maybe try check Homo_floresiensis and Pygmy peoples
from:https://prehistoric-fauna.com/Homo-floresiensis

from:https://en.wikipedia.org/wiki/Pygmy_peoples#Rampasasa

theory regarding Homo Floresiensis
Aside from smaller body size, the specimens seem otherwise to resemble H. erectus, a species known to have been living in Southeast Asia at times coincident with earlier finds purported to be of H. floresiensis.4 These observed similarities form the basis for the suggested phylogenetic relationship. Controversially, the same team has reported finding material evidence (stone tools) on Flores of a H. erectus occupation dating back 840,000 years ago, but not remains of H. erectus itself or transitional forms.[36]
To explain the small stature of H. floresiensis, Brown et al. have
suggested that in the limited food environment on Flores, H. erectus
evolved a smaller body size via insular dwarfism.3 This form of
speciation has been observed in other species on Flores also, as a
result of selective pressures acting on island populations – including
several species of the proboscidean genus Stegodon, an elephant-like
creature. (A dwarf stegodont species of Flores, Stegodon sondaari,
became extinct by about 850,000 years ago and was replaced by another
species of normal size, Stegodon florensis, which then also evolved
into a dwarf form, Stegodon florensis insularis, which disappeared
about 12,000 years ago.)[37][38] This theory posits that the tropical
rainforests on the island are a calorically impoverished environment,
causing a dietary strain on hominins, especially in the absence of
agriculture. Because of reduced resources, smaller individuals have an
advantage because of their lower energy requirements.[39] This
selection can also greatly affect sensory organs such as the brain,
which could explain the small endocranial volume present in H.
floresiensis.
The insular dwarfism hypothesis has been criticized by Teuku Jacob and
colleagues[28] who argue that LB1 is similar to the pygmy peoples who
populate a Flores village, Rampasasa,[40] – and who point out that
size can vary substantially in pygmy populations. Contradictory
evidence has emerged.[41] A 2018 study concluded that the Rampasasa
pygmies are unrelated to H. floresiensis and represent an independent
evolution of small stature via insular dwarfism.
theory regarding pygmy short stature
Various theories have been proposed to explain the short stature of pygmies. Some studies suggest that it could be related to adaptation to low ultraviolet light levels in rainforests.[9][10] This might mean that relatively little vitamin D can be made in human skin, thereby limiting calcium uptake from the diet for bone growth and maintenance, and leading to the evolution of the small skeletal size.[11]
Other explanations include lack of food in the rainforest environment,
low calcium levels in the soil, the need to move through dense jungle,
adaptation to heat and humidity, and as an association with rapid
reproductive maturation under conditions of early mortality.[12] (See
also Aeta people § Demographics.) Other evidence points towards
unusually low levels of expression of the genes encoding the growth
hormone receptor and growth hormone compared to the related tribal
groups, associated with low serum levels of insulin-like growth
factor-1 and short stature.[13]
regarding Insular_dwarfism
Insular dwarfism, a form of phyletic dwarfism,1 is the process and
condition of large animals evolving or having a reduced body size[a]
when their population's range is limited to a small environment,
primarily islands. This natural process is distinct from the
intentional creation of dwarf breeds, called dwarfing. This process
has occurred many times throughout evolutionary history, with examples
including dinosaurs, like Europasaurus, and modern animals such as
elephants and their relatives. This process, and other "island
genetics" artifacts, can occur not only on islands, but also in other
situations where an ecosystem is isolated from external resources and
breeding. This can include caves, desert oases, isolated valleys and
isolated mountains ("sky islands"). Insular dwarfism is one aspect of
the more general "island effect" or "Foster's rule", which posits that
when mainland animals colonize islands, small species tend to evolve
larger bodies (island gigantism), and large species tend to evolve
smaller bodies.