Back in October, I wrote that floresiensis is either descended from Erectus or habilis, since those were the only two hominins in the region. Yesterday a study was published titled The affinities of Homo floresiensis based on phylogenetic analyses of cranial, dental, and postcranial characters (Argue et al, 2017), in which Argue et al argue that floresiensis was not descended from a shipwrecked Erectus, as is a popular view. Another theory is that floresiensis is descended from habilis. The third theory is that floresiensis is Homo sapiens with a pathology, but that has been disproven (Falk et al, 2009). It was commonly thought that the LB1 floresiensis specimen was a pathological human inflicted with Laron syndrome which is a type of growth hormone deficiency (Laron and Klinger, 1994).
Argue et al found that floresiensis and erectus had completely different bone structures, particularly in the pelvis and jaw. They now believe that the theory that floresiensis is a derived form of an erectus that swam or rafted to Flores has been defintively refuted. They found that floresiensis was a sister species to habilis. So either a common ancestor of floresiensis or habilis swam to Flores from Africa, or floresiensis evolved in Africa and swam to Flores. They used new phylogenetic techniques to ascertain that floresiensis is stil a part of our lineage, but shows no phylogenetic relationship to erectus on the tree.
According to Baab (2016), biogeography shows that Indonesian erectus is the best fit with what is currently known. She says if floresiensis was derived from erectus that it “implies some degree of body size reduction and more marked brain size reduction.”
Kubo, Kono, and Kaifu (2013) conclude that the evolution of floresiensis from early Javanese erectus is possible when comparing the brain cases of both specimens. However, if floresiensis descended from habilis, then the brain size reduction wouldn’t be as marked (and is still due to island dwarfism, just not on as large of a scale as it would be if floresiensis were descended from erectus). The LB1 specimen also shows the closest neural affinities to early Asian erectus (Baab, Mcnulty, and Harvati, 2013; but see Vannuci, Barron, and Holloway, 2013 for the microcephalic view). Weston and Lister, (2009) showed that there was a 30 percent reduction in brain size in Magalasy hippos, which lends credence to the insular dwarfism hypothesis for floresiensis. Craniofacial morphology also shows that floresiensis evolved from Asian erectus (Kaifu et al, 2011).
The teeth of unknown hominin found at Mata Menge are intermediate between floresiensis and erectus, being 600,000 years older than where floresiensis was found (van den Bergh et al, 2016). This lends credence to the hypothesis that floresiensis is derived from erectus. Furthermore, insular dwarfism is seen in primate species isolated on islands, with changes in body size seen in child populations even on large islands not far from the mainland (Bromham and Cardillo, 2007, Welch, 2009). Genetically isolated on islands, primates can become bigger if the parent population was smaller, or smaller if the parent population was bigger. This is due to differing energy demands relative to the parent population, along with differing predators/prey.
The island rule even holds in the deep sea. As is the case with islands, the deep sea is also associated with decreased food availability. Looking at several species of gastropods, McClain, Boyer, and Rosenberg (2006) found that the island rule held in small-bodied shallow species. They were found to have larger bodied deep-sea representatives, with the same being true for large bodied deep-sea gastropods. Further, island dwarfism in elephants on the islands Sicily, Malta, Cyprus; mammoths on the California channel islands; and red deer on the island Jersey involved body mass changes of 5- to 100-fold over 2,300 to 120,000 generations (Evans et al, 2012).
So the overall hypothesis that island dwarfism is still intact, albeit if floresiensis is derived from habilis, the reduction in brain/body size would be smaller than if floresiensis evolved from early Asian erectus.
Further evidence for brain/body size reduction due to less food availability is noted by Daniel Lieberman in his book The Story of the Human Body: Evolution, Health, and Disease (Lieberman, 2013). While talking about the evolution of floresiensis on page 123 he writes:
The same energetic constraints and processes also affect hunter-gatherers . 62
And in the 62nd footnote on page 391 he writes:
Several human “pygmy” populations (people whose height does not exceed 150 centimeters, or 4.9 feet) have evolved in energy limited places like rain forests or islands. Perhaps the small size of the Dmansi hominins from Georgia also reflected selection to save energy among the first colonists of Eurasia.
Either way, if floresiensis evolved from erectus or habilis, considerable reductions in brain size have to be explained, since the smallest erectus brain ever found is 600 cubic centimeters while the smallest habilis brain ever found is 510 cubic centimeters (Lieberman, 2013: 124), with floresiensis having a brain 417 cubic centimeters (Falk et al, 2007).
What is most important about the insular dwarfism hypothesis in regards to the evolution of floresiensis is the effect of energy reduction/food availability and quality in regards to populations isolated on islands from parent populations. Floresiensis was able to survive on about 1200 kcal by shrinking, needing to consume about 1400 kcal during lactation compared to 1800 kcal for an erectus female who needed about 2500 kcal during lactation (Lieberman, 2013: 125). The cognitive price for the reduction in the brain size of floresiensis is not known, but since brains are so energy expensive (Aiello and Wheeler, 1995; Herculano-Houzel and Kaas, 2011; Fonseca-Azevedo and Herculano-Houzel, 2012), the reduction seen in floresiensis is no surprise.
Energy is one of the most important drivers for the evolution of a species, the evolution of floresiensis is one major example of this. Whether floresiensis evolved from habilis or erectus, reduced energy on the island caused the brain and body size of floresiensis to get smaller to cope with fewer things to eat. Keep in mind that habilis was a meat-eater as well, and with lower-quality energy on the island, the brain would have to reduce in size as it’s one of the most expensive organs in the body. As I’ve been saying for a long time now, the quality of energy is most important to the evolution of a species—especially Man. Cooking was imperative to our evolution, and with a lower-quality diet, we, too, would evolve smaller brains and bodies to compensate for reduced energy consumption since our brains take 25 percent of our daily energy requirements to power despite being 2 percent of our overall body weight.
The evolution of floresiensis shows how important energy is in the evolution of species. Its biggest implication—no matter if floresiensis evolved from habilis or erectus—is how important diet quality is to evolution, as I’ve noted here, here, here, here, here, and here. Without our high-quality diet, we, too, would suffer the same body/brain size reductions that floresiensis did.
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