In 2009, the Paleobiomics team discovered a 2.5 million year old ancestral human tooth in Malawi belonging to the oldest known species of Homo – the same genus as modern-day man.

This tooth was discovered several hundred meters from the site where a tooth belonging to Paranthropus, another hominid genus, was unearthed five years earlier. While anthropologists believe that Homo and Paranthropus co-existed in Africa, the discovery marks the first time that scientists have been able to determine that fossils found at the same site are from earliest Homo and earliest Paranthropus. The finding is thus the strongest support to date for the hypothesis that the two genera coexisted at the same time in the same biome.

“When I examined the microanatomy of the 2.5 million-year-old ancestral human tooth fragment, I found that it displayed characteristics that are associated more with those of earliest Homo than other early human species,” said Dr. Kullmer. “Those characteristics reflect an adaptation to the environmental changes occurring 2.5 million years ago, when there was a significant cooling of the earth’s climate. As the earth cooled, habitats became more arid, vegetation became tougher, and mammals adapted by developing larger teeth with more chewing capacity,” he added.

Why do rats live faster and die younger than humans? A biological clock discovered in 2008 provides tantalizing clues. This clock, or biological rhythm, controls many metabolic functions and is based on the circadian rhythm, which is a roughly 24-hour cycle that is important in determining sleeping and feeding patterns, cell regeneration, and other biological processes in mammals.

The newly discovered rhythm, like the circadian rhythm, originates in the hypothalamus, a region of the brain that functions as the main control center for the autonomic nervous system. But unlike the circadian rhythm, this clock varies from one organism to another, operating on shorter time intervals for small mammals, and longer ones for larger animals. For example, rats have a one-day interval, chimpanzees six, and humans eight.

Dr. Bromage discovered the rhythm while observing incremental growth lines in tooth enamel, which appear much like the annual rings on a tree. He also observed a related pattern of incremental growth in skeletal bone tissue — the first time such an incremental rhythm has ever been observed in bone. Dr. Bromage said, “The same biological rhythm that controls incremental tooth and bone growth also affects bone and body size and many metabolic processes, including heart and respiration rates. In fact, the rhythm affects an organism’s overall pace of life, and its life span. So, a rat that grows teeth and bone in one-eighth the time of a human also lives faster and dies younger.”

Humans have by far the most variation in these long-term incremental growth rhythms, with some humans clocking as few as five days, and others as many as ten. Correspondingly, humans have the most variability in body size among mammals. Future research will assess whether there is a link between slower growth rhythms and growth disorders. Since the autonomic nervous system controls human behavior, future research will also assess whether growth rhythms can be linked to variations in human behavior.

The finding of UR 501 among a faunal assemblage of eastern African endemics proved to be prophetic with the recovery in 1996 of the maxillary jaw fragment RC 911 from a fossil-rich horizon at Malema, which derives from the same sedimentary unit as UR 501.

RC 911 represents the hyper-robust early hominin taxon Paranthropus boisei, previously known only from eastern African Plio-Pleistocene deposits.

Analysis of the Chiwondo Beds fauna associated with the finds suggest that the Homo and Paranthropus genera arose during, and partly as a result of the global cooling event between 3 and 2.5 ma.  Evidence of the two genera located in the Chiwondo Beds of the Malawi Rift is one of the earliest records of the co-existence of the two hominid lineages.

The early hominin mandible, UR 501, was recovered from the Chiwondo Beds, northern Malawi, by the Hominid Corridor Research Project in 1991, and then again of an important molar fragment in 1992.

Its accession number is named after the village name where  the mandible was found, Uraha. The jaw is referred to the genus/species Homo rudolfensis, in deposits near Uraha Hill and dated, by means of faunal correlation, to ca. 2.4 Ma. UR501 is the first early hominin to have been found in the region between well known eastern and southern African Plio-Pleistocene fossil-bearing sites.

The development of East African savannas is crucial for the origin and evolution of early hominins. These ecosystems, however, vary widely in their fraction of woody cover and today range from closed woodland to open grassland savanna. The paleobiomics team has, for the first time, presented the first Plio-Pleistocene long-term carbon isotope record from pedogenic carbonate and Suidae teeth in the southern East African Rift.

The associated hominin localities (Uraha and Malema) are situated between the well-known hominin bearing sites of the Somali-Masai Endemic Zone in the Eastern Rift and the Highveld Grassland in southern Africa, and fill an important geographical gap for hominin research. Analyses show that the overall fraction of woody cover of 60-70% reflects significantly higher canopy density in the Malawi Rift than the Eastern Rift through time. The discrepancy between the two savanna types originated in the Late Pliocene, when the Somali-Masai ecosystem started to show increasing evidence for open landscapes.

Based on the Malawi data, the evolution of savanna ecosystems in Eastern Africa followed different patterns along the north-south extent of the EAR. The appearance of grasses is considered a driver of evolutionary faunal shifts, but despite the difference of ecosystem evolution in the north, similar hominins and suids occurred in both landscapes, pointing to distinct habitat flexibility and also nutritional versatility.