The Sediments of Time - Book Review

 

This account of Meave Leakey’s search for human ancestors in the Turkana region of Kenya is at once intensely personal and scientifically sound.

Born Meave Epps in 1942 she read marine biology at Bangor but found herself without a job because research ships lacked facilities for women. On a whim she answered an advertisement by Louis Leakey who was recruiting for a primate research centre in Kenya. Once there she soon found herself looking for hominin fossils with Louis’s son Richard whom she later married. Their life together was full of drama as Richard suffered both kidney failure and the loss of his legs in a plane crash.

Reconstruction of Homo rudolfensis
(KNM-ER 1470) discoved by Meave Leakey 
Photo byy Don Hitchcock CC BY-SA 4.0

Meave soldiered on and discovered or co-discovered significant specimens of several hominins ranging from australopithecines through early members of our genus (above) to Homo erectus. The first part of the book details this story and gives a fascinating account of work in the field (with no facilities for men or women!) and the ever present need to find fossils attractive enough to ensure continued funding. In the second part the emphasis shifts towards putting individual fossils in the context of work by others (including mother-in-law Mary Leakey) and painting a broader view of human evolution. The final part continues the story of exploration while explaining the changes in biology that led to evolution of our species.

Meave and Richard had two daughters. Louise followed in the Leakey family business of finding fossils while Samira co-authored this book. One chapter considers the importance of grandmothers for human reproduction and indeed there are grandchildren. Who knows if a fourth generation of Leakeys will search for clues to our past?

There are excellent photos from life in the field and some very useful line drawings. But surprisingly few photos of the fossils themselves. That is really my only criticism of an excellent book. I found it useful to have the well illustrated book Our Human Story to hand as a complement to the text (reviewed here).

Our Human Story - Book Review



ISBN 978 0 565 09391 4 Cover Price £14.99

This short book (160 pages) can be highly recommended to anyone who, like me, often loses the plot when reading papers on human evolution. It covers all phases in hominin evolution during the past 7 million years. The most important fossils are named (and the names explained), illustrated, and placed in geographical context by some excellent maps.



There is a good index so next time you are unsure what is referred to by KNM-ER 1470 you can quickly look it up!


I had anticipated that the book might lack the very latest info such as the redating of the early humans from Jebel Irhoud or the early dispersals to Arabia and India. But Louise Humphrey and Chris Springer have it all. Only the 120,000 year-old human fossil from Misliya, Israel (here) was published too late to make it into their book.


Chris Stringer is a strong proponent of the Out of Africa hypothesis that has all modern populations deriving from a single dispersal 45-55,000 years ago. But in this book alternative scenarios are given a fair treatment.


Near the end there is a neat diagram summarizing human evolution during the last million years.




Hobbits in the headlines again

Liang Bua, the cave where Homo floresiensis was found.
This image was originally posted to Flickr by Rosino (CC-BY-SA-2.0).

When a new hominin was described from Flores in Indonesia (here), it was quickly dubbed "hobbit" with reference to its small stature (1.1 m) and relatively large feet. Even more sensational, however, was the date of 15 thousand years ago (kya) based on charcoal from the same deposit. The implication was that the "hobbit" (Homo floresiensis) overlapped in time with our own species.

Yesterday my Twitter feed lit up with news of a paper (here) that drastically revised the age of these fossils to between 60-100 kya. Briefly there had been slippage of more recent material, including charcoal, into an eroded area where the bones were found. The new study used several methods to obtain the earlier date. Unlike in the original report, these included dating of the bones themselves.

Skull of Homo floresiensisThis image was originally posted to Flickr (CC-BY-SA-2.0).

The new dates match those of stone tools ranging from 50-190 kya. The most recent of those dates corresponds with the arrival of H. sapiens in the region, leading to conjecture that this caused the demise of the "hobbits."

There is a new flurry of speculation about the origin of this species. One idea (discussed here) is that it is derived from Homo erectus (previous post) and its small stature is an example of Island Dwarfism (as seen in pygmy elephants from Flores and pygmy hippopotami from Madagascar).

Flores lies East of the Wallace Line, a water barrier that separates the Southeast Asian and Australasian flora and fauna (previous post). It seems not to have presented a barrier to hominins. The enigmatic Denisovans also crossed the Wallace Line (previous post).

Defining the genus Homo

Reconstruction of Homo erectus georgicus by Élisabeth Daynes
Licensed under CC BY-SA 3.0 via Wikipedia Commons

A thought provoking essay in the current issue of Science (here) asserts definitions of the genus Homo and the species assigned to it remain "as fuzzy as ever." They drive home their point by showing, on the one hand, specimens attributed to Homo with australopithecine features and, on the other, australopithecine fossils with features hitherto claimed to be confined to Homo.

This is a brief but instructive read. The take home message is that hominid systematics needs to be rethought. In the process we may need to scrap "the iconic list of names in which fossil specimens have historically been trapped."

Cover of Third Edition 1956

One name that may have to go is Homo habilis (previous post), the handy man. Louis Leakey, it is suggested, was keen (perhaps too keen) to identify this fossil as the maker of simple tools following the dictum of Man the Toolmaker. It was a pleasant surprise to find Kenneth P. Oakley's booklet cited as an influence on previous and current thinking. My well thumbed copy dates from my schooldays.

East African fossils cast new light on the origins of Homo

Reconstructed skull of Homo rudolfensis (KNM ER 1470)
Wikipedia Commons (CC) Durova

This week two important papers address the antiquity and diversity of the genus Homo.

A study published in Nature (here) takes a fresh look at Homo habilis, "The Handy Man," first described half a century ago (see previous post). The mandible (lower jaw) of the type specimen (OH 7) is badly distorted, but has been reconstructed using state-of-the-art computer tomography and 3D imaging technology. Comparison with other fossil mandibles from the region shows that not all can be ascribed to H. habilis. Indirectly. this supports the validity of Homo rudolfensis (pictured) as a distinct species.

A similar approach yielded a new estimate for the endocranial volume of OH 7 (a proxy for brain size). Interestingly, similar values are obtained for H. habilis, H. rudolfensis and H. erectus. 

A new fossil from Ethiopia, described in Science (here and here), is too incomplete to assign to a species. It is exciting because it can be assigned to the genus Homo and is 400,000 years older than all previous fossils. It pushes the origin of our genus back to at least 2.8 million years ago. There could well be overlap with Australopithecus afarensis best known from the skeletal remains of "Lucy"

Was Homo erectus the fourth hominin?

Skull of Homo erectus (Wikimedia Commons)

The current issue of Nature has a comprehensive analysis of the genome of Neanderthals and comparisons with modern humans and Denisovans (here). The supplementary material alone fills 16 Mb but there is an excellent summary (here) entitled "Four makes a party." As it says, "it does seem that Eurasia during the Late Pleistocene was an interesting place to be a hominin, with individuals of at least four quite divergent groups living, meeting and occasionally having sex."

The fourth hominin was alluded to in a previous post and is inferred from analysis of the Denisovan genome (previous post). The current study estimates that this putative hominin's ancestor diverged from other hominins 0.9-1.4 million years ago. This date is compatible with the unknown hominin being Homo erectus a hominin well known from the fossil record.