Evidence for Macroevolution and Common Descent

As threatened promised, here's the first part of my summary of the essay 29+ Evidences for Macroevolution: The Scientific Case for Common Descent, from the talk.origins archive. Note that the author and the archive don't know I'm doing this. My summary's open to correction - please comment!

Firstly, some points from the Introduction:

- Macroevolution means the appearance of new species (and larger groups, such as families and classes). ("Microevolution" is changes within species.)

- Universal common descent is the idea that all organisms (plants, animals, people, etc) are related to each other; that they all ultimately descend from a common ancestor - one original species.

- How life got started in the first place, abiogenesis, is a separate question to macroevolution and common descent and isn't addressed in the essay.

There's a good explanation of the scientific method in the essay, under the heading "What is Meant by 'Scientific Evidence' for Common Descent?". Briefly, a scientist comes up with a hypothesis - in everyday language, a theory. That hypothesis is then tested against the evidence, and discarded if it's shown to be wrong. So the hypothesis has to be able to make a prediction - if it's true, then we should see such and such evidence - and it has to be falsifiable - if it's false, we should see so and so evidence.

Universal common descent is accepted as a fact by scientists because:

- So many predictions from this hypothesis have been found to be true
- No significant evidence that it's wrong has been found
- Large amounts of evidence show that other explanations are wrong
- Many other explanations can't be tested at all.

That's my summary of the Introduction. Next up: phylogenetics, or family trees of living things!

Endosymbiosis for fun and profit

Speaking of evolution, a neat thing I spotted in a recent New Scientist: a newly discovered microbe called Hatena has been seen incorporating an algal cell into its body. It's long been known that eukaryotes (fungi, plants, animals, us) got their start when simple cells took on board other cells as lodgers - algae became the chloroplasts inside plant cells, bacteria became the mitochondria which power our cells. But this is the first time the process has been directly observed.

Hatena is Japanese for (roughly) "What th-!?".