Research Profiles : The genes that lie beneath :
Testing hypotheses in the fossil record
Of course, ultimately, in order to apply our understanding of phenotypes to extinct organisms and deep evolutionary history, we need fossil data. According to Leslea, "Every fossil is a test of a hypothesis...This is why people are all in a tizzy with almost every new hominid fossil because it could upset somebody's hypothesis or everybody's hypothesis if it just wasn't what we were expecting."
Leslea is hopeful that for human evolution, the search for fossils will pay off: "We always talk about the paucity of the fossil record for hominids and there are some gaps, and there are just a handful of fossils from some time periods. But when you compare it to another family, the hominid record is a really good record. I mean we actually have a pretty good understanding of what happened in human evolution if you compare it to chimps or to many other mammalian families...We have a lot better understanding than what gets portrayed in the popular literature...We actually do have the fossil data to figure out how our ancestors evolved."
Leslea's work on baboons may help us understand modern organisms better but the questions that drive her concern evolutionary history: "I always want to keep the fossil perspective in mind. I got into this because I love to find fossils...When it comes right down to it: every new fossil that's where the data is going to come from. The way that we interpret those data may change but that fossil I found will still be there, and will be interpreted in new and better ways."
Discussion and extension questions:
- Review the process of natural selection. Explain why variation is so key to that process.
- Imagine two populations of fruit flies: Population A contains 1000 flies with almost identical wing lengths, and Population B contains 1000 flies with wing lengths that vary a lot from individual to individual. Assume that wing length is genetically-encoded. If natural selection acts on wing length, which population is more likely to evolve? Explain your reasoning.
- What is the difference between genetically-based variation and environmentally-based variation? Explain that difference, and give an example not mentioned in this profile for each.
- How does Leslea figure out which aspects of baboon tooth shape and composition are genetically influenced? Why is it important that she know how all the baboons are related to one another?
- In 2004, scientists reported the discovery of Homo floresiensis (Flo), a partial fossil skeleton of a single individual. These fossils have inspired a scientific controversy: some scientists argue that Flo represents a new hominid species and others argue that she is simply a small Homo sapiens with a growth disorder. To clear up this controversy, what sort of evidence would be useful? Why is it important to understand the degree of variation in Flo's species and in Homo sapiens in order to solve the mystery?