u/SocialAmoebae

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Hi!

I have a question regarding the ways we can come to know that all species have a common origin.

In trying to teach myself phylogenetics, one of the basic inferences I see used to produce trees is: the degree of resemblance between species is "inversely proportional" to the degree of genealogical distance between them.

The resemblance in question can be genetic, embryological, morphological, behavioral, etc.

In The Origin of Species, Darwin uses this inference to conclude that Linnean classification actually reflected genealogical relations between species.

But what warrants us to use this inference to begin with? That's my question.

I am just trying to get the reasoning ironclad here, because once this inference is justified, and given modern comparative evidence, the common origin of life follows quite naturally.

I also have a very curious nephew who likes nature and asks a lot of questions, and it would be nice to have a simple way of explaining to him that all life shares a common origin!

PS : I know that there are also other lines of evidence such species geographical distributions and fossil as proof of transition, but I would like to stick to the basic inference for phylogenetics.

Thanks for reading 🙏

Hi!

I have a question regarding the ways we can come to know that all species have a common origin.

In trying to teach myself phylogenetics, one of the basic inferences I see used to produce trees is: the degree of resemblance between species is "inversely proportional" to the degree of genealogical distance between them.

The resemblance in question can be genetic, embryological, morphological, behavioral, etc.

In The Origin of Species, Darwin uses this inference to conclude that Linnean classification actually reflected genealogical relations between species.

But what warrants us to use this inference to begin with? That's my question.

I am just trying to get the reasoning ironclad here, because once this inference is justified, and given modern comparative evidence, the common origin of life follows quite naturally.

I also have a very curious nephew who likes nature and asks a lot of questions, and it would be nice to have a simple way of explaining to him that all life shares a common origin!

PS : I know that there are also other lines of evidence such species geographical distributions and fossil as proof of transition, but I would like to stick to the basic inference for phylogenetics.

Thanks for reading 🙏

Hi!

I have a question about genetic diversity seen as an ecological feature of the environment.

Let me preface this by saying that although I have a BS in Biology, I now study something else.

It remains something I am deeply interested in though!

Here is my question: Is the level of genetic diversity in a population a parameter to which organisms adaptively react?

For example, one could hypothesize that low diversity increases risks related to inbreeding, which would favor out-migration or outbreeding.

Another hypothesis is that since a low genetic diversity leads a niche to be more saturated and increases the risk of competitive exclusion, it would also favor emigration.

Yet another hypothesis is that in a low-diversity population, since the background similarity is high, the extra similarity added by close genealogical relations is comparatively low, which would make the payoff of kin altruism smaller. By contrast, the gradients of similarity are steeper in a high-diversity population, which would increase the payoff for kin altruism.

Since lines of descent, throughout the generations, may find themselves in ecological configurations that vary with some regularity, it is not completely implausible that phenotypic expression during development is modulated by genetic diversity, as it can also be modulated by population density.