain that?
Let me give you some examples. A few years ago, a scientific study demonstrated that neighboring groups of chimpanzees, living in the same location, fed themselves in a different way. They were all chimpanzees, eating the same food (tree branches), but in a different manner. Clearly what had happened in this location was the following: some chimpanzee invented a more efficient and different way to eat, which was adopted by the other members of the group, and afterwards passed on from generation to generation. Something similar happens with humans. In one place on the planet, 100% use chopsticks to eat. At another, 100% of the people use a knife and fork. They are distinct cases of cultural evolution. Of course, human evolution is more complex (than that of the chimpanzees).

In which sense?
It changes more rapidly. However, this shows that it is not an absolute difference between the two species. The same thing occurs with language. Chimpanzees can learn a lot. They can pronounce a word, even put two words together. However, even with a lot of training, they are not going to master our sophisticated language. This, however, doesn’t mean that language is an absolute difference between man and the chimpanzee. Again, it is one more type of difference of grade. This type of thing you learn when you begin to study the chimpanzee in depth.

Today, confronted by two fragments of DNA, one from a human being and the other from a chimpanzee, is it possible to state the origin of each one of these sequences?
It is not possible. They are very similar. Without a lot of information about the variations of this piece of DNA, it is not possible to say if it is a man or a chimpanzee. These two fragments could be from one species only.

Should the number of genes of the chimpanzee be similar to that of humans?
Certainly, the number of genes of the chimpanzee must be very close to that found for humans. There could be some duplicated or lost genes, but, up until now, all of the 5,000 cDNAs (complementary copy of the original DNA) of the chimpanzees sequenced, found there correspondent in the cDNAs ofhumans.

In evolutionary terms, does it make any difference for the human being to have 30,000 or 60,000 genes?
I don’t think so. When the sequencing of the human genome was released, it was stated that the 30,000 genes was a sign of the complexity of how these genes are used. However, if we were to have 60,000 genes, this doesn’t mean to say that we wouldn’t be less complex.

Is there a time limit for finishing the chimpanzee’s genome?
No. We don’t even know for sure who will carry out all of the work. Unless somebody comes forward with the money, this project, which should cost close to US$60 million, will take years to be completed. At the moment there is an initiative under way in Japan about the genome of the chimpanzee. Shortly, we should have the money, coming from Japan and from Germany to sequence chromosomes 22 and 23 of the chimpanzee, which correspond to chromosomes numbers 21 and 22 in man.

Why did you say that the sequencing of the genome of the chimpanzee is moving slowly due to apprehension over the comparisons and conclusions that could come from this work?
For whomever is a fervent Christian, who believes that the creation described word by word in the Bible is true, realizing the chimpanzees are so close to us is a disturbing conclusion. In the United States, this could be an important theme. The differences between men and the great apes could reveal the fundamental genetics of our rapid cultural evolution and geographical expansion, which began between 50,000 and 150,000 years ago and has led us to our current authoritarian domination of the Earth. The perception that one or more genetic accidents turned human history possible is going to propitiate a new group of philosophical questions about which we will have to reflect.

Will the comparative study of the genomes of man and of other species, lead us to a revision of the history of our species?
Probably we won’t have to rewrite it, but we will have a type of additional history, a type of genomic history. We might be able to say how our genome is distributed in the world, how we are different from our closest parents on the planet. We are going to have an additional history, different from the written sources and of archeological and paleoontological material. It is important to emphasize that a genetic history is not the history of humanity, but only one aspect of it.

What will be the major contribution of genomic studies to this new form of history?
In a certain manner, they will give us a more objective way of looking at our genetic history. We could produce good insights about how we think about our species. An example of this type of insight is the result of the work such as of Sérgio Danilo Pena (a researcher at the Federal University of Minas Gerais). He demonstrated that, in spite of many Brazilians being classified as white, their genome may be, in the majority of cases, of African origin.

Are people still surprised by the origins of humanity being in Africa?
In the end, the information coming out of the study of genomes and of science in general, will not finish with racism or with prejudice. The best that information can do is not to stimulate this type of sentiment and to show how things are. I believe that it is healthy to see that weare all very similar, that we are a mixture that has little variation. This will contribute to show that we are all very similar, but it is not going to end prejudice. The fight against prejudice has more to do with public policies, with the way the people are educated in schools, with the manner in which the press deals with this question.

Among human beings, does prejudice make any sense?
It doesn’t make any sense from the scientific point of view. We have always known that the notion of race never made any sense. We have found the same sequences of DNA throughout the world. If you are in Europe and journey to the east, where do the people stop being Europeans and begin to become Asians? This is totally arbitrary. It is a social question. In a certain manner, it makes sense to work with a concept of populations, in spite of the definition of the black population, for example, also not being very clear.

Do you not ask yourself, from time to time, if all of this emphasis given to genomic research is not a little exaggerated?
Clearly there is some exaggeration, as in everything. However, I believe that this line of research represents something which is very fundamental, as it permits us to understand the structure of each genome, the location of the genes of our chromosomes, and this is something fundamental.

But don’t you believe that some researchers forget a little of the influence of the other sciences in the study of man?
I believe that, with the increase in the number of genomes sequenced, there will be a return to basic biology. That is to say that, when we speak of transcriptome, of proteome (the grouping of the proteins of an organism), we are taking steps backwards towards physiology. In a certain way, when we speak of the proteome we are speaking about physiology. However, today people don’t use this term. To understand how the proteins work, how they influence the cells and the organisms, this is physiology. Genomics will penetrate through all of biology.