Download Species Specifics

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 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 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 now dead in the
sciences. Although people define racial differences between people, our genes do not show any
differences at all! In fact there is more genetic difference between individual humans at random
than there are between so called races. 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 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 division system (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 Linnaeus not 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 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 interbreed with neanderthals?