Can Apes Evolve Into Humans Again

April 04, 2022 Post a Comment

When I am on Twitter, every now and and then a witty or funny tweet catches my attention. I laugh, and sometimes re-tweet. More often, nevertheless, I read tweets that cause feet and make me frown at my computer screen with the countenance of a distraught fish. I am talking about tweets like this ane (Fig. 1):

A screenshot of a tweet Tim Allen posted on August 16th, 2017. It reads "If we evolved from apes, why are there still apes?" — Figure 1: A tweet by Tim Allen.

Here is what Mr. Allen most likely imagines when he thinks about evolution: At some bespeak in the by, this monkey-like animal with long limbs that you can come across at the zoo – what Mr. Allen calls an "ape" – had a infant that looked less "ape-ish" and more than "human-ish". Over many generations, this process culminated in us (Fig. 2). The small-scale-scale equivalent (if yous "zoomed in") would exist the linear genealogical concatenation from grandparent to grandchild.

Figure 2: A (terrible) cartoon representing how many people imagine evolution happens. Co-ordinate to the drawing, development is strictly linear, with more "primitive" creatures evolving into "less primitive" ones. Modified from original, CC By-SA 2.0

Mr. Allen's question could exist a publicity stunt, or mayhap he is just a provocateur, but many of the 50,000 "likes" his tweet has at the moment are probably 18-carat. This gives me cold sweats. Why? Permit me use the smaller scale generational parallel to rephrase his tweet, even if I take chances jumping the gun on my own argument: "If I am granddad Allen's grandson, how come I have Allen cousins?". This question reveals a fundamental misunderstanding of the natural phenomenon of evolution. For an evolutionary biologist living in the 21st century like me, this is as misguided equally asking why people on the other side of the globe practise not fall into the void of space.

Evolution is not a linear process that starts with more "primitive" looking organisms we tin can observe today, and ends in mankind (as shown in Fig. 2). Erase this simplistic cartoon from your listen, Mr. Allen. Instead, await intently at figure 3. Biologists have given diagrams like this a fancy proper noun: cladogram. Unlike effigy 2, a cladogram captures the near important (and ongoing!) attribute of the evolutionary process: "branching," or what biologists refer to as cladogenesis. Cladogenetic events are the moments in time during which 1 species "splits" into two species – these events are also known as speciation events. In figure 3, these events are represented by the points at which one line "bifurcates" into two lines.

This figure shows a diagram comprised of lines that sequentially bifurcate, resembling the stick-figure of a tree. One of the bifurcations is circled and labeled "A speciation event". At the tip of each line, to the right of the diagram, there is an animal silhouette followed by a corresponding name. The names read bonobo, chimpanzee, human, gorilla, orangutan and gibbon. An arrow at the bottom gives the time scale, with the past on the left and present on the right. — Effigy 3: A diagram (too known every bit cladogram) that accurately depicts development. Ii or more species originate from ancestral species due to speciation (or cladogenetic) events – when a line splits into ii. By starting at the present and going backwards in time, it is articulate that any one species finds a mutual ancestor with any other species at some point in the past. This means all species share some ancestor, and consequently are always related; this powerful idea is referred to every bit mutual descent, and was proposed by Charles Darwin and Alfred Russell Wallace. Modified from original, CC0 (public domain).

The branching nature of cladogenesis has two important consequences. First, because 2 or more than new species always originate from an ancestor species (and this process has been occurring since the origin of life), any ii species nosotros find in the present are related. The truth might hurt, merely yes, humans and chimpanzees are (afar) relatives. And so are blue whales, white sharks, sequoia trees, mushrooms, flies, earthworms, bacteria, etc. They are all relatives of yours.

This thought of universal relatedness, also known as common descent, was proposed past none other than Charles Darwin himself in On the origin of species [1], simply also past the often neglected Alfred Russell Wallace [2]. Common descent is arguably the most important, overwhelmingly accepted idea in biology.

The 2d consequence is that when biological classification is performed, cladogenesis leads to a natural bureaucracy of groups, in which one can be nested into another. Sometimes 1 wait is worth a chiliad words, so take a peek at figure 4. These primate species have many characteristics that allow us to classify them into successively more inclusive groups. Hominidae consists of all humans, chimpanzees and bonobos, gorillas, and orangutans. If we add gibbons to the mix, we now have the Hominoidea (or "apes"). Finally, if we include quondam earth (e.g., a macaque) and new earth (e.g., a marmoset) monkeys, nosotros get the Anthropoidea (or "simians"). Hominids are nested within the hominoids, which in plough are nested within the anthropoids. And the more securely nested a group is, the more than alike its species will tend to be.

For the most part, today'due south biological classification observes the rules of cladistics, a framework for studying biodiversity proposed by German entomologist Willi Hennig [3]. Cladistics is a large subject field, but we can focus on its main tenet: The merely biological classifications that make evolutionary sense are those nested groups (such equally those highlighted in Fig. 4) which include an antecedent and all its descendants. These nested groups are called clades.

Think about clades every bit being incredibly large and onetime "families" that include a not bad-great-keen-swell-(many, many weblog pages afterwards)-slap-up-grandpa/mother and all its gazillion descendants into the present. The "apes" (also known as Hominoidea, as divers above), are a clade to which nosotros humans vest, together with bonobos, chimpanzees, gorillas, orangutans, and gibbons. We are apes ourselves.

This figure shows a diagram comprised of lines that sequentially bifurcate, resembling the stick-figure of a tree. It is the same diagram shown in figure 3, but with two additional lines. At the tip of each line, to the right of the diagram, there is an animal silhouette followed by a corresponding name. The names read bonobo, chimpanzee, human, gorilla, orangutan, gibbon macaque and marmoset. A blue line circles the first five names and their lines, and is labeled "Hominidae". This circle is nested within a larger orange circle that includes gibbon, and reads "Hominoidea or apes". This orange circle is in turn nested within a larger pink circle that includes macaque and marmoset, and reads "Anthropoidea or simians". — Figure 4: A cladogram with eight primate species. The different colored lines highlight nested groups – clades – of species. Clades include an antecedent species (which lived at the point where a line splits into two) and all its descendants. Hominidae is nested inside Hominoidea, which is in turn nested inside Anthropoidea. Biologists go far at these groups by comparing species with respect to many of their characteristics, including at the DNA and protein level. Annotation that a man is equally much of a simian as a macaque is, and an orangutan is as much of a hominid as a human is, but that a macaque is not a hominid.

We at present have everything we need to answer Mr. Allen's question. If y'all have only skimmed the rest of the post, here is the accept-home message.

Nosotros did not evolve from a modern, living ape, similar a chimpanzee. We evolved and descended from the common antecedent of apes, which lived and died in the distant by. This ways that we are related to other apes and that we are apes ourselves . And alongside us , the other living ape species have too evolved from that same mutual ancestor, and exist today in the wild and zoos.

Being able to observe ape species other than us humans in the nowadays moment poses no problem to evolution whatsoever — if anything, observing and learning almost them can teach us more about ourselves!

References
[1] Darwin, C. R. (1859). On the origin of species by means of natural selection, or preservation of favoured races in the struggle for life. London: John Murray.
[two] Darwin, C. R., Wallace, A. R. (1858). On the Trend of Species to course Varieties; and on the Perpetuation of Varieties and Species past Natural Means of Selection, Zoological Periodical of the Linnean Society, 3(9), 45–62.
[3] Hennig, Willi (1966). Phylogenetic Systematics. University of Illinois Printing.

Edited by Lana Ruck and Liz Rosdeitcher.