Species Specifics
What distinguishes one species from another? In the 1960's when Jane Goodall first observed chimpanzees using sticks as tools, anthropologists (scientists who study human origins) debated whether chimpanzees now should be considered humans as well since tools (technology) are a sign of human culture. Of course we now know that many animals use tools to one degree or another and all social mammals have some form of culture. Culture must be learned to be shared within a group. It is not past from one generation to the next in genes. One definition of primate culture is all the combined knowledge between members of a social group and their use of tools. But what humans know, and how we use tools is so far beyond what chimps know and how they use tools that it is clear they are not humans. In fact chimps aren't even in our genus, Homo. They are in their own genus, Pan and there are two species of Pan: the Bonobo (once called the dwarf chimpanzee) and the African Chimpanzee. The way that scientists define a species has changed over the time that the naming divisions (taxonomy) were first invented by Carl Linnaeus in the 18th century. Linnaeus determined relationships between organisms by their physical characteristics. He developed the basic divisions that we still use today of dividing all creatures into one of five kingdoms (today there are six) and then subdividing groups into further categories of phylum, class, order, family, genus, and species. Humans are in the animal kingdom, the chordate (backbone) phylum, the mammal class, the primate order, the hominid (great ape) family, the Homo genus, and our species name is sapien (wise ones). But what Linnaeus could not examine, nor know about in his day was the microscopic coils of DNA in the cells of all creatures than encode the genetic instructions for every individual organism. Today we compare the differences in the bases of the DNA molecules as one important indicator to determine species. If we assume that all life on Earth is related, and we know the rate that genes mutate (change at random) over time then we have an idea of how far in the past two different species diverged from each other. For example chimpanzees share at least 98% of the exact same base order in their DNA as humans. (Some research is reporting even more shared DNA!) so we can estimate that chimps and humans diverged from a common ancestor about 5-6 million years ago. Another test of different species is the inability to interbreed. For example a horse can breed with a donkey and produce a mule, but the mule is almost always sterile (can't reproduce) and thus horses and donkeys are considered different species by this test. But occasionally mules can interbreed! As you can see the definition of species is far from determined. This problem of determining species is more evidence that all life on our planet shares a common origin. The best evidence for shared origins is that that all life shares the same genetic material and the same genetic code. A gene that codes for a particular protein in a bacteria is the same gene that codes for the same protein in a human or a pine tree. In 2003 the Human Genome Project completed mapping all 25,000 genes in every cell in every human body. Once we had a map of our genes we could compare the differences that occur though random mutation between all other species on Earth thus gaining a better picture of the inter-relatedness of all life on our planet as well as the differences between individual humans. One interesting finding is that the concept of race is not recognized by science. The word is meaningless. Although people define racial differences between people, our genes do not show any significant differences at all! In fact there is more genetic difference betweenmembers of a “so called” race than between individual humans selected at random from all “so called” races. Simply put, we are all one species: Homo sapiens.
Answer the questions below based on what you just read.
1. What caused anthropologists in the 1960's to debate whether or not chimpanzees should be classified as human? What did they decide?
2. What is one definition of primate culture? How is culture shared within a group?
3. What is the genus name of chimpanzees and what are the names of the two species?
4. Who invented a naming divisionsystem (taxonomy) in the 18th century? What are the seven basic subdivisions (starting with kingdom)? How many kingdoms are their today? What is the name of the order that humans are a member of? What is the name of our family?
5. What could Linnaeusnot have known about that we use today to determine species? Why do you think Linnaeus would not have known about this important molecule of heredity? What percentage of DNA do humans share with chimps?
6. When horses interbreed with donkeys what is the result? Can mules interbreed?
7. How many genes are in every human cell? What was the name of the project that mapped all the human genes in 2003? What do scientists say about the concept of race?
Homo neanderthals were the last remaining human species to live alongside Homo sapiens and went extinct very recently right before the end of the last great ice age some 20,000-40,000 years ago. Some scientist think they have identified neanderthal genes in modern Homo sapiens. That would have meant that we were able to interbreed (reproduce) at least with some of them. Use the graphic to answer the questions below.
8. If modern humans do have some neanderthal genes which three groups seem to have the neanderthal genes? Which two groups do not have the genes?
9. French, Han-Chinese and Papuan peoples all live in countries outside of Africa. Did Homo sapiens who remained in Africa (Yoruba, San) interbreed with neanderthals?