"Humans (some of them) have the conscious foresight to see ahead to the disastrous consequences of over-population"
We are by most metrics currently living over earth's ecological capacity. Humanity is currently using nature 73% faster than ecosystems can regenerate, the equivalent of living off 1.73 Earths. 2026 had "overshoot day" earlier than ever before. https://overshoot.footprintnetwork.org/newsroom/eod-2026-en/
"It is no use appealing to advances in agricultural science-'green revolutions' and the like. Increases in food production may temporarily alleviate the problem, but it is mathematically certain that they cannot be a long-term solution; indeed, like the medical advances that have precipitated the crisis, they may well make the problem worse by speeding up the rate of the population expansion." (Page 111)
Our world is unable to withstand continued population growth & continued agricultural expansion. We will simply run out of resources, and it will lead to deaths on a mass scale. It makes sense that in many places the birth rate is falling.
Given the world we live in and how aware many of us are that we are running out of resources, it is no doubt that many people are deciding not to have kids. As well it is a fact of life that the birth rate tends to fall in first world countries, as the child mortality rate lowers, the number of children people tend to have lowers. This combined with economic and social factors around having children, education for women, people getting married later in life, etc. It is no surprise that in many places the birth rates are falling.
Global population growth is declining, it peaked in 1963 at ~2.2% according to the UN.
"Depending on the ecological details of the species, various mixes of caring and bearing strategies can be evolutionarily stable. The one thing that cannot be evolutionarily stable is a pure caring strategy. If all individuals devoted themselves to caring for existing children to such an extent that they never brought any new ones into the world, the population would quickly become invaded by mutant individuals who specialized in bearing. Caring can only be evolutionarily stable as part of a mixed strategy-at least some bearing has to go on" (Pg 109) (I can't figure out how to do a highlight box on my laptop)
It is interesting to consider the variety of strategies that different species have when it comes to birthing and raising young. This brings to mind when I learned about K species and r species, where K species have very few young but are very focused and grounded in the raising process of the young, so more of them are able to reach maturity, whereas the r species have a lot of young but less energy is put into raising and caring for them, so they have a higher mortality rate and fewer of them reach maturity. These are specialized strategies so that still a specific amount of the young of each type is able to reach reproduction age in order to continue the survival of the species.
We can clearly see why those animals which cannot cross wide spaces of ocean, as frogs and terrestrial mammals, should not inhabit oceanic islands; and why, on the other hand, new and peculiar species of bats, which can traverse the ocean, should so often be found on islands far distant from any continent.
There are definitely some species found on islands that wouldn't be capable of crossing oceans. If they were there when for example a piece of land broke into 2 for example.
In both varieties and species, use and disuse seem to have produced some effect; for it is difficult to resist this conclusion when we look, for instance, at the logger-headed duck, which has wings incapable of flight, in nearly the same condition as in the domestic duck; or when we look at the burrowing tucutucu, which is occasionally blind, and then at certain moles, which are habitually blind and have their eyes covered with skin; or when we look at the blind animals inhabiting the dark caves of America and Europe.
If all species were created as they are, why would there be some traits that don't have a purpose? Wouldn't all species be created perfectly for their existence & survival?
But on the view of each species constantly trying to increase in number, with natural selection always ready to adapt the slowly varying descendants of each to any unoccupied or ill-occupied place in nature, these facts cease to be strange, or perhaps might even have been anticipated.
Species find their niches with the least competition / best ability to survive. Behavioural adaptations to find an ecological niche.
there will be a constant tendency in natural selection to preserve the most divergent offspring of any one species. Hence during a long-continued course of modification, the slight differences, characteristic of varieties of the same species, tend to be augmented into the greater differences characteristic of species of the same genus
the concept of 'divergent evolution', wherein individuals that lie on the far ends of the spectrum of varieties are more advantageous than those that lie somewhere in the middle. (Grizzly bear & polar bear) -> distinct differences that provide different advantages for the environments.
This seems to be mainly due to the reproductive system being eminently susceptible to changes in the conditions of life; so that this system, when not rendered impotent, fails to reproduce offspring exactly like the parent-form. Variability is governed by many complex laws,—by correlation of growth, by use and disuse, and by the direct action of the physical conditions of life.
Sort of referring to genetic mutation and recombination without an actual understanding of genetics and the fact that mutations exist??? I think that's pretty cool. Seemingly being aware that these changes occur regardless, and for many complex reasons.
But further down in the paragraph, essentially saying as long as the mutation remains advantageous for the environment & conditions of life, the variation will continue to occur (because the individuals with the variation are more able to pass on the trait). His lack of understanding of genetics shows a bit here though, because as he says, "by use and disuse" - this aligns with the ideas of the 'Inheritance of Acquired Characteristics' theory by Lamarck, which we now know to be false.
Numerous existing doubtful forms could be named which are probably varieties; but who will pretend that in future ages so many fossil links will be discovered, that naturalists will be able to decide, on the common view, whether or not these doubtful forms are varieties?
i.e. when Darwin held the Neanderthal skull, just thinking it was a anatomically modern human skull.
A broken or interrupted range may often be accounted for by the extinction of the species in the intermediate regions.
Some environments are more suitable for certain species than others, therefore able to survive in some areas and not others, even in regions close to one another.
Could this also be explained by the founder effect or bottleneck effect (genetic drift)? Maybe certain regions have more predators or competition for resources than others.
With respect to the almost universal sterility of species when first crossed, which forms so remarkable a contrast with the almost universal fertility of varieties when crossed
This variation within species vs. between species conversation makes me think a lot about the definitions of species. Of course, generally the idea is that a species is a group that can interbreed and produce fertile offspring. To me, this makes me think about what we consider a distinct species in the conversation of hominids & human ancestors.
I know there are the 2 groups of scientists (splitters & lumpers), but it is interesting to consider what defines a distinct species. I am sure we will be discussing this later in class regarding Neanderthals, but the fact that many of us have a small % of Neanderthal DNA (among some other extinct hominid species, I believe, like floresiensis), tells us that there was obviously some interbreeding and production of fertile offspring. I think this is also likely true of some animal species, ones we are aware of and ones we might not be. But the idea of "species" as a distinct classification, and where people disagree on what constitutes a species, is quite interesting to me.
either do now exist or could have existed, each good of its kind
I do think this "could have existed" point is a bit interesting, and not one I have heard discussed in the conversation of evolution via natural selection. Of course, as mutations are random and unpredictable, this makes sense. There is the potential for mutations in a species that simply didn't occur, and therefore we have no way to know whether they would've been advantageous or disadvantageous.