I’m trying again to figure out approximately how many humans constituted the first generation, especially reproducers, else in total. An answer would help but also knowing what terminology would ease finding scientific answers online would help a lot.
Two being the limit is statistically almost impossible: If a predecessor species produced only one human offspring, unless that offspring reproduced with a nonhuman (possibly possible) and begot a human (even less likely) then that human lineage would have ended. If a predecessor species produced two or more human babies, they would have to have been of both sexes, one baby of each sex would have had to have lived long and healthily enough to reproduce, the babies who grew up would had to have reproductive ability during overlapping time periods, they had to have been near enough each other to meet, there couldn’t have been effectively a taboo against sibling intercourse or incest (such as if their ancestral species did not have that taboo), and the new offspring would have had to have a 100% chance of survival for enough further reproduction until the odds could drop to below 100% without threatening species survival. Genetic diversity is another matter.
For terminology, mitochondrial Eve or Adam turns out to mean most recent mitochondrial Eve or Adam, producing an age somewhere like 50-200,000 years ago as of 2013 (https://www.livescience.com/38613-genetic-adam-and-eve-uncovered.html (50,000) and https://www.nature.com/news/genetic-adam-and-eve-did-not-live-too-far-apart-in-time-1.13478 (200,000)) (the durations may have changed with newer research), whereas humans have existed for 6-7 million years (https://humanorigins.si.edu/evidence/human-fossils/species/sahelanthropus-tchadensis) and counting, or if all of that species’ descendant species long since died out then 1.4-2.4 million years ago (Homo habilis (https://humanorigins.si.edu/evidence/human-fossils/species/homo-habilis)).
I’ve been told that today’s genetic diversity gives a clue to the number needed for the first mitochondrial generation (Were there multiple lineages from primate to human?), so I suppose the same principle applies to the first generation ever.
I had thought that evolution was so gradual that if we could travel in a time machine with all of our lab equipment and identify human #1 and the last prehuman who was the human’s direct ancestor and there was at least one generation in between then we with the time machine likely would not know in what species the generation/s in between belonged. But scientists who got published in Human Evolution in 2018 (https://phys.org/news/2018-05-gene-survey-reveals-facets-evolution.html) say maybe not, in that the boundary is relatively distinct (although maybe not knife-sharp).
I originally posted at Were there multiple lineages from primate to human? roughly four years ago. Apparently, the science has been added to since.
(I skipped https://biologos.org/articles/series/genetics-and-the-historical-adam-responses-to-popular-arguments/adam-eve-and-human-population-genetics except for the January note, due to revisions pending, and the related three in a series, because I don’t know how to separate the biology from the theology in them and because I found the statement “our lineage became human as a population – one that has not numbered below about 10,000 individuals over the last 18 million years or more” unclear given the presently-known shorter age of humanity. The language evolution article link is broken or dead. The URLs are as accessed Jun. 20, 2020.)
(One tag available was for “pear-reviewed”, either a typo or a mystery. I’m interested in peer-reviewed science or the closest we have to it.)