The Haldane, a unit of evolutionary change named after JBS Haldane, represents the number of standard deviations by which the mean of individual traits in a population changes per generation. However, the average time for a population to acquire a specific trait is a concept that varies depending on the type of trait considered, and it is only applicable to discrete traits. Furthermore, the time required for trait acquisition differs significantly from one trait to another and is highly influenced by the starting point of the evolutionary process.
To begin, you mention
[..]evolution is nowadays pretty much analyzed through phylogenetic trees[..]
. While many evolutionary biologists heavily rely on phylogenetic methods, a significant portion of them (likely the majority) do not directly utilize these methods in their work.
Although I may not fully comprehend your inquiry, I hope the following suggestions can assist you in comprehending the matter or refining your question. Please note that I am not a phylogeneticist, and I am uncertain if such a term even exists.
How is “Node” defined in the field of Phylogenetics?
I believe your understanding of a
could be unconventional. In the context of phylogeny, a node refers to the shared most recent common ancestor between two sister lineages.
The measurement of time within a phylogenetic tree.
When examining a phylogenetic tree, the axis depicting lineage diversification corresponds to time (measured in years). Various approaches, such as assessing the rate of neutral substitutions, are employed to estimate this real time. It may be beneficial to familiarize yourself with the concept of the molecular clock.
Has there been a development delay for every subsequent node?
I’m uncertain about your intention behind the word “develop” in this context. Typically, development refers to the phenotypic changes that occur in an individual or organism throughout its lifetime. For more information, you can refer to the field of Developmental Biology.
The average duration for an organism to either lose or acquire a specific trait.
Once again, it is unclear whether you are referring to development or evolution, as you mention “any organism” instead of “any population”. Regardless, the concept of an average time for a population to acquire a specific arbitrary trait has several considerations. Firstly, it is only applicable to discrete traits. Secondly, the timeframe greatly depends on the type of trait being considered. Thirdly, the duration varies significantly between different traits. Lastly, the starting point of the evolutionary process towards the development of the specific trait heavily influences the result. Consequently, this concept lacks coherence.
The existing “standard evolutionary time unit” is currently in use.
The concept described can also be applied to quantitative traits. The Darwin (d), which was named after C. Darwin and created by Haldane, represents a unit of evolutionary change. Specifically, it is defined as an e-fold (e≈2.7) increase in the average value of an individual’s trait within a population over millions of years.
The Haldane, which is named after JBS Haldane but I am unsure of its inventor, is a measure of evolutionary change. It represents the number of standard deviations that the mean of an individual trait in a population changes per generation. The Haldane unit is influenced by factors such as selection pressure, genetic variance (both additive and non-additive), environmental variance (including heritability), and mutational pressures.
There is indeed a concept similar to what you are describing, known as a molecular clock. By examining the rate of change in specific genes and non-coding sequences, scientists have been able to correlate it with other evidence, such as the fossil record. This correlation enables the estimation of the natural timespan required for a specific set of mutations to occur.
Please note that not all genes possess the necessary characteristic of accumulating mutations at a relatively consistent rate over time. The majority of genes accumulate mutations in a more random manner.