Menarche — She completely left out what I think is the most probable cause INCREASINGLY BETTER NUTRITION.

I am basing this on stuff I read about horse nutrition during their growing years. IIRC keeping a young horse too thin was much better for them then too fat, 👉because they would make up the lack of inches later on.👈 Yearlings that were ‘finished’ so they would win in yearling in-hand classes were found to do poorly later in life. Fat does wonders for hiding conformation defects. Also horses at the ideal weight with a bit of rib showing (look at a race horse) are considered ‘starved’ by the ‘soft hearted’

Let me reiterate that. In growing animals, periods of time when they are a bit starved, like in the winter, are common. Nature has taken that into account and will make up for the lack of growth later when food is plentiful as long as the growth plates have not closed. In horses that is at 7 years in humans ~25 years.

I think this periodic lack of growth due to lack of food will influence the timing of menarche in mammals.

CANNED FOOD
In 1809 with the incentive of Napoleon’s hefty cash award,  Nicolas Appert, developed a method of sealing food in glass jars. A couple years later Durand patented food storage in tinned cans. The market was the British Army and navy due to the expense. With industrialization and the movement of population into cities, canned food became popular in the mid 1800s.

WIKI

…Demand for canned food greatly increased during wars. Large-scale wars in the nineteenth century, such as the Crimean War, American Civil War, and Franco-Prussian War, introduced increasing numbers of working-class men to canned food, and allowed canning companies to expand their businesses to meet military demands for non-perishable food, enabling companies to manufacture in bulk and sell to wider civilian markets after wars ended. Urban populations in Victorian Britain demanded ever-increasing quantities of cheap, varied, quality food that they could keep at home without having to go shopping daily. In response, companies such as Underwood, Nestlé, Heinz, and others provided quality canned food for sale to working class city-dwellers. The late 19th century saw the range of canned food available to urban populations greatly increase, as canners competed with each other using novel foodstuffs, highly decorated printed labels, and lower prices…

FROZEN FOOD
WIKI

In 1861 Thomas Sutcliffe Mort established at Darling Harbour in Sydney, Australia, the world’s first freezing works, which later became the New South Wales Fresh Food and Ice Company. Mort financed experiments by Eugene Dominic Nicolle, a French born engineer who had arrived in Sydney in 1853 and registered his first ice-making patent in 1861. The first trial shipment of frozen meat to London was in 1868. Although their machinery was never used in the frozen meat trade, Mort and Nicolle developed commercially viable systems for domestic trade. The financial return on that investment was minimal for Mort. Regular shipments of frozen meat from Australia and New Zealand to Europe began in 1881, with a consignment of frozen New Zealand sheep exported to London on board the Dunedin.

By 1885 a small number of chickens and geese were being shipped from Russia to London in insulated cases using this technique. By March 1899, the “British Refrigeration and Allied Interests” reported that a food importing business, “Baerselman Bros”, was shipping some 200,000 frozen geese and chickens per week from three Russian depots…

From 1929, Clarence Birdseye introduced “flash freezing” to the American public. Birdseye first became interested in food freezing during fur-trapping expeditions to Labrador in 1912 and 1916, where he saw the natives use natural freezing to preserve foods.[5] A 1920s hunting trip to Canada, where he witnessed the traditional methods of the indigenous Inuit people, directly inspired Birdseye’s food preserving method.

The Icelandic Fisheries Commission was created in 1934 to initiate innovation in the industry, and encouraged fishermen to start quick-freezing their catch. Íshúsfélag Ísfirðinga, one of the first frozen fish companies, was formed in Ísafjörður, Iceland, by a merger in 1937.[7] More advanced attempts include food frozen for Eleanor Roosevelt on her trip to Russia. Other experiments involving orange juice, ice cream and vegetables were conducted by the military near the end of World War II…

Then there is iodine. NC is in the goiter belt.

Research on Iodine Deficiency and Goiter in the 19th and Early 20th Centuries – ScienceDirect

In the first 2 decades of the 20th century, pioneering studies by Swiss and American physicians demonstrated the efficacy of iodine prophylaxis in the prevention of goiter and cretinism. Switzerland’s iodized salt program has been operating uninterrupted since 1922.

The History of Vitamins | Timeline | Supplement Factory

In 1912, scientists set out to address health issues and discovered that food contained more than just the three known nutrients. Initially referred to as “accessory substances,” these compounds were later termed “vitamines” in scientific papers…

In the 1920s, sales of vitamin A and C soared as the public adopted the belief that supplements containing vitamins also held other beneficial compounds. By 1922, multivitamin-type products were widely advertised as remedies for a range of issues..

Discovery date of specific vitamins 

** 1910 – Vitamin B1 (Thiamine)

** 1913 – Vitamin A

** 1920 – Vitamin C; Vitamin D; Vitamin B2 (Riboflavin)

** 1922 – Vitamin E

** 1929 – Vitamin K1

** 1931 – Vitamin B5 (Pantothenic acid)

** 1934 – Vitamin B6 (Pyridoxine)

** 1936 – Vitamin B7 (Biotin); Vitamin B3 (Niacin)

** 1941 – Vitamin B9 (Folic acid)

** 1948 – Vitamin B12 (Cobalamins)

…In 1943, the first one-a-day multivitamin was introduced. By the 1950s, multivitamins had become widely available and were commonly promoted as a staple to be kept on the dining table for use at meal times….

In 1973, MegaFood pioneered the production of vitamins made from real food, prompting other companies to follow suit by using plant-based ingredients instead of synthetic compounds and artificial additives.

Over time, as more nutrients and superfoods were discovered, they were incorporated into multivitamin blends. With the evolution of these products, regulations emerged to ensure they suited the public.