Collaborative Research: Human Evolution, Rift Valley Environments and Orbitally Forced Climate Change

探索人类进化的历程超越了对早期人类化石的发现和描述。为了理解导致人类关键特征的进化过程，如直立行走、大脑、工具制造和使用以及行为灵活性，有必要为这些创新建立一个背景。塑造和指导人类进化的环境力量是什么？人类进化是早期原始人与其物理和生物环境相互作用的结果，需要结合原始人的发现具体重建这些参数。然而，在陆地记录中记录相关规模的古环境，并在进化和环境变化之间建立因果联系仍然很困难。因此，人类进化的各个方面都是在海洋记录中的环境数据的背景下进行解释的，海洋记录提供了大规模气候变化的详细记录。只有当全球或区域现象与当地原始人生态系统的具体变化之间的联系能够得到证明时，这种方法才是有效的。这项建议试图通过审查一系列环境指标来直接解决这些问题，以便为东非裂谷中的原始人序列建立一个高分辨率的古环境框架。然后，这可以与全球气候变化联系在一起。这项工作的焦点是暴露在图根山中的一个200-300万年前的沉积序列，图根山是肯尼亚巴林戈湖附近裂谷中的一个断块。这个序列显示了主要淡水湖系统的突然和重复的循环，反映了波动的气候条件。在最近的研究中，该项目已经在这些短期振荡(每23000年一次)和米兰科维奇周期之间建立了明确的联系，米兰科维奇周期是由大气顶部接收的太阳辐射的变化引起的，受地球几何形状的变化控制。这些变化代表了地球气候系统在一段时间内的主要驱动力，包括冰川-间冰期周期。36个脊椎动物化石地点，包括3个原始人地点，可以直接与这个序列联系起来，为建立动物和植物对这些短期变化的反应模式提供了机会。这项研究是开发多种环境和生态指标的第一次尝试，这些指标可以直接与陆地裂谷背景下的米兰科维奇自行车有关。这些数据将被用来洞察过去600万年来非洲原始人生态系统对这些普遍存在的气候振荡的进化反应。虽然这些数据与巴林戈盆地的化石原始人及其脊椎动物群落直接相关，但将当地的生态变化与轨道强迫的日照模式联系起来，就有可能推断过去气候振荡对陆地生态系统的影响。有了这些数据，我们可以开始建立高分辨率的模型来解释气候和人类进化之间的相关性，并阐明环境变化作为一般哺乳动物进化，特别是人类进化的潜在驱动力所起的作用。这项研究将促进高度跨学科和协作的研究，这对于发展进化和生态之间的多维联系的观点至关重要。这里概述的项目代表了一个理想的论坛，在这个论坛上，可以产生和整合跨越传统不同学术学科的研究想法。这项研究将扩大机会，使肯尼亚国家博物馆的研究生和研究人员能够参与。

Exploring the course of human evolution extends beyond the discovery and description of the fossils of early humans. To understand the evolutionary processes that led to key human features such as upright walking, a large brain, tool manufacture and use, and behavioral flexibility, it is necessary to develop a context for these innovations. What were the environmental forces that shaped and directed human evolution? Human evolution is a consequence of the interactions of early hominids with their physical and biological surroundings and there is a need to specifically reconstruct these parameters in association with discoveries of hominids. Documenting paleoenvironments at a relevant scale in the terrestrial record and developing causal links between evolution and environmental change, however, remains difficult. As a result, aspects of human evolution have been interpreted in the context of environmental data from the marine record, which provide a detailed record of large scale climatic change. This approach is valid only if links between global or regional phenomena and specific shifts in local hominid ecosystems can be demonstrated.This proposal seeks to address directly these issues by examining a series of environmental indicators to develop a high-resolution paleoenvironmental framework for a hominid-bearing sequence in the East African Rift Valley. This can then be linked to global climate changes. The work has at its focus a 2-3 million year old sedimentary sequence exposed in the Tugen Hills, a fault block within the rift valley near Lake Baringo in Kenya. This sequence exhibits abrupt and repeated cycling of major freshwater lake systems reflecting fluctuating climatic conditions. In recent research, this project has established a clear link between these short term oscillations (every 23 thousand yrs) and Milankovitch cycles that result from variations in the solar radiation received at the top of the atmosphere, controlled by variations in the geometry of the earth''s orbit. These changes represent the major driving force in the earth climate system through time, including glacial-interglacial cycles. Thirty-six vertebrate fossil localities, including three hominid sites, can be linked directly to this sequence, providing an opportunity to establish patterns of response by animals and vegetation to these short term shifts. This research represents the first attempt to develop multiple environmental and ecological indicators that can be linked directly to Milankovitch cycling in a terrestrial rift valley context. These data will be used to generate insights into the evolutionary response of hominid ecosystems to these pervasive climatic oscillations over the last six million years in Africa. While these data relate directly to fossil hominids and their vertebrate communities in the Baringo Basin, linking local ecological shifts with orbitally-forced patterns of insolation affords the prospect of extrapolating the affects of climatic oscillations on terrestrial ecosystems regionally in the past. With these data, we can begin to formulate high-resolution models for interpreting correlations between climate and human evolution, and elucidate the role of environmental change as a potential driving force in mammalian evolution in general and human evolution in particular. This research will foster highly interdisciplinary and collaborative studies, essential in developing perspectives of the multi-dimensional links between evolution and ecology. The project outlined here represents an ideal forum in which to generate and integrate research ideas cutting across traditionally disparate academic disciplines. The study will broaden opportunities and enable the participation of graduate students as well as research personnel from the National Museums of Kenya.