|In 1925, Albert Weiss, in his "rain-drop analogy" shows the silliness in thinking, via anthropomorphic reasoning, that the "purpose" of every drop of water in the atmosphere is to get to the ground or ocean; and that human behavior is but a more complicated form of the same forces that act on rain drops.|
Purpose | Terminology reform
See main: Purpose terminology reformThe first to explain purpose in a non-theological, non-teleological, and non-anthropomorphic way, were Harold Blum (1934) and Bruce Lindsay (1983), independently, in terms of thermodynamic potential wells (i.e. Gibbs energy minimums); some of this has been expanded on by Libb Thims, via the "Gates model", in the "Smartest Person Existive (2014)" video series and "Zerotheism for Kids" (2015) video lecture.
In the absence or questionability of religious belief, the modern person, according to the recent conversations on religion and science interviews of Steve Paulson (2010), is left with a semblance of the following view:
“Is it just a crazy, cosmic stroke of luck that we’re here at all? Or do human beings have some larger, mysterious purpose?”
Said another way, the general non-religious alternative explanation to the big question explanation of purpose and meaning, according to Paulson, is that humans are lucky accidents resulting from random genetic mutations. 
See main: Random chanceInto the early 20th century, following the publication of English naturalist Charles Darwin’s 1859 Origin of Species, which introduced the theory of the origin of life by evolution to the world, in replacement to the Christian-Ra theology based theory of creation of life by god, followed by Dutch botanist Hugo de Vries’ 1901 gene-centric mutation theory of evolution, the non-religious view began to emerge that humans are accidental collections of atoms, formed though evolution, as a result of blind random chance mutations of genes.  The following is a representative 1923 quote of this view by American mathematician-philosopher Bertrand Russell: 
“That man is the product of causes which had no prevision of the end they were achieving; that his origin, his growth, his hopes and fears, his loves and beliefs, are but the outcome of accidental collections of atoms.”
The main issue with this model, is that a human is 26-element, heat-driven, surface-catalyzed, turnover rate human molecule, formed not by accident, but rather by a very precise consorted chemical mechanism of synthesis, quantified by free energy change measurements. Russell, to note, was a mathematician, not a physicist nor a chemical engineer or physical chemist, and hence prone, as are all mathematicians towards these types of unfounded suppositions.
Purposeless universe model
See main: Purposeless universe hypothesisInto the latter half of the 20th century, following the discovery of DNA by James Watson and Francis Crick in 1953, a DNA-centric, blind watchmaker model of purpose began to emerge. This is exemplified in the works of English zoologist Richard Dawkins, namely The Selfish Gene (1976) and The Blind Watchmaker (1986), as is summarized in his famous 1991 quote: 
“We are machines built by DNA whose purpose is to make more copies of the same DNA. That is exactly what we are here for. We are machines for propagating DNA, and the propagation of DNA is a self-sustaining process. It is every living object’s sole reason for living.”
Dawkin’s popular assertion, according to American science-religion scholar, theologian-physicist Ian Barbour, shows that the presence of chance indicates that this is a purposeless universe, whereby natural selection is a mechanism that makes highly improbable molecular combinations probable by the accumulation of many small adaptive improvements. 
A variation of this view is held by American physicist Steven Weinberg who claims that humans are insignificant specks in a meaningless universe. 
|The toothpaste maker Colgate indicates that the sodium fluoride NaF has a "purpose", which in some way, supposedly, contradicts the "purposeless universe hypothesis" advocated by many leading modern scientists, which holds that purpose does not exist in the universe, and that by repercussion chemicals and molecules, and presumably human molecules (people), do not likewise have purpose.|
See main: Chemical teleologyThe following labeling notation on a tube of toothpaste indicates that the chemical compound sodium fluoride NaF has an "anticavity" PURPOSE, in the structure of the universe, or at least according to Colgate, namely to prevent cavities in the teeth human molecules (people), a labeling which would seem to contradict the "purposeless universe hypothesis" advocated by many leading scientists:
See main: Human chemical thermodynamicsThe quick and short chemical thermodynamics answer to the big question of purpose and meaning of human existence and movement is still a nascent subject, albeit one with a general outline and protocol, and certainly several grades above the so-called meaningless-purposeless model trumpeted about by individuals like Russell, Dawkins, and Weinberg.
