What does Darwin’s theory of evolution explain about the natural world

1). All living organisms are constantly involved in 'a struggle for existence'.

2). In a population, those that tend to survive and reproduce are the individuals whose variations gives them competitive advantage over the rest.

Explanation:

Darwin, thus, identified environmental pressures as the main cause of natural selection. They cause favourable variations to accumulate and unfavourable ones to be weeded out. Over thousands of generations, favourable variations, naturally selected by he environment, accumulate sufficiently to give rise to new species from ancestral species. Therefore, according to Darwin, natural selection, acting through environmental pressure, is the driving force behind evolutionary change in the natural world.

halogen, any of the six nonmetallic elements that constitute group 17 (group viia) of the periodic table. the halogen elements are fluorine (f), chlorine (cl), bromine (br), iodine (i), astatine (at), and tennessine (ts).

the level of progesterone is low at the pre-ovulatory phase of the cycle but it gradually increases and the levels are high at the luteal phase. if pregnancy occurs, the level of progesterone will be high throughout the pregnancy.

if egg is fertilized and the mother gets pregnant, progesterone starts preparing the uterus for the implantation. it starts building up the lining of uterus and make it hostile of the period of pregnancy.