Without a fossil representation, how do we know that mammals share a common ancestor?

[Paprika]

These days we use rRNA from the 18S subunit for phylogenetic trees and similar 'who's the daddy species' type stuff. These are common in all organisms from Archaea to Mammals and everything in between, with common motifs between all organisms, and variable regions that vary heavily depending on the organism's species, family etc, and are used to determine how closely species are related. Different diverging types of rRNA demonstrate common ancestors, not just through mammals but right back to with Bacteria and stuff. No fossils needed!

[Dunbaratu]

3) DNA evidence is harder to use than you suggest. We typically do not have DNA samples from extinct species, so you can't just compare.

Correction, it's harder than what your strawman OF me suggested. At no point did I suggest the DNA evidence comes from extinct species. I was referring to determining how far apart two modern species are based on their DNA. You can get a pretty good time estimate for the first mammal this way by looking at modern mammals' DNA.

Aside from that one strawmanning of my post, the rest of your points are good and I concede them.

[Pugspaceprogram]

Aside from that one strawmanning of my post, the rest of your points are good and I concede them.

I agree...

[xclusiv8]

The title gives it away, this is a unanswered question in science, and i want to know your thoughts. Have fun with your creative ideas and theories.

Remember, there is (currently) no right or wrong answer, just theories.

You obviously do not know the meaning of a scientific theories. There are no such things as "just theories". For example, The theory of evolution is not "just a theory". Its fact.

Wiki explination:

A scientific theory is a well-substantiated explanation of some aspect of the natural world, based on a body of knowledge that has been repeatedly confirmed through observation and experiment.[1][2] Scientists create scientific theories from hypotheses that have been corroborated through the scientific method, then gather evidence to test their accuracy. As with all forms of scientific knowledge, scientific theories are inductive in nature and do not make apodictic propositions; instead, they aim for predictive and explanatory force.[3][4]

The strength of a scientific theory is related to the diversity of phenomena it can explain, which is measured by its ability to make falsifiable predictions with respect to those phenomena. Theories are improved as more evidence is gathered, so that accuracy in prediction improves over time. Scientists use theories as a foundation to gain further scientific knowledge, as well as to accomplish goals such as inventing technology or curing disease.

Scientific theories are the most reliable, rigorous, and comprehensive form of scientific knowledge.[3] This is significantly different from the word "theory" in common usage, which implies that something is unsubstantiated or speculative.[5]

[Dieselpower]

That's really sloppy terminology from wikipedia. A theory is not a fact and can be debated / falsified.

To start with, theories describe interaction and direction between an independent and a dependent variable in a general fashion.

Good theories are generalisable and specifically precise as to advance our understanding of the world.

However, it is quite possible that you have two competing plausible theories explaining the same outcome.

That's why in scientific circles these theories are constantly tested and improved in new research.

From years of research in a certain direction the scientific community starts to accept certain theories and viewpoints above others.

This creates a scholarly paradigm, which is basically a set of believes and theories that is regarded as the closest thing to the truth.

Examples of paradigms are Einstein's relativity theory and plate tectonics, and there are many more in social sciences but that's due to their highly complicated testing of empirical rigorousness and constructivist nature.

[xclusiv8]

That's really sloppy terminology from wikipedia. A theory is not a fact and can be debated / falsified.

To start with, theories describe interaction and direction between an independent and a dependent variable in a general fashion.

Good theories are generalisable and specifically precise as to advance our understanding of the world.

However, it is quite possible that you have two competing plausible theories explaining the same outcome.

That's why in scientific circles these theories are constantly tested and improved in new research.

From years of research in a certain direction the scientific community starts to accept certain theories and viewpoints above others.

This creates a scholarly paradigm, which is basically a set of believes and theories that is regarded as the closest thing to the truth.

Examples of paradigms are Einstein's relativity theory and plate tectonics, and there are many more in social sciences but that's due to their highly complicated testing of empirical rigorousness and constructivist nature.

What I was trying to say was that there are no such things as "just theories". Theories by their own nature are already researched, tested and explained with variouse methods. Therefor there is more truth to a theory than anything else.

[Kerbface]

The main problem I think is when people think of theories as just an idea someone had one day, that doesn't have to have any evidence or testing or verifiability at all.

The difference between a conventional theory and a scientific theory should be taught in primary school. I get so tired of people saying "Well, it's ONLY a theory, you can't prove it".

[xclusiv8]

The main problem I think is when people think of theories as just an idea someone had one day, that doesn't have to have any evidence or testing or verifiability at all.

The difference between a conventional theory and a scientific theory should be taught in primary school. I get so tired of people saying "Well, it's ONLY a theory, you can't prove it".

+1

I totally agree!

[K^2]

That's really sloppy terminology from wikipedia. A theory is not a fact and can be debated / falsified.

Whether it is a fact or not depends on your definition of fact. How would you define it? Can you give me an example of something that is a fact?

Defining fact as anything that is supported by well-established theory is not a bad way to define it. That's a good, pragmatic definition that a lot of people hold to.

But yes, theory by its very design must be falsifiable. Otherwise, it is useless. The only theory that cannot be falsified is a theory that makes no testable predictions. And if it makes no testable predictions it makes no predictions that we can make use of.