Without going into details of the chemical thermodynamics explanation of purpose, to point out a number of salient difficulties exist in the modernized, dumbed-down, so-called gene-centric, DNA model of purposeless existence, particularly in the context of the laws of thermodynamics, which govern the operation of the universe. Firstly, chemical synthesis is the correct name for the process by which humans came about over billions of years from hydrogen atom precursors, as first enunciated in French philosopher Jean Sales' 1798 human molecular hypothesis, not by English naturalist Charles Darwin's 1859 evolution theory, which is only a partial theory of a bigger process.
Secondly, a human is not a living object, but rather an animated or reactive entity. Thirdly, human chemical reactions are not self-sustaining, a process that amounts to a perpetual motion claim, but rather heat-driven.
|The materialist explanation of purpose and meaning, according to American materialist philosopher Owen Flanagan, is called "the really hard problem" in modern philosophy. |
Forth, humans are not machines (human machines), which is a defunct 19th century theory, but rather molecules (human molecules).
Fifth, and most incorrect among his many grandiose claim of the purposeless existence model, the sole reason for an animated molecule's existence is not "propagation of DNA", but rather, in the confines of earth-system surface reactions, a reaction path dictated by Gibbs free energy change, governed by the Lewis inequality for natural processes, as these local free energy differentials are coupled to the spins and heat cycles of the universe. Hence, to further understand purpose of human movement, one must become a student of the joint study of the dynamics of universe, from the sub-atomic to the super-galactic, all in the context of thermodynamics.
The following are related quotes:
“Destiny urges me to a goal of which I am ignorant. Until that goal is attained I am invulnerable, unassailable. When destiny has accomplished her purpose in me, a fly may suffice to destroy me.”— Napoleon Bonaparte (1816), In His Own Words
“Life is meaningless so find a purpose.”— Dilvinder Singh (2016), “Thread post #53” (Ѻ), Apr 9; brother of Inderjit Singh; see: Thims’ response; thread post #54; and follow-up thread: “Is There Truly a Greater Purpose or Meaning to Life?” (Ѻ), Apr 10
● Einstein on purpose
|The above “tell me, what is it you plan to do with your one wild and precious life?” question, a popular 1992 quote (Ѻ) by American poet Mary Oliver, from her The Summer Day, seems to well-capture the gist of what most conceptualize by the term "purpose", which often has association with the connective terms: destiny and meaning, and tends to lead into ideas, religious models aside, about following, doing, or going after, what one is passionate about (Ѻ) or into plans about doing makes one “come alive”, as Howard Thurman suggests.|
1. Paulson, Steve. (2010). Atoms & Eden: Conversations on Religion and Science (pg. 1; Flanagan, pg. 7; Weinberg, pg. 16). Oxford University Press.
2. (a) De Vries, Hugo. (1904). Species and Varieties: their Origin by Mutation. Open Court Publishing.
(b) De Vries, Hugo. (1909). The Mutation Theory: Volume 1. Open Court Publishing.
3. (a) Russell, Bertrand. (1923). “A Free Man’s Worship”, T.B. Mosher.
(b) Russell, Bertrand. (1961). “A Free Man’s Worship”, in: R.E. Egner and L.D. Dennon, eds., The Basic Writings of Bertrand Russell 1903-1959. Simon and Schuster.
4. Dawkins, Richard. (1991). “The Ultraviolet Garden”, Royal Institute Christmas Lecture, No. 4.
5. Barbour, Ian G. (2000). When Science Meets Religion (pg. 155). Harper Collins.
● Cameron, Don. (2001). The Purpose of Life: Human Purpose and Morality from an Evolutionary Perspective. Woodhill.
● Rosch, Staks. (2009). “Atheism 101: The Purpose of Life”, Jul 22, Examiner.com.
● Schneider, Eric and Sagan, Dorion. (2010). The Purpose of Life: Closing the Gap Between Science and Religion. Chelsea Green Publishing.
● Purpose – Wikipedia